United States Air and Radiation EPA420-P-99-002
Environmental Protection August 1999
Agency M6.SPD.002
&EPA Facility-Specific
Speed Correction Factors
Draft
> Printed on Recycled Paper
-------
EPA420-P-99-002
August 1999
Draft
David J. Brzezinski
Phil Enns
Constance J. Hart
Assessment and Modeling Division
Office of Mobile Sources
U.S. Environmental Protection Agency
NOTICE
This technical report does not necessarily represent final EPA decisions or positions.
It is intended to present technical analysis of issues using data which are currently available.
The purpose in the release of such reports is to facilitate the exchange of
technical information and to inform the public of technical developments which
may form the basis for a final EPA decision, position, or regulatory action.
-------
Table Of Contents
1.0 ABSTRACT AND SUMMARY 1
2.0 BACKGROUND 3
3.0 VEHICLE TESTING 5
3.1 New Driving Cycles 5
3.2 Sample Selection 7
3.3 Vehicle Testing 7
4.0 STATISTICAL ANALYSES 7
4.1 Emitter Status 9
4.2 Roadway Type 10
4.3 Vehicle Class 11
4.4 Emission Standard 11
4.5 Convergence of Freeways and Arterial/Collectors 12
4.6 Summary 13
5.0 EMISSION LEVEL CALCULATION 14
5.1 Freeway Versus Arterial/Collector Effects 14
5.1.1 High Speeds 15
5.1.2 Intermediate Speed Freeways 15
5.1.3 Low Speed Freeways 15
5.1.4 Arterial/Collectors 16
5.1.5 Extremely Low Speeds and Idle 16
5.2 Local Roadways and Freeway Ramps 16
5.3 Special Cases 17
6.0 SPEED CORRECTION FACTORS 17
6.1 Basic Modeling Approach 18
6.2 Emission Offsets 19
6.2.1 Freeway Emission Offset Calculation 19
6.2.2 Arterial/Collector Emission Offset Calculation 20
6.3 Calculating Speed Correction Factors 20
6.4 Effect of the NLEV Standards and the Supplemental FTP 21
6.5 Application in MOBILE6 22
7.0 COMPARISON TO MOBILES 24
8.0 COMMENTS 25
References 27
Tables 28
Figures 55
Appendices 72
-------
1.0 ABSTRACT AND SUMMARY
Abstract
In MOBILES, adjustments were made to the basic exhaust emission estimates to account
for the effects of area wide average trip speeds using speed correction factors developed from a
number of driving cycles with varying average speeds. For MOBILE6 we propose to adjust for
differences in driving behavior versus roadway (facility) type and aggressive driving effects as
well as average speed. EPA has developed new facility-specific inventory driving cycles, based
on real-world driving studies, and tested vehicles using these cycles to address these purposes.
This report describes the analysis of the new driving cycle data and presents the resulting speed
correction factors proposed for use in MOBILE6.
Summary
Although the adjustments described in this document are called "speed" correction
factors, the adjustments include all of the effects on emissions caused by differences in driving
behavior, of which average speed is the most obvious and easiest to measure. The speed
correction factors described in this document are proposed to be used in MOBILE6 to replace the
speed correction factors now used in MOBILES for all light duty passenger cars and light duty
trucks of all model years and technologies. The speed correction factors for heavy duty vehicles,
diesel fueled vehicles and motorcycles from MOBILES would be retained for use in MOBILE6.
This document also proposes a method for applying the new speed correction factors to future
technology vehicles for which no data is yet available.
The new MOBILE6 speed correction factors specifically account for aggressive driving
behavior not represented in older driving cycles. They also allow for evaluation of vehicle
emissions by roadway type (facility) and by roadway segments (links). There are four roadway
types modeled in MOBILE6:
Freeways
Arterial/Collectors
Freeway Ramps
Local Roadways
The proposed speed correction factors for freeways and arterial/collectors depend on both
speed and basic emissions level of the vehicles. The correction factors for freeway ramps and
local roadways depend only on emission level and cannot be adjusted for average speeds
different than the national average. All speed corrections are based on new driving cycles
designed to reflect real-world driving behavior, including the effects of aggressive driving not
found in the standard vehicle FTP certification driving cycle (Urban Dynamometer Driving
Cycle) and most older driving cycles used in emission testing.
DRAFT M6.SPD.002h 1 August 24, 1999
-------
Since the data for this analysis was collected using the new, realistic driving cycles, an
emission impact of aggressive driving is included in the effect of the new speed correction
factors on emissions. The introduction of the new Supplemental FTP (SFTP) into vehicle
emission certification will require the reduction of the emission effects from aggressive driving
for future vehicle certification. The impact of the SFTP on emissions will be addressed in a
separate document.
Table 16 contains our proposed speed correction factors for freeways. Table 17 contains
the proposed speed correction factors for arterial/collector roadways. For MOBILE6, the
correction factor for Local Roadways and Freeway Ramps assume a national average speed and
will not have an adjustment for local average speeds. The speed correction factors for freeways
and arterial/collectors converge below 7.1 mph and at higher speeds, depending on the pollutant
and emission level. At those points the freeway and arterial/collector speed correction factors
become identical. The speed correction factors for speeds below 7.1 mph will remain the same
as in MOBILES, adjusted to account for the difference between the old and new speed correction
factors where they intersect at 7.1 mph.
MOBILES did not model average speeds above 65 miles per hour. The new driving
cycles also do not address average speeds above 65 miles per hour. EPA will consider whether
sufficient information is available to model average speeds above 65 miles per hour in MOBILE6
and will present any proposals for these higher speeds in a separate document. As in MOBILES,
MOBILE6 will not explicitly address average speeds less than 2.5 miles per hour. Idle emissions
will be assumed to be the same as the grams per hour emitted at an average speed of 2.5 miles
per hour. This "idle" emission rate will be available as an output from MOBILE6.
Table 13 shows the coefficients used to calculate the freeway ramp and local roadway
emissions from the basic emission rate. Table 14 and 15 show the additive offsets used to
calculate the adjusted basic emission rate which is adjusted by the speed correction factors.
Appendix B has an example calculation of the application of speed correction factors to the base
emissions calculated by MOBILE6.
Figures 4a through 4c show the effect of emission level on the speed correction factors.
Figures 5a through 5c compare the new MOBILE6 speed correction factors with selected
MOBILES speed correction factors. Care should be taken in interpreting these figures, since
there are many differences in how these factors are applied in MOBILE6 as compared to
MOBILES. These figures are discussed in more detail in Chapter 7.
The report is organized into sections which address various aspects of the analysis.
Chapter 2 gives a brief background of the need for new, facility based, speed correction
factors.
Chapter 3 discusses the development of the facility cycles and the emission testing
DRAFT M6.SPD.002h 2 August 24, 1999
-------
sample used in the development of the proposed speed correction factors.
Chapter 4 discusses the statistical analysis of the data sample.
Chapter 5 describes the approach developed to summarize the emissions data.
Chapter 6 uses the emission levels developed in Chapter 5 to develop the proposed speed
correction factors for MOBILE6.
Chapter 7 compares the speed correction factors developed in Chapter 6 to the existing
speed correction factors in MOBILES.
Chapter 8 describes how to contact EPA in order to comment on this document.
EPA is requesting that MOBILE model stakeholders and other knowledgeable readers
comment on the methodology and validity of the assumptions used to determine the speed
correction factors proposed in this document.
2.0 BACKGROUND
EPA's highway vehicle emission factor model, MOBILE, is used for inventory modeling.
MOBILE has historically been based on emission testing using the Federal Test Procedure (FTP)
used to certify all light duty vehicles sold in the United States. The FTP uses a driving cycle (the
Urban Dynamometer Driving Cycle, commonly referred to as the LA4) which simulates urban
driving on a laboratory dynamometer. Correction factors for various conditions (e.g., average
speed, temperature, fuels) are applied to emissions measured at the FTP "standard" conditions.
The speed correction factors were based on test results for vehicles tested on both the LA4
(Urban Dynamometer Driving Cycle) and several other cycles, each having a different average
speed. MOBILE6 will address two areas not adequately addressed in previous versions of the
model. These are real world driving behavior and the expanded use of transportation models in
determination of area-wide inventories.
"Real- World Driving "
The FTP has been used for emissions certification of all light duty vehicles sold in the
United States. The Clean Air Act Amendments of 1990 mandated a closer look at "real-world
driving" - that is, driving modes that are not covered by the FTP (and the Urban Dynamometer
Driving Cycle). EPA organized the Federal Test Procedure Review Project to address this
mandate. A new Supplemental FTP (SFTP) rule was finalized in October 1996. This rule
specifies the addition of a new certification cycle with more aggressive driving and associated
standards.
DRAFT M6.SPD.002h 3 August 24, 1999
-------
MOBILE6 must address both the emission impacts of more aggressive driving than is
covered in the driving cycles that were used to develop MOBILES and the effects of the new
SFTP standards on future model year vehicles. A special EPA emission testing project was
initiated to address these concerns. The results of that testing are the basis for the analysis in this
document.
Transportation Models
The current and older versions of the MOBILE model were developed to estimate area-
wide emission inventories using trip-based emission estimates with trip-based adjustments for
average speed. Vehicle trips are defined as all driving from key-on to key-off, including a variety
of roadways and speeds.
Local officials have begun to integrate transportation models into their regional air quality
planning processes. Most transportation models represent the roadway system as a network of
"nodes," which are usually intersections, connected by "links," which represent a particular type
of roadway or "facility." Transportation models generate link-specific estimates of speed and
traffic volume. Transportation planners have begun using MOBILE to generate link-specific
emissions estimates for planning purposes.
Recent data from instrumented vehicles and chase car studies show that some types of
facility-specific driving contain more frequent and more extreme acceleration and deceleration
than others1. Different facilities may have similar average speeds, but may differ significantly in
the amount of steady cruise. These differences suggest that there is a need to quantify the
emission differences (if any) between facilities in order to evaluate facility-specific speed related
traffic control measures in inventory modeling.
For example, at an average speed of 25 mph, travel over surface streets is likely have a
relatively low level of traffic congestion, but will include many stops for traffic signals. Travel
on a freeway at 25 mph may indicate a high congestion level, but may include fewer stops.
MOBILES's trip based emission estimates do not differentiate between roadway types. If these
models are used for each roadway separately, they would not account for any differences in
emissions resulting from these differences in driving behavior.
Other Approaches
California is also updating it's highway emission factor model. However, California has
taken a different approach to modeling the effects of changes in vehicle speeds. Rather than
attempt to discern what the driving behavior is for various facilities at various average speeds,
they divide all observed driving into speed bins. Each bin contains "microtrips" with similar
average speeds, regardless of the roadway type where the driving was observed. By weighting
the results of the various speed bins, any areawide average speed can be modeled. Changes in
driving behavior can be modeled by varying the distribution of speeds.
DRAFT M6.SPD.002h 4 August 24, 1999
-------
This approach requires areas to evaluate their fleet activity as "trips", where individual
vehicles travel over a variety of roadway types at varying speeds to reach a destination. These
trips are then used to develop a distribution of average trip speeds. Transportation models
generally do not produce trip statistics and transportation planners would need to adjust their
models to generate these distributions. Any changes in the roadway system resulting in changes
in average speeds on specific roadways will require a change in the full areawide distribution of
trip speeds. Evaluation of the emission impact of changes in the specific roadways will require
new estimates of the areawide emission levels.
One important advantage of California's approach is the need for fewer driving cycles.
Given limited testing budgets, this allows more vehicles to be tested over each cycle, thus
increasing the statistical confidence in the emission test results. Development of the driving
cycles themselves requires fewer assumptions such as decisions about where and under what
conditions the observed driving occurred. The resulting trip-based California driving cycles are
also similar in concept to the trip-based Unified Driving Cycle (or LA92), which is used by
California as the basis for the highway vehicle emission factors. The approach we have proposed
for MOBILE6 requires more driving cycles with more detailed information about driving
conditions and location.
The most important disadvantage of California's approach is the dependence on vehicle
trip information. Since vehicle trips occur over a variety of roadways at a variety of average
speeds, evaluation of trips is most relevant for only areawide emission estimates. The confidence
in the estimate of emissions will decrease as the size of the area to be modeled is decreased or if
only specific roadways or links are to be modeled. In addition, many transportation planners do
not currently generate trip speed distributions and other trip information from their models. This
will mean that changes will need to be made in the transportation models in many cases in order
to effectively use the California emission factors. In comparison, the approach proposed for
MOBILE6 is more compatible with analysis by roadway type and link. Since most transportation
models already estimate speeds and miles traveled by link, MOBILE6 will not normally require
major changes in the output from existing transportation models. Using MOBILE6, the areawide
emissions are still able to be estimated by compiling the results from the four roadway types.
A more detailed description of the California approach or a comparison of the two
approaches is beyond the scope of this document. Readers are encouraged to obtain information
directly from California to compare with the results documented in this report.
3.0 VEHICLE TESTING
3.1 New Driving Cycles
The basis for the analysis found in this report is a set of vehicles recruited and tested in
1997. The testing included new driving cycles specifically designed to address the effects of in-
use driving behavior on emissions. Table 1 gives a brief description of the new cycles that were
DRAFT M6.SPD.002h 5 August 24, 1999
-------
used in the testing. Collectively, these new driving schedules will be referred to in this document
as "facility" cycles. The driving behavior in each driving schedule is selected from data collected
from a particular roadway type during periods of various congestion levels. These congestion
levels have been roughly grouped into "levels of service" (LOS) using letters A through G,
similar to congestion category designations used in transportation models. Briefly, LOS "A"
refers to "free flow" (uncongested) situations and the subsequent letters indicate increasing levels
of congestion. The definition of these categories is discussed in more detail in a separate EPA
report describing the development of the new facility driving cycles1.
Table 2 compares the new cycles' statistics to the target population statistics for each
cycle. The statistics for each cycle will differ from the statistics of the population of driving
which the cycle is designed to simulate (or "target population"). For example, the highest
average speed of the arterial/collector cycles is 24.8 mph. We know that driving on
arterial/collectors can have average speeds higher than that. The maximum speed of the
arterial/collector cycles is only 58.9 mph, while the maximum speed of the targeted population is
74.9 mph. This is a result of the cycle development process which chooses the best combination
of microtrips to match the target population. The microtrip which contains the maximum
observed speed may over-represent certain aspects of driving behavior and cannot be used within
the confines of a single driving cycle of limited duration.
Each cycle was designed to result in emission levels representative of the emissions we
would expect from the driving behavior observed in the target population. Characteristics which
were deemed important to the match were specific power, speed, and amount of acceleration,
deceleration and idle. The factor which most affects emissions, shown from previous experience
in development of the Supplemental FTP, is the power distribution. The average speed or
maximum speed of the resulting cycles may not exactly match the target population. More
importantly, however, the cycles approximate the power distribution of the target population.
We feel that the emissions generated from the new cycles are a true representation of the
expected emissions from the driving behavior that was observed in the target population from
which the cycle was generated.
In addition to the new cycles described in Table 1, each vehicle was also tested using the
following cycles:
- Federal Test Procedure (FTP), with an additional hot running 505 seconds of the LA4
(Urban Dynamometer Driving Cycle).
- California Air Resources Boards (CARB) area-wide Unified Cycle (LA92).
- New York City Cycle (NYCC), a low speed cycle which has previously been used for
speed correction factors in the MOBILE model.
- ST01, a cycle based on instrumented vehicle data representing the beginning of trips
which is the first 258 seconds of the vehicle certification air conditioning cycle (SC03).
Table 3 shows more information on these additional cycles.
DRAFT M6.SPD.002h 6 August 24, 1999
-------
3.2 Sample Selection
The vehicle sample for this analysis came from EPA Emission Factor testing performed
at both the Automotive Testing Laboratories, Inc. (ATL), in Ohio and EPA's National Vehicle
and Fuels Emission Laboratory (NVFEL), in Ann Arbor, Michigan, in the spring of 1997. All of
the vehicles at ATL were recruited at Inspection and Maintenance lanes run by the State of Ohio,
and were tested in an as-received condition (without repairs). At the time of this analysis, a total
of 62 1983 through 1996 model year vehicles had been recruited and had completed testing in
Ohio, and 23 1990 through 1996 model year vehicles recruited and tested in Ann Arbor. The
sample of 85 vehicles includes 22 light-duty trucks. Most of the 85 vehicles were fuel injection,
with 3 carbureted passenger cars and 4 carbureted light duty trucks.
The vehicles tested at the EPA laboratory were recruited randomly. The vehicles tested at
ATL were selected as a stratified random sample, with strata corresponding to EVI240 pass or fail
outcome determined at state run EVI240 inspection stations in Ohio. ATL used the final phase-in
cutpoints recommended by EPA for use in I/M programs using the EVI240 test procedure to
identify vehicles in need of maintenance. Twenty of the vehicles in the ATL sample failed the
EVI240 test. Proper analysis of the ATL data requires careful weighting of the passing and failing
vehicles if emitter status is not considered as a factor in the analysis.
Table 4 shows the mix of EPA vehicle emission certification standards and fuel delivery
technology in the sample used in this analysis. Table 5 lists all of the vehicles individually,
showing vehicle make and model, odometer mileage, engine size and whether the vehicle passed
or failed an EVI240 test procedure using final phase-in cutpoints. Table 6 shows the mix of
model years and vehicle class (car or truck) in the sample.
3.3 Vehicle Testing
All vehicles were tested in the as-received condition using vehicle certification test fuel.
Testing of all cycles were done in random order to reduce any order bias. Vehicles were tested at
FTP ambient conditions. Emission results were measured both as composite "bags" and in
grams second by second. Only the bag results were used in this analysis.
4.0 STATISTICAL ANALYSES
The purpose of the testing using the new facility cycles was to determine the effects of
average speed on emissions using "real world" driving cycles. Separate cycles were developed
for freeway and arterial/collector roadways to allow comparison of those two roadway types.
