United States Air and Radiation EPA420-D-03-001
Environmental Protection November 2003
Agency
&EPA Draft Analysis of
Heavy-Duty Diesel Vehicle
Idle Emission Rates
> Printed on Recycled Paper
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EPA420-D-03-001
November 2003
Of
Idle
David J. Brzezinski
Edward L. Glover
Assessment and Standards Division
Office of Transportation and Air Quality
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 that 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.
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1.0 INTRODUCTION
This report describes EPA's preliminary analysis of heavy-duty diesel vehicle emission
data under engine idle operating conditions, where vehicle velocity is zero. It presents analysis
and results for several pollutants and operating parameters. The pollutants include emissions of
nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbons (HC) and particulate matter (PM)
emissions. The operating parameters include the effects of both non-discretionary idle and
discretionary idle, extended idle modes, temperature and parasitic load effects (A/C, heater,
refrigeration, etc.).
For purposes of this report, the term "non-discretionary" represents vehicle idle operation
in which the vehicle typically encounters during normal road operation. It includes the idle
operation which a vehicle experiences while waiting at a traffic signal or during a relatively short
stop that lasts less than an hour. It is characterized by an engine speed which is at or near the
vehicle minimum (typically 600 to 1000 RPM). For future technology vehicles it will
characterize vehicle operation in which the vehicle's catalytic converter or other emission
control system is operating. Throughout this report, the term non-discretionary idle will also be
known as "curb idle."
The second term of "discretionary" idle operation is characterized by extending idle
periods that are frequently several hours in duration, include higher engine speed settings which
are made by the vehicle operator through the use of a mechanical switch or lever controlled by
the operator. Discretionary idling most often occurs during long layovers between trips where
the truck is used as a residence, often referred to as "hoteling." The use of accessories such as
air conditioning systems or heating systems will also likely occur during discretionary idling and
affect emissions. For future technology vehicles discretionary idling will include the effect of
cool-down of the vehicle's catalytic converter system or other exhaust emission treatments.
Throughout this report, the term discretionary idle will also be known as "extended idle" or
"hoteling."
EPA has done only limited testing to investigate the emission effects of idle emissions
from heavy-duty diesel vehicles. Instead, this report is primarily the product of a literature
search of available test results from heavy-duty diesels. As such, it combines the data and
observations from a variety of recent studies.
This document is structured into three primary sections and an Appendix section.
Section 1.0 is this introduction. Section 2.0 briefly describes the databases used in the analysis
and development of the emission factors. Section 3.0 contains two primary sub-sections. The
first sub-section describes the analysis of the non-discretionary idle data and presents the
resulting curb idle emission factors. The second sub-section describes the analysis of the effects
of accessory load, extended idling and other parameters on idling emissions and uses these
results to generate extended, discretionary, idle emission rates.
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2.0 DATA
This study did not include vehicle emission testing. Instead it is a literature review and
compilation of existing idle emission data from heavy-duty diesel vehicles. It includes idle
emission results currently available from eight separate test programs conducted by a variety of
researchers.
2.1 High Altitude Study - "Idle Emissions from Heavy-Duty Diesel and Natural Gas
Vehicles at High Altitude," Robert McCormick, et al, Colorado Institute for Fuels and
Engine Research, Colorado School of Mines, Journal of the Air and Waste Management
Association, Revised May 3, 2000.
Testing was conducted on twelve heavy-duty diesel trucks and twelve transit buses in
Colorado. Ten of the trucks were Class 8 heavy-duty axle semi-tractors, one was a Class
7 truck, and one of the vehicles was a school bus. The model year range was from 1990
through 1998. A typical Denver area wintertime diesel fuel (NFRAQS) was used in all
tests. Idle measurements were collected during a 20 minute time period. All testing was
done at 1,609 meters above sea level (high altitude).
2.2 CCD Study - "Study of Exhaust Emissions from Idling Heavy-duty Diesel Trucks and
Commercially Available Idle Reducing Devices," Han Lim, US EPA Office of
Transportation and Air Quality, September 2002.
Testing was conducted on five trucks in May 2002. The model years ranged from 1985
through 2001. The vehicles were put through a battery of tests including a variety of
discretionary and non-discretionary idling conditions.
2.3 Clean Air Study - "Preliminary Results for Stationary and On-Road Testing of Diesel
Trucks in Tulare, California," Douglas Lambert, et al, Clean Air Technologies Inc., May
15,2002.
Testing was conducted on 42 diesel trucks in parallel with roadside smoke opacity
testing. All tests were conducted by the California Air Resources Board (CARB) at a rest
area near Tulare, California in April 2002. Data collected during this study were
included in the data provided by IdleAire (below) used in the analysis.
2.4 IdleAire Study - "NOx Emissions and Fuel Consumption of HDDVs during Extended
Idle," David K. Irick, University of Tennessee, Bob Wilson, IdleAire Technologies Inc.,
Coordinated Research Council 12th Annual On-Road Vehicle Emission Workshop, San
Diego, California, April 15-17, 2002.
A total of 63 trucks (nine in Tennessee, 12 in New York and 42 in California) were tested
over a battery of idle test conditions including with and without air conditioning. Not all
trucks were tested under all conditions. Only results from the testing in Tennessee and
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New York are described in the IdleAire report. The Tulare, California, data are described
in the Clean Air Study cited above. All analytical equipment for all testing was operated
by Clean Air Technologies.
2.5 CRC E-55 Study - "Heavy-duty Vehicle Chassis Dynamometer Testing for Emissions
Inventory, Air Quality Modeling, Source Apportionment and Air Toxics Emissions
Inventory," Phase I Interim Report, CRC Project No. E-55/E-59, Mridul Gautam and
Nigel N. Clark, et al, West Virginia University Research Corporation, July 2002.
Fourteen trucks were tested with idling times either 900 or 1,800 seconds long.
2.6 NCHRP Study - "Heavy-duty Vehicle Emissions," National Cooperative Highway
Research Program Project 25-14, Cambridge Systematics, Inc., with Battelle, Sierra
Research and West Virginia University. October 2002.
The idling portion of continuous sampling during transient testing was used to determine
idling emission rates on two trucks.
2.7 Metropolitan New York Study - "Internal Report - Idle Emissions from Heavy-Duty
Diesel Trucks in the New Your Metropolitan Area," Tang and Munn, New York State
Dept of Environmental Conservation, November 9, 2001.
A total of 33 heavy-duty diesel trucks were tested in this study. The model years ranged
from 1984 through 1999. One hundred seconds of idling were added at the end of the
WVU five mile transient test driving cycle.
2.8 UC Davis Study - "Potential Benefits of Utilizing Fuel Cell Auxiliary Power Units in
Lieu of Heavy-Duty Truck Engine Idling," Broderick, Dwyer, et al. Institute of
Transportation Studies, University of California - Davis.
A Class 8 Freightliner Century with a 1999 engine was testing using EPA's on-road
emissions testing trailer based in Research Triangle Park, North Carolina. Both short (10
minute) and longer (five hour) measurements were made during idling. Some testing was
also done on three older trucks. This data was obtained too late to be included in the
analysis data used for this report.
2.9 Oak Ridge Study - "Particulate Matter and Aldehyde Emissions from Idling Heavy-
Duty Diesel Trucks," John M.E. Storey, John F. Thomas, Samuel A. Lewis, Sr., Thang Q.
Dam, K. Dean Edwards. Oak Ridge National Laboratory. Gerald L. DeVault, Y-12
National Security Complex. Dominic J. Retrossa, Aberdeen Test Center. Five heavy-
duty trucks were tested for particulate and NOx emissions under a variety of conditions.
These are the same trucks used in the CCD study.
A full set of all of the individual vehicle results used in this analysis with a description of
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the vehicles tested will be made available electronically along with this report.
3.0 ANALYSIS
For purposes of this report, heavy-duty diesel engine idle emissions are modeled by
determining the curb idle emission factor and adjusting it to account for a range of observed
idling operational behavior. The development of the curb (or non-discretionary idle mode) idle
mode emission factors are discussed in Section 3.1. The adjustment factors to account for
extended idling periods, engine idle speed, and use of accessories such as air conditioning (A/C)
and heaters are discussed in Section 3.2. All of the adjustments are multiplicative factors that are
applied to the curb idle emission factors. The general form of the equation is shown in Equation
3-1.
Idle EF = Curbjdle EF * IdleTimeAdj * IdleSpeedAdj * AccessoryAdj Eqn 3-1
Technically, curb idle and other idle conditions are separate operating modes with unique
engine operating parameters. However, the limited available samples at all modes suggest that
statistical characterization of the differences in these modes can provide a more consistent
estimate of the idle emission rates in each mode rather than independent estimates based on
small samples.
3.1 Development of Non-Discretionary Idle Emission Factors
Test data from the test programs were processed and combined into a comprehensive data
set. Only those vehicles with results from idle operation similar to which the vehicle typically
encounters during normal road operation were included in this part of the analysis. Some trucks
and buses received repeat tests. In these cases, the individual test results were combined into a
vehicle average emission result. The resulting data set contains 109 trucks and 13 buses.
The goal of the analysis was to produce average non-discretionary idling emission factors
in terms of grams per hour for each of four pollutants (NOx, PM, HC, and CO). Once
determined, these idle emission factors will be used as the basis for the calculation of
discretionary idle emissions.
The data set also contained information on vehicle class type, altitude, engine build year
and odometer readings. From an engineering perspective, these parameters may affect
emissions. The thinner air of a high altitude region may lead to higher PM and CO emissions and
possibly lower NOx emissions as a result of less oxygen in the combustion process. Smaller and
newer vehicles may generally have less emissions than older and larger vehicles. Regression or
T-Test analysis was performed on the data sample to determine which of these parameters have a
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significant statistical relationship with the observed emission levels.
3.1.1 NOx Emission Factors for Non-Discretionary Idle Operation
The NOx emission analysis explored several factors that include the effect of vehicle
class, the effect of altitude, the effect of engine model year, the effect of engine size and the
effect of age as measured by the odometer reading. Only vehicle class (truck versus bus) and
model year have statistically significant effects. The results suggest that buses have higher non-
discretionary idle NOx emissions than trucks, and that the older (pre-1988 model year) trucks
have lower rates than the subsequent 1988 through 2006 model year trucks. Other possible
parameters were also tested using various statistical tests, but were found to be statistically
insignificant (95% confidence interval).
