Environmental Protection Agency
Region IX
100 California Street
San Francisco/ California 94111
Oct. 30, 1973
Technical Support Document
For The San Diego
Intrastate Air Quality Control Region
Transportation Control Plan Final Promulgation
Published In
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I. Introduction:
This document is in support of the EPA promulgated
California Transportation Control Plan for the San Diego
Air Quality Control Region (AQCR), signed on October 30,
1973 by Acting Administrator John Quarles, and published
in the November 12, 1973 Federal Register.
The determination of the maximum amount of allowable
emissions consistent with the attainment of the Environ-
mental Protection Agency (EPA) promulgated National Am-
bient Air Quality Standards, and the emission reduction
strategies needed to reduce emissions to the maximum
allowable levels, are outlined and discussed in the
following two sections. More detailed information on the
control strategies and technical details involved in the
plan are found in the Appendices.
II. Determination of Allowable Emissions to Meet Federal
Ambient Air Quality Standards:
The National Ambient Air Quality Standard for photo-
chemical oxidant has been exceeded in this AQCR. The
photochemical oxidant control strategy discussed in
this report involves the control of high reactive hydro-
carbon and other reactive organic gases (RHC). Where
possible, the RHC are defined by the most recent EPA
guidance on organic gas reactivity. Using the EPA de-
finition of RHC, only the following five hydrocarbons
are considered as low or non reactive: Methane, ethane,
propane, benzene and acetylene. The EPA definition of
RHC was applied to all mobile exhaust emission sources,
and to gasoline vapor emissions from stationary as well
as mobile sources.
Due to the lack of a detailed breakdown of the organic
emissions from stationary sources, the San Diego County
Air Pollution Control District (APCD) Rule 66 chemical
definition of reactivity was used for the remaining
stationary sources. Application of the Rule 66 chemical
definition of reactivity means that only those organic
gases listed under Sections 1., 2., 3. of paragraph k
of Rule 66 (e.g. toluene, aromatic compounds with eight
or more carbon atoms, olefinic hydrocarbons), are inven-
toried as RHC and considered for control. It is expected
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that in the future, a more detailed stationary organic
gas emission inventory will be available, which will
allow for a completely consistent definition of RHC to
be made for both mobile and stationary emission sources
of organic gases. An observation that can be made is
that the RHC definition inconsistency between the
mobile and stationary source emissions in the present
RHC inventory, results in the stationary source emissions
(except stationary gasoline vapor emissions) being arti-
ficially low in relation to mobile source emissions.
The nitrogen dioxide ambient air quality standard has
not been exceeded in the AQCR, and no violation is fore-
seen in the future. Therefore, a control strategy for
this pollutant is not considered.
The carbon monoxide (CO) standard has been exceeded, with
a high 8-hour reading of 18 parts per million (p.p.m.)
occurring in 1972, versus the standard of 9 p.p.m. The
control of RHC for meeting the photochemical oxidant
standard is the controlling or critical factor however,
and the strategies required to meet the oxidant standard
should more than result in the attainment of the CO
standard.
The photochemical oxidant 1-hour standard is .08 p.p.m.
The critical yearly high photochemical oxidant reading
of .32 p.p.m., occurred in this AQCR at Escondido in
1972. The stationary RHC emissions in 1972 are esti-
mated to be 55.2 tons/day, and the mobile RHC emissions
are estimated to be 152.4 tons/day.
As a result of recommendations received at EPA public
hearings and technical meetings, EPA did a statistical
analysis of ambient photochemical oxidant data. The
statistical analysis entitled "Methodology For Determining
The Base Year Oxidant Level," is found in Appendix B.
The results of this study validate the use of the observed
AQCR yearly high 1-hour 1972 oxidant reading of .32 p.p.m.,
for control strategy planning purposes.
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The high 1-hour ambient photochemical oxidant reading
is considered to be directly proportional to the amount
of RHC emissions occurring on the high oxidant day. In
other words, a straight line proportionality is assumed
to exist between the RHC emission inventory and the re-
sulting yearly high ambient photochemical oxidant reading.