The testing program also "over sampled" high emitting vehicles in order to provide a sufficient
sample size to allow separate analysis of high emitting vehicles. Although vehicle mileage (or
vehicle age) is considered important for estimating emissions, it is not thought that vehicle
mileage is a factor in the effect of average speed on emissions. Together, the following testing
DRAFT M6.SPD.002h 7 August 24, 1999
-------
and vehicle parameters were considered as potentially important in determining the effect of
average speed on emissions:
1. Emitter status.
2. Roadway type.
3. Vehicle class.
4. Exhaust Emission Standard.
The data from the vehicles tested using the new facility cycles were evaluated to
determine if the effect of the average speed on emissions differed significantly by these
parameters. The sections below (Sections 4.1 through 4.4) discuss the statistical results for each
parameter evaluated. Section 4.5 discusses the statistical support for the convergence of the
freeway and arterial/collector estimates. Section 4.6 summarizes the conclusions derived from
the statistical analysis. Chapter 5 describes the final proposed methodology.
Other factors were considered. Although there is a large range of model years (1983
through 1996 model years), the sample size (85 vehicles) was not sufficient for analysis explicitly
by model year or age. For the analysis, the difference in model years is assumed to be captured
by the difference in emission standards.
Table 7(a-c) shows sample means and standard deviations for the combined dataset for
each cycle, stratified into high and normal emitter levels. A vehicle may be a Normal emitter for
one pollutant, but considered a High emitter for another. In some cases the sample sizes
(Normal and High) do not sum to 85 vehicles. This is because some test results on some vehicles
were voided due to errors in the testing or sampling and could not be used. No valid emission
test results were eliminated from the analysis.
Figure l(a-c) graphically shows the effects of average speed on emissions. Each point is
the ratio of the mean for the emissions of each of the 14 facility cycles versus mean emissions for
the LA4 (Urban Dynamometer Driving Cycle) for the same vehicles. The data show that the
high emitting vehicles do not exhibit as much sensitivity to speed, resulting in smaller ratios.
It was expected that as the average speed increases the difference between emissions from
cycles representing arterial/collector roadways and emissions from cycles representing freeways
would decrease. A special analysis was done to confirm the observed convergence of freeway
and arterial/collector roadway emissions versus average speed. This analysis is discussed in
Section 4.5 below.
The method of analysis of variance was used to judge the effect of the above parameters
on the relation between average speed and emissions. The dependent variables in these analyses
were chosen to be the logarithm of grams-per-hour emissions. The grams-per-hour measure is
more stable than grams-per-mile, particularly at lower speeds, where very little distance is
traveled over a long time. The log transformation yields values that better satisfy the ANOVA
DRAFT M6.SPD.002h 8 August 24, 1999
-------
test requirements of normally distributed constant-variance errors. In the actual fitting of speed
correction factor equations, described in Section 5, gram-per-hour units were used for analysis at
average speeds less than 30 mph. However, at high speeds (average speeds above 30 mph),
using a linear fit and grams per hour units, when converted back to grams per mile, forces a curve
shape which does not match the data trends. For speeds above 30 mph, gram per mile units were
used.
Table 8 reports the ANOVA results in terms of p-values associated with tests of the
various factors described above. The p-value gives a concise way of judging statistical
significance. The p-value of a test is the smallest level of significance at which the null
hypothesis can be rejected. In these models, the null hypothesis states that the levels of a given
factor, e.g., roadway type, have equal effect on emissions. The level of significance for this test is
the probability of Type I error, i.e., of rejecting the null hypothesis when it is true, that is, of
falsely concluding that a difference exists. By convention, the level of significance is chosen to
be arbitrarily small, typically 0.05, in order to limit the occurrence of Type I error. If p is smaller
than the chosen level of significance, the null hypothesis is rejected in favor of the claim that a
difference exists.
For example, in comparing the normal and high emitter classes of total hydrocarbons,
Table 8 reveals a p-value of 0.000 for the main effect of the emitter class. In graphical terms, the
main effect captures the intercept of a line relating (log) emissions to speed. Thus, the small p-
value agrees with the rather obvious hypothesis that high emitters have different average
emissions than normal emitters. However, for the interaction of emitter class with speed, the p-
value is 0.1411, implying that difference in the slopes (the relationship between emissions versus
average speed) of the normal and high emitter lines (regressions) is not statistically significant.
Further, more detailed ANOVA results are shown in Appendix A at the end of this report.
We now consider the statistical results for the individual factors.
4.1 Emitter Status
The sample was separated into "emitter status groups" based on their Hot Running LA4
exhaust emissions. Hot Running LA4 are emissions that would result from an FTP test which
does not include any engine starts. These emissions are intended to be the basic unit of exhaust
emissions for use in MOBILE61. The emitter status groups were defined by the following
pass/fail cutpoints:
0.8 g/mi Total Hydrocarbons (THC)
15 g/mi Carbon Monoxide (CO)
2.0 g/mi Oxides of Nitrogen (NOx)
These are the final phase-in cutpoints recommended by EPA for use in I/M programs
using the EVI240 test procedure to identify vehicles in need of maintenance. A vehicle is
DRAFT M6.SPD.002h 9 August 24, 1999
-------
considered a Normal emitter if its emissions are less than or equal to the outpoint level for that
pollutant. It is considered a High emitter if its emissions exceed the cutpoint level for that
pollutant. Once a vehicle is identified by emitter status for a pollutant using the Hot Running
LA4 emission results, it is always categorized that way in this analysis, regardless of its emission
results on another driving cycle. The cutpoints were not used in combination. A vehicle could
be considered as a Normal emitter for the CO analysis even if it were designated as a High
emitter for NOx or THC.
Table 8 confirms that the average emissions differ statistically by emitter class. The
speed variable also is significant, i.e., emissions vary with average speed. However, except for
CO, the emitter class-speed interaction is statistically non-significant.
While it is not always the case that the other factors - roadway type, vehicle type, and
emissions standard - interact statistically with emitter class, engineering judgement warrant
modeling these factors separately for normal and high emitters. Statistical conclusions for these
factors are presented next.
4.2 Roadway Type
For modeling in MOBILE6, four roadway types are considered: arterial/collectors,
freeways, freeway ramps and local roads. With arterial/collectors and freeways, the range of
average speeds in the facility cycles overlaps at speeds below 30 mph. At higher speeds, only
freeway cycles are available. The interaction between roadway type and vehicle type and
between roadway type and emission standard was examined.
Figure 2 (a-c) shows the effects of average speed on emissions in terms of the ratio of the
means for the emissions versus emissions for the LA4 (Urban Dynamometer Driving Cycle) for
normal emitting vehicles. The cycles representing freeway driving and arterial/collector driving
are connected with lines to show the difference in these road types versus average speed. The
Unified Cycle (LA92), the Area-wide Non-Freeway cycle, Local Roadway cycle and Freeway
Ramp cycle results are also shown in the figures. The same vehicles were tested on all cycles, so
differences between freeways and arterial/collectors are controlled for the vehicle effect.
The emissions data were compared statistically to determine if there is reason to model
arterial/collectors and freeways separately. The ANOVA results appear in Table 8. For all
pollutants in the normal emitter class, the main effects are statistically significant. The speed
interaction effects also are significant, albeit marginally so for hydrocarbons. Among high emitter
vehicles, only NOx exhibits a significant difference between the arterial/collector and freeway
road types.
Since only freeway cycles are represented at speeds over 30 mph, no comparisons of
roadway type are required. Local roadways and freeway ramps are represented by only a single
cycle each and therefore cannot be analyzed for the effect of average speed.
DRAFT M6.SPD.002h 10 August 24, 1999
-------
4.3 Vehicle Class
Of the 85 vehicles in the facility cycle sample, 22 are light duty trucks. The high emitters
among the trucks number three for NOx, six for CO and 10 for THC/NMHC. In the freeway and
arterial/collector roadway categories, for the normal emitters, the ANOVA results for passenger
cars versus light duty trucks in Table 8 show significant main effects. However, the interaction
with speed effects all are non-significant. For the high emitters, none of the vehicle type
comparisons is statistically significant at the 0.05 level.
For the local and freeway ramp driving cycles, the results are mixed for normal emitter
vehicles. NOx emissions differ at the 0.05 level on both cycles and CO is significant for the
ramp cycle. Among high emitters, vehicle type is not significant for any of the pollutants on
either cycle.
4.4 Emission Standard
It was expected that vehicles certified to the new Tier 1 exhaust emission standards would
exhibit a different response to average speed than the Tier 0 vehicles. Since the facility cycle
sample contains only 12 Tier 1 vehicles, a method was developed for increasing the sample size
by reclassifying a portion of the Tier 0 vehicles in the sample. Vehicles were defined as "Clean"
Tier 0 vehicles if their emissions were less than 70% of both the NMHC and NOx Tier 1
certification standard as measured on the standard FTP test. The Tier 1 standards are:
o NMHC standard: 0.25 g/mi (< 50,000 miles), 0.31 g/mi (>50,000 miles).
o NOx standard: 0.4 g/mi (< 50,000 miles), 0.6 g/mi (>50,000 miles).
A total of eight clean Tier 0 vehicles were identified by this criterion. One Tier 0 vehicle
(number 5016) had low FTP Bag 1 and Bag 3 emissions and technically qualified for
reassignment. However, because it had large Bag 2 and EVI240 emissions, it was not considered
representative of Tier 1 emission behavior and thus retained Tier 0 status under the new
definition. The clean Tier 0 vehicles were used both in the analysis of both Tier 0 and Tier 1
emission levels. Table 9 shows the subset of 20 vehicles used to represent Tier 1 emission
behavior. Tables 11 (a-d) show the average emissions for each driving cycle in the sample of
normal emitting Tier 0 vehicles, high emitting Tier 0 vehicles and the expanded sample of
vehicles considered normal emitting Tier 1 vehicles. Figure 3 (a-c) compares the Tier 0 and the
expanded Tier 1 sample of vehicles for the difference in the effects of average speed on
emissions. Emissions are shown in terms of the ratio of the means for the emissions versus
emissions for the LA4 (Urban Dynamometer Driving Cycle).
The ANOVA results in Table 8 compare emissions of the Tier 0 and Tier 1 vehicles for
the reallocated sample. On the arterial/collector and freeway cycles, for normal emitters the
emissions standard main effect is highly significant for all pollutants, and the interaction with
speed is significant for hydrocarbons. (The results are similar for the official emission standard
DRAFT M6.SPD.002h 11 August 24, 1999
-------
classification.) For the local and freeway ramp facility cycles, all main effects are also significant.
There were no high emitter Tier 1 vehicles for any of the pollutants, so no test of the
standard factor can be made for that emitter class.
4.5 Convergence of Freeways and Arterial/Collectors
The data show a statistical difference between the freeway and arterial/collector cycles
below 30 mph, where the data overlaps. However, there are no arterial/collector cycles above
24.8 mph and there are no freeway cycles below 13.1 mph. If the speed correction factors for
both of these roadway types are to cover the entire spectrum of average speeds available in the
MOBILE6 model (0 to 65 mph), then some assumptions about the effect of average speed on
emissions will need to be made for the speeds outside the typical range for these roadways.
Based on the facility cycle emission testing results, it appears that as average speed
increases there is a decrease in the difference between emission results for arterial/collector
cycles and freeway cycles at the same average speed. This suggests, that above a certain average
speed, the same relationship between average speed and emissions can be used for both freeways
and arterial/collector roadways.
Support for the hypothesis that mean gram-per-hour emissions of arterial and highway
driving converge in the neighborhood of 30 mph can be found in the data from tests on the cycles
that represent these two forms of driving. Consider the following model of emissions:
Y = b0 + bjX + b2*D + b3X*D
where Y is emissions (in grams/hour) of a given pollutant; X is average speed of the cycle tested;
and D is a dummy variable representing road type (D = 0 for arterial, D = 1 for highway). This
equation effectively models two lines. When D = 0, the function estimates emissions versus
speed for arterials, with slope bl and intercept b0. When D = 1, the line represents highway
emissions with slope (bx + b3) and intercept (b0 + b2).
This model is useful for examining differences between arterial and freeway emissions.
The basic question of whether the linear functions differ is answered by testing the coefficients of
terms involving variable D. If both these coefficients (b2 and b3) are zero, then the road types are
judged to be the same. For the 85 car sample, tests of this hypothesis are rejected for all
categories of emission standard and emission level.
Given that arterial and highway speed-emissions lines are significantly different, we now
ask if they differ at a chosen speed, e.g., 30 miles per hour. This is answered by constructing an
appropriate function of the linear model described above. When X = 30, the function becomes:
DRAFT M6.SPD.002h 12 August 24, 1999
-------
Y= b + 30 forarterials
Y= b0 + b1*30 + b2*l+b3*l*30
= (b0 + b2) + (bj + b3)*30 for highways
The two functions are identical when the linear combination b2 + b3*30 equals zero. This
hypothesis can be tested using the ESTIMATE feature of the SAS GLM procedure.
Table 10 presents results of these tests for Tier 0 normal and high emitters, and for Tier 1
normal emitters. At the five percent level, a significant difference is found in only in one case,
for Tier 0 normal CO emissions. This gives strong support for the claim that arterial/collector
roadway and freeway emissions are similar at speeds around 30 mph, even though their
relationship at average speeds below 30 mph is different. Based on this convergence, we propose
that the relationship between average speed and emissions for arterial/collector roadways and
freeways should be the same at average speeds above 30 mph.
4.6 Summary
The statistical analysis of the important parameters resulted in the following decisions
about how the data would be grouped for the MOBILE6 analysis:
Roadway Type
There will be different equations for the two roadway types (freeways and
arterial/collectors) for CO and NOx emission at both High and Normal emitter groups. There
will be different equations for the two roadway types for THC and NMHC emissions only for
normal emitting vehicles. Since the equations converge, there will be only one equation for all
roadway types and pollutants at average speeds above about 30 mph. The exact average speed
where the equations converge varies. For high emitting Tier 0 vehicles there will be no
difference between the two roadway types for THC and NMHC emissions at any average speed.
Vehicle Class
There will not be different equations for vehicle class (car versus truck). The equations
will depend on emission level (below), which will adequately cover any emission standard
differences between cars and trucks. Splitting the data by both emission standard (below) and
vehicle class would make sample sizes much too small for any meaningful results.
Emission Standard
There will be separate equations for Tier 0 and Tier 1 emission standard vehicles for
normal emission levels. There are no high emitting Tier 1 vehicles in the sample.
DRAFT M6.SPD.002h 13 August 24, 1999
-------
Emission Levels
The Tier 0 emission standard data will be further separated by emitter status (Normal and
High) for all pollutants with separate speed equations for each. For the purpose of analysis, this
effectively results in three samples of vehicles representing three distinct emission levels:
Level 1 : Tier 1 (Normal emitter)
Level 2 : Tier 0 (Normal emitter)
Level 3 : Tier 0 (High emitter)
5.0 EMISSION LEVEL CALCULATION
Once the appropriate aggregations for the existing data were determined as described in
the previous section, least square linear regressions were fit to the emission results versus
average speed. This was done in a "multi-linear" fashion, rather than using a single line or using
another non-linear curve shape. Attempts to fit non-linear curves to the total data sample
resulted in unacceptably high error coefficients. A linear fit of smaller groupings of the data
provided a closer fit to the data. A separate linear regression was done for different groupings of
cycles based on ranges of average speeds. Together, these lines will define the change in
emissions of the sample over the entire range of average speeds.
5.1 Freeway Versus Arterial/Collector Effects
As discussed in the previous section, the data show a statistical difference between the
freeway and arterial/collector cycles below 30 mph, where the data overlap. However, there are
no arterial/collector cycles above 24.8 mph and there are no freeway cycles below 13.1 mph. If
the speed correction factors for both of these roadway types are to cover the entire spectrum of
average speeds available in the MOBILE6 model (0 to 65 mph), then some assumptions about
the effect of average speed on emissions will need to be made for the speeds outside the range for
which we have data.
Logically, both curves will converge at idle (zero mph). Idling emissions should not
depend on roadway type. Also, it is logical to assume that driving which has a high average
speed must consist almost entirely of cruise with little stopping or idle, regardless of roadway
type. This suggests a model where freeways and arterial/collector roadways have different
emissions at normal arterial/collector average speeds, but have the same emissions at extremely
low speeds (and idle) and at higher speeds. Based on this model, we have defined the following
speed/facility segments:
o High Speeds (above about 30 mph) for both freeways and arterial/collectors.
o Intermediate Speed Freeways (from 13.1 to about 30 mph) for freeways.
o Low Speed Freeways (from 7.1 to 13.1 mph) for freeways.
DRAFT M6.SPD.002h 14 August 24, 1999
-------
o Arterial/Collectors (from 7.1 to about 30 mph) for arterial/collectors.
o Extremely Low Speed and Idle (less than 7.1 mph) for both freeways and
arteri al/coll ector s.
We propose to use a combined emission estimate for both arterial/collector and freeway
facilities for THC and NMHC at the highest emission level. This will mean that, at high emitting
THC and NMHC emission levels, that there will be no emission difference between the two
facility types. There would still be separate freeway and arterial/collector estimates for CO and
NOx emissions at high emitting levels.
5.1.1 High Speeds
A regression was done of emissions versus average speed for the three emission
standard/emitter groups described above for the four freeway cycles with an average speed above
30 mph (Freeway at 30.5 mph, Freeway at 52.9 mph, Freeway at 59.7 mph and Freeway at 63.2
mph) in grams per mile for each pollutant. Tables 12a, 12b, 12c and 12d show the results of
those regressions. All of the slope coefficients of the regressions are statistically significant,
meaning that the increase or decrease in emissions versus average speed is different than zero.
These regressions will be used to estimate the emissions of vehicles on both freeway and
arterial/collector roadways at average speeds above the point where the equations converge.
5.1.2 Intermediate Speed Freeways
A regression was done of emissions versus average speed for each of the emission
standard/emitter groups described above for the four freeway cycles representing freeway driving
in the most congested conditions (Freeway at 13.1 mph, Freeway at 18.6 mph and Freeway at
30.5 mph) in grams per hour for each pollutant. Tables 12a, 12b, 12c and 12d show the results of
those regressions. These regressions will be used to estimate the emissions of vehicles on
freeways between average speeds of 13.1 mph and about 30 mph. Note that the freeway cycle at
30.5 mph was included in both the intermediate speed freeway and high speed estimates. It is
expected that the two regressions should converge at about this average speed.
5.1.3 Low Speed Freeways
None of the existing facility cycles for freeway driving have an average speed below 13.1
mph. It will be assumed that at speeds lower than 7.1 mph (the average speed of the New York
City Cycle) the effect of average speed on emissions will be the same for freeways and
arterial/collector roadways. The emissions of freeway driving for average speeds between 13.1
mph and 7.1 mph will be calculated by linear interpolation between these emission levels in
grams per hour. Tables 12a, 12b, 12c and 12d show the resulting equations representing this
interpolation. Most freeway travel will occur at average speeds well above this range.