Since the results were somewhat surprising, it should be noted that the sample sizes for
buses and for model years prior to 1988 are rather small. Also, not all of the data points have
engine size and odometer information to use in the analysis. When additional data becomes
available, it is recommended that some attention be devoted to further exploring whether transit
buses have truly different curb idle emission rates than trucks, and further explore potential age
and mileage effects on curb idle NOx emissions.
3.1.1.1 NOx Effect of Vehicle Class (Truck versus Bus)
The first parameter to be analyzed was the effect of vehicle class on NOx emissions.
This analysis consisted of comparing the mean NOx emission results from the sample of trucks
and the sample of cars. A standard single sample T-Test was performed, and the results are
shown in Tables A-l and A-2 in Appendix A of this document. The sample of 114 trucks shows
a mean idle NOx emission level of 82.6 g/hr NOx, and the sample of 13 buses shows an emission
level of 118.9 g/hr. Levene's test of equal variances shows that equal variances cannot be
assumed at a 95% confidence level. However, the T-Test result when equal variances are not
assumed shows a statistically valid relationship with a 2-tailed significant of 0.005 and a T
statistic of-3.331. These are clearly less than the required 0.05 (95% CI) level, and lead to the
conclusion that trucks and buses have different mean curb idle NOx emissions.
The difference between trucks and buses seen in Tables A-l and A-2 may be the result of
the confounding effects of high and low altitude on curb idle NOx emissions. To confirm and
eliminate these altitude effects, the high altitude vehicles were analyzed separately. A one
sample T-Test was done on eleven trucks and thirteen buses and the results are shown in Table
A-3 and Table A-4. For high altitude trucks, the mean curb idle NOx emission level was 84.0
g/hr and the bus mean was 118.9 g/hr. The test was statistically significant at a 95% confidence
level. This confirms that even among the high altitude vehicles, truck and buses have different
curb idle NOx emissions.
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3.1.1.2 NOx Effect of Altitude
All of the buses in the sample are high altitude tests. A T-Test of using altitude was also
done on the sample of trucks from both high and low altitude (buses were excluded) to determine
if altitude is a factor in curb idle emission rates. The statistical results of this test are shown in
Tables A-5 and A-6 in Appendix A. Here 103 low altitude trucks were tested against eleven
high altitude ones. The results show statistically similar means of 82.4 g/hr and 84.0 g/hr NOx.
These two samples cannot be considered different at a 95% confidence level (significance is
0.769). This suggests that vehicle class is a more important determinant than altitude for NOx
idle emissions.
3.1.1.3 NOx Effect of Engine Model Year
A scatter plot of the curb idle NOx emissions versus engine model year for the trucks in
the sample is shown in Figure 3-1. We might expect that idle emissions should be decreasing as
a function of engine model year since emission standards have gradually been made more
stringent with successive years. However, a regression of the idle NOx emissions versus model
year (Table A-10 in Appendix A) showed no statistically significant relationship (r2 value is
0.01 and the significance is 0.260 - these are low values that indicate little correlation). Also,
with the exception of the pre-1987 model years, the NOx curb idle emissions versus engine
model year shows no general relationship.
The idle NOx emissions for the older vehicles in the sample are significantly lower than
the newer vehicles in the sample. The sample was divided into two strata, using the 1987 model
year as the dividing point. The pre-1988 model years have a mean idle NOx emission level of
50.5 g/hr, and the 1988 and later sample has a mean of 85.3 g/hr NOx. A statistical T-Test (see
Tables A-7 and A-8 in Appendix A) shows a statistically difference between the two sample at a
greater than 95% confidence level (signification = 0.023). The 1987/1988 model year split
corresponds to a more stringent NOx emission standards for heavy-duty diesels were put into
effect in the 1988 model year. Engine improvements, such as higher injection pressures, all tend
to increase engine efficiency and, correspondingly, increase NOx. Newer vehicles also tend to
have more accessories, which increase overall engine load and introduce transient loads at idle.
As a result of this analysis, separate idle NOx emission factors were developed for pre-
1988 and for 1988 and later model year vehicles. However, since the sample sizes are quite
small (only nine pre-1987 model years), it is recommended that this be an area for future
research.
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Figure 3-1 NOx Curb Idle Emissions Versus Engine Model Year
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NOx Effect of Engine Size
Theoretically, the larger engines should emit more NOx per hour than a smaller one
given a relatively constant exhaust concentration at idle and no after-treatment. This idea was
explored in a statistical analysis of curb idle NOx emissions versus engine size in liters of
displacement. Regression analysis of NOx curb idle emissions and engine size was done and the
results are shown in Table A-9. The results show a small correlation coefficient ฎ squared of
0.028) with no statistical significance (0.114). A graph of average NOx curb idle emissions
versus the engine size category is shown in Figure 3-2. The wide error bands (95% confidence
intervals) around the means, the small sample size at the lower engine sizes and general up and
down nature of the mean values indicate no obvious relationship between engine size and NOx
emissions in this sample.
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Figure 3-2 Mean Curb Idle NOx Emissions Versus Engine Size
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3.1.1.5
NOx Effect of Test Program
The idle NOx emission results were also analyzed versus test program to see if any large
statistical differences could be observed between the test programs. Large differences between
the results from different programs might indicate testing or design biases between the programs
that lead to erroneous conclusions. A list of the test programs is shown in Table A-l la and the
mean idle NOx emission results for each test program are show in Table A-l Ib. The CRC E-55
program (5) is somewhat different with a mean curb idle NOx of 68.0 g/hr versus means from
the other programs which are generally in the 80 g/hr range. Program 6 (NCHRP) is
considerably different with a mean of 46.9 g/hr, however this program contains results from only
two vehicles. A statistical ANOVA analysis (Table A-l Ic) shows that only program 1 and 5 are
statistically different from each other at a 95% confidence level (significance = 0.035). Program
#1 was a high altitude program and that it contained buses (Program #5 was from a low altitude
area and did not include buses). The general conclusion from this statistical test is the
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differences that do exist between the samples are reasonable and may be explained by
differences in sampling.
3.1.1.6 Pre-2007 Non-Discretionary Idle NOx Emission Factors
Based on the statistical analysis of the available data, the curb idle NOx emissions for
model years prior to 2007 are projected to be:
All Pre-1988 Model Year Trucks and Buses 71.32 g/hr
All 1988 and Later Trucks 84.69 g/hr
All 1988 and Later Buses 110.50 g/hr
3.1.1.7 Estimated 2007 and Later Non-Discretionary Idle NOx Emission Factors
The 2007 model year heavy duty trucks requires new stringent NOx emission standards.
These are not directly aimed at idle emissions; however, the new NOx catalysts and paniculate
traps should be effective for non-discretionary idle periods such as waiting at a traffic light for a
minute or even during a limited idle period up to an hour in length. After this point, it is
reasonable to assume that the catalyst will be ineffective due to cool down and that idle
emissions will begin to increase.
Since no data are available on 2007 and later engines are prototypes the idle NOx
emission factors will be developed using the ratio of the certification standards in the 1991
through 1998 time frame (this represents most of the data sample) to those in 2007. The non-
discretionary idle NOx emissions will be reduced accordingly.
Given certification standards of:
5.0 g/bhp-hr in 1991 - 1998 time frame for certification
0.2 g/bhp-hr in 2007+
Calculating the ratio of the standards gives:
0.2/5.0 = 0.04
Applying the ratio to the pre 2007 model year truck and bus emission factors produces the
2007 and later model year non-discretionary idle NOx emission factors of:
Truck: 0.04 * 84.69 g/hr = 3.39 g/hr Idle NOx
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Bus: 0.04 * 110.50 g/hr = 4.42 g/hr Idle NOx
3.1.2 Particulate Matter (PM) Emission Factors for Non-Discretionary Idle Operation
3.1.2.1 Pre-2007 Non-Discretionary Idle PM Emission Factor
The PM emission analysis explored several factors that include the effect of vehicle class,
the effect of altitude, and the effect of engine model year. These are the same parameters as
were available for the NOx emission analysis. However, PM emission were not available from
all of the studies. The High Altitude Study provided 24 vehicle tests. The IdleAire Study
provided 49 vehicle tests. The CRC E-55 Study provided 14 vehicle tests. The Oak Ridge
Study provided 5 vehicle tests.
The conclusion from the analysis suggests that none of the parameters have a statistically
significant effect on curb idle PM emissions at a confidence level of 95 percent. As a result, this
paper is proposing that an average curb idle PM emission factor be used for all heavy-duty diesel
vehicle classes, altitudes and model years prior to 2007. This factor is:
3.38 g/hr with a standard error of 0.428 g/hr
Some caution must be used in using this value, since paniculate measurements are quite
variable and easily affected by small differences in the measurement techniques used. The
available data is not adequate to address these concerns directly.
Below and in Appendix A the emission statistics are presented that were used to
determine the average curb idle PM emission factor. Table A-12 shows the mean emission
factors by altitude type and class type (truck or bus). With the exception of the High Altitude
Truck results, the curb idle PM emissions were fairly consistent. The eleven high altitude trucks
show a mean emission factor of 1.41 g/hr and the corresponding low altitude trucks have a mean
emission factor of 3.78 g/hr. This seems like a sizeable difference. However, an independent
sample T-Test was done to determine if the results for trucks and buses at high altitude are
statistically different at a 95% confidence level. The results in Table A-13 show a significance
of 0.07; this indicates that at high altitude the vehicle classes are not significantly different at
95% CI, although nearly so. When the combined sample of trucks and buses at high altitude
(2.34 g/hr) are compared with the low altitude trucks (3.78 g/hr), the difference due to altitude is
not significant. Table A-14 shows the sample statistics comparing high and low altitude. Table
A-15 shows the sample statistics comparing trucks and buses. Figure 3-3 graphically shows
mean curb idle PM emissions versus engine model year. This figure shows considerable
variance (the 95% confidence intervals are frequently larger than the mean values) of curb idle
PM versus model year, but no discernable trend in the model year averages.
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Figure 3-3 Curb Idle PM versus Engine Model Year
3.1.2.2
2007 and Later Non-Discretionary Idle PM Emission Factor
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Since no data are available on 2007 and later model year heavy-duty real engines or
prototype engines, the curb idle PM emission factors were developed by a ratio of the 2007
certification standards to those in the 1991 through 1998 time frame (this represents most of the
data sample). The non-discretionary idle NOx emissions are reduced accordingly.