Straight line proportional rollback is then used to pre-
dict or calculate the maximum emissions that can be
allowed for attainment of the standard.
Based on the Federal .08 p.p.m. maximum 1-hour oxidant
standard, the 1972 high 1-hour oxidant reading of .32
p.p.m. and the 1972 RHC emission inventory, the allowable
RHC emissions are determined as follows, using the pro-
portional rollback method:
.08
.32 (55.2 + 152.4) = 51.9 tons RHC/day
III. Control Strategy Outline:
The EPA proposed rules and regulations that are to
affect the emission reductions outlined in this and the
previous section, are identified in Section "I. Intro-
duction", of this document. A compilation of the stra-
tegies and their affect on emission reductions is shown
in the following table.
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SUMMARY OF IMPACT OF
TRANSPORTATION CONTROL REGULATIONS
IN THE SAN DIEGO REGION IN 1977
Emissions and Reductions
of Reactive Hydrocarbons
Emission Source and Control Measures (tons/day)
Stationary source emissionsV 20.6
without EPA control
strategy
Expected reductions
1. Surface coating restrictions, -15.8
Dry-cleaning and
Degreasing controls
Stationary emissions remaining 4.8
Mobile source emissions without!/ 86.4
EPA control strategy
Expected reductions
1. Reductions from only EPA -6.4
promulgated* control
strategies, assuming a
conservative 11% VMT reduction^/
2. Catalyst retrofit, and mandatory -12.9
inspection and maintenance
3. Motorcycle limitations -1.4
4. VMT reductions and evaporative -19.0
emission reductions necessary
from additional control strategies
to be implemented in 1977.
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Mobile emissions remaining
46.7
Total emissions remaining 51,5
Allowable emissions for attainment 51.9
of standard for photochemical
oxidant
*VMT is an abbreviation for "Vehicle Miles Traveled."
i/ Stationary Source
Emission Breakdown:
Power Plants .7
Paint Solvents 13.4
Degreasing Solvents 1.9
Drycleaning Solvents 2.1
Petroleum Marketing 2.5
W7T
2/ Mobile Source Emission
Breakdown:
Ships & RR .6
Aircraft 11.4
Motorcycle 5.8
Heavy Duty Vehicle
(HDV) Diesel 3.2
HDV Gasoline 7.5
Light Duty Vehicle
(LDV) Gasoline 57.9
3F7T
1/ Using optimistic assumptions for both EPA and local VMT
reductions measures, a total reduction of 29% VMT or 16.9
tons/day could occur. A discussion of the basis or
rationale for the VMT reductions, is found in Appendix C
"California VMT Reductions Summary".
Technical reports, control tactics (including such details as
the emission control reduction factors, the population fraction
affected by the tactics), and other data and information needed
to calculate the emission inventory in the preceding table,
are outlined or referenced in the appendices.
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APPENDIX A
Data and References Used In
Emission Inventory Calculations
A. Stationary, Aircraft, Ship, and Railroad Emissions
1) Stationary and aircraft RHC emissions are basi-
cally derived from Rand Corp. -IREM interim draft
reports, and discussions with the San Diego Co.
APCD. The Rand analysis categorizes aircraft
emissions under the stationary emission category.
Future or projected emissions, not considering
proposed or additional controls, are estimated
by applying the appropriate growth factors (see
Section D.) to the 1970 or 1975 emissions in the
following table.
RHC Emissions Per Rand - IREM Estimates Without EPA Proposals
(Exceptions & revisions where notedfl
Emission Category 1970 (tons/day) 1975 (tons/day)
Petroleum Handling 27.4* 32.1**
Solvent Users 23.7 16***
Aircraft 13.2* 10.6*****
Ships & Railroads .5***#*
Power Plants .6 .7
~Considering EPA reactivity factor, see Section E.
**Considering EPA reactivity factor and EPA growth
projections, see Sections D. and E.
***This includes a Rand-IREM estimate of 6.7 tons/day plus
an additional EPA estimate