DRAFT M6.SPD.002h 15 August 24, 1999
-------
5.1.4 Arterial/Collectors
The freeway cycle at 30.5 mph (already included in the freeway estimate) was included in
the arterial/collector roadway estimates as well. It was shown that the two regressions should
converge at about this average speed. The New York City Cycle was also included in the
arterial/collector roadway estimates. The New York City Cycle was not derived from the same
chase car or instrumented data used to develop the other facility cycles. However, the New York
City Cycle was originally developed as a speed correction cycle and, as shown in Table 3, does
contain acceleration rates higher than the contained in the LA4 (Urban Dynamometer Driving
Schedule). It was deemed that the New York City Cycle was representative of "real world"
driving and could be included in the analysis as another facility cycle.
A regression was done of emissions versus average speed for each of the emission
standard/emitter groups described above for the arterial/collector cycles (Arterial/Collector at
11.6 mph, Arterial/Collector at 19.2 mph, Arterial/Collector at 24.8 mph) in grams per hour for
each pollutant. Included in that regression was data from the New York City Cycle (with and
average speed of 7.1 mph) and the Freeway at 30.5 mph cycle for the same vehicles.
Tables 12a, 12b, 12c and 12d show the results of those regressions. These regressions
will be used to estimate the emissions of vehicles on arterial/collector roadways in this range of
average speeds.
5.1.5 Extremely Low Speeds and Idle
No data was collected for the vehicles in the sample at speeds lower than 7.1 mph (the
average speed of the New York City Cycle). In this range the model will assume that the effect
of average speed on emissions will be the same for freeways and arterial/collector roadways.
Since the MOBILES model already has estimates for the effect of average speed on vehicles at
speeds from 2.5 to 7.1 mph, and since there is no need to differentiate this effect by facility type,
the existing speed correction factors in MOBILES will be used for this range of average speeds
for both freeways and arterial/collectors.
The MOBILES speed correction factors do not match the new proposed speed correction
factors at 7.1 mph. This discontinuity will be resolved by adding the difference in the two
estimates to values calculated using the old MOBILES speed correction factors. As in
MOBILES, emissions at idle will be assumed to be the same (in grams per hour) as the emissions
at 2.5 mph (the lowest average speed modeled).
5.2 Local Roadways and Freeway Ramps
There is only one cycle each to represent driving on local roadways and freeway ramps.
As a result, these cycles are not included in the analysis of emissions versus average speed.
However, the data from these cycles were separated using the same sample splits by emission
DRAFT M6.SPD.002h 16 August 24, 1999
-------
standard (Tier 0 versus Tier 1) and emitter status (Normal versus High) as are used for the
freeway and arterial/collectors. The average emission levels were analyzed as a linear function
of the base emission rate (hot running LA4 emissions). These regressions will be used to
estimate the emission levels for these roadway types as a function of the base emission rate
calculated in MOBILE6. The coefficients for these regressions are shown in Table 13.
5.3 Special Cases
Ideally, the equations above would define a rational, smooth relationship for emissions
versus average speed for the range of 0 to 65 mph for each pollutant based on the available data.
However due to vagaries of using real-world data and the use of a multi-linear modeling
approach, some of the equations resulting from the general approach will cause small
discontinuities in the overall relationship. For example, the intermediate speed freeway emission
level for NOx (computed in gram per hour) does not intersect with the high speed freeway
emission level estimate (computed in grams per mile) at any speed. These discontinuities, when
examined, do not cast doubt on the overall relationship, but will require special handling to be
coded mathematically. A single smooth curve could be fit to the data over all speeds. This
would generate different and more difficult problems, however, such as an unacceptably poor fit
in certain speed ranges. For MOBILE6, some basic "rules" will be used to assure that there are
no abrupt or counter-intuitive changes in emissions versus average speed.
1) If at 30.5 mph, the emission estimate for the intermediate speed freeway equation is still
higher than the emissions for freeways calculated using the high speed equation, the
emission value calculated for 30.5 mph using the intermediate speed freeway equation
will be used for speeds greater than 30.5 mph until the value for the high speed equation
for that speed exceeds the intermediate speed freeway value. This rule keeps the
intermediate speed freeway value from increasing beyond the emission level calculated at
30.5 mph, which is the highest average speed data point used in the regression (no
extrapolations).
2) When calculating the emissions of an arterial/collector roadway, the arterial/collector
estimate for emissions will be used unless the estimate for freeways at that same speed
are higher than the arterial/collector estimate. This rule defines at what average speed the
arterial/collector and freeway emission estimates will converge. Above that speed the
arterial/collector and freeway emission estimates will be assumed to be the same. All of
the MOBILE6 arterial/collector equations intersect with the freeway estimate between 24
and 34 mph.
6.0 SPEED CORRECTION FACTORS
Using the methods in the previous section, the emission data can be described as a series
of continuous, smooth functions for the two roadway types (freeways and arterial/collectors) by
emission levels for all pollutants over the entire range of average speeds in MOBILE6 (2.5 to 65
DRAFT M6.SPD.002h 17 August 24, 1999
-------
mph). This generalized relationship between emissions and average speed for any emission level
is referred to in the model as speed correction factors. These speed correction factors are the
values which will be stored and used in MOBILE6 to adjust the basic exhaust emission estimate
for average speed. Freeway ramps and local roadways, however, have only a single cycle and
cannot vary by average speed. MOBILE6 must also estimate speed effects for groups of vehicles
with basic emission rates that differ from those in the data sample.
6.1 Basic Modeling Approach
The basic exhaust emission rate generated by MOBILE6 will be based on a hot running
LA4 emission estimate with an average speed of 19.6 mph. In MOBILE6 Freeway Ramp and
Local Roadway emissions do not depend on speed and can be determined directly from the basic
exhaust emission rate. For freeways and arterial/collector roadways, the adjustment to account
for the average speed and facility type includes an multiplicative part and a additive part. The
multiplicative part accounts primarily for the difference in emissions due to changes in average
speed. The additive part accounts primarily for the difference between the basic emission rate,
based on the running emissions for the LA4 cycle, and the running emissions on the facility at the
same average speed. In MOBILE6, we propose that the basic emission rate be adjusted using the
following general method:
Adjusted BER = (BER + EO) * SCF + AEO
Where:
BER = Basic Emission Rate (running emissions for the LA4 cycle).
EO = Emission Offset (a function of BER emissions)
SCF = Multiplicative Speed Correction Factor (a function of speed and
emissions).
AEO = Arterial/Collector Emission Offset (a function of speed and emissions).
For freeways, the AEO would be zero, since it only applies to arterial/collector roadways.
Using the above equation, with a BER identical to the average hot running LA4 emissions of
each sample of vehicles in each of the three emission level groupings described in Section 4.6,
the estimate of emissions at any speed for each facility will match the average emission level
predicted by the regression equations from the facility cycle data from that vehicle sample. For
cases where the BER is not identical to the average hot running LA4 emissions of any of the
facility cycle sample emission level groupings, the EO will still be calculated as a function of the
BER, however the SCF and AEO adjustments will be interpolated using the three emission level
sample estimates. The interpolation would be determined by the emission level of the sum of the
BER and the EO. There are five cases:
DRAFT M6.SPD.002h 18 August 24, 1999
-------
o If the emissions are between the Level 1 and the Level 2 emission levels, the SCF
and AEO factors would be interpolated between those two curves.
o If the emissions were between the Level 2 and the Level 3 emission levels, the
SCF and AEO factors would be interpolated between those two curves.
o If the emissions were equal to the Level 2 emission level, the Level 2 SCF and
AEO factors would be used.
o If the emissions were equal to or above Level 3 emission level, the Level 3 SCF
and AEO factors would be used.
o If the emissions were equal to or below Level 1 emission level, the Level 1 SCF
and AEO factors would be adjusted proportionally to the change in the BER and
accounting for differences in the emission standards. This will be discussed in
Section 6.4 below.
In this way, an emission offsets and an effect of average speed can be calculated for any
basic exhaust emission rate for any average speed allowed in MOBILE6 for each facility type.
6.2 Emission Offsets
In order to appropriately apply the multiplicative (proportional) speed correction factors
(SCF) of the form described in Section 6.1, first the basic exhaust running emission rate (BER)
must be adjusted to match the emissions observed on the freeway cycles at the same speed as the
BER (19.6 mph). All other speed adjustments are applied to this new, adjusted BER emission
level.
6.2.1 Freeway Emission Offset Calculation
The emission offset is simple in concept. It is simply the difference between the average
emissions of vehicles from the Hot Running LA4 cycle (the basis of the BER) and the predicted
average emissions of the same vehicles from the regressions using the freeway cycles from
Section 5.0 above.
Emission Offset = Freeway Cycle at 19.6 mph - Hot Running LA4 Cycle
The emission offset (EO) is calculated for each of the three emission levels (see Section
4.0). Table 14 shows the emission offsets calculated for the three emission levels. As described
in Section 6.1, the EO values can be adjusted to reflect any BER emission levels greater than
Level 1 directly by interpolation. Emission levels less than Level 1 (Tier 1) are discussed in
Section 6.4 below.
DRAFT M6.SPD.002h 19 August 24, 1999
-------
6.2.2 Arterial/Collector Emission Offset Calculation
Arterial/collector cycles have higher emissions than freeway cycles at the same average
speed. For MOBILE6, we propose to account for this difference as an additional emission offset
effect, beyond that already accounted for by the freeway emissions estimate. Since the difference
between the emissions of arterial/collector cycles and freeway cycles varies with average speed,
this additional emission offset effect will be dependent on average speed.
AEO at X mph = Arterial/Collector emissions at X mph - Freeway emissions at X mph
The arterial/collector emission offset (AEO) is calculated for each of the three emission
levels (see Section 4.0). Table 15 shows the arterial/collector emission offsets calculated for the
three emission levels at each speed. As described in Section 6.1, the AEO values can be adjusted
to reflect any BER emission levels greater than Level 1 directly by interpolation. Emission levels
less than Level 1 (Tier 1) are discussed in Section 6.4 below. The AEO is always zero below 7.1
mph and above about 30 mph where arterial/collector and freeway estimates are identical. The
AEO is also zero for Level 3 THC and NMHC emissions, since the freeway and arterial/collector
emission estimates are the same for this emission level/pollutant.
6.3 Calculating Speed Correction Factors
As discussed in Section 6.2, for MOBILE6 we propose to adjust the basic exhaust
emission rates (BER) by first adding an emission value (emission offset, EO) to adjust the BER
to the level of the freeway emissions. This EO value will be a function of the basic exhaust
emission rate. An additional offset (the Arterial/Collector Emission Offset (AEO)) is added to
the freeway emission level to account for arterial/collector driving effects. The speed correction
factors are applied to the sum of the BER and the EO.
As the data has shown, the effect of average speed on emissions depends on emission
level. Therefore, the appropriate form for speed correction would be a multiplicative adjustment,
making the change in emissions due to change in average speed proportional to the basic exhaust
emission rate.
For MOBILE6, the speed correction factor (SCF) is defined as the ratio of the predicted
emissions at any average speed to the predicted emissions at 19.6 mph for freeways for the same
vehicle. The freeway emission levels are defined for all average speeds from 2.5 to 65 mph.
Using the emission level equations described in Section 5, a set of SCFs will be determined for
each speed in increments of 5 mph beginning at 5 mph through 65 mph and at 2.5 mph for each
of the three emission levels within MOBILE6. These increments correspond to the proposed
increments of average speed for the VMT distribution for freeways and arterial/collector
roadways which we propose as input to MOBILE6. We propose to have MOBILE6 calculate
DRAFT M6.SPD.002h 20 August 24, 1999
-------
these speed correction factors directly from the emission levels, rather than store the resultant
speed correction factors themselves. Table 16 shows the freeway SCF sets for the three emission
levels. These SCF sets are shown graphically in Figures 5a, 5b, 5c and 5d. Table 16 shows the
freeway emissions at 19.6 mph for each emission level. Table 17 shows the arterial/collector
SCF sets for the three emission levels.
Speed correction factors for emission levels below Level 1 (Tier 1) must account for the
effects of more stringent emission standards. This is discussed in Section 6.4 below.
6.4 Effect of the NLEV Standards and the Supplemental FTP
Starting in the 2001 model year, light-duty vehicles will be certified for sale using a new
test procedure, referred to as the Supplemental Federal Test Procedure (SFTP). Vehicles
certified using this test procedure will have lower emissions during typical driving than vehicles
certified using the current test procedures, primarily by requiring reductions in emissions during
hard accelerations and with accessory loads, like air conditioning. These vehicles will also have
to meet tighter National Low Emission Vehicle (NLEV) emission standards. The effects of
speed (including aggressive driving) on NLEV may differ from current vehicles. However,
speed corrections for NLEVs cannot be determined directly from the available NLEV emission
data. Not enough data on in-use NLEV vehicles is available yet.
The basic exhaust emission rates and emission offsets for NLEV will differ from Tier 1
vehicles in several ways. In addition to lower exhaust emission standards, the emission offsets
for normal emitting NLEV vehicles will be affected by the SFTP. Although high emitting
NLEV standard vehicles will have basic exhaust running emission rate (BER) emissions higher
than Level 1 (average emissions based on the sample of normal emitting Tier 1 vehicles), the
effect of the SFTP will likely reduce the offset for these vehicles as well. The amount of this
reduction will be addressed in a separate document describing the effects of the SFTP. It is
sufficient to know here that a separate set of emission offsets will be used for NLEV vehicles
which reflect the effect of the SFTP.
In addition to the adjustments to the EO and AEO, the multiplicative speed correction
factors (SCF) for Level 1 (Tier 1) will also be adjusted to account for the change in emission
standards for basic exhaust running emission rates less than Level 1. Using the multiplicative
Level 1 SCF without adjustment would assume that the change in standards had affected all types
of driving behavior emission effects proportionally. If we compare the Tier 1 SCFs to the Tier 0
normal SCFs (as in Figures 5a-d), the effect appears to increase as emission levels decrease. It is
likely that NLEV standard vehicles should be more sensitive to changes in average speed than
Tier 1 vehicles.
An alternative to using the Tier 1 multiplicative SCFs would be to use the same change in
emissions observed in Tier 1 vehicles versus speed (additively) to represent the effects of speed
for NLEV standard vehicles. This additive approach would match the trend in SCFs, but
DRAFT M6.SPD.002h 21 August 24, 1999
-------
assumes that there is no effect from new standards on the emission effects from changes in
average speed. It is likely that NLEV standard vehicles are less sensitive to changes in average
speed than estimated by the additive approach.
The two alternatives (multiplicative and additive) discussed above can be summarized as
the following two sets of equations:
BERspeed=BER*SCFmult
and
SCFadd = (SCFTierl - 1.0) * Tier 1 Sample Average Emission Level
BERspeed= BER + SCFadd
where
is the speed corrected basic emission rate.
SCFmult is the speed correction factor assuming a multiplicative adjustment.
SCFadd is the speed correction factor assuming an additive adjustment.
SCFTierl is the speed correction factor for Tier 1 vehicles at a given speed.
BER is the NLEV basic emission rate, unadjusted for speed.
Rather than choose between the additive and multiplicative approaches described above
for NLEV standard vehicles, we propose to choose SCF values that lie between these two
estimates. These SCFs would be used for all NLEV standard vehicles, and other vehicles with
emission standard levels less than Tier 1, regardless of emission level. We strongly encourage
readers to comment on this issue and propose alternate solutions to selecting SCFs for NLEV
standard vehicles.
6.5 Application in MOBILE6
We propose to apply the speed corrections described in this document to gasoline fueled,
light-duty vehicles (cars and light trucks) of all model years and technologies. The speed
correction factor would be applied to the basic exhaust hot running emission rates, adjusted to
freeway emission levels at 19.6 mph. Additional adjustment would be made to the freeway
emission estimate between 7.1 and about 30 mph to account for arterial/collector roadways.
MOBILE6 would continue to use the existing speed correction factors and methodology found in
MOBILES for diesel vehicles, gasoline fueled heavy-duty vehicles and motorcycles. Heavy-duty
diesel vehicles will also be adjusted for NOx excess emissions separately from the MOBILE6
speed correction factors.
DRAFT M6.SPD.002h 22 August 24, 1999
-------
In MOBILE6, the daily average emission rate will be calculated by VMT weighting an
emission estimate for each hour of the day. Within each hour of the day, there will be a
distribution of speeds for freeways and arterial/collectors, either a default national average or a
user supplied distribution. The speed correction would be applied to the estimate of Normal and
High emitters within each model year separately. Older (pre-1981) model year gasoline fueled,
light-duty vehicles will have only composite (combined Normal and High) basic exhaust
emission rates. In these cases the speed correction will be applied to the composite basic exhaust
emission rates (including both Normal and High emitters). Speed correction factors will not be
applied to the effects of engine start on emissions estimated by MOBILE6.
The speed distribution in MOBILE6 will consist of average speed "bins" from 5 to 65
mph in 5 mph increments and for 2.5 mph (14 speed bins) representing the distribution of
average speeds within each hour. Each hour of the day will have an estimate of the distribution
of vehicle miles traveled (VMT) on freeways, ramps, local and arterial/collector roadways.
These distributions will be used to weight together the emission estimates in each speed bin to
give an hourly emission estimate. Freeway Ramps and Local Roadways will have hourly
emission estimates and VMT estimates, but will not have speed distributions. The hourly
emission estimates will be weighted by the hourly VMT distribution separately for each facility.
Finally, the VMT distribution between facilities will be used to combine the results into an area-
wide running exhaust emission estimate. Emissions due to engine start within each hour will be
calculated separately. In summary, MOBILE6 will:
o Determine the basic running exhaust emission rate (BER).
o For each hour, correct the BER for temperature and fuel effects.
o Using the corrected BER, calculate the emissions for Freeway Ramps, Local
Roadways and for the 14 speed bins for freeways and arterial/collectors using the
appropriate emission offsets and speed correction factors described in this
document.
o Using the speed distributions, weight the freeways, ramps, local and
arterial/collector speed bin results to get hourly emissions.
o Using the hourly VMT distributions, weight together the hourly facility results to
get daily emissions by facility.
o Using the facility VMT distribution, weight the daily facility emissions to get the
area-wide running exhaust emission estimate.
o Combine the running exhaust emission estimate with the engine start emissions to
get the composite exhaust emission rate.