Given certification standards of:
0.10 g/bhp-hr in 1991 - 1998 time frame for certification
0.01 g/bhp-hr in 2007+
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Calculating the ratio of the standards gives:
0.01/0.1 = 0.1
Applying the ratio to the pre 2007 model year truck and bus emission factors produces the
2007 and later model year non-discretionary idle PM emission factors of:
Truck: 0.1 * 3.38 g/hr= 0.34 g/hr Idle PM
3.1.3 Hydrocarbon (HC) Emission Factors for Non-Discretionary Idle Operation
3.1.3.1 HC Effect of Vehicle Class (Truck versus Bus) and Altitude
Appendix A contains the HC emission statistics that were used to determine the average curb
idle HC emission factors. Table A-17 shows the mean emission factors by altitude type and class
type (truck or bus). In general, the mean curb idle emission factors seem to be similar by vehicle
class (truck and bus) and by high and low altitude. The accompanying T-Tests in Tables A-18 and
A-19 confirm no statistically significant differences at a 95% CI exist between classes and altitudes.
For example, a T-Test of HC and vehicle class shows a significance of more than 0.90 (a very low
level). Likewise, a T-Test of HC and altitude (See Table A-19) shows a significance of more than
0.40 (a low level of significance).
3.1.3.2 HC Effect of Engine Size
Curb Idle HC Emissions were analyzed versus engine size using least squares regression
analysis. The results are shown in Tables A-20 in Appendix A. The regression shows poor
correlation between curb idle HC and engine size. The R Square value is 0.001 and the regression
significance (Sig.) is 0.736.
3.1.3.3 HC Effect of Vehicle Odometer
Curb Idle HC Emissions were analyzed versus odometer using least squares regression
analysis. The results are shown in Table A-21 in Appendix A. The regression shows poor
correlation between curb idle HC and odometer. The R Square value is 0.008 and the regression
significance (Sig.) is 0.468.
3.1.3.4 HC Effect of Model Year
Curb Idle HC Emissions were analyzed versus model year using least squares regression
analysis. The results are shown in Table A-22 in Appendix A. The regression shows modest
correlation between curb idle HC and model year. The R Square value is 0.132 and the regression
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significance (Sig.) of 0.000 is statistically significant at more than a 95% Confidence Interval.
The Curb Idle HC Emissions and the linear regression equation of HC versus model year are
shown plotted versus engine model year in Figure 3-4. The open green squares are the actual data
points and the solid blue squares are the predicted values from the regression. The data shows
considerable scatter and a general lack of data on the older model years. The regression fits the
expected prediction of lower HC emissions with newer model years. The relatively low value 0.132
for the r-square correlation coefficient reflects the considerable scatter in the emission data.
Figure 3-4 Idle HC Emissions Versus Engine Model Year
Data and Predicted Results
3.1.3.5
Pre-2007 Non-Discretionary Idle HC Emission Factor
The HC emission analysis explored several factors that include the effect of vehicle class,
the effect of altitude, the effect of engine size and the effect of engine model year. These are the
same parameters as were available for the NOx and PM emission analysis. The HC emission
data-set contained 122 cases and included members from all of the test programs. The
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conclusion from the analysis suggests that only the engine model year parameter was a
statistically significant effect on curb idle HC emissions at a confidence level of 95 percent.
This was determined through least squares linear regression analysis. The function shown in
Equation 3-2 and 3-3 would be used to model average curb idle HC emissions for all heavy-duty
diesel vehicle classes, altitudes and model years between 1978 and 2006.
Curb Idle HC (g/hr) = 1294.063 - 0.644 * Model Year Eqn 3-2
Given:
Curb Idle HC = 20.23 g/hr for Pre-1978 MY Eqn 3-3
Curb Idle HC = 2.20 g/hr for 2006 MY Eqn 3-4
Curb Idle HC = 0.22 g/hr for 2007 and later MY Eqn 3-5
Where Model Year is the engine model year (i.e., 1999).
The upper curb idle HC emission factor of 20.23 g/hr given in Eqn 3-3 is the value for the
1978 model year. No earlier engine model year data were available; thus, continuation of
Equation 3-2 would be extrapolation. Rather than such extrapolation, the emission factor is
fixed at the 1978 model year level for all previous model years. Additional justification for this
assumption is that generally the pre-1978 model years were either non-regulated or only lightly
regulated for PM emissions and should be similar between model years.
All values past model year 2002 are extrapolation. This extrapolation was done through
2006 to reflect a gradual possible introduction of diesel catalyst technology. The value for the
2006 model year is shown as 2.20 g/hr in Equation 3-4.
The 2007 and later value represents a special problem to model since the new stringent
PM and NOx standards are applied starting in 2007. These new regulations will likely force the
complete introduction of catalytic converters and other exhaust after-treatment devices. Such
devices may drive curb idle HC emissions to near zero levels. This analysis attempts to model
this future event by reducing the 2006 model year level by 90%. The 90% reduction is
analogous to the required PM emission reduction in the 2007 diesel rule. It has the effect of
producing an average curb idle HC emission factor of 0.22 g/hr. This is considerably lower than
the minimum HC value recorded by a current uncontrolled engine of 1.80 g/hr HC. However, it
still might be an environmentally conservative estimate given the claims of some future
technology proponents.
3.1.4 Carbon Monoxide (CO) Emission Factors for Non-Discretionary Idle Operation
3.1.4.1 CO Effect of Vehicle Class. Altitude and Model Year
A single sample T-Test was used to determine the statistical significance of altitude and
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least squares linear regression was used to determine the effects of engine model year.
Below and in Appendix A are the emission statistics that were used to determine the
average curb idle CO emission factors. Table A-23 shows the mean emission factors by altitude
type and class type (truck or bus). In general, the mean curb idle emission factors seem to be
similar by vehicle class (truck and bus), but vary considerably by altitude. For example, the
mean high altitude CO level is 75.3 g/hr while the low altitude mean value is 22.1 g/hr. The
difference between the two values makes engineering sense since the combustion air at high
altitude generally has less oxygen per pound of air than low altitude. If not compensated by the
engine or after-treatment devices, this oxygen deficiency would lead to higher CO emission
factors at the tailpipe. The accompanying T-Tests (see Table A-24) confirm a statistically
significant differences at a 95% CI exist between altitudes. For example, a T-Test of HC and
vehicle class shows a significance of 0.00 (a high level of statistical significance).
A similar T-Test analysis of CO emissions versus vehicle class done on the high altitude
sample of 11 trucks and 13 buses (see Table A-25) shows a low level of statistical significance
(significance = 0.339). As a result, this test eliminated vehicle class as a significant parameter
in the CO curb idle emission analysis.
The low altitude curb idle CO emissions were analyzed versus model year using least
squares regression analysis. The results are shown in Table A-26 in Appendix A. The
regression shows modest correlation between curb idle CO and model year. The R Square value
is 0.142, and the regression significance (Sig.) of 0.000 is statistically significant at more than a
95% Confidence Interval.
The Curb Idle CO Emissions are shown plotted versus engine model year in Figure 3-5.
The open green squares are the actual data points and the solid blue squares are the predicted
values from the linear regression. The data shows considerable scatter and a general lack of
data on the older model years. Nevertheless, the regression is statistically significant and it fits
the expected prediction of lower CO emissions with newer model years.
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Figure 3-5 Idle CO Emissions Versus Engine Model Year
Data and Predicted Results
CO
c
o
'(fl
CO
E
LU
-------
LOW ALTITUDE
Curb Idle CO (g/hr) = 2415.728-1.20* Model Year Eqn 3-6
Given:
Curb Idle CO = 42.13 g/hr for Pre-1978 MY Eqn 3-7
Curb Idle CO = 8.53g/hr for 2006 MY Eqn 3-8
Curb Idle CO = 0.85 g/hr for 2007 and later MY Eqn 3-9
HIGH ALTITUDE
Curb Idle CO = 75.3 g/hr for Pre-2007 MY Eqn 3-10
Curb Idle CO = 0.85 g/hr for 2007 and later MY Eqn 3-11
Where Model Year is the engine model year (i.e., 1999).
The upper curb idle CO emission factor of 42.13 g/hr is the value for the 1978 model
year. No earlier engine model year data were available; thus, continuation of Equation 3-6
would be extrapolation. Rather than such extrapolation, the emission factor is fixed at the 1978
model year level.
All values past model year 2002 are extrapolation. This extrapolation was done through
the 2006 model year. The value for the 2006 model year is shown as 8.53 g/hr in Equation 3-7.
The 2007 and later value represents a special problem to model since the new stringent
PM and NOx standards are applied starting in 2007. These new regulations will likely force the
complete introduction of catalytic converters and other exhaust after-treatment devices. Such
devices may drive curb idle CO emissions to near zero levels. This analysis attempts to model
this future event by reducing the 2006 model year level by 90%. The 90% reduction is
analogous to the required PM emission reduction in the 2007 diesel rule. It has the effect of
producing an average curb idle CO emission factor of 0.85 g/hr. This is considerably lower than
the minimum CO value recorded by a current uncontrolled engine of 4.45 g/hr CO. However, it
still might be an environmentally conservative estimate given the claims of some future
technology proponents. The same value of 0.85 g/hr was also assumed for high altitude 2007
and later model years. The assumption is that the high altitude and low altitude vehicles will be
equally controlled as a result of the stringent 2007 diesel rule requirements.
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3.2 Development of Discretionary Idle Emission Factors
Once the non-discretionary or curb idle emission factors are available, they become the
base emissions to which multiplicative correction factors can be applied to produce load adjusted
and discretionary or extended idle emission factors for estimating the emission impacts of
hoteling behavior. The correction factors were determined by analyzing operating parameters
such as load on the engine (e.g., AC or heat), the speed of the engine or rpm, the amount of time
spent in idle operation, and impacts of upcoming EPA regulations.
LOAD
Engine load during idle is expected to significantly effect idle NOx emission rates. In
simple terms, the greater the load the greater the emission. However, determining typical load at
idle requires looking at the average uses of on-board truck and bus systems. Base electrical
loads, such as lights, battery charger, communications, and computer need about 1-5 kW of
power. Hoteling loads, such as lighting, simple HVAC, and appliances will need 3-5 kW of
power. For full truck electrification which includes all of the above, plus water and oil pumps,
starter, cooling fans, transmission and hydraulic system, brake compressors, and fuel and air
handling systems requires 5-15 kW of power. According to the American Trucking Association
(ATA), typical engine load during extended idling operation is in the range of 10 to 30 brake
horsepower (The Maintenance Council of the American Trucking Associations, The Fleet
Manager's Guide to Fuel Economy, 1998).