Appendix B shows an example calculation.
The national average default factors proposed to be used in MOBILE6 for VMT
weighting the speed-corrected, facility-type emissions into a single area-wide running emissions
rate is described in a report prepared for EPA by Systems Applications International3. This
report also contains the default distributions of average speeds on each facility over the day. All
DRAFT M6.SPD.002h 23 August 24, 1999
-------
of these default values can be overridden by the user with local information using methods
described in a separate guidance document4.
The operating mode inputs used in MOBILES will not be needed for MOBILE6. Instead,
MOBILE6 uses values for the number of engine starts, the distribution of soak times between
engine starts, the mileage accumulation rates and the distribution of these factors over the day5.
These values are used to determine the weighting of the running exhaust emissions with the
effects of engine starts to calculate a composite exhaust emission factor. Although MOBILE6
contains default values, these default values will normally be overridden by user supplied local
information.
Similarly, once the composite running and engine start emissions are calculated, the
composite exhaust HC emissions can be combined with the calculated non-exhaust HC
emissions. The reader should refer to the reports regarding the non-exhaust emission estimates
and their associated activity for more details on how these values are calculated.
7.0 COMPARISON TO MOBILES
Figures 6a, 6b, and 6c show the proposed MOBILE6 speed correction factors (SCFs) for
freeways compared to selected speed correction factors used in MOBILES. This comparison
cannot be made clearly, since the two versions of the model use very different approaches.
The proposed MOBILE6 SCFs depend on emission level and the MOBILES SCFs
do not.
The MOBILES SCFs are applied to a composite exhaust emission rate, including
engine start emissions. The MOBILE6 SCFs will only be applied to the hot
running exhaust emissions, before the effects of engine start are added.
The MOBILE6 SCFs are intended to estimate the effects on freeways excluding
ramp activity, but the MOBILES SCFs are a composite of all roadway types.
The MOBILE6 SCFs include the effect of additional aggressive driving effects on
emissions missing from the MOBILES SCFs.
The overall shape of the MOBILES and MOBILE6 SCFs is similar. The MOBILE6
SCFs are flatter at speeds greater than 55 mph than in MOBILES, especially for CO and NOx.
This may be due largely to the fact that the old speed cycles above 48 mph all started from idle
(zero mph) and accelerated to a speed higher than the average speed of the cycle. This extra
acceleration, which is not generally found on cruising vehicles on limited access freeways, adds
to the power demand, therefore likely increasing emissions in the old high speed cycles relative
to lower speed cycles. The acceleration to reach freeway speeds is now contained in the separate
ramp cycle. This additional ramp cycle will allow this effect to be weighted appropriately with
freeway driving. The effect from starting and ending at idle is less pronounced in the lower
speed cycles since they inherently have a higher percentage of driving at idle.
DRAFT M6.SPD.002h 24 August 24, 1999
-------
In Figure 6a (THC), the MOBILE6 SCF for the lowest emission level (based Tier 1
vehicles) has a positive slope beyond about 30 mph, indicating increasing THC emissions with
increasing average speed. However, as shown in Figure 4a, Tier 1 vehicles are much cleaner at
all speeds than the normal emitting Tier 0 vehicles. The shape of the THC MOBILE6 SCFs for
the higher emission levels (based on Tier 0 vehicles, Normal and High) is very close to the shape
of MOBILES SCFs.
For higher average speeds (above 19.6 mph) the proposed MOBILE6 SCFs for CO
emissions (Figure 6b) have a strongly positive slope at lower emission levels (based on Tier 0
Normals and Tier 1 vehicles). This is very different from the SCFs used in MOBILES. The
proposed MOBILE6 SCFs for THC/NMHC emissions for Tier 0 Normal vehicles have a negative
slope. However CO emissions are more sensitive to aggressive driving than THC/NMHC
emissions, which may explain the difference in the trends.
The proposed MOBILE6 SCFs for NOx emissions (Figure 6c) for the higher emission
levels (based on Tier 0 vehicles) have a slight upward trend at higher speeds, similar to the
MOBILES trends. The lowest emission level SCFs (based on Tier 1 vehicles) has a steep slope,
similar to the oldest MOBILES SCF. All of the proposed MOBILE6 SCFs tend to rise as average
speeds decrease, which is expected with more accelerations and decelerations (stop and go
driving) present in the driving patterns. However, the MOBILE6 SCFs rise much more steeply
and to higher levels than the MOBILES SCFs.
Since the Freeway Ramp and Local Roadway emissions are estimated directly from the
basic exhaust emission rate (based on the hot running LA4 emissions), they cannot be compared
to the speed correction factor used in MOBILES. When MOBILE6 is nearer completion, it will
be possible to create a composite result containing a weighted sum of all of the roadway types in
MOBILE6 that can be more fairly compared to MOBILES results.
8.0 COMMENTS
EPA is requesting that MOBILE model stakeholders and other knowledgeable readers
comment on the methodology and validity of the assumptions used to determine the speed
correction factors proposed in this document. Comments should clearly distinguish between
recommendations for clearly defined improvements that can be readily made in the short term
based on data reasonably at hand to EPA and improvements that are long term, exploratory or
dependent on data not currently available to EPA. The schedule for MOBILE6 will not allow for
the serious consideration of proposed long term improvements. However, these long term
comments will be considered for future data collection and data analysis. General areas for
review include:
Report clarity;
Overall methodology
Appropriateness of data sets selected;
DRAFT M6.SPD.002h 25 August 24, 1999
-------
Statistical approaches used;
Empirical relationships selected;
Appropriateness of the conclusions;
Recommendations for alternate data sources or methods.
Comments on this report and its proposed use in MOBILE6 may be submitted
electronically to:
mobile@epa.gov
or by fax to:
(734)214-4939
or by mail to:
MOBILE6 Review Comments
2000 Traverwood
US EPA Assessment and Modeling Division
Ann Arbor MI 48105
Electronic submission of comments is preferred. All comments may be made public. In
your comments, please note clearly the document that you are commenting on. Please be sure to
include your name, address, affiliation, and any other pertinent information.
DRAFT M6.SPD.002h 26 August 24, 1999
-------
References
1. Carlson, T.R., et al., "Development of Speed Correction Cycles," MOBILE6 Stakeholder
Review Document (M6.SPD.001). Prepared for EPA by Sierra Research, Inc., 1997.
2. Brzezinski, D.J., et al., "Coefficients for the Determination of Engine Start and Running
Emissions From FTP Bag Emissions," MOBILE6 Stakeholder Review Document
(M6.STE.002), 1997.
3. "Development of Methodology for Estimating VMT Weighting by Facility Type,"
MOBILE6 Stakeholder Review Document (M6.SPD.003) EPA420-P-99-006. Prepared
for EPA by Systems Applications International, Inc., 1998.
4. "Guidance for the Development of Facility Type VMT and Speed Distributions,"
MOBILE6 Stakeholder Review Document (M6.SPD.004) EPA420-P-99-004. Prepared
for EPA by Systems Applications International, Inc., 1998.
5. Glover, E.L., et al., "Soak Length Activity Factors for Start Emissions," MOBILE6
Stakeholder Review Document (M6.FLT.003),
DRAFT M6.SPD.002h 27 August 24, 1999
-------
Tables
DRAFT M6.SPD.002h 28 August 24, 1999
-------
Table 1
New Facility-Specific/Area-Wide Speed Correction Cycle
Statistics
Cycle*
Freeway, High Speed
Freeway, LOS A-C
Freeway, LOS D
Freeway, LOS E
Freeway, LOS F
Freeway, LOS "G"
Freeway Ramps
Arterial/Collectors
LOS A-B
Arterial/Collectors
LOS C-D
Arterial/Collectors
LOS E-F
Local Roadways
Non-Freeway Area-
Wide Urban Travel
Average
Speed
(mph)
63.2
59.7
52.9
30.5
18.6
13.1
34.6
24.8
19.2
11.6
12.9
19.4
Maximum
Speed
(mph)
74.7
73.1
70.6
63.0
49.9
35.7
60.2
58.9
49.5
39.9
38.3
52.3
Maximum
Accel Rate
(mph/s)
2.7
3.4
2.3
5.3
6.9
3.8
5.7
5.0
5.7
5.8
3.7
6.4
Length
(seconds)
610
516
406
456
442
390
266
737
629
504
525
1,348
Length
(miles)
10.72
8.55
5.96
3.86
2.29
1.42
2.56
5.07
3.36
1.62
1.87
7.25
* LOS (level of service) refers to roadway congestion categories. See Section 4.6.
DRAFT M6.SPD.002h
29
August 24, 1999
-------
Table 2
Comparison of Key Representativeness Statistics
For Facility-Specific Cycle Schedules
Versus Total Vehicle Observations
Driving Cycle
Freeway High-Speed
Freeway LOS A-C
Freeway LOS D
Freeway LOS E
Freeway LOS F
Freeway LOS G
Freeway Ramp
Arterial LOS A-B
Arterial LOS C-D
Arterial LOS E-F
Local Roadways
Unified Cycle
Mean
Speed
(mph)
Cyc.
63.2
59.7
52.9
30.5
18.6
13.1
34.6
24.8
19.2
11.6
12.8
24.6
Obs.
62.7
59.2
52.0
32.1
19.9
14.4
35.4
25.2
18.9
12.0
14.6
26.3
Maximum
Speed
(mph)
Cyc.
74.7
73.1
70.6
63.0
49.9
35.7
60.2
58.9
49.5
39.9
38.3
67.2
Obs.
80.9
83.2
75.8
71.3
69.5
49.1
79.1
74.9
71.3
56.8
62.7
80.3
Maximum
Accel Rate
(mph/sec)
Cyc.
2.7
3.4
2.3
5.3
6.9
3.8
5.7
5.0
5.7
5.8
3.7
6.9
Obs.
5.8
6.8
6.1
8.5
9.6
5.7
9.3
14.9
10.4
10.2
12.5
10.4
Total
SAFD
Difference
(%)
9.41
12.12
15.10
25.17
23.83
18.80
42.74
17.04
16.86
17.86
21.80
30.27
High-Power
Difference
(%)
0.16
0.39
0.35
0.18
0.06
0.10
0.99
0.40
0.21
0.24
0.11
0.19
DRAFT M6.SPD.002h
30
August 24, 1999
-------
Table 3
Statistics for Additional Tested Cycles
Cycle
LA4
(Urban Dynamometer
Driving Cycle)
Running 505
(First 505 seconds of the
Urban Dynamometer
Driving Cycle)
Unified Cycle (LA92)
ST01
(Engine Start Cycle)
New York City Cycle
(NYCC)
Average
Speed
(mph)
19.6
25.6
24.6
20.2
7.1
Maximum
Speed
(mph)
56.7
56.7
67.2
41.0
27.7
Maximum
Accel Rate
(mph/s)
3.3
3.3
6.9
5.1
6.0
Length
(seconds)
1368
505
1435
248
600
Length
(miles)
7.45
3.59
9.81
1.39
1.18
Table 4
Distribution of the Vehicle Sample
By Emission Standard and Technology
Fuel Delivery
Carburetor
Throttle Body FI
Multi-Port FI
Total Sample
TIER 0 Emission
Standard
7
27
39
73
TIER 1 Emission
Standard
1
11
12
Total
Sample
7
28
50
85
DRAFT M6.SPD.002h
31
August 24, 1999
-------
Table 5
Vehicle Sample Description
Site
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
Veh.
No.
5001
5002
5003
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
Veh.
Class
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDT1
LDV
LDV
LDV
LDT1
LDV
LDV
LDV
LDT1
LDT1
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDT1
LDV
LDT1
VIN
1G4AH51R7J6401871
1G3NL54UXKM283722
2FACP74F3MX162914
1G1JC14GOM7126454
1G1JC111XK7150483
1G3HY54C9JW3 12653
1FACP57U5NG145893
1G2WP14T6KF307905
4T1SK12E9PU184046
2C1MS2468P6704533
1G2NV54D9JC821314
1G2NE5434PC795009
1G6CD53B7M4272204
1G2NE5438PC758996
1G4HR54C5KH488839
WVWEB5159MK012875
1B3ES27C9SD221573
1G1FP23TXLL1 11092
1FACP5245NG196687
1B3ES67C2SD188892
1G1JC1112KJ207455
1FAPP36X6JK249611
2FAPP36X8MB1 16542
1N6SD16S6MC351945
1 MEBM50U3KG663746
JE3CU14A1NU003588
1YVGE22A8P5138202
1P4FH4430KX568849
1FABP29D9GA165884
JT2SV24E8J3 189405
1MEBP923XFA603099
1GCBS14E3H2170996
1GCBS14A3F2156946
1FABP37X6HK239681
JN1HM05S8HX081093
1P3BP49CXDF305484
2G1WL52M2T9212643
1HGED3554JA017137
2HGED6359KH534893
JT2EL32G3H0076681
1GCDM15NXFB180388
2HGED6349KH537915
1GTBS14E5J2520442
Mod.
Yr.
88
89
91
91
89
88
92
89
93
93
88
93
91
93
89
91
95
90
92
95
89
88
91
91
89
92
93
89
86
88
85
87
85
87
87
83
96
88
89
87
85
89
88
Make
BUICK
OLDSMOBILE
FORD
CHEVROLET
CHEVROLET
OLDSMOBILE
FORD
PONTIAC
TOYOTA
GEO
PONTIAC
PONTIAC
CADILLAC
PONTIAC
BUICK
vw
DODGE
CHEVROLET
FORD
DODGE
CHEVROLET
FORD
FORD
NISSAN
MERCURY
EAGLE
MAZDA
PLYMOUTH
FORD
TOYOTA
MERCURY
CHEVROLET
CHEVROLET
FORD
NISSAN
PLYMOUTH
CHEVROLET
HONDA
HONDA
TOYOTA
CHEVROLET
HONDA
CHEVROLET
Mod.
CENT
CUTL
CROW
CAVA
CAVA
DELT
TAUR
GRAN
CAMR
METR
GRAN
GRAN
SEDA
GRAN
LESA
CABR
NEON
CAMA
TAUR
NEON
CAVA
TEMP
TEMP
HARD
SABL
SUMM
626
VOYA
TAUR
CAMR
COUG
S10
S10
TEMP
STAN
RELI
LUMI
CIVI
CIVI
TERC
ASTR
CIVI
S15
Std.
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
Tier 1
TierO
TierO
Tier 1
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
Tierl
TierO
TierO
TierO
TierO
TierO
TierO
Miles
129,698
61,956
53,003
54,658
107,611
101,534
74,078
155,181
29,392
105,445
89,764
72,348
51,707
58,538
65,212
67,496
20,855
71,258
84,148
28,525
110,929
107,979
97,522
103,346
107,075
129,457
103,171
118,586
50,755
197,090
113,584
128,681
89,435
118,148
58,173
94,399
16,557
184,457
161,598
136,654
179,855
122,821
115.693
Eng.
Size
2.5
2.5
5.0
2.2
2.0
3.8
3.0
3.1
2.2
1.0
2.3
2.3
4.9
2.3
3.8
1.8
2.0
3.1
3.8
2.0
2.0
2.3
2.3
2.4
3.0
1.5
12
3.0
2.5
2.0
14
2.5
1.9
2.5
2.0
2.2
3.1
1.5
12
1.5
4.3
1.5
2.5
Fuel
Inj.
TBI
TBI
PFI
TBI
TBI
PFI
PFI
PFI
TBI
TBI
TBI
PFI
TBI
PFI
TBI
TBI
TBI
PFI
TBI
PFI
TBI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
TBI
PFI
TBI
TBI
NO
TBI
PFI
NO
PFI
TBI
TBI
NO
NO
TBI
TBI
IM240
PASS
FAIL
PASS
PASS
PASS
PASS
PASS
FAIL
PASS
PASS
PASS
PASS
FAIL
PASS
FAIL
PASS
PASS
FAIL
PASS
PASS
PASS
PASS
FAIL
PASS
FAIL
FAIL
FAIL
PASS
FAIL
FAIL
FAIL
PASS
PASS
FAIL
PASS
FAIL
PASS
FAIL
PASS
PASS
FAIL
PASS
FAIL
DRAFT M6.SPD.002h
32
August 24, 1999
-------
Table 5
Vehicle Sample Description
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
AA
A A
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5213
5217
5218
5219
5220
5221
5222
5223
5224
5225
5227
5228
5229
5230
5231
5232
5233
5234
5235
5237
5239
5240
^941
LDV
LDT1
LDT1
LDT1
LDV
LDT1
LDV
LDV
LDT2
LDV
LDT1
LDT1
LDV
LDT1
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDT2
LDT2
LDV
LDV
LDV
LDT1
LDT2
LDV
LDV
LDT1
LDV
LDV
LDT1
LDV
LDT1
LDV
LDT1
LDV
T DV
1G2WH54T6PF250844
1FTCR1056FUD20466
1FTDE14N8MHB05052
1FTCR10A2KUB93426
2G1AW19X5G1258479
1FDDE14F9FHA59240
1G1JF11W1K7156403
1G1JC14GXM7146551
1FDEE14NOMHB15171
1FAPP1282MW3 14230
2P4GH25K6MR240965
1GNDM15Z4MB190115
1G1LT53T9PY237873
1GCCS19Z5P0178401
4T1SK11E4PU252562
1HGCB7658PA075439
JN1HJ01POLT397615
JE3CA11A7PU098450
1G2WJ52M7TF204255
JT2AE94A5N0273089
1HGCD5632TA260884
1G8ZF5498NZ175489
1G1LW13T4NY109988
1FTEF14N3RLB27661
1FTEF1549TLB25543
JM1BG2263N0464490
2G1WL52M2T9212643
1G1JC5447N71 16728
1FTCR10A9TPB08548
1GNEV16K9LF116974
2C3ED56F7RH211101
1HGEJ8142TL073569
1 GNDM 1 9WXRB229457
1G8ZK5570RZ145840
KMHJF22M5RU669848
1GNDU06D3NT 126706
1FARP15J9RW262996
2P4FH5532LR534285
2G1WN54X7N91 17726
1GMDU06LXRT234029
4T1BF12K3TU871236
1B3XC56R3T D749334
93
85
91
89
86
85
89
91
91
91
91
91
93
93
93
93
90
93
96
92
96
92
92
94
96
92
96
92
96
90
94
96
94
94
94
92
94
90
92
94
96
90
PONTIAC
FORD
FORD
FORD
CHEVROLET
FORD
CHEVROLET
CHEVROLET
FORD
FORD
PLYMOUTH
CHEVROLET
CHEVROLET
CHEVROLET
TOYOTA
HONDA
NISSAN
EAGLE
PONTIAC
TOYOTA
HONDA
SATURN
CHEVROLET
FORD
FORD
MAZDA
CHEVROLET
CHEVROLET
FORD
CHEVROLET
CHRYSLER
HONDA
CHEVROLET
SATURN
HYUNDAI
CHEVROLET
FORD
PLYMOUTH
CHEVROLET
PONTIAC
TOYOTA
DODGF
GRAN
RANG
ECON
RANG
CELE
ECON
CAVA
CAVA
E150
ESCO
VOYA
ASTR
CORS
S10
CAMR
ACCO
MAXI
SUMM
GRAN
CORO
ACCO
SL
BERR
F150
F150
PROT
LUMI
CAVA
RANG
SURE
LHS
CIVI
ASTR
SL
ELAN
LUMI
ESCO
VOYA
LUMI
TRAN
CAMR
DYNA
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
TierO
Tier 1
TierO
Tier 1
TierO
TierO
TierO
Tier 1
TierO
Tier 1
TierO
Tier 1
TierO
TierO
Tier 1
TierO
TierO
TierO
TierO
Tier 1
TierO
TierO
Tier 1
Tier 1
Tier 0
85,789
56,488
79,573
123,419
131,601
86,203
123,581
90,945
97,531
105,861
72,032
90,880
41,766
48,578
67,344
61,163
120,786
52,447
20,451
77,310
7,573
89,995
94,316
97,629
12,877
10,727
17,233
90,196
10,064
97,658
59,937
9,433
77,178
25,930
57,960
33,872
51,168
98,530
16,133
68,305
18,992
6 813
3.4
2.8
5.8
2.3
2.8
5.8
3.1
2.2
5.8
1.8
2.5
4.3
3.4
4.3
2.2
2.2
3.0
1.5
3.1
1.6
2.2
1.9
3.1
5.8
4.9
1.8
3.1
2.2
2.3
5.7
3.5
1.6
4.3
1.9
1.8
3.1
1.9
3.0
3.4
3.8
3.0
3 3
PFI
NO
PFI
TBI
NO
NO
PFI
TBI
PFI
PFI
TBI
TBI
PFI
TBI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
TBI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
TBI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFT
FAIL
FAIL
FAIL
PASS
PASS
PASS
PASS
PASS
FAIL
FAIL
PASS
PASS
PASS
PASS
PASS
PASS
PASS
PASS
PASS
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NUT T
DRAFT M6.SPD.002h
33
August 24, 1999
-------
Table 6
Distribution of Vehicle Sample
By Vehicle Class and Model Year
Model Year
1983
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
TOTAL
Passenger
Car
1
1
2
3
6
9
3
7
9
10
4
2
6
63
Light-Duty Truck
(0-6000 GVW)
4
1
1
2
1
4
1
1
2
1
18
Light-Duty Truck
(6000-8500 GVW)
1
1
1
1
4
Total
1
5
2
4
7
11
5
12
10
11
7
2
8
85
DRAFT M6.SPD.002h
34
August 24, 1999
-------
Table 7a
Facility-Specific/Area-Wide Speed Correction Cycles Test Results
Total Hydrocarbons (THC)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps (34.6 mph)
Arterial/Collectors
at 24.8 mph
Arterial/Collectors
at 19.2 mph
Arterial/Collectors
at 11.6 mph
Local Roadways (12.9 mph)
Non-Freeway Area-Wide
Urban Travel (19.4 mph)
FTP (19.6 mph)
Running 505 (25.6 mph)
Unified Cycle (24.6 mph)
STO 1(20.2 mph)
NYCC(7.1 mph)
Normal Emitters
N
61
61
61
61
61
61
61
61
61
61
61
60*
61
61
60*
61
61
Mean
(g/mile)
0.15
0.16
0.14
0.21
0.25
0.27
0.34
0.22
0.26
0.45
0.28
0.26
0.38
0.17
0.24
2.32
0.62
STD
0.19
0.17
0.17
0.26
0.30
0.33
0.46
0.26
0.32
0.84
0.34
0.31
0.27
0.23
0.27
2.29
1.09
High Emitters
N
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
23*
24
Mean
(g/mile)
1.80
1.77
1.70
2.52
3.67
4.13
3.04
3.03
3.97
5.15
4.48
3.57
3.49
2.57
3.16
6.88
7.31
STD
1.66
1.69
1.38
2.12
3.75
4.06
2.21
3.07
4.79
5.63
5.07
3.06
2.77
2.51
3.33
5.36
7.82
* Test not done
DRAFT M6.SPD.002h
35
August 24, 1999
-------
Table 7b
Facility-Specific/Area-Wide Speed Correction Cycles Test Results
Carbon Monoxide (CO)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps (34.6 mph)
Arterial/Collectors
at 24.8 mph
Arterial/Collectors
at 19.2 mph
Arterial/Collectors
at 11.6 mph
Local Roadways (12.9 mph)
Non-Freeway Area-Wide
Urban Travel (19.4 mph)
FTP (19.6 mph)
Running 505 (25.6 mph)
Unified Cycle (24.6 mph)
ST01 (20.2 mph)
NYCC(7.1 mph)
Normal Emitters
N
70
70
70
70
70
70
70
70
70
70
70
69*
70
70
69*
70
70
Mean
(g/mile)
6.96
6.96
5.53
4.48
5.19
4.79
10.06
4.28
5.22
5.94
4.23
4.80
5.05
3.04
5.93
24.55
7.88
STD
7.71
6.12
5.33
4.01
4.90
4.45
10.79
3.87
5.01
5.65
4.14
4.62
3.70
2.75
5.34
16.54
8.12
High Emitters
N
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
14*
15
Mean
(g/mile)
66.76
65.63
54.45
66.38
74.39
82.09
84.02
75.24
80.79
116.57
92.41
86.63
79.92
74.04
77.94
111.2
158.04
STD
52.09
54.63
41.82
43.18
63.48
77.01
57.32
59.12
62.65
94.9
87.81
62.32
56.89
57.5
58.19
70.30
136.34
* Test not done
DRAFT M6.SPD.002h
36
August 24, 1999
-------
Table 7c
Facility-Specific/Area-Wide Speed Correction Cycles Test Results
Nitrogen Oxides (NOx)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps (34.6 mph)
Arterial/Collectors
at 24.8 mph
Arterial/Collectors
at 19.2 mph
Arterial/Collectors
at 11.6 mph
Local Roadways (12.9 mph)
Non-Freeway Area-Wide
Urban Travel (19.4 mph)
FTP (19.6 mph)
Running 505 (25.6 mph)
Unified Cycle (24.6 mph)
ST01 (20.2 mph)
NYCC(7.1 mph)
Normal Emitters
N
72
72
72
72
72
72
72
72
72
72
72
71*
72
72
71*
72
72
Mean
(g/mile)
0.77
0.74
0.70
0.63
0.72
0.51
0.98
0.68
0.79
0.96
0.73
0.71
0.70
0.59
0.84
1.85
0.95
STD
0.71
0.65
0.60
0.54
0.59
0.39
0.81
0.55
0.66
0.78
0.63
0.57
0.53
0.50
0.66
1.11
0.69
High Emitters
N
13
13
13
13
13
13
13
13
13
13
13
13
13
13
13
12*
13
Mean
(g/mile)
3.35
3.27
3.20
3.15
3.73
2.81
4.00
3.47
3.77
4.44
3.74
3.56
3.25
3.67
3.83
3.78
4.07
STD
1.07
1.02
0.97
1.00
1.34
0.99
1.43
1.07
1.46
1.84
1.46
1.18
1.04
1.13
1.23
1.34
1.45
* Test not done
DRAFT M6.SPD.002h
37
August 24, 1999
-------
Table 8
Analysis of Variance Results (ANOVA P- Values)
All Roadways
Factor*
Speed
Emitter Class
Speed*Emitter Class
THC
0.0000
0.0000
0.1411
CO
0.0000
0.0000
0.0152
NOx
0.0000
0.0000
0.9894
NMHC
0.0001
0.0000
0.1271
. .
Normal remitters
Arterial/Collector
and Freeway
Local Roadway
Freeway Ramp
Factor*
Roadway Type**
Speed*Roadway Type**
Vehicle Class
Speed*Vehicle Class
Standard***
Speed* Standard***
Vehicle Class
Standard***
Vehicle Class
Standard***
THC
0.0046
0.0354
0.0016
0.1754
0.0000
0.0002
0.0830
0.0000
0.2922
0.0003
CO
0.0006
0.0020
0.0031
0.8680
0.0000
0.0576
0.4038
0.0000
0.0443
0.0002
NOx
0.0000
0.0000
0.0012
0.5723
0.0000
0.6491
0.0124
0.0028
0.0018
0.0000
NMHC
0.0050
0.0440
0.0404
0.1802
0.0000
0.0001
0.5008
0.0000
0.7707
0.0007
. , .
rlign remitters
Arterial/Collector
and Freeway
Local Roadway
Freeway Ramp
Factor*
Roadway Type**
Speed*Roadway Type**
Vehicle Class
Speed*Vehicle Class
Vehicle Class
Vehicle Class
THC
0.1236
0.1176
0.5942
0.0641
0.8787
0.3701
CO
0.3307
0.6233
0.8984
0.0241
0.5511
0.1471
NOx
0.0000
0.0000
0.3961
0.9560
0.6093
0.6942
NMHC
0.1307
0.1203
0.5693
0.0699
0.8821
0.4075
* All emissions in Log (gram/hour) space.
** Freeways versus Arterial/Collectors limited to speeds < 30 mph, including a
vehicle term.
*** There are no Tier 1 High emitters in sample. Some low emitting Tier 0 vehicles
are considered both as Tier 0 and as Tier 1 vehicles (see text).
DRAFT M6.SPD.002h
38
August 24, 1999
-------
Table 8
Analyses of Variance Results (ANOVA p values)
Factor*
Emitter Level
Roadway type**
Vehicle Class
Standard***
Local/ Vehicle Class
Local/Standard
Ramp/ Vehicle Class
Ramp/Standard
Roadway type**
Vehicle Class
Standard***
THC
.0000
NMHC
.0000
CO
.0000
NOx
.0000
Normal Emitters Only
.0006
.0001
.0001
.0476
.0001
.0396
.0001
.0003
.0004
.0001
.1490
.0001
.0983
.0001
.0206
.0001
.0001
.0325
.0001
.0107
.0001
.0000
.0001
.0001
.2753
.0001
.0871
.0001
High Emitters Only
.3094
.067
NA
.3281
.067
NA
.0318
.0004
NA
.0000
.144
NA
* All emissions in Log (gram/hour) space.
** Freeways versus Arterial/Collectors limited to speeds < 30 mph, including a
vehicle term.
*** There were no Tier 1 High emitters in sample. Some low emitting Tier 0 vehicles
were considered both as Tier 0 and as Tier 1 vehicles (see text).
DRAFT M6.SPD.002h
39
August 24, 1999
-------
Table 9
Description of Sample Vehicles Used for Tier 1 Analysis
Veh
No.
5007
5010
5013
5015
5017
5018
5021
5038
5059
5060
5063
5217
5218
5221
5223
5225
5229
5234
5239
5240
Test
Site
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
E.LIB
AA
AA
AA
AA
AA
AA
AA
AA
AA
Tier
Std.
0
0
0
0
0
1
1
1
0
0
1
1
0
1
1
1
1
1
1
1
Mileage
101536
29392
72348
58538
67496
20855
28525
16557
6734
61163
20451
7573
89995
12877
17233
10064
9433
51168
68305
18992
FTP
NMHC
0.13
0.12
0.08
0.07
0.15
0.12
0.12
0.12
0.13
0.11
0.16
0.09
0.19
0.10
0.21
0.12
0.17
0.15
0.19
0.21
FTP
NOx
0.23
0.21
0.18
0.41
0.13
0.10
0.10
0.34
0.28
0.27
0.26
0.20
0.39
0.53
0.49
0.40
0.10
0.26
0.71
0.31
Veh
Class
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDV
LDT2
LDV
LDT1
LDV
LDV
LDT1
LDV
Model
Yr.
88
93
93
93
91
95
95
96
93
93
96
96
92
96
96
96
96
94
94
96
Eng.
Size
3.80
2.20
2.30
2.30
1.80
2.00
2.00
3.10
2.20
2.20
3.10
2.20
1.90
4.90
3.10
2.20
1.60
1.90
3.80
3.00
Fuel
Inj.
PFI
TBI
PFI
PFI
TBI
TBI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
PFI
IM240
Status
PASS
PASS
PASS
PASS
PASS
PASS
PASS
PASS
PASS
PASS
PASS
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
VIN
1G3HY5C9JW312653
4T1SK12E9PU18406
1G2NE5438PC758996
1G2NE5438PC758996
WVWEB5159MKO 12875
1B3ES27C9SD221573
1B3ES67C2SD188892
2GIWL52M2T92 12643
4T1SK11E4PU252562
1HGCB7658PA075439
1G2WJ52M7TF204255
1HGCD5632TA260884
1G8ZF5498NZI75489
1TEF1549TLB25543
2G1WL52M2T9212643
1FTCR10A9TPB08548
1HGEJ8142TL073569
1FARP15J9RW262996
1GMDU06LXRT234029
4T1BF12K3TU871236
DRAFT M6.SPD.002h
40
August 24, 1999
-------
Table 10
Tests of Convergence in Arterial and Freeway Estimates at 30 mph
Tier 0 Normal Emitter Sample
Parameter
THC
NMHC
CO
NOx
Estimate
0.18089092
0.15532642
1.63652794
0.05946957
T for HO:
Parameter = 0
1.84
1.83
2.96
1.24
p value
Pr>|T
0.0670
0.0688
0.0033
0.2160
Standard Error
of the Estimate
0.09840365
0.08503405
0.55229111
0.04797825
Tier 0 High Emitter Sample
Parameter
THC
NMHC
CO
NOx
Estimate
0.95357931
0.84766279
24.7784634
-0.00945343
T for HO:
Parameter = 0
1.52
1.58
1.48
-0.04
p value
Pr>|T
0.1304
0.1161
0.1430
0.9705
Standard Error
of the Estimate
0.62676490
0.53612496
16.7645083
0.25464544
Tier 1 Normal Emitter Sample
Parameter
THC
NMHC
CO
NOx
Estimate
0.01509669
0.00615421
0.25453921
0.04101364
T for HO:
Parameter = 0
1.15
0.71
0.83
1.20
p value
Pr>|T
0.2534
0.4813
0.4114
0.2350
Standard Error
of the Estimate
0.01310665
0.00869272
0.30796933
0.03423678
DRAFT M6.SPD.002h
41
August 24, 1999
-------
Table lla
Average Emissions by Emission Standard and Emission Level
Total Hydrocarbons (THC)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps
(34.6 mph)
Arteri al/C oil ector s
at 24. 8 mph
Arteri al/C oil ector s
at 19.2 mph
Arteri al/C oil ector s
at 11. 6 mph
NYCC(7.1mph)
Local Roadways
(12.9 mph)
Non-Freeway
Areawide Urban
Travel (19. 4 mph)
Hot Running LA4
(19.6 mph)
Unified Cycle
(24.6 mph)
Tier 1*
N
20
20
20
20
20
20
20
20
20
20
20
20
19
20
19
Mean
(g/mi)
0.050
0.066
0.035
0.038
0.044
0.046
0.083
0.044
0.060
0.063
0.122
0.053
0.057
0.036
0.060
Std.
Dev.
0.032
0.038
0.019
0.031
0.036
0.040
0.080
0.035
0.054
0.045
0.111
0.056
0.047
0.019
0.049
Tier 0 Normal
N
49
49
49
49
49
49
49
49
49
49
49
49
49
49
48
Mean
(g/mi)
0.183
0.187
0.171
0.253
0.305
0.330
0.408
0.262
0.318
0.551
0.744
0.336
0.311
0.199
0.282
Std.
Dev.
0.200
0.180
0.178
0.272
0.318
0.341
0.488
0.278
0.341
0.917
1.183
0.360
0.325
0.201
0.287
Tier 0 High
N
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
Mean
(g/mi)
1.798
1.771
1.702
2.523
3.672
4.127
3.036
3.028
3.970
5.155
7.306
4.478
3.571
3.175
3.158
Std.
Dev.
1.656
1.688
1.384
2.124
3.745
4.063
2.205
3.072
4.794
5.630
7.824
5.075
3.060
2.945
3.328
DRAFT M6.SPD.002h
42
August 24, 1999
-------
Table lib
Average Emissions by Emission Standard and Emission Level
Carbon Monoxide (CO)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps
(34.6 mph)
Arteri al/C oil ector s
at 24. 8 mph
Arteri al/C oil ector s
at 19.2 mph
Arteri al/C oil ector s
at 11. 6 mph
NYCC(7.1mph)
Local Roadways
(12.9 mph)
Non-Freeway
Areawide Urban
Travel (19. 4 mph)
Hot Running LA4
(19.6 mph)
Unified Cycle
(24.6 mph)
Tier 1
N
20
20
20
20
20
20
20
20
20
20
20
20
19
20
19
Mean
(g/mi)
1.862
3.045
1.381
1.305
1.513
1.264
2.803
1.271
1.562
1.538
2.652
1.249
1.357
0.892
1.892
Std.
Dev.
1.765
1.446
1.179
1.636
1.570
1.564
2.651
1.215
1.638
1.699
3.068
1.727
1.580
0.846
2.104
Tier 0 Normal
N
58
58
58
58
58
58
58
58
58
58
58
58
58
58
57
Mean
(g/mi)
8.157
7.755
6.449
5.218
5.978
5.596
11.665
4.934
6.052
6.902
9.061
4.924
5.497
3.569
6.855
Std.
Dev.
7.945
6.410
5.403
3.998
4.997
4.464
11.170
3.921
5.103
5.727
8.384
4.212
4.696
2.997
5.394
Tier 0 High
N
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
Mean
(g/mi)
66.763
65.632
54.448
66.377
74.390
82.087
84.016
75.235
80.793
116.569
158.041
92.412
86.628
82.194
77.941
Std.