RPM
Truck manufacturers generally recommend higher (than curb idle) engine idle speeds
when extended idling is expected. Here are a few examples found in operating manuals.
Caterpillar: "If extended idle time is required, control the engine RPM to 1000 RPM or
above 1000 RPM." (Operation and Maintenance Manual, SEBU7186-04, May 2001,
page 83. This is the manual for C-10, C-12, 3406E, C-15, and C-16 Truck Engines).
Detroit Diesel: "When prolonged idling is necessary, maintain at least 850 RPM
spring/summer and 1200 RPM fall/winter." (Operations Guide 6 SE 484 0106, page 8)
International: "Maintain a minimum of 1250 idle RPM by use of the Hand Throttle."
(Bulletin TSI 96-12-29, "Cold Weather Operation of International Engines." Guidelines
for cold weather operation)
Cummins: "Operating engines at idle RPM (650 to 1000) in cold ambient temperatures
wastes fuel, accelerates wear and can result in serious engine damage. . . . If the operator
insists on prolonged idling, it is recommended that the engine be idled at an RPM which
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is adequate to maintain coolant temperatures above 140 ฐF (60 ฐC). In 0 ฐF ambient (-18
ฐC), the engine may have to be idled above 1200 RPM." (Company Bulletin 3379009-03)
A recent IdleAire survey was done of 100 drivers (through truck stop interviews) and 100
fleet maintenance managers (by phone) regarding engine speeds used during extended idling.
(David Irick and Bob Wilson report). The average, weighted by days of operation per year, was
964 rpm for drivers and 965 rpm for maintenance managers. Nearly 70 percent of these 100
drivers indicated they operated their trucks at 800 rpm or higher during extended idle. Nearly
half the drivers indicated that they operate their engines during extended idling at 1000 rpm or
higher, with about 40 percent reporting the range between 1000 and 1100 rpm. This suggests that
operating in this rpm range is an established practice by a substantial proportion of drivers.
As with the driver survey, the fleet survey showed that a high percentage of drivers, 85.5
percent, use extended idling speeds greater than 800 rpm. Fleets say 76.8 percent of their trucks
idle at 900 rpm or greater and 56.5 percent use an extended idling speed of 1000 rpm or greater.
There was little apparent connection between the size of the fleet and the choice of idling
rpm. On average, fleets of 1000 or fewer trucks chose idling rpm of 965, identical to the overall
average. The average fleet in the 1000-2999 size range chose a lower engine speed level (with a
mean 871 rpm), while fleets with 3000 or more trucks reported an average idling engine speed of
988 rpm. A common theme among fleet owners is that, although most fleets have an official idle
speed recommendation, it is the driver who chooses idle speed. More often than not, fleet owners
observe that drivers may choose a speed higher than company recommendations to maximize
driver comfort levels during extended rest periods.
In general, the fleet maintenance manager survey may be more reliable. Truck drivers
are notoriously suspicious of authority and likely to offer socially acceptable answers. The fleet
maintenance manager data has a more normal, bell shaped, distribution and may have less reason
to bias their answers either higher or lower.
IDLE TIME
Idle duration is an important factor because of engine and future after-treatment device
cool-down. During long durations (called extended idling) the engine begins from a high
operating temperature (just off the road) and then cools to a stabilized cooler operating
temperature as time goes on. Cool down gradually makes engine and after-treatment devices
less efficient and causes more water condensation in the exhaust. Low exhaust flow rates and
cool down may also affect emissions by condensing unburned fuel (HC) and collecting
particulates in the exhaust system.
NEW REGULATIONS
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The new emission standards beginning in 2007 do not require control of emissions during
extended idling. However, it is reasonable to assume that the emission control strategies used to
reduce driving emissions from these trucks will have an effect on idling emissions, but only as
long as the devices remain effective once driving has ceased. It is reasonable to assume that
engine-out idling emission rates will be similar in future model years, but that after-treatment
devices used to reduce driving emissions will affect the resulting tailpipe idling emissions during
curb idling.
Idling emissions during the first minutes of idling will likely be most affected by after-
treatment devices because conversion efficiency of the after-treatment devices remains high.
Extended idling or "hoteling" idling may last 8 hours per day. Because the effectiveness of
after-treatment devices will decline as the time spent at idle grows, emission rates of trucks with
after-treatment devices will increase as idling time increases. The overall fleet average idling
emission rate from extended idling for trucks certified to the new emission standards will depend
on the average length of time for extended idling, and the effect of the new standards on idling
emission rates.
ELECTRONIC CONTROLS
The introduction of electronic controls allows engine designers to optimize engine
performance to the operating mode. At curb idle conditions, the engine designer takes advantage
of a mode where no useful work is done to adjust engine parameters to minimize emissions.
However, when idle speed is increased or high load accessories (such as air conditioning) are
detected, electronic controls allows the engine designer to optimize for power or fuel economy.
However, the limited available samples at all modes suggest that statistical characterization of
the differences in these modes can provide a more consistent estimate of the idle emission rates
in each mode rather than independent estimates based on small samples.
3.2.1 Discretionary Idle NOx Emission Effects
3.2.1.1 NOx Effects of Accessory Load
The CCD study and the IdleAire study include paired test samples showing the effects of
accessory load on idling NOx emissions from heavy-duty vehicles. The vehicle data from these
two studies were combined. A truck was tested three times in the CCD study at 600 rpm with no
load. The value reported in the table, and used in the analysis, is the average of these three
values. The CCD study results are confounded by the fact that the temperature and humidity
used with the heater on and the air conditioning on are different than the "no load" case.
However, since the real-world use of heater and air conditioning accessories are strongly
correlated to the temperature, the observed effect is appropriate for modeling those cases. A
sample comparison t-test of the effects observed in the two study samples are not significantly
different, which suggests that the effects of temperature on idling NOx emissions are not
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significant. For purposes of this analysis, all the observed effect will be assumed to be the result
of the accessory loading only and not from any change in temperature. The NOx values in the
CCD study were adjusted for differences in humidity using the standard Federal Test Procedure
methods (CFR 86.1342-90).
A paired sample t-test was used to compare the means of the idle NOx emission tests
with and without the accessory loads. The t-test indicates that the load effects of air
conditioning on NOx emissions are significant (0.000) at both low and high idle speeds, while
the effects of heater load are not significant. The t-test statistics are shown in Appendix B.
3.2.1.2 NOx Effects of Engine Idle Speed
The CCD study and IdleAire study results used to evaluate the effects of accessory load
were also used to investigate the effects of idle speed on NOx emissions. A paired sample t-test
was used to compare the means of the idle NOx emission tests at low (non-discretionary "curb)
idle speeds and high (discretionary) idle speeds. The t-test indicates that the effects of
discretionary idle speeds on NOx emissions are significant (from 0.000 to 0.002) at all loads.
The t-test statistics are shown in Appendix C.
3.2.1.3 NOx Effects of Engine Idling Time
The CCD and the IdleAire study measured the idling NOx emissions from five heavy-
duty vehicles continuously (second-by-second). All trucks were fully warm when idling began.
Although data from the CCD study indicated a small (7%) decrease in NOx emissions,
information from the IdleAire data contradicts this conclusion. Since both samples are
extremely small, the direct effects of idle time will be assumed to be negligible for this analysis.
As discussed earlier, the new exhaust after-treatment devices used for 2007 and later
model years should be effective for non-discretionary idle periods such as waiting at a traffic
light or during a limited idle period. However, during extended idling periods, the effectiveness
of these controls will likely fade substantially. This will make the overall average idling
emission rate for the extended idling period much higher than the expected non-discretionary
idling emission rate.
Since no data are available on 2007 and newer engines, the curb idle NOx emission
factors developed for the estimate of non-discretionary idle NOx emissions will be used to
represent idling emission rates for the first hour of idling. The idling emission rate after one
hour of idling will be assumed to return to pre-controlled (pre-2007 model year) rates. Then,
assuming that all extended idling periods are eight hours long, we can calculate the average
idling emission rate for extended idling periods for the 2007 and newer engines:
2007 Extended Idling Rate = (1/8)*2007 Idle Rate + (7/8)*Pre-2007 Idle Rate
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This method can also be used to determine idle emission rates for idling time periods
which are less than the eight hours assumed here. The 2007 idle emission rate is a function of
the pre-2007 idle emission rate, so the extended idle emission rate for 2007 and newer model
years can be determined directly from the idle emission estimate for pre-2007 model year
vehicles.
2007 Extended Idling Rate = [(1/8)* (0.2/5.0) + (7/8)] * Pre-2007 Idle Rate
These estimates are affected strongly by the assumption of total hours of discretionary
idling, the effectiveness of the new technologies on idling emissions and the length of time the
new technologies remain effective during extended idling. As new information is obtained about
the emission performance of these vehicles, these estimates will need to be updated.
3.2.1.4
Discretionary NOx Idling Emission Factors
Table 3-1 summarizes the effect of air conditioning observed in the sample as a
multiplicative adjustments to the basic idle NOx emissions measured with no load. The
discretionary idling adjustments are a composite of the effects of higher idling speeds and
extended idling time. The adjustments assume no interactions.
Table 3-1
Discretionary Effects of on Idle NOx Emissions
Description
Non-Discretionary with A/C On
Discretionary with No Load
Discretionary with A/C On
2007+ Discretionary with No Load
2007+ Discretionary with A/C On
Adjustment to Base Idle NOx Emission
Rate
Speed
NA
55.5%
32.6%
55.5%
32.6%
Air
Conditioning
23.7%
NA
26.5%
NA
26.5%
Composite
23.7%
55.5%
67.7%
55.5%
67.7%
Using these adjustments, the non-discretionary idle emission rates described in Section
3.1 and the travel fractions for Class 8 heavy duty diesel trucks from MOBILE6, we can
calculate annual average idle emission rates for the fleet for calendar year 2004. This calculation
assumes that idle times are proportional to vehicle miles traveled and that air conditioning is
used for five months of the year. The results are shown in Table 3-2.
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Table 3-2
Average Heavy Duty Truck Idle NOx Emission Rates
By Calendar Year
Calendar
Year
2004
Travel Fraction
Pre-
1988
0.058
1988-
2004
0.942
Average
Idle NOx Emission Rate in
Non-Discretionary
No A/C
83.91
* Annual assumes five months of A/C use and
A/C On
103.80
Annual*
92.20
Grams per Hour
Discretionary (Hoteling)
No A/C
130.49
seven months with no A/C load.
A/C On
140.72
Annual*
134.75
3.2.2 Particulate Matter (PM) Emission Factors for Discretionary Idle Operation
The particulate matter measurements made on four of the five heavy duty trucks in the
Oak Ridge Study were used to estimate the emission rates for PM during modes characteristic of
discretionary idling, rather than adjusting the non-discretionary, curb idling emission rates for
particulate matter. The IdleAire study did include 49 paired test samples showing the effects of
accessory load and idle speed on idling PM emissions from heavy-duty vehicles. These effects
are discussed below.
3.2.2.1
PM Effects of Accessory Load
A paired sample t-test was used to compare the means of the idle PM emission tests with
and without the accessory loads in the IdleAire study. The t-test indicates that neither the load
effects on PM emissions of air conditioning nor heater load are significant at either low or high
idle speeds. All of the t-test statistics are shown in Table B-4 in Appendix B.
3.2.2.2
PM Effects of Engine Idle Speed
A paired sample t-test was used to compare the means of the idle PM emission tests at
low (non-discretionary "curb) idle speeds and high (discretionary) idle speeds in the IdleAire
study. The t-test indicates that the effects of discretionary idle speeds on PM emissions are
significant only with the air conditioning on. All of the t-test statistics are shown in Table C-4 in
Appendix C.
3.2.2.3
PM Effects of Idling Time
None of the studies contain the information needed to resolve the effects of extended
idling time on PM emissions. Pre-2007 model year trucks will be assumed to have the same PM
emission rate during all hours of operation. This is supported by results in the Oak Ridge study,
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where PM idling rates appear to be constant over idling time periods exceeding an hour.
For PM, it is expected that the new after-treatment devices used for 2007 and later model
years should be effective for both short term non-discretionary idle periods and during extended
idling periods. No adjustment to the non-discretionary PM idling emission factor is therefore
needed to account for long-term, discretionary idling. This expectation is quite different than the
assumptions used for the other pollutants (HC, CO and NOx).
3.2.2.4
Adjustments to PM Idling Emission Factors
Table 3-3 summarizes the effect of air conditioning load in combination with high idle
speeds observed in the sample as a multiplicative adjustments to the basic idle PM emissions
measured with no load. The idling adjustments are a composite of the effects of higher idling
speeds and extended idling time, and are applicable to extended idling periods. The time
adjustment for the 2007 and newer engines is applied to the estimate for pre-2007 model year
non-discretionary idling PM emission rates and includes the effect of the new standards. The
adjustments assume no interactions.
Table 3-3
Adjustments to Idle PM Emissions
Description
Extended Idle with A/C On
2007+ Extended Idle with No Load
2007+ Extended Idle with A/C On
Adjustment to Base Idle PM Emission Rate
Time
NA
-11.3%
-11.3%
Speed/ Air
Conditioning
46.9%
NA
46.9%
Composite
46.9%
-11.3%
30.3%
3.2.2.5
Discretionary PM Idling Emission Factors
In the case of particulate matter emissions, it was felt that an adjustment of the base curb
idle PM emission rate would not be appropriate for use in modeling the effects of extended
idling (hoteling). Instead, the parti culate matter measurements made on four of the five heavy
duty trucks in the Oak Ridge Study were used to estimate the emission rates for PM during
modes characteristic of discretionary idling, rather than adjusting the non-discretionary, curb
idling emission rates for PM.
Table D-l in Appendix D shows the PM measurements on the five trucks in the study
during the different seasonal operating modes with corresponding engine loading. All results
shown are for the high idling speed case, which is typical of hoteling behavior. The 1992 Ford
truck has unusually high PM emissions and was dropped from the averages shown in Table D-2.
Each seasonal average was weighted by the number of months associated with the season (3
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months for winter, 4 months for spring and fall and 5 months for summer. The resulting
seasonally weighted average PM emissions are shown in Table 3-4. This number is slightly
larger than the PM emission factor estimated for non-discretionary idling in Section 3.1.2.1.
For 2007 model year and later trucks, the emission rate for pre-2007 trucks was adjusted
using the ratio of the standards, as described in Section 3.1.2.2 and the results are shown in Table
3-4. This result is slightly lower than the estimate for non-discretionary idle PM emissions
estimated in Section 3.1.2.2.
Table 3-4
Annual Average Discretionary (Hoteling) Idle PM Emissions
Truck Model Year
2006 and earlier
2007 and later
PM Emission Factor (g/hr)
3.68
0.33
3.2.2 Discretionary Idle HC Emission Effects
3.2.2.1
HC Effects of Accessory Load
The CCD study has not yet been summarized for HC emissions. However, the IdleAire
study include paired test samples showing the effects of accessory load on idling HC emissions
from heavy-duty vehicles. A paired sample t-test was used to compare the means of the idle HC
emission tests with and without the accessory loads. The t-test indicates that neither the load
effects on HC emissions of air conditioning nor heater load are significant at either low or high
idle speeds. All of the t-test statistics are shown in Appendix B.
3.2.2.2
HC Effects of Engine Idle Speed
The IdleAire study results used to evaluate the effects of accessory load were also used to
investigate the effects of idle speed on HC emissions. A paired sample t-test was used to
compare the means of the idle HC emission tests at low (non-discretionary "curb) idle speeds
and high (discretionary) idle speeds. The t-test indicates that the effects of discretionary idle
speeds on HC emissions are significant at all loads. All of the t-test statistics are shown in
Appendix C.
3.2.2.3 HC Effects of Engine Idling Time
The CCD study has not yet been summarized for HC emissions. None of the other
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studies contains the information needed to resolve the effects of idling time on HC emissions.
As discussed earlier, the new exhaust after-treatment devices used for 2007 and later
model years should be effective for non-discretionary idle periods such as waiting at a traffic
light or during a limited idle period. However, during extended idling periods, the effectiveness
of these controls will fade substantially. This will make the overall average idling emission rate
for the extended idling period much higher than the expected non-discretionary idling emission
rate.
Since no data are available on 2007 and newer engines, the curb idle HC emission factors
developed for the estimate of non-discretionary idle HC emissions will be used to represent
idling emission rates for the first hour of idling. The idling emission rate after one hour of idling
will be assumed to return to pre-controlled (pre-2007 model year) rates. Then, assuming that all
extended idling periods are eight hours long, we can calculate the average idling emission rate
for extended idling periods for the 2007 and newer engines:
2007 Extended Idling Rate = (1/8)*2007 Idle Rate + (7/8)*Pre-2007 Idle Rate
This method can also be used to determine idle emission rates for idling time periods
which are less than the eight hours assumed here. The 2007 idle emission rate is assumed to be
10% of the pre-2007 idle emission rate, so the extended idle emission rate for 2007 and newer
model years can be determined directly from the idle emission estimate for pre-2007 model year
vehicles.
2007 Extended Idling Rate = [(1/8)* (0.10) + (7/8)] * Pre-2007 Idle Rate
As new information is obtained about the emission performance of these vehicles, these
estimates will need to be updated.
3.2.2.4 Discretionary HC Idling Emission Factors
Table 3-5 summarizes the effect of discretionary (extended) idling observed in the
sample as a multiplicative adjustments to the basic idle HC emissions measured with no load.
The discretionary idling adjustments are a composite of the effects of higher idling speeds and
extended idling time. The time adjustment for the 2007 and newer engines is applied to the
estimate for pre-2007 model year non-discretionary idling HC emission rates and includes the
effect of the new standards. The adjustments assume no interactions.
Table 3-5
Discretionary Effects of on Idle HC Emissions
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Description
Discretionary
2007+ Discretionary
Adjustment to Base Idle HC Emission Rate
Speed
82.6%
82.6%
Time
NA
Composite
82.6%
3.2.3 Discretionary Idle CO Emission Effects
3.2.3.1 CO Effects of Accessory Load
The CCD study has not yet been summarized for CO emissions. However, the IdleAire
study include paired test samples showing the effects of accessory load on idling CO emissions
from heavy-duty vehicles. A paired sample t-test was used to compare the means of the idle CO
emission tests with and without the accessory loads. The t-test indicates that only the load
effects on CO emissions of air conditioning are significant, and only at low idle speeds. All of
the t-test statistics are shown in Appendix B.
3.2.3.2 CO Effects of Engine Idle Speed
The IdleAire study results used to evaluate the effects of accessory load were also used to
investigate the effects of idle speed on CO emissions. A paired sample t-test was used to
compare the means of the idle CO emission tests at low (non-discretionary "curb) idle speeds
and high (discretionary) idle speeds. The t-test indicates that the effects of discretionary idle
speeds on CO emissions are significant at all loads. All of the t-test statistics are shown in
Appendix C.
3.2.3.3 CO Effects of Engine Idling Time
The CCD study has not yet been summarized for CO emissions. None of the other
studies contains the information needed to resolve the effects of idling time on CO emissions.
As discussed earlier, the new exhaust after-treatment devices used for 2007 and later
model years should be effective for non-discretionary idle periods such as waiting at a traffic
light or during a limited idle period. However, during extended idling periods, the effectiveness
of these controls will fade substantially. This will make the overall average idling emission rate
for the extended idling period much higher than the expected non-discretionary idling emission
rate.
Since no data are available on 2007 and newer engines, the curb idle CO emission factors
developed for the estimate of non-discretionary idle CO emissions will be used to represent
idling emission rates for the first hour of idling. The idling emission rate after one hour of idling
will be assumed to return to pre-controlled (pre-2007 model year) rates. Then, assuming that all
extended idling periods are eight hours long, we can calculate the average idling emission rate
for extended idling periods for the 2007 and newer engines:
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2007 Extended Idling Rate = (1/8)*2007 Idle Rate + (7/8)*Pre-2007 Idle Rate
This method can also be used to determine idle emission rates for idling time periods
which are less than the eight hours assumed here. The 2007 idle emission rate is assumed to be
10% of the pre-2007 idle emission rate, so the extended idle emission rate for 2007 and newer
model years can be determined directly from the idle emission estimate for pre-2007 model year
vehicles.