Dev.
52.094
54.628
41.822
43.185
63.484
77.005
57.322
59.118
62.646
94.897
136.341
87.806
62.322
64.114
58.194
DRAFT M6.SPD.002h
43
August 24, 1999
-------
Table lie
Average Emissions by Emission Standard and Emission Level
Oxides of Nitrogen (NOx)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps
(34.6 mph)
Arteri al/C oil ector s
at 24. 8 mph
Arteri al/C oil ector s
at 19.2 mph
Arteri al/C oil ector s
at 11. 6 mph
NYCC(7.1mph)
Local Roadways
(12.9 mph)
Non-Freeway
Areawide Urban
Travel (19. 4 mph)
Hot Running LA4
(19.6 mph)
Unified Cycle
(24.6 mph)
Tier 1
N
20
20
20
20
20
20
20
20
20
20
20
20
19
20
19
Mean
(g/mi)
0.331
0.340
0.241
0.234
0.231
0.187
0.324
0.233
0.376
0.416
0.353
0.311
0.253
0.191
0.357
Std.
Dev.
0.353
0.287
0.164
0.158
0.168
0.143
0.222
0.163
0.476
0.605
0.292
0.426
0.159
0.123
0.255
Tier 0 Normal
N
60
60
60
60
60
60
60
60
60
60
60
60
60
60
59
Mean
(g/mi)
0.840
0.806
0.789
0.709
0.817
0.585
1.106
0.769
0.905
1.093
1.093
0.830
0.796
0.591
0.943
Std.
Dev.
0.736
0.674
0.619
0.558
0.591
0.386
0.823
0.559
0.660
0.777
0.672
0.637
0.583
0.457
0.678
Tier 0 High
N
13
13
13
13
13
13
13
13
13
13
13
13
13
13
13
Mean
(g/mi)
3.354
3.270
3.200
3.155
3.727
2.805
3.998
3.473
3.774
4.435
4.072
3.735
3.561
3.245
3.830
Std.
Dev.
1.069
1.021
0.970
0.996
1.339
0.995
1.435
1.068
1.461
1.841
1.455
1.463
1.179
1.045
1.230
DRAFT M6.SPD.002h
44
August 24, 1999
-------
Table lid
Average Emissions by Emission Standard and Emission Level
Non-Methane Hydrocarbons (NMHC)
Cycle
Freeway at 63.2 mph
Freeway at 59.7 mph
Freeway at 52.9 mph
Freeway at 30.5 mph
Freeway at 18.6 mph
Freeway at 13.1 mph
Freeway Ramps
(34.6 mph)
Arteri al/C oil ector s
at 24. 8 mph
Arteri al/C oil ector s
at 19.2 mph
Arteri al/C oil ector s
at 11. 6 mph
NYCC(7.1mph)
Local Roadways
(12.9 mph)
Non-Freeway
Areawide Urban
Travel (19. 4 mph)
Hot Running LA4
(19.6 mph)
Unified Cycle
(24.6 mph)
Tier 1
N
19
20
19
19
16
17
18
20
18
20
19
17
18
20
19
Mean
(g/mi)
0.038
0.052
0.026
0.025
0.031
0.027
0.068
0.029
0.042
0.034
0.082
0.038
0.038
0.020
0.041
Std.
Dev.
0.023
0.035
0.015
0.020
0.031
0.022
0.069
0.028
0.041
0.022
0.089
0.045
0.033
0.009
0.039
Tier 0 Normal
N
49
49
48
49
48
49
47
49
48
49
49
48
49
49
48
Mean
(g/mi)
0.148
0.154
0.140
0.207
0.250
0.259
0.357
0.214
0.264
0.458
0.622
0.280
0.257
0.157
0.232
Std.
Dev.
0.177
0.162
0.159
0.246
0.288
0.310
0.444
0.252
0.304
0.805
1.024
0.334
0.301
0.176
0.265
Tier 0 High
N
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
Mean
(g/mi)
1.633
1.601
1.537
2.290
3.347
3.740
2.767
2.737
3.616
4.665
6.571
4.059
3.245
2.945
2.860
Std.
Dev.
1.524
1.518
1.231
1.847
3.295
3.463
1.957
2.672
4.291
4.888
6.609
4.426
2.635
2.770
2.930
DRAFT M6.SPD.002h
45
August 24, 1999
-------
Table 12a
Regressions of Emissions Versus Average Speed
Total Hydrocarbons (THC)
Emissions = Constant + a*(Average Speed)
Roadway Type
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Arterial/
Collector
Arterial/
Collector
Arterial/
Collector
Emission Level
1
(Tier 1)
1
(Tier 1)
1
(Tier 1)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
3
(Tier 0 High)
O
(Tier 0 High)
3
(Tier 0 High)
1
(Tier 1)
2
(Tier 0 Normal)
O
(Tier 0 High)
Speed Data
Range (mph)
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 -24.8
7.1 -24.8
7.1 -24.8
Constant
(p value)
1.034*
0.202
(.4780)
0.019
(.2157)
6.672*
1.933
(.2284)
0.315
(.0000)
44.558**
(.0013)
44.558**
(.0013)
3.193
(.0000)
0.690
(.0009)
4.891
(.0001)
44.558**
(.0013)
a
(p value)
-0.032*
0.032
(.0175)
0.001
(.0533)
-0.170*
0.192
(.0094)
-0.00226
(.0570)
1.202**
(.0908)
1.202**
(.0908)
-0.024
(.0836)
0.017
(.0958)
0.081
(.1930)
1.202**
(.0908)
Units
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per hour
* The values are calculated based on the NYCC at 7.1 mph and Freeway at 13.1 mph cycles.
** Freeway and Arterial/Collector cycles were combined.
DRAFT M6.SPD.002h
46
August 24, 1999
-------
Table 12b
Regressions of Emissions Versus Average Speed
Carbon Monoxide (CO)
Emissions = Constant + a*(Average Speed)
Roadway Type
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Arterial/
Collector
Arterial/
Collector
Arterial/
Collector
Emission Level
1
(Tier 1)
1
(Tier 1)
1
(Tier 1)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
3
(Tier 0 High)
O
(Tier 0 High)
3
(Tier 0 High)
1
(Tier 1)
2
(Tier 0 Normal)
O
(Tier 0 High)
Speed Data
Range (mph)
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 -24.8
7.1 -24.8
7.1 -24.8
Constant
(p value)
14.730*
1.655
(.9045)
0.246
(.7436)
46.679*
15.273
(.4824)
2.398
(.1526)
1206.641*
365.822
(.4888)
64.691
(.0147)
10.036
(.1950)
36.128
(.0054)
863.64
(.0114)
a
(p value)
0.280*
1.278
(.0454)
0.032
(.0263)
2.390*
4.788
(.0000)
0.0872
(.0060)
-9.747*
54.438
(.0275)
-0.0269
(.9559)
0.941
(.0138)
3.877
(.0000)
38.563
(.0202)
Units
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per hour
: The values are calculated based on the NYCC at 7.1 mph and Freeway at 13.1 mph cycles.
DRAFT M6.SPD.002h
47
August 24, 1999
-------
Table 12c
Regressions of Emissions Versus Average Speed
Oxides of Nitrogen (NOx)
Emissions = Constant + a*(Average Speed)
Roadway Type
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Arterial/
Collector
Arterial/
Collector
Arterial/
Collector
Emission Level
1
(Tier 1)
1
(Tier 1)
1
(Tier 1)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
3
(Tier 0 High)
O
(Tier 0 High)
3
(Tier 0 High)
1
(Tier 1)
2
(Tier 0 Normal)
O
(Tier 0 High)
Speed Data
Range (mph)
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 -24.8
7.1 -24.8
7.1 -24.8
Constant
(p value)
4.625*
-0.855
(.5289)
0.126
(.2886)
8.291*
-0.957
(.7262)
0.594
(.0008)
24.889*
0.423
(.9717)
2.980
(.0000)
2.325
(.1066)
5.123
(.0027)
14.609
(.0471)
a
(p value)
-0.154*
0.264
(.0001)
0.0031
(.1667)
0.121*
0.761
(.0000)
0.00373
(.2575)
1.364*
3.232
(.0000)
0.00512
(.6389)
0.170
(.0167)
0.567
(.0000)
2.812
(.0000)
Units
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per hour
: The values are calculated based on the NYCC at 7.1 mph and Freeway at 13.1 mph cycles.
DRAFT M6.SPD.002h
48
August 24, 1999
-------
Table 12d
Regressions of Emissions Versus Average Speed
Non-Methane Hydrocarbons (NMHC)
Emissions = Constant + a*(Average Speed)
Roadway Type
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Freeway
Arterial/
Collector
Arterial/
Collector
Arterial/
Collector
Emission Level
1
(Tier 1)
1
(Tier 1)
1
(Tier 1)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
2
(Tier 0 Normal)
3
(Tier 0 High)
O
(Tier 0 High)
3
(Tier 0 High)
1
(Tier 1)
2
(Tier 0 Normal)
O
(Tier 0 High)
Speed Data
Range (mph)
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 - 13.1
13.1 -30.5
30.5-63.2
7.1 -24.8
7.1 -24.8
7.1 -24.8
Constant
(p value)
0.685*
0.00266
(.9892)
0.00475
(.6971)
5.796*
1.328
(.3602)
0.259
(.0000)
40.178*
37.404
(.0580)
2.899
(.0000)
0.399
(.0082)
4.111
(.0003)
42.589
(.0023)
a
(p value)
-0.028*
0.0236
(.0105)
0.000592
(.0115)
-0.176*
0.165
(.0131)
-0.00189
(.0773)
1.103*
1.107
(.2142)
-0.022
(.0773)
0.0118
(.1048)
0.0617
(.2612)
1.017
(.1299)
Units
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per mile
grams
per hour
grams
per hour
grams
per hour
: The values are calculated based on the NYCC at 7.1 mph and Freeway at 13.1 mph cycles.
DRAFT M6.SPD.002h
49
August 24, 1999
-------
Table 13
Freeway Ramp and Local Roadway Emissions
As a Function of Hot Running LA4 Emissions
In Grams/Hour
Emissions (g/hr) = Constant + a*(LA4) + b*(LA42)
where LA4 is the hot running LA4 emissions in g/hr
Roadway Type
Freeway Ramp
(34.6 mph)
Freeway Ramp
(34.6 mph)
Freeway Ramp
(34.6 mph)
Freeway Ramp
(34.6 mph)
Local Roadways
(12.9 mph)
Local Roadways
(12.9 mph)
Local Roadways
(12.9 mph)
Local Roadways
(12.9 mph)
Pollutant
THC
CO
NOx
NMHC
THC
CO
NOx
NMHC
Constant
(p value)
4.560
(.0302)
224.333
(.0010)
5.353
(.1103)
4.368
(.0193)
-0.479
(.8627)
13.795
(.7042)
1.870
(.0424)
-0.896
(.7115)
a
(p value)
2.046
(.0000)
2.040
(.0000)
2.863
(.0000)
2.014
(.0000)
1.045
(.0000)
0.721
(.0000)
0.701
(.0000)
1.135
(.0000)
b
(p value)
-0.00356
(.0000)
-0.000145
(.0074)
-.0101
(.0019)
-0.00387
(.0000)
-0.000724
(.3090)
0.000
(.9600)
0.000609
(.4803)
-0.00161
(.0201)
R2
0.934
0.848
0.866
0.934
0.765
0.803
0.919
0.764
DRAFT M6.SPD.002h
50
August 24, 1999
-------
Table 14
Emission Offset
(Predicted Freeway Emissions - Average Hot Running LA4 Emissions)
THC
CO
NOx
NMHC
Level 1 (Tier 1)
(grams per mile)
Fwy
0.042
1.363
0.220
0.024
LA4
0.036
0.892
0.191
0.020
Offset
0.006
0.471
0.029
0.004
Level 2 (Tier 0)
(grams per mile)
Fwy
0.290
5.567
0.712
0.233
LA4
0.199
3.569
0.591
0.157
Offset
0.091
1.998
0.121
0.076
Level 3 (High Emitters)
(grams per mile)
Fwy
3.476
73.102
3.253
3.153
LA4
3.175
82.194
3.245
2.945
Offset
0.301
-9.092
0.008
0.208
DRAFT M6.SPD.002h
51
August 24, 1999
-------
Table 15
Arterial/Collector Emission Offsets
(Predicted Arterial/Collector Emissions - Predicted Freeway Emissions)
Pollutant
THC
CO
NOx
NMHC
Average Speed*
(miles per hour)
10
15
20
25
30
10
15
20
25
30
10
15
20
25
30
10
15
20
25
30
Level 1
(grams per mile)
0.014
0.018
0.009
0.005
0.001
0.192
0.222
0.082
0
0
0.094
0.118
0.065
0.033
0.012
0.012
0.015
0.008
0.004
0.001
Level 2
(grams per mile)
0.073
0.086
0.037
0.007
0
0.431
0.479
0.131
0
0
0.171
0.211
0.110
0.049
0.009
0.069
0.082
0.035
0.008
0
Level 3
(grams per mile)
0
0
0
0
0
14.010
17.313
9.016
4.038
0.719
0.420
0.526
0.290
0.148
0.053
0
0
0
0
0
* Arterial/Collector Emission Offsets below 10 mph and over 30 mph are zero.
DRAFT M6.SPD.002h
52
August 24, 1999
-------
Table 16
Speed Correction Factors
For Freeways
By Emission Level*
Avg.
Speed
(mph)
7.1
10
15
19.6
20
25
30
35
40
45
50
55
60
65
Total Hydrocarbons
(THC)
Level 1
2.71
1.71
1.08
1.00
1.00
0.95
0.91
0.91
0.97
1.04
1.10
1.17
1.24
1.30
Level 2
2.65
1.71
1.10
1.00
0.99
0.93
0.88
0.81
0.77
0.73
0.69
0.65
0.61
0.57
Level 3
2.15
1.63
1.20
1.00
0.99
0.86
0.77
0.68
0.64
0.61
0.57
0.54
0.50
0.47
Carbon Monoxide
(CO)
Level 1
1.73
1.29
1.02
1.00
1.00
0.99
0.98
1.00
1.12
1.24
1.36
1.47
1.59
1.71
Level 2
1.61
1.27
1.04
1.00
1.00
0.97
0.95
0.98
1.06
1.14
1.21
1.29
1.37
1.45
Level 3
2.19
1.52
1.08
1.00
0.99
0.94
0.91
0.87
0.87
0.87
0.87
0.86
0.86
0.86
Oxides of Nitrogen
(NOx)
Level 1
2.26
1.40
0.94
1.00
1.00
1.04
1.07
1.07
1.14
1.21
1.28
1.35
1.42
1.49
Level 2
1.81
1.28
0.98
1.00
1.00
1.01
1.02
1.02
1.04
1.07
1.09
1.12
1.15
1.17
Level 3
1.50
1.18
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.01
1.02
Non-Methane HC
(NMHC)
Level 1
2.87
1.69
1.00
1.00
1.00
1.00
1.00
1.07
1.20
1.32
1.45
1.57
1.70
1.82
Level 2
2.75
1.73
1.09
1.00
0.99
0.94
0.90
0.83
0.79
0.74
0.70
0.66
0.62
0.58
Level 3
2.14
1.62
1.20
1.00
0.99
0.86
0.77
0.68
0.64
0.61
0.57
0.54
0.50
0.47
* Emission levels shown as Fwy emissions in Table 14. See Section 4.6.
DRAFT M6.SPD.002h
53
August 24, 1999
-------
Table 17
Speed Correction Factors
For Arterial/Collector Roadways
By Emission Level*
Avg.
Speed
(mph)
7.1
10
15
20
25
30
35
40
45
50
55
60
65
Total Hydrocarbons
(THC)
Level 1
2.71
2.04
1.49
1.22
1.05
0.95
0.91
0.97
1.04
1.10
1.17
1.24
1.30
Level 2
2.65
1.96
1.40
1.12
0.95
0.88
0.81
0.77
0.73
0.69
0.65
0.61
0.57
Level 3
2.15
1.63
1.20
0.99
0.86
0.77
0.68
0.64
0.61
0.57
0.54
0.50
0.47
Carbon Monoxide
(CO)
Level 1
1.73
1.43
1.18
1.06
0.99
0.98
1.00
1.12
1.24
1.36
1.47
1.59
1.71
Level 2
1.61
1.35
1.13
1.02
0.97
0.95
0.98
1.06
1.14
1.21
1.29
1.37
1.45
Level 3
2.19
1.71
1.32
1.12
1.00
0.92
0.87
0.87
0.87
0.87
0.86
0.86
0.86
Oxides of Nitrogen
(NOx)
Level 1
2.26
1.82
1.47
1.30
1.19
1.12
1.07
1.14
1.21
1.28
1.35
1.42
1.49
Level 2
1.81
1.52
1.28
1.16
1.08
1.04
1.02
1.04
1.07
1.09
1.12
1.15
1.17
Level 3
1.50
1.31
1.16
1.09
1.04
1.01
1.00
1.00
1.00
1.00
1.00
1.01
1.02
Non-Methane HC
(NMHC)
Level 1
2.87
2.18
1.62
1.34
1.17
1.06
1.07
1.20
1.32
1.45
1.57
1.70
1.82
Level 2
2.75
2.03
1.44
1.15
0.97
0.90
0.83
0.79
0.74
0.70
0.66
0.62
0.58
Level 3
2.14
1.62
1.20
0.99
0.86
0.77
0.68
0.64
0.61
0.57
0.54
0.50
0.47
* Emission levels shown as Fwy emissions in Table 14. See Section 4.6.
DRAFT M6.SPD.002h
54
August 24, 1999
-------
Figures
DRAFT M6.SPD.002h 55 August 24, 1999
-------
c
0)
O)
s c
o c
(0 / \
a: y
0.500
0.000
+
+
Figure 1a.
Facility Cycles Ratio of Means, HC by
Emitter Level Groups
4.000
3.500
3.000
2.500
2.000
1.500
1.000
* Low Emitters
n High Emitters
n n
+
20 40 60
Average Speed (mph)
80
Figure 1b.
Facility Cycles Ratio of Means, CO by
Emitter Level Groups
0 Cftft
(/) ^f
S3
0) O)
^ .E
M- C
o c
o 3
S O
9,
*j
3
2
2
1
1
0
0
'
.000 -
.500 -
.000 -
.500 -
.000 -
.500 -
.000 -
n * *
nT ^ * *
° cP Q D
D
1
» Low Emitters
n High Emitters
*
+
D
n
1 1
0 20 40 60
*
n
80
Average Speed (mph)
DRAFT M6.SPD.002h
56
August 24, 1999
-------
Figure 1c.
Facility Cycles Ratio of M
eans, NOx
by Emitter Level Groups
^
g <
0 °»
^ ^
^ '=
0 =
O Q£
re "x
fk O
2
1
1
1
1
1
0
0
0
n
V
0
.000 -i
.800 -
.600 -
.400 -
.200 -
.000 -
.800 -
.600 -
.400 -
200 -
^ V V
.000 -
~
»
n* C
n * * n
» n
n
1 1
0 20 40
Average Speed
»
n n n
» Low Emitters
D H ig h Em itters
I
60
(mph)
80
DRAFT M6.SPD.002h
57
August 24, 1999
-------
^^
w 3
C _]
re
0 O)
^ c
M- C
0 c
0 =
5 ^
2 ^
I
Figure 2a.
Facility Cycle Data, HC
4000
.www n
3.500 -
3.000 -
2.500 -
2.000 -
1.500 -
1.000 -
0.500 -
0.000 -
- \
\
\
V
\
fc"»»»J^l
^^^^"""""Wfc^
^^********^^^^^^,
I I I
0 20 40 60 80
Average Speed
Legend for Figures 2a, b and c
.* .Arterial/Collectors
.^^Freeways
O LA92
^ A re a-wide, non-free way
X Local
+ Ram p
DRAFT M6.SPD.002h
58
August 24, 1999
-------
Figure 2b.
3.500 -.
^ 3.000 -
<
5 -1 2.500 -
0) O)
S .E 2.000 -
0 = 1.500 -
O
re 5 1-000 -
^ 0.500 -
0.000 -
C
Facility Cycle Data, CO
- \
^^^^^^
i i i
) 20 40 60 8
0
Average Speed
w <
c -i
UJ 0)
c
^ c
o =
.2 9;
"Jo ^<
K O
z
F ig u re 2c.
Facility Cycle Data, NOx
0 000
^ m\J \J \J
1.800 -
1.600 -
1.400 -
1.200 -
1.000 -
0.800 -
0.600 -
0.400 -
0.200 -
0.000 -
- «-N
> 0
^l
/^^"^ ,.
f
I I 1
0 20 40 60 80
Average Speed
DRAFT M6.SPD.002h
59
August 24, 1999
-------
w <
c _i
(0 m
o w
Ratio of l\
'HC/Runni
^
Figure 3a.
4.000 -i
3.500 -
3.000 -
2.500 -
2.000 -
1.500 -
1.000 -
0.500 -
0.000 -
(
Facility Cycle Data, THC
* Tier 0 vs. Tier 1
X \
. V
: l^r^A
I I I
) 20 40 60
Average Speed
i
80
Legend for Figures 3a, 3b and 3c
- Arterial/Collectors, Tier 0
Freeways, TierO
o Local, Tier 0
n Ramp, Tier 0
o LA92, TierO
A Area-wide, non-freeway, Tier 0
-*- -Arterial/Collectors, Tier 1
- Freeways, Tierl
x Local, Tier 1
Ramp, Tier 1
LA92, Tier 1
x Area-wide, non-freeway, Tier 1
DRAFT M6.SPD.002h
60
August 24, 1999
-------
OS =
6.000
5.000 -
4.000 -
M- = < 3.000
O Q£ _5
.2 0
2.000 +
1.000
0.000
Figure 3b.
Facility Cycle Data, CO
Tier 0 vs. Tier 1
20 40 60
Average Speed
80
Figure 3c.
Facility Cycle Data, NOx
2.500 -i
w < 2.000 -
c -1
|£ i* 1 .500 -
0 (£ 1.000 -
-15 ~s
Cw ^
°^ § 0.500 -
0.000 -
(
Tier 0 vs. Tier 1 ^
_ *
^-^ n *
Si
o
^
. * /***
i i i
) 20 40 60
Average Speed
i
80
DRAFT M6.SPD.002h
61
August 24, 1999
-------
8.0
7.0 -
6.0 -
Si 5.0 -
0.
Cfl
2
O 4.0 -
3.0 -
2.0 -
1.0 -
0.0
Figure 4a
Total Hydrocarbon (THC)
Freeway Emission Levels
-Level 1 (Tier 1 Normal)
-Level 2 (Tier 0 Normal)
-Level 3 (Tier 0 High)
20 25
Average Speed (mph)
180
160
140
= 120
100
80
60
40
20
10
Figure 4b
Carbon Monoxide (CO)
Freeway Emission Levels
15
*Level 1 (Tier 1 Normal)
--Level 2 (Tier 0 Normal)
--Level 3 (Tier 0 High)
20 25
Average Speed (mph)
30
35
40
DRAFT M6.SPD.002h
62
August 24, 1999
-------
Figure 4c
Oxides of Nitrogen (NOx)
Freeway Emission Levels
4.5
4.0
3.5
o>
£ 3.0
tfl
£
0 2.5
^
° 2.0
V)
1
111 1 5
1.0
0.5
\
\^
* Level 1 (Tier 1 Normal)
-Level 2 (Tier 0 Normal)
--Level 3 (Tier 0 High)
^-^_
5 10 15 20 25
30 35
40
Average Speed (mph)
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Figure 4d
Non-Methane Hydrocarbons (NMHC)
Freeway Emission Levels
-*-Level 1 (Tier 1 Normal)
--Level 2 (Tier 0 Normal)
--Level 3 (TierO High)
10
15
20 25
Average Speed (mph)
30
35
40
DRAFT M6.SPD.002h
63
August 24, 1999
-------
Figure 5a
Freeway Speed Correction Factors for
Total Hydrocarbons (THC)
5
re
u.
c
o
S 1.5
o
o
T3
8
£ 1.0
-Emission Level 1
(0.04 g/mi)
-Emission Level 2
(0.29 g/mi)
Emission Level 3
(3.48 g/mi)
30 40
Average Speed (mph)
Figure 5b
Freeway Speed Correction Factors for
Carbon Monoxide (CO)
re
U- 1.5
-o-Emission Level 1
(1.4 g/mi)
-o-Emission Level 2
(5.6 g/mi)
-o-Emission Levels
(73.1 g/mi)
30 40
Average Speed (mph)
DRAFT M6.SPD.002h
64
August 24, 1999
-------
Figure 5c
Freeway Speed Correction Factors for
Oxides of Nitrogen (NOx)
Emission Level 1
(0.22 g/mi)
-Emission Level 2
(0.71 g/mi)
-Emission Level 3
(3.25 g/mi)
30 40
Average Speed (mph)
Figure 5d
Freeway Speed Correction Factors for
Non-Methane Hydrocarbons (NMHC)
o
O 1.5
Emission Level 1
(0.02 g/mi)
Emission Level 2
(0.23 g/mi)
Emission Level 3
(3.15 g/mi)
30 40
Average Speed (mph)
DRAFT M6.SPD.002h
65
August 24, 1999
-------
Figure 6a
Comparison to MOBILES
Speed Correction Factors for
Total Hydrocarbons (THC)
OJ 1.5
|
Q. 1.00
Emission Level 1 (0.04 g/mi)
Emission Level 2 (0.29 g/mi)
Emission Level 3 (3.48 g/mi)
M5 1975 MYR
M5 1981 MYR
M5 1991+ MYR
30 40
Average Speed (mph)
c
o
*o
-------
Figure 6c
Comparison to MOBILES
Speed Correction Factors for
Oxides of Nitrogen (NOx)
-Emission Level 1 (0.22 g/mi)
-Emission Level 2 (0.71 g/mi)
-Emission Level 3 (3.25 g/mi)
-M5 1975 MYR
-M5 1981 MYR
-M5 1993+ MYR
30 40
Average Speed (mph)
Figure 7a
Arterial/Collector Speed Correction Factors
Total Hydrocarbons (THC)
Level 1 Emissions (0.04 g/mi)
3.0
2.0 -
0.5 -
-M5 1975 MYR
-M5 1981 MYR
-M5 1993+ MYR
-Freeway Level 1
-Arterial/Collector Level 1
10
15
20 25
Average Speed (mph)
30
35
40
DRAFT M6.SPD.002h
67
August 24, 1999
-------
Figure 7b
Arterial/Collector Speed Correction Factors
Total Hydrocarbons (THC)
Level 2 Emissions (0.29 g/mi)
M5 1975 MYR
M5 1981 MYR
M5 1993+ MYR
Freeway Level 1
Arterial/Collector Level 1
20 25
Average Speed (mph)
Figure 7c
Arterial/Collector Speed Correction Factors
Total Hydrocarbons (THC)
Level 3 Emissions (3.48 g/mi)
-M5 1975 MYR
-M5 1981 MYR
-M5 1993+ MYR
Freeway Level 3
-Arterial/Collector Level 3
20 25
Average Speed (mph)
DRAFT M6.SPD.002h
68
August 24, 1999
-------
Figure 7d
Arterial/Collector Speed Correction Factors
Carbon Monoxide (CO)
Level 1 Emissions (1.36 g/mi)
M5 1975 MYR
M5 1981 MYR
M5 1993+MYR
Freeway Level 1
Arterial/Collector Level 1
20 25
Average Speed (mph)
2.0
1.0
0.5 -
Figure 7e
Arterial/Collector Speed Correction Factors
Carbon Monoxide (CO)
Level 2 Emissions (5.57 g/mi)
M5 1975 MYR
M5 1981 MYR
M5 1993+MYR
Freeway Level 2
Arterial/Collector Level 2
10
15
20 25
Average Speed (mph)
30
35
40
DRAFT M6.SPD.002h
69
August 24, 1999
-------
Figure 7f
Arterial/Collector Speed Correction Factors
Carbon Monoxide (CO)
Level 3 Emissions (73.1 g/mi)
M5 1975 MYR
M5 1981 MYR
M5 1993+ MYR
Freeway Level 3
Arterial/Collector Level 3
20 25
Average Speed (mph)
2.5
0.5
Figure 7g
Arterial/Collector Speed Correction Factors
Oxides of Nitrogen (NOx)
Level 1 Emissions (0.22 g/mi)
M5 1975 MYR
M5 1981 MYR
M5 1993+ MYR
Freeway Level 1
Arterial/Collector Level 1
10
15
20 25
Average Speed (mph)
30
35
40
DRAFT M6.SPD.002h
70
August 24, 1999
-------
Figure 7h
Arterial/Collector Speed Correction Factors
Oxides of Nitrogen (NOx)
Level 2 Emissions (0.71 g/mi)
Speed Correction Factor
3 O -* -* IO N
3 bi b bi b c
-*-M5 1975 MYR
M5 1981 MYR
--M5 1993+ MYR
-o- Freeway Level 2
^t^ -o-Arterial/Collector Level 2
-^^^--l -r-^-rrnTrr'"
5 10 15 20 25 30 35 40
Average Speed (mph)
1.0
0.5
0.0
Figure 7i
Arterial/Collector Speed Correction Factors
Oxides of Nitrogen (NOx)
Level 3 Emissions (3.25 g/mi)
-M5 1975 MYR
-M5 1981 MYR
-M5 1993+ MYR
-Freeway Level 3
-Arterial/Collector Level 3
20 25
Average Speed (mph)
DRAFT M6.SPD.002h
71
August 24, 1999
-------
Appendices
DRAFT M6.SPD.002h 72 August 24, 1999
-------
Appendix A
MAIN EFFECTS & INTERACTIONS WITH SPEED
All Vehicles
FACTOR
S
EMIT CLASS
S*EMIT CLASS
THC
0.0000
0.0000
0 . 1411
NMHC
0.0001
0.0000
0.1271
CO
0.0000
0.0000
0.0152
NOX
0.0000
0.0000
0.9894
DRAFT M6.SPD.002h
73
August 24, 1999
-------
EMIT NORMAL - ACTUAL TIER CLASS
ROAD
ART/FWY
LOCAL
RAMP
FACTOR
ROADTYPE
S*ROADTYPE
VEH TYPE
S*VEH TYPE
STANDARD
S* STANDARD
VEH TYPE
STANDARD
VEH TYPE
STANDARD
EMIT HIGH - A
THC
0.0046
0.0354
0.0016
0 . 1754
0.0000
0.0002
0.0830
0.0000
0.2922
0.0003
CTUAL TI
NMHC
0.0050
0 . 0440
0 . 0404
0.1802
0.0000
0.0001
0.5008
0.0000
0 .7707
0.0007
ER CLASS
CO
0.0006
0.0020
0.0031
0.8680
0.0000
0.0576
0.4038
0.0000
0.0443
0.0002
NOX
0.0000
0.0000
0.0012
0.5723
0.0000
0.6491
0.0124
0.0028
0.0018
0.0000
ROAD
ART/FWY
LOCAL
RAMP
FACTOR
ROADTYPE
S* ROADTYPE
VEH TYPE
S*VEH TYPE
STANDARD
S* STANDARD
VEH TYPE
STANDARD
VEH TYPE
STANDARD
THC
0.1236
0.1176
0.5942
0.0641
N/A
N/A
0 . 8787
N/A
0.3701
N/A
NMHC
0.1307
0.1203
0.5693
0.0699
N/A
N/A
0.8821
N/A
0.4075
N/A
CO
0.3307
0.6233
0.8984
0.0241
N/A
N/A
0.5511
N/A
0 . 1471
N/A
NOX
0.0000
0.0000
0.3961
0.9560
N/A
N/A
0.6093
N/A
0.6942
N/A
DRAFT M6.SPD.002h
74
August 24, 1999
-------
EMIT NORMAL - CLEAN TIER 0 CLASS
THC NMHC CO NOX
ROAD FACTOR
ART/FWY
LOCAL
RAMP
ROADTYPE
0.0046
0.0050
0.0006
0.0000
S*ROADTYPE 0.0354 0.0440 0.0020 0.0000
VEH TYPE 0.0004 0.0243 0.0062 0.0026
S*VEH TYPE 0.1322 0.1476 0.8361 0.5608
CLEANTO 0.0000 0.0000 0.0000 0.0000
S*CLEANTO 0.0002 0.0001 0.0576 0.6491
VEH TYPE 0.0572 0.4049 0.1660 0.0184
CLEANTO 0.0000 0.0000 0.0000 0.0028
VEH TYPE 0.1570 0.5501 0.0201 0.0009
CLEANTO 0.0003 0.0007 0.0002 0.0000
EMIT HIGH - CLEAN TIER 0 CLASS
THC NMHC CO NOX
ROAD FACTOR
ART/FWY
LOCAL
RAMP
ROADTYPE
0.1236
0.1307
0.3307
0.0000
S*ROADTYPE 0.1176 0.1203 0.6233 0.0000
VEH TYPE 0.5942 0.5693 0.8984 0.3961
S*VEH TYPE 0.0641 0.0699 0.0241 0.9560
CLEANTO ....
S*CLEANTO ....
VEH TYPE 0.8787 0.8821 0.5511 0.6093
CLEANTO ....
VEH TYPE 0.3701 0.4075 0.1471 0.6942
CLEANTO ....
DRAFT M6.SPD.002h
75
August 24, 1999
-------
EMIT NORMAL
ROAD
ART/FWY
LOCAL
RAMP
FACTOR
ROADWAY TYPE
VEHICLE CLASS
STANDARD
VEHICLE CLASS
STANDARD
VEHICLE CLASS
STANDARD
P
THC
PROB
0.0001
0.0000
0.0000
0 . 1017
0.0000
0.2047
0.0000
NMHC
PROB
0.0000
0.0640
0.0000
0.5022
0.0000
0.6109
0.0000
CO
PROB
0.0405
0.0000
0.0000
0.1380
0.0000
0.0213
0.0000
NOX
PROB
0.0000
0.0000
0.0000
0.0408
0.0000
0.0035
0.0000
EMIT HIGH
ROAD
ART/FWY
FACTOR
ROADWAY TYPE
VEHICLE CLASS
STANDARD
P
THC
PROB
0.9736
0.0667
NMHC
PROB
0.9570
0.0873
CO
PROB
0.0151
0.0004
NOX
PROB
0.0201
0 . 1444
Note: these probabilities are for tests of factor main effects, not
interactions with speed.
DRAFT M6.SPD.002h
76
August 24, 1999
-------
EMIT NORMAL - CLEAN TIER 0 CLASS
THC NMHC
ROAD FACTOR
ART/FWY
LOCAL
RAMP
ROADTYPE 0 . C
)001 0.0000
CO
0.0405
NOX
0.0000
VEH TYPE 0.0000 0.0186 0.0000 0.0000
STANDARD 0.0000 0.0000 0.0000 0.0000
VEH TYPE 0.0572 0.4049 0.1660 0.0184
STANDARD 0.0000 0.0000 0.0000 0.0028
VEH TYPE 0.1570 0.5501 0.0201 0.0009
STANDARD 0.0003 0.0007 0.0002 0.0000
EMIT NORMAL - ACTUAL TIER CLASS
THC NMHC CO NOX
ROAD FACTOR
ART/FWY
LOCAL
RAMP
ROADTYPE 0 . C
)001 0.0000
0.0405
0.0000
VEH TYPE 0.0000 0.0686 0.0001 0.0000
STANDARD 0.0000 0.0000 0.0000 0.0000
VEH TYPE 0.0830 0.5008 0.4038 0.0124
STANDARD 0.0002 0.0001 0.0000 0.0024
VEH TYPE 0.2922 0.7707 0.0443 0.0018
STANDARD 0.0013 0.0002
0.0001
0.0010
EMIT HIGH
THC NMHC CO NOX
ROAD FACTOR
ART/FWY
LOCAL
RAMP
ROADTYPE 0 . i
3736 0.9570
0 .0151
0 .0201
VEH_TYPE 0.0667 0.0873 0.0004 0.1444
STANDARD
VEH_TYPE 0.8787 0.8821 0.5511 0.6093
STANDARD
VEH_TYPE 0.3701 0.4075 0.1471 0.6942
STANDARD ....