2007 Extended Idling Rate = [(1/8)* (0.10) + (7/8)] * Pre-2007 Idle Rate
As new information is obtained about the emission performance of these vehicles, these
estimates will need to be updated.
3.2.3.4
Discretionary CO Idling Emission Factors
Table 3-6 summarizes the effect of discretionary (extended) idling and the effect of air
conditioning load at low idle speeds observed in the sample as a multiplicative adjustments to
the basic idle CO emissions measured with no load. The discretionary idling adjustments are a
composite of the effects of higher idling speeds and extended idling time. The time adjustment
for the 2007 and newer engines is applied to the estimate for pre-2007 model year non-
discretionary idling CO emission rates and includes the effect of the new standards. The
adjustments assume no interactions.
Table 3-6
Discretionary Effects of on Idle CO Emissions
Description
Non-discretionary with A/C On
Discretionary
2007+ Discretionary
Adjustment to Base Idle CO Emission Rate
Speed
NA
217.2%
217.2%
Time
NA
NA
Air
Conditioning
13.4%
NA
NA
Composite
13.4%
217.2%
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Appendix A
Non-Discretionary Idle Analysis Sample and Statistics
Table A-l
Average Curb Idle NOx Emissions by Vehicle Class
Class
Truck
Bus
Mean
114
13
N
82.585212
118.910769
Std. Deviation
32.298661
37.775149
Median
3.025047
10.476941
Table A-2
T-Test Statistics for Curb Idle NOx by Vehicle Class
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
1.059
Sig
.305
Independent Samples t-test for Equality of Means
t
-3.776
-3.331
df
125
14.074
Sig.
(2-tailed)
.000
.005
Mean
Difference
-36.325558
-36.325558
Std. Error
Difference
9.620520
10.904917
95% Confidence Interval of
the Difference
Lower
-55.365761
-59.702773
Upper
-17.285355
-12.948342
Table A-3
Average High Altitude Curb Idle NOx Emissions by Vehicle Class
Class
Truck
Bus
Mean
11
13
N
84.038182
118.910769
Std. Deviation
24.324821
37.775149
Median
7.334209
10.476941
Table A-4
T-Test Statistics for High Altitude Curb Idle NOx by Vehicle Class
Levene's Test for Equality of
Variances
Equal variances
assumec
Equal variances
not assumec
F
3.696
Sig
.068
Independent Samples t-test for Equality of Means
t
-2.630
-2.727
df
22
20.683
Sig.
(2-tailed)
.015
.013
Mean
Difference
-34.872587
-34.872587
Std. Error
Difference
13.257826
12.788938
95% Confidence Interval of
the Difference
Lower
-62.367636
-61.493510
Upper
-7.377538
-8.251665
-29-
-------
Table A-5
Average Truck Only Curb Idle NOx Emissions by Altitude
Altitude
Low
High
Mean
103
11
N
82.430040
84.038182
Std. Deviation
33.127697
24.324821
Median
3.264169
7.334209
Table A-6
T-Test Statistics for Truck Only Curb Idle NOx by Altitude
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
2.065
Sig
.153
Independent Samples t-test for Equality of Means
t
-.156
-.200
df
112
14.299
Sig.
(2-tailed)
.876
.844
Mean
Difference
-1.608142
-1.608142
Std. Error
Difference
10.289751
8.027791
95% Confidence Interval of
the Difference
Lower
-21.995963
-18.792332
Upper
18.779680
15.576049
Table A-7
Average Truck Only Curb Idle NOx Emissions by Model Year Group
Model Year
Pre-1988
1988 and Newer
Mean
9
105
N
50.475000
85.337515
Std. Deviation
36.277026
30.583874
Median
12.092342
2.984680
Table A-8
T-Test Statistics for Truck Only Curb Idle NOx by Model Year Group
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
.337
Sig
.563
Independent Samples t-test for Equality of Means
t
-3.235
-2.799
df
112
9.002
Sig.
(2-tailed)
.002
.021
Mean
Difference
-34.862515
-34.862515
Std. Error
Difference
10.775837
12.455242
95% Confidence Interval of
the Difference
Lower
-56.213455
-63.037336
Upper
-13.511576
-6.687695
-30-
-------
Table A-9
ANOVA Statistics for Curb Idle NOx by Engine Size
Regression
Residual
Total
Sum of Squares
2926.367
102179.084
105105.451
(Constant)
Size
Jnstandardized
Coefficients
B
56.531
2.541
R
.167
df I
1
89
90
Std. Erro
19.490
1.592
R Square Ad
.028
VIean Square
2926.367
1148.080
Standardized
Coefficients
r Beta
r
.167 1
usted R Squa
.017
F
2.549
t Sig.
L
..900 .005
.597 .114
re Std. Error of the Estimate
33.883323
Significance
.114
95% Confidence Interval
forB
ower Bound
17.804
-.621
Upper Bound
95.258
5.703
i Predictors: (Constant), Engine Size
) Dependent Variable: NOx
Table A-10
ANOVA Statistics for Curb Idle NOx by Model Year
R
.101
R Square
.010
Adjusted R Square
.002
Std. Error of the Estimate
34.5115302
Regression
Residual
Total
Sum of Squares
1522.991
148880.714
150403.705
df
1
125
126
Mean Square
1522.991
1191.046
F
1.279
Significance
.260
(Constant)
Year
[Jnstandardized
Coefficients
B
-1432.999
.762
Standardized
Coefficients t Sig.
Std. Error Beta
1343.572 -1.067 .288
.673 .101 1.131 .260
95% Confidence Interval
forB
Lower Bound
-4092.094
-.571
i Predictors: (Constant), Model Year
) Dependent Variable: NOx
Upper Bound
1226.097
2.094
-31-
-------
Table A-l la
Testing Program Descriptions
Program
Number
Program
Description
1
High Altitude
Study
"Idle Emissions from Heavy-Duty Diesel and Natural Gas Vehicles at High
Altitude," Robert McCormick, et al, Colorado Institute for Fuels and Engine
Research, Colorado School of Mines, Journal of the Air and Waste
Management Association, Revised May 3, 2000.
CCD Study
"Study of Exhaust Emissions from Idling Heavy-duty Diesel Trucks and
Commercially Available Idle Reducing Devices," Han Lim, US EPA Office of
Transportation and Air Quality, September 2002.
Clean Air Tech
& IdleAire
Study
"NOx Emissions and Fuel Consumption of HDDVs during Extended Idle,"
David K. Irick, University of Tennessee, Bob Wilson, IdleAire Technologies
Inc., Coordinated Research Council 12th Annual On-Road Vehicle Emission
Workshop, San Diego, California, April 15-17, 2002. Also "Preliminary Results
for Stationary and On-Road Testing of Diesel Trucks in Tulare, California,"
Douglas Lambert, et al, Clean Air Technologies Inc., May 15, 2002.
CRC E-55 Study
"Heavy-duty Vehicle Chassis Dynamometer Testing for Emissions Inventory,
Air Quality Modeling, Source Apportionment and Air Toxics Emissions
Inventory," Phase I Interim Report, CRC Project No. E-55/E-59, Mridul
Gautam and Nigel N. Clark, et al, West Virginia University Research
Corporation, July 2002.
NCHRP Study
"Heavy-duty Vehicle Emissions," National Cooperative Highway Research
Program Project 25-14, Cambridge Systematics, Inc., with Battelle, Sierra
Research and West Virginia University. October 2002.
Metropolitan
New York Study
"Internal Report - Idle Emissions from Heavy-Duty Diesel Trucks in the New
Your Metropolitan Area", Tang and Munn, New York State Dept of
Environmental Conservation, November 9, 2001.
Table A-l lb
NOx Emissions Summarized by Testing Program
Program
Number
1.00
2.00
4.00
5.00
6.00
8.00
Total
N
24
5
49
14
2
33
127
Mean
102.927500
98.207764
87.088510
68.033929
46.921667
81.381818
86.303576
Std. Deviation
36.2877542
39.8360597
31.4434295
30.0143504
29.1351564
34.3725313
34.5496773
Std. Error
7.4072068
17.8152275
4.4919185
8.0216726
20.6016667
5.9834897
3.0657881
95% Confidence Interval for
Mean
Lower Bound
87.604525
48.744763
78.056902
50.704159
-214.847328
69.193849
80.236471
Upper Bound
118.250475
147.670765
96.120117
85.363699
308.690661
93.569788
92.370680
Minimum
25.4400
63.3462
46.8921
15.6950
26.3200
25.2000
15.6950
Maximum
166.0200
141.6049
166.9950
106.7100
67.5233
187.2000
187.2000
-32-
-------
Table A-llc
Multiple Comparisons of Testing Programs
Dependent Variable: NOx
Bonferroni
(I)
Program
1.00
2.00
4.00
5.00
6.00
8.00
(J)
Program
2.00
4.00
5.00
6.00
8.00
1.00
4.00
5.00
6.00
8.00
1.00
2.00
5.00
6.00
8.00
1.00
2.00
4.00
6.00
8.00
1.00
2.00
4.00
5.00
8.00
1.00
2.00
4.00
5.00
6.00
Mean Difference*
(I-J)
4.719736
15.838990
34.893571
56.005833
21.545682
-4.719736
11.119254
30.173835
51.286097
16.825946
-15.838990
-11.119254
19.054581
40.166843
5.706691
-34.893571
-30.173835
-19.054581
21.112262
-13.347890
-56.005833
-51.286097
-40.166843
-21.112262
-34.460152
-21.545682
-16.825946
-5.706691
13.347890
34.460152
Std. Error
16.3873777
8.3053676
11.2104552
24.5339313
8.9428496
16.3873777
15.6500211
17.3671625
27.8901024
15.9974557
8.3053676
15.6500211
10.1020452
24.0476775
7.5067682
11.2104552
17.3671625
10.1020452
25.1989279
10.6323443
24.5339313
27.8901024
24.0476775
25.1989279
24.2752182
8.9428496
15.9974557
7.5067682
10.6323443
24.2752182
Sig.