GLM P-VALUES FOR MODELS WITH NO SPEED INTERACTIONS (FROM FACVEHA.SAS)
DRAFT M6.SPD.002h
77
August 24, 1999
-------
EMIT NORMAL - CLEAN TIER 0 CLASS
ROAD FACTOR
ART/FWY
S*ROADTYPE
P
THC
NMHC CO NOX
PROB PROB PROB PROB
0.0354
0.0440 O.C
)020 0.0000
S*VEH TYPE 0.1322 0.1476 0.8361 0.5608
S*STANDARD 0.0002
0.0001 0.0576 0.6491
EMIT HIGH - CLEAN TIER 0 CLASS
ROAD FACTOR
ART/FWY
S*ROADTYPE
P
THC
NMHC CO NOX
PROB PROB PROB PROB
0.1176
0.1203 0.«
5233 0.0000
S*VEH TYPE 0.0641 0.0699 0.0241 0.9560
S* STANDARD ....
EMIT NORMAL - CLEAN ACTUAL TIER CLASS
ROAD FACTOR
ART/FWY
S*ROADTYPE
P
THC
NMHC CO NOX
PROB PROB PROB PROB
0.0354
0.0440 O.C
)020 0.0000
S*VEH TYPE 0.1754 0.1802 0.8680 0.5723
S*STANDARD 0.0024
EMIT HIGH - CLEAN ACTUAL
ROAD FACTOR
ART/FWY
S*ROADTYPE
0.0020 0.0560 0.0151
TIER CLASS
P
THC
NMHC CO NOX
PROB PROB PROB PROB
0.1176
0.1203 0.«
5233 0.0000
S*VEH TYPE 0.0641 0.0699 0.0241 0.9560
S* STANDARD ....
GLM P-VALUES FOR MODELS WITH NO SPEED INTERACTIONS (FROM FACVEHA.SAS)
DRAFT M6.SPD.002h
78
August 24, 1999
-------
EMIT NORMAL - CLEAN TIER 0 CLASS
ROAD
ART/FWY
FACTOR
ROADTYPE
VEH TYPE
STANDARD
P
THC
PROB
0.0046
0 .0004
0.0000
NMHC
PROB
0.0050
0 .0243
0.0000
CO
PROB
0.0006
0 .0062
0.0000
NOX
PROB
0.0000
0 .0026
0.0000
EMIT HIGH - CLEAN TIER 0 CLASS
ROAD
ART/FWY
FACTOR
ROADTYPE
VEH TYPE
STANDARD
P
THC
PROB
0.1236
0 .5942
NMHC
PROB
0.1307
0 .5693
CO
PROB
0.3307
0 .8984
NOX
PROB
0.0000
0 .3961
EMIT NORMAL - CLEAN ACTUAL TIER CLASS
ROAD
ART/FWY
FACTOR
ROADTYPE
VEH TYPE
STANDARD
P
THC
PROB
0.0046
0 .0016
0.0000
NMHC
PROB
0.0050
0 .0404
0.0000
CO
PROB
0.0006
0 .0031
0.0000
NOX
PROB
0.0000
0 .0012
0.0000
EMIT HIGH - CLEAN ACTUAL TIER CLASS
THC
PROB
I
NMHC
PROB
D
CO
PROB
NOX
PROB
ROAD
ART/FWY
FACTOR
ROADTYPE
VEH TYPE
STANDARD
0.1236
0 .5942
0.1307
0 .5693
0.3307
0 .8984
0.0000
0 .3961
GLM P-VALUES FOR MODELS WITH NO SPEED INTERACTIONS (FROM FACVEHA.SAS)
DRAFT M6.SPD.002h
79
August 24, 1999
-------
Appendix B
Example Application of Speed Adjustment to Exhaust Emissions
The following description is meant as an example of how the basic exhaust emission rates
estimated by MOBILE6 will be adjusted for the effects of average speed and roadway type. The
example will show how the various parts of the overall emission estimate are weighted together.
It is beyond the scope of this document to explain fully the derivation of the basic exhaust
emission estimates or the weighting factors. The derivation of these distributions are described
in other documents. It is also not the intent of this example to reveal the values for emissions or
weighting factors that are proposed to be used in MOBILE6. All of the values shown in this
example should, therefore, be considered as draft and may not match values shown in other
documents. This should not detract from the value of this example in showing the process of
how the basic emission rates are adjusted for speed.
Basic Emission Rates
For each scenario, MOBILE6 will calculate a basic exhaust emission rate (BER) for two
emission levels (high and normal) for each pollutant for each model year for each vehicle class.
The basic unit for the BER is the hot running LA4 (with an average speed of 19.6 mph) at
standard operating conditions (i.e., temperature, humidity, etc.). The effect of engine starts on
emissions is calculated separately and is not adjusted for the effects of average speed.
MOBILE6 calculates the emissions for each hour of the day, so the first step is to adjust
the BER for the conditions that affect exhaust emissions. For example, the temperature at 6 a.m.
will be different than the temperature at 1 p.m., so the BER at 6 a.m. will not be the same as the
BER at 1 p.m. after adjustment for temperature. Some adjustments (such as the effects of fuel
sulfur content) will not vary by time of day. Ultimately, there will be 24 values, one for each
hour of the day calculated from the same BER, adjusted for hourly conditions. There will be two
sets of adjusted BER values, one for normal emissions and one for high emitters.
Example Basic Emission Rates
For this example, we will follow the calculation of NOx emissions from a 1990 model
year passenger car. The calculation would be similar for the other pollutants and other vehicle
classes. This example will not fabricate values for all hours. The calculations will be similar in
all hours, so a single hour example is all that should be required. So, for a given hour, the NOx
emissions (BERs) for our vehicles will be assumed to be:
0.65 g/mi for normal emitters
2.10 g/mi for high emitters
DRAFT M6.SPD.002h 80 August 24, 1999
-------
After adjustment, these values must be weighted together by their occurrence in the fleet.
The number of high emitters will depend on many things (i.e., age, I/M programs, OBD, etc.),
but for our example, we will assume that high emitters are 10% of 1990 model year passenger
cars in this scenario.
Freeway Ramps and Local Roadways
There are four basic roadway types; freeways, arterial/collectors, freeway ramps and local
roadways. The freeway ramps and local roadways can be determined directly from the BER,
since they do not vary with average speed. The freeway ramp and local roadway emissions are a
function of the BER (see Table 13). The NOx BERs we will use (described above) are in grams
per mile units and must be converted to grams per hour. The average speed of the hot running
LA4 is 19.6 miles per hour. For normal emitters, 0.65 grams per mile times 19.6 miles per hour
is 12.74 grams per hour. For high emitters, 2.10 grams per mile times 19.6 miles per hour is
41.16 grams per hour. Using the equation shown in Table 13, the freeway ramp and local
roadway emissions in grams per hour are:
Normal Ramp = 5.353 + 2.863*(12.74) - 0.0101*(12.74)2 = 40.19 g/hr
Normal Local = 1.870 + 0.701 *(12.74) + 0.000609*(12.74)2 = 10.90 g/hr
High Ramp = 5.353 + 2.863*(41.16) - 0.0101*(41.16)2 = 106.08 g/hr
High Local = 1.870 + 0.701 *(41.16) + 0.000609*(41.16)2 = 31.75 g/hr
The results will be weighted using VMT and must be converted to grams per mile units.
The freeway ramp cycle has an average speed of 34.6 miles per hour and the local roadway cycle
has an average speed of 12.9 miles per hour.
Normal Ramp = (40.19 g/hr) / 34.6 mph =1.16 g/mi
Normal Local = (10.90 g/hr) / 12.9 mph = 0.84 g/mi
High Ramp = (106.08 g/hr) / 34.6 mph = 3.07 g/mi
High Local = (31.75 g/hr) / 12.9 mph = 2.46 g/mi
Since we have assumed that 10% of the vehicles are high emitters, we can now weight the
normal and high emitter results to give a complete freeway ramp and local roadway estimate for
the 1990 model year in this hour.
Freeway Ramp = 1.16* 0.90 + 3.07 * 0.10= 1.35 g/mi
Local Roadway = 0.84 * 0.90 + 2.46 * 0.10 = 1.01 g/mi
Each hour will have its own basic exhaust emission rate. Since the Freeway Ramp and
Local Roadway emission levels depend on the basic exhaust emission rate, a separate calculation
will be done for each hour of the day.
DRAFT M6.SPD.002h 81 August 24, 1999
-------
Emission Offset
The emission offset (EO) represents the difference between the LA4-based BER and
freeway emissions at 19.6 miles per hour. The values for the EO are shown in Table 14. Since
the BER values lie between the LA4 values (0.591 and 3.245 g/mi) shown in Table 14, the EO
must be calculated using interpolation.
Normal EO = 0.121 + ((0.008-0.121)/(3.245-0.591))*(0.65-0.591) = 0.12 g/mi
HighEO = 0.121 + ((0.008-0.121)/(3.245-0.591))*(2.10-0.591) = 0.06 g/mi
An additional emission offset is used for arterial/collector roadways, however this offset
depends on average speed and emissions. These are shown in Table 15. The ratio of the freeway
emission level at each speed plus the arterial/collector offset for that speed, divided by the
freeway emission level at 19.6 miles per hour is the arterial/collector speed correction factor.
These are shown in Table 17.
Freeway Emissions
Freeway emissions depend on average speed. For each hour of the day, MOBILE6 has a
default distribution of average speeds for freeways. Users will be able to enter local distributions
of freeway average speeds. This is not the same as a distribution of speeds on a particular
freeway.
The MOBILE6 default distribution of average speeds for freeways assumes that there are
many freeways in the area and the distribution represents the average speeds observed from the
different freeways at that hour. The cycles used to develop the speed correction factors each
contain the entire range of vehicle speeds on freeways grouped by ranges of observed congestion.
So, changing speed in the MOBILE6 model is changing the average speed of the combination of
all vehicles on freeways. MOBILE6 does not effectively model the effect of average speed on
individual vehicles or small groups of vehicles within a single freeway section. If you wish to
model a specific freeway, you would want to reduce the default distribution down to a single,
average speed for the freeway of interest.
In each hour, MOBILE6 will calculate values for each average speed "bin" from 5 to 65
mph in 5 mph increments and for 2.5 mph (14 speed bins) by applying the speed correction
factors from Table 16 to the base freeway emission level at 19.6 mph. The base freeway
emission level is simply the sum of the BER and the adjusted off-cycle emissions (EO).
Normal Base Freeway Emission at 19.6 mph = 0.65 + 0.12 = 0.77 g/mi
High Base Freeway Emission at 19.6 mph = 2.10 + 0.06 = 2.16 g/mi
There are three sets of speed correction factors in Table 16, one for each of three emission
levels. Both the Normal and High base freeway emission levels we have calculated lie between
DRAFT M6.SPD.002h 82 August 24, 1999
-------
the Level 2 and Level 3 emission levels, shown in Table 16. So the speed correction factor will
be interpolated between the values for Level 2 and Level 3 in Table 16. However, these speed
correction factors do not apply below 7.1 mph. We propose that MOBILE6 will use the
MOBILES speed correction factors (See Table 1.6B in AP-42) for speeds below 7.1 mph. For
our example, the NOx speed correction factors for the 1990 model year have A and B
coefficients of 1.456 and 0.926 respectively, where the form of the equation is A/speed + B,
resulting in the following speed correction factors:
SCF for 2.5 mph = (1.456/2.5) + 0.926 =1.51
SCF for 5.0 mph = (1.456/5.0) + 0.926 = 1.22
SCF for 7.1 mph = (1.456/7.1)+ 0.926= 1.13
The MOBILES speed correction factor at 7.1 mph (1.13) was applied to all emission
levels in MOBILES. The MOBILES speed correction factors will be adjusted to match the speed
correction factors in Table 16 for NOx at 7.1 mph of 2.26, 1.81 and 1.50 for emission levels 1, 2
and 3 respectively by adding the difference to each value.
Level 1 SCF for 2.5 mph = 1.51 +(2.26- 1.13) = 2.63
Level 1 SCF for 5.0 mph = 1.22 + (2.26 - 1.13) = 2.34
Level 2 SCF for 2.5 mph = 1.51 +(1.81 - 1.13) = 2.19
Level 2 SCF for 5.0 mph = 1.22+ (1.81 - 1.13)= 1.90
Levels SCF for 2.5 mph = 1.51 +(1.50- 1.13)= 1.87
Levels SCF for 5.0 mph = 1.22+ (1.50- 1.13)= 1.58
Using the average emissions for each speed correction factor emission level (from Table
14) of 0.712 and 3.253 g/mi NOx for Level 2 and Level 3 respectively and the predicted base
freeway emission rates of 0.77 and 2.16 g/mi for Normals and High categories, weighting factors
can be derived for interpolating between the speed correction factors. The sum of the two
weighting factors will equal 1.
Normal Level 2 Weighting = (3.253 - 0.77)/(3.253 - 0.712) = 0.978
Normal Level 3 Weighting = (1.0 - 0.978) = 0.022
High Level 2 Weighting = (3.253 - 2.16)/(3.253 - 0.712) = 0.431
High Level 3 Weighting = (1.0 - 0.431) = 0.569
These weighting factors are used to combine the Level 2 and Level 3 speed correction
factors for the calculated base freeway emission case. A new weighted speed correction factor is
calculated for each of the fourteen speed bins for Normals and Highs. For example, the 10 mph
speed bin speed correction factors (using values from Table 16) would be:
DRAFT M6.SPD.002h 83 August 24, 1999
-------
Normal SCF for 10 mph = 0.978 * 1.28 + 0.022 * 1.18 = 1.28
High SCF for 10 mph = 0.431 * 1.28 + 0.569* 1.18= 1.22
These speed correction factors are applied to the predicted base freeway emission rates to
determine speed corrected emission rates for each speed bin. For example the speed corrected
emission rates for the 10 mph speed bin would be:
Normal emission level for 10 mph = 1.28 * 0.77 = 0.99 g/mi
High emission level for 10 mph = 1.22 * 2.16 = 2.64 g/mi
Each hour has a default VMT distribution of average freeway speeds that correspond to
these speed bins. The emission rates for each of the bins can be weighted, using this VMT
distribution, to give a composite freeway emission rate. This weighting is repeated for normal
and high emitters, and the two emitter groups can be combined to give an overall freeway NOx
emission rate for 1990 model year vehicles for that hour of the day.
Arterial/Collector Emissions
The arterial/collector speed correction factors shown in Table 17 are applied to the base
freeway emission rate calculated for the freeway emission levels. Since the three emission level
groups are identical for arterial/collector roadways and freeways, the same weighting factors are
used to interpolate between the speed correction factors. For example, the 10 mph speed bin
speed correction factors (using values from Table 17) would be:
Normal SCF for 10 mph = 0.978 * 1.52 + 0.022* 1.31 = 1.52
High SCF for 10 mph = 0.431 * 1.52 + 0.569* 1.31 = 1.40
These speed correction factors are applied to the base freeway emission levels to
determine emission levels for each speed bin. For example the emission levels for the 10 mph
speed bin would be:
Normal emission level for 10 mph = 1.52 * 0.77 =1.17 g/mi
High emission level for 10 mph = 1.40 * 2.16 = 3.02 g/mi
Since the speed correction factors for arterial/collectors (shown in Table 17) converge
with freeway speed correction factors (shown in Table 16) at higher speeds and below 7.1 mph,
the emission rate for arterial/collectors and freeways will be the same for some speed bins. All of
the speed bins are combined, weighted by the fraction of VMT in that speed bin for that hour.
The composite arterial/collector emissions for Normals and Highs are combined weighted by
their proportions in the fleet for that model year.
DRAFT M6.SPD.002h 84 August 24, 1999
-------
Areawide Emissions
Once a fleetwide (combined Normal and High), hourly (combined speed bins) estimate is
available for each roadway type (freeway, arterial/collector, freeway ramp and local roadway),
these estimates can be combined in a variety of ways, depending on the needs of the user. If an
areawide, hourly result is needed, the results for the four roadway types can be combined,
weighted by the fraction of VMT for each roadway for that hour. An areawide daily result can be
obtained by combining the hourly results weighted by the VMT fraction for each hour. Although
there are default values for the fraction of VMT for each roadway and the VMT fraction for each
hour, users may substitute their own values.
Composite Engine Start and Running Emissions
The emission rates addressed in this document do not contain the effects of engine starts.
The effect of engine start on emissions is calculated separately and is calculated in units of grams
per engine start. These emission effects resulting from engine starts are not determined by
roadway type and do not depend on average trip speed. They can, however, be combined with
the running emissions to give an overall exhaust emission estimate.
Since the MOBILE6 model does not include a distribution of the effects of engine start on
emissions by roadway type, the combination of the effects of engine start and running emissions
is best done on areawide (combined roadway) emission results. This can be done on an hourly or
daily basis.
MOBILE6 has an estimate of the average daily vehicle miles traveled (VMT) for each
model year in a given calendar year and a distribution of that average VMT over the day by hour.
MOBILE6 also has an estimate for the number of engine starts per day and the distribution of
those starts over the day by hour. For a given hour, the grams due to engine starts in that hour are
calculated as:
Grams / Engine Start * Fraction of Starts in the Hour * Number of Starts / Day
This value can be converted to grams per mile by determination of the average number of
miles traveled by vehicles in that hour:
Hourly VMT = Daily VMT * Fraction of VMT in the Hour
Once the effect of engine start on emissions is converted to grams per mile, it can be
added directly to the areawide emission estimate for that hour.
Total Exhaust = Engine Start / Hourly VMT + Areawide Emissions for the Hour
DRAFT M6.SPD.002h 85 August 24, 1999
-------
Similarly, a daily total exhaust emission rate can be calculated. Although there are
default values for the number of daily engine starts, the fraction of engine start in each hour, the
daily VMT and the fraction of VMT in each hour, users may substitute their own values.
A calculation is done for each model year of each vehicle class. These values are
weighted using travel fractions (as is done in MOBILES) to calculate areawide, daily emission
rates for highway mobile sources.
FTP Emissions
The Federal Test Procedure (FTP) is a special case of vehicle driving. It can be simulated
in MOBILE6 by careful choice of weighting factors for engine start soak time, vehicle miles
traveled and roadway types. Since this case will be of special interest for comparison of
MOBILE6 emission rates to Federal certification standards, we plan to build in the appropriate
weighting factors so that calculation of FTP emission estimates using MOBILE6 can be done
simply and consistently.
DRAFT M6.SPD.002h 86 August 24, 1999
------- |