1.000
.883
.035
.363
.262
1.000
1.000
1.000
1.000
1.000
.883
1.000
.925
1.000
1.000
.035
1.000
.925
1.000
1.000
.363
1.000
1.000
1.000
1.000
.262
1.000
1.000
1.000
1.000
95% Confidence Interval
Lower Bound
-44.353838
-9.032229
1.322788
-17.463377
-5.234539
-53.793311
-35.746235
-21.833799
-32.233489
-31.079970
-40.710210
-57.984743
-11.196962
-31.846234
-16.773046
-68.464355
-82.181469
-49.306124
-54.348345
-45.187464
-129.475043
-134.805684
-112.179920
-96.572868
-107.154621
-48.325903
-64.731861
-28.186429
-18.491685
-38.234318
Upper Bound
53.793311
40.710210
68.464355
129.475043
48.325903
44.353838
57.984743
82.181469
134.805684
64.731861
9.032229
35.746235
49.306124
112.179920
28.186429
-1.322788
21.833799
11.196962
96.572868
18.491685
17.463377
32.233489
31.846234
54.348345
38.234318
5.234539
31.079970
16.773046
45.187464
107.154621
* The mean difference is significant at the 0.05 level.
-33-
-------
Table A-12
Average Curb Idle PM Emissions by Altitude and Vehicle Class
Altitude
^ow
iigh
Total
Class
Truck
All
Truck
3us
All
Truck
Bus
All
Mean
3.778967
3.778967
1.418182
3.110769
2.335000
3.428039
3.110769
3.380631
N
63
63
11
13
24
74
13
87
Std. Deviation
4.428443
4.428443
0.367201
2.916523
2.288833
4.170067
2.916523
3.995079
Median
2.230947
2.230947
1.380000
2.220000
1.410000
1.996531
2.220000
2.017305
Table A-13
T-Test Statistics for High Altitude Curb Idle PM by Vehicle Class
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
11.232
Sig
.003
Independent Samples t-test for Equality of Means
t
-1.906
-2.073
df
22
12.449
Sig.
(2-tailed)
.070
.060
Mean
Difference
-1.692587
-1.692587
Std. Error
Difference
.888243
.816440
95% Confidence Interval of
the Difference
Lower
-3.534692
-3.464373
Upper
.149517
7.91985E-02
-34-
-------
Table A-14
Curb Idle PM Statistics by Altitude
ALTITUDE
Low
High
Mean
95% Confidence Interval
for Mean
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
Mean
95% Confidence Interval
for Mean
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
Lower Bounc
Upper Bounc
Lower Bounc
Upper Bounc
Statistic
3.778967
2.663678
4.894256
3.206624
2.230947
19.611
4.428443
.0800
23.2782
23.1982
3.431699
2.293
6.110
2.335000
1.368511
3.301489
2.034444
1.410000
5.239
2.288833
.3600
10.3800
10.0200
1.575000
2.425
6.279
Std. Error
.557931
.302
.595
.467206
.472
.918
-35-
-------
Table A-15
Curb Idle PM Statistics by Vehicle Class
CLASS
Truck
Bus
Mean
95% Confidence Interval
for Mean
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
Mean
95% Confidence Interval
for Mean
5% Trimmed Mean
Median
Variance
Std. Deviation
Minimum
Maximum
Range
Interquartile Range
Skewness
Kurtosis
Lower Bounc
Upper Bounc
Lower Bounc
Upper Bounc
Statistic
3.428039
2.461913
4.394165
2.854778
1.996531
17.389
4.170067
.0800
23.2782
23.1982
3.222327
2.552
7.612
3.110769
1.348332
4.873207
2.859744
2.220000
8.506
2.916523
.3600
10.3800
10.0200
3.810000
1.514
2.078
Std. Error
.484760
.279
.552
.808898
.616
1.191
-36-
-------
Table A-16
Vehicle Sample Size with Available HC Emissions
THC * Class * Altitude
Cases Included
N
122
Percent
92.4%
Excluded
N
10
Percent
7.6%
Total
N
132
Percent
100.0%
Table A-17
Average Curb Idle HC Emissions by Vehicle Class and Altitude
Class
Truck
Bus
Total
Altitude
Low
High
Total
High
Total
Low
High
Total
Mean
10.495414
7.690909
10.212391
10.476923
10.476923
10.495414
9.200000
10.240578
N
98
11
109
13
13
98
24
122
Std. Deviation
8.393333
2.495281
8.035518
9.491434
9.491434
8.393333
7.191662
8.159247
Table A-18
T-Test Statistics for Curb Idle THC by Vehicle Class
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
.750
Sig
.388
Independent Samples t-test for Equality of Means
t
-.110
-.096
df
120
14.128
Sig.
(2-tailed)
.913
.925
Mean
Difference
-.264533
-.264533
Std. Error
Difference
2.403949
2.742658
95% Confidence Interval of
the Difference
Lower
-5.024184
-6.141961
Upper
4.495119
5.612896
-37-
-------
Table A-19
T-Test Statistics for Curb Idle THC by Altitude
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
.118
Sig
.732
Independent Samples t-test for Equality of Means
t
.696
.764
df
120
39.852
Sig.
(2-tailed)
.488
.449
Mean
Difference
1.295414
1.295414
Std. Error
Difference
1.862257
1.695246
95% Confidence Interval of
the Difference
Lower
-2.391725
-2.131201
Upper
4.982553
4.722029
Table A-20
ANOVA Statistics for Curb Idle HC by Engine Size
R
.036
R Square
.001
Adjusted R Square
-.010
Std. Error of the Estimate
8.535066
Regression
Residual
Total
Sum of Squares
8.329
6337.720
6346.049
df
1
87
88
Mean Square
8.329
72.847
F
.114
Significance
.736
(Constant)
Size
Jnstandardized
Coefficients
B
12.184
-.136
Standardized
Coefficients t Sig.
Std. Error Beta
4.910 2.481 .015
.401 -.036 -.338 .736
95% Confidence Interval
forB
Lower Bound
2.425
-.933
i Predictors: (Constant), Engine Size
) Dependent Variable: THC
Upper Bound
21.944
.662
-38-
-------
Table A-21
ANOVA Statistics for Curb Idle HC by Odometer Mileage
R
.087
R Square
.008
Adjusted R Square
-.007
Std. Error of the Estimate
7.146260
Regression
Residual
Total
Sum of Squares
27.220
3574.833
3602.053
df
1
70
71
Mean Square
27.220
51.069
F
.533
Significance
.468
(Constant)
Miles
Jnstandardized
Coefficients
B
9.270
2.863E-06
Standardized
Coefficients t Sig.
Std. Error Beta
1.449 6.397 .000
.000 .087 .730 .468
95% Confidence Interval
forB
Lower Bound
6.380
.000
i Predictors: (Constant), Odometer Mileage
) Dependent Variable: THC
Upper Bound
12.160
.000
Table A-22
ANOVA Statistics for Curb Idle HC by Model Year
Regression
Residual
Total
Sum of Squares
1063.204
6992.167
8055.371
(Constant)
Year
Jnstandardized
Coefficients
B
1294.063
-.644
R
.363
df I
1
120
121
Std. Erro
300.548
.151
R Square Ad
.132
VIean Square
1063.204
58.268
Standardized
Coefficients
r Beta
4
-.363
usted R Squa
.125
F
18.247
t Sig.
L
L306 .000
1.272 .000
re Std. Error of the Estimate
7.633352
Significance
.000
95% Confidence Interval
forB
ower Bound
699.000
-.942
Upper Bound
1889.127
-.345
i Predictors: (Constant), Model Year
) Dependent Variable: THC
-39-
-------
Table A-23
Average Curb Idle CO Emissions
by Vehicle Class and Altitude
Class
Truck
Bus
Total
Altitude
Low
High
Total
High
Total
Low
High
Total
Mean
22.101692
68.078182
26.741521
81.383077
81.383077
22.101692
75.285000
32.563982
N
98
11
109
13
13
98
24
122
Std. Deviation
15.182583
31.830396
22.235472
34.330353
34.330353
15.182583
33.185489
29.065045
Table A-24
T-Test Statistics for Truck Only Curb Idle CO by Altitude
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
40.902
Sig
.000
Independent Samples t-test for Equality of Means
t
-11.714
-7.657
df
120
25.403
Sig.
(2-tailed)
.000
.000
Mean
Difference
53.183308
53.183308
Std. Error
Difference
4.540246
6.945407
95% Confidence Interval of
the Difference
Lower
-62.172678
-67.476156
Upper
-44.193937
-38.890460
-40-
-------
Table A-25
T-Test Statistics for High Altitude Curb Idle CO by Vehicle Class
Levene's Test for Equality of
Variances
Equal variances
assumed
Equal variances
not assumed
F
Sig
Independent Samples t-test for Equality of Means
t
-.978
-.984
df
22
21.785
Sig.
(2-tailed)
.339
.336
Mean
Difference
-13.304895
-13.304895
Std. Error
Difference
13.608256
13.519105
95% Confidence Interval of
the Difference
Lower
-41.526691
-41.357821
Upper
14.916900
14.748031
Table A-26
ANOVA Statistics for Curb Idle CO by Model Year
R
.377
R Square
.142
Adjusted R Square
.133
Std. Error of the Estimate
14.
133510
Regression
Residual
Total
Sum of Squares
3182.964
19176.587
22359.551
df
1
96
97
Mean Square
3182.964
199.756
F
15.934
Significance
.000
(Constant)
Year
LJnstandardized
Coefficients
B
2415.728
-1.200
Standardized
Coefficients t Sig.
Std. Error Beta
599.642 4.029 .000
.301 -.377 -3.992 .000
95% Confidence Interval
forB
Lower Bound
1225.449
-1.796
i Predictors: (Constant), Model Year
) Dependent Variable: CO
Upper Bound
3606.007
-0.603
-41-
-------
Appendix B
Engine Load Analysis Statistics
Table B-l
Idle HC Emissions Versus Engine Load (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
Curb idle with Heater On
Curb idle with No Load
Curb idle with A/C On
High idle with No Load
High idle with A/C On
Mean
11.55440
11.26400
10.73851
11.22044
17.45338
16.67390
N
10
10
18
18
34
34
Std. Deviation
4.123644
3.651550
3.896791
3.080620
8.815857
8.191705
Std. Error Mean
1.304011
1.154722
0.918482
0.726109
1.511907
1.404866
Paired Sample Correlations
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
Correlation
10
18
34
0.781
0.758
0.931
Significance
0.008
0.000
0.000
Paired Differences
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
Mean
-0.2904
-0.48193
-0.77948
df
9
17
33
Std. Deviation
2.609318
2.547206
3.219075
Std. Error Mean
0.825139
0.600382
0.552067
Paired Differences
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
95% Confidence Interval
of the Difference
Lower
-2.156994
-1.74862
-1.90267
Upper
1.57619
0.784769
0.343705
t
-0.352
-0.803
-1.412
Sig. (2-tailed)
0.733
0.433
0.167
-42-
-------
Table B-2
Idle CO Emissions Versus Engine Load (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
Curb idle with Heater On
Curb idle with No Load
Curb idle with A/C On
High idle with No Load
High idle with A/C On
Mean
28.01
30.184
26.2485
29.77747
54.63609
53.24851
N
10
10
18
18
34
34
Std. Deviation
12.58176
14.6011
11.27232
13.41937
41.07124
37.30385
Std. Error Mean
3.978702
4.617274
2.656911
3.162975
7.043659
6.397557
Paired Sample Correlations
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
Correlation
10
18
34
0.984
0.947
0.986
Significance
0.000
0.000
0.000
Paired Differences
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
Mean
2.174
3.52896
-1.38758
df
9
17
33
Std. Deviation
3.142922
4.545774
7.518805
Std. Error Mean
0.993879
1.071449
1.289464
Paired Differences
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
Hish Idle with A/C On
95% Confidence Interval
of the Difference
Lower
-0.074311
1.2684
-4.01102
Upper
4.42231
5.78952
1.235855
t
2.187
3.294
-1.076
Sig. (2-tailed)
0.056
0.004
0.290
-43-
-------
Table B-3
Idle NOx Emissions Versus Engine Load (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Pair 4
Pair 4
Description
Curb idle with No Load
Curb idle with Heater On
Curb idle with No Load
Curb idle with A/C On
High idle with No Load
High idle with Heater On
High idle with No Load
High idle with A/C On
Mean
127.754
122.458
125.430
155.199
150.600
156.800
126.468
159.960
N
13
13
22
22
5
5
39
39
Std. Deviation
36.296
36.373
32.433
38.982
64.682
80.260
52.893
77.232
Std. Error Mean
10.067
10.088
6.915
8.311
28.927
35.893
8.470
12.367
Paired Sample Correlations
Pair 1
Pair 2
PairS
Pair 4
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with Heater On
High Idle with A/C On
Correlation
13
22
5
39
0.566
0.835
0.801
0.855
Significance
0.044
0.000
0.104
0.000
Paired Differences
Pair 1
Pair 2
PairS
Pair 4
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with Heater On
High Idle with A/C On
Mean
-5.296
29.769
6.200
33.492
df
12
21
4
38
Std. Deviation
33.843
21.449
48.080
42.121
Std. Error Mean
9.386
4.573
21.502
6.745
Paired Differences
Pair 1
Pair 2
PairS
Pair 4
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with Heater On
High Idle with A/C On
95% Confidence Interval
of the Difference
Lower
-25.747
20.259
-53.499
19.838
Upper
15.154
39.279
65.899
47.147
t
-0.564
6.510
0.288
4.966
Sig. (2-tailed)
0.583
0.000
0.787
0.000
-44-
-------
Table B-4
Idle PM Emissions Versus Engine Load (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
Curb idle with Heater On
Curb idle with No Load
Curb idle with A/C On
High idle with No Load
High idle with A/C On
Mean
6.588975
5.661299
6.846186
6.333916
4.513723
4.475141
N
10
10
11
11
34
34
Std. Deviation
5.060315
3.289959
4.875843
3.516132
6.044245
6.336543
Std. Error Mean
1.600212
1.040376
1.470122
1.060154
1.03658
1.086708
Paired Sample Correlations
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
Correlation
10
11
34
0.829
0.887
0.987
Significance
0.003
0.000
0.000
Paired Differences
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
High Idle with A/C On
Mean
-0.927676
-0.512271
0.03858
df
9
10
33
Std. Deviation
2.973875
2.391163
1.049061
Std. Error Mean
0.940422
0.720963
0.179912
Paired Differences
Pair 1
Pair 2
PairS
Curb Idle with Heater On
Curb Idle with A/C On
Hish Idle with A/C On
95% Confidence Interval
of the Difference
Lower
-3.055058
-2.118676
-0.327453
Upper
1.19971
1.09413
0.40462
t
-0.986
-0.711
0.214
Sig. (2-tailed)
0.350
0.494
0.832
-45-
-------
Appendix C
Engine Idle Speed Analysis Statistics
Table C-l
Idle HC Emissions Versus Idle Speed (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
High idle with No Load
Curb idle with Heater On
High idle with Heater On
Curb idle with A/C On
High idle with A/C On
Mean
9.555759
17.45338
11.264
20.0038
11.22044
17.44223
N
34
34
10
10
18
18
Std. Deviation
4.395221
8.815857
3.65155
7.443559
3.08062
7.567212
Std. Error Mean
0.753774
1.511907
1.154722
2.35386
0.726109
1.783609
Paired Sample Correlations
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Correlation
34
10
18
0.714
0.732
0.687
Significance
0.000
0.016
0.002
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Mean
7.897625
8.739800
6.221792
df
33
9
17
Std. Deviation
6.460725
5.379976
5.893289
Std. Error Mean
1.108005
1.701298
1.389061
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
95% Confidence Interval
of the Difference
Lower
5.643372
4.891197
3.291129
Upper
10.15188
12.58840
9.152456
t
7.128
5.137
4.479
Sig. (2-tailed)
0.000
0.001
0.000
-46-
-------
Table C-2
Idle CO Emissions Versus Idle Speed (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
High idle with No Load
Curb idle with Heater On
High idle with Heater On
Curb idle with A/C On
High idle with A/C On
Mean
17.22332
54.63609
30.184
73.742
29.77747
67.15153
N
34
34
10
10
18
18
Std. Deviation
8.772249
41.07124
14.6011
29.07419
13.41937
38.21423
Std. Error Mean
1.504428
7.043659
4.617274
9.194065
3.162975
9.00718
Paired Sample Correlations
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Correlation
34
10
18
0.630
0.751
0.724
Significance
0.000
0.012
0.001
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Mean
37.41277
43.558
37.37407
df
33
9
17
Std. Deviation
36.194
20.51483
29.96987
Std. Error Mean
6.20722
6.48736
7.063967
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
95% Confidence Interval
of the Difference
Lower
24.78409
28.88257
22.4704
Upper
50.04146
58.23343
52.27773
t
6.027
6.714
5.291
Sig. (2-tailed)
0.000
0.000
0.000
-47-
-------
Table C-3
Idle NOx Emissions Versus Idle Speed (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
High idle with No Load
Curb idle with Heater On
High idle with Heater On
Curb idle with A/C On
High idle with A/C On
Mean
81.12896
126.1909
120.6394
160.8317
154.5816
204.9348
N
38
38
14
14
23
23
Std. Deviation
33.21055
53.57418
35.60214
48.30586
38.20029
58.08001
Std. Error Mean
5.387463
8.690879
9.515073
12.91028
7.965311
12.11052
Paired Sample Correlations
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Correlation
38
14
23
0.711
0.628
0.492
Significance
0.000
0.016
0.017
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Mean
45.06191
40.19236
50.35326
df
37
13
22
Std. Deviation
37.98222
37.94282
51.47647
Std. Error Mean
6.161529
10.14065
10.73359
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
95% Confidence Interval
of the Difference
Lower
32.57747
18.28482
28.09316
Upper
57.54635
62.09989
72.61335
t
7.313
3.963
4.691
Sig. (2-tailed)
0.000
0.002
0.000
-48-
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Table C-4
Idle PM Emissions Versus Idle Speed (g/hr)
T-Test Paired Samples Statistics
Pair
Pair 1
Pair 1
Pair 2
Pair 2
Pair3
Pair3
Description
Curb idle with No Load
High idle with No Load
Curb idle with Heater On
High idle with Heater On
Curb idle with A/C On
High idle with A/C On
Mean
3.536667
4.513723
5.661299
8.196625
6.333916
9.301994
N
34
34
10
10
11
11
Std. Deviation
4.831247
6.044245
3.289959
5.722588
3.516132
6.954408
Std. Error Mean
0.828552
1.03658
1.040376
1.809641
1.060154
2.096833
Paired Sample Correlations
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Correlation
34
10
11
0.353
0.628
0.876
Significance
0.040
0.052
0.000
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
Mean
0.977056
2.535326
2.968078
df
33
9
10
Std. Deviation
6.264895
4.463751
4.229222
Std. Error Mean
1.074421
1.411562
1.275159
Paired Differences
Pair 1
Pair 2
PairS
Speed with No Load
Speed with Heater On
Speed with A/C On
95% Confidence Interval
of the Difference
Lower
-1.20887
-0.65785
0.126848
Upper
3.162981
5.728501
5.809309
t
0.909
1.796
2.328
Sig. (2-tailed)
0.370
0.106
0.042
-49-
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Appendix D
Discretionary Idling Particulate Matter Statistics
Table D-l
Oak Ridge Study Idle PM Emissions Measurements
Vehicle Description
1998 Freightliner with Cummins N14
1998 Freightliner with Cummins N14
1998 Freightliner with Cummins N14
1992 Ford with Caterpillar 3406
1992 Ford with Caterpillar 3406
1992 Ford with Caterpillar 3406
1999 Volvo truck, DDC series 60
1999 Volvo truck, DDC series 60
1999 Volvo truck, DDC series 60
Freightliner, DDC Series 60
Freightliner, DDC Series 60
Freightliner, DDC Series 60
Exact97 International Caterpillar
Exact97 International Caterpillar
Exact97 International Caterpillar
Temperature (F)
0
65
90
0
65
90
0
65
90
0
65
90
0
65
90
Load Type
Heater on
No load
A/Con
Heater on
No load
A/Con
Heater on
No load
A/Con
Heater on
No load
A/Con
Heater on
No load
A/Con
PM (g/hr)
5.603
3.136
2.946
6.885
20.386
20.574
4.790
3.904
5.061
8.208
2.480
3.312
3.347
2.200
1.439
Table D-l
Oak Ridge Study Idle PM Emissions Measurements
(Excluding the 1992 Ford)
Temperature (F)
0
65
90
Total
Seasonal Weighting
N
4
4
4
12
Mean
5.487167
2.930185
3.18931
3.868887
3.677399
Minimum
3.34689
2.20022
1.43929
1.43929
Maximum
8.20828
3.90439
5.06079
8.20828
Std. Deviation
2.039957
0.758637
1.487654
1.826509
Wgt. Std. Error
0.42709
Weighting
0.250
0.333
0.417
1.000
-50-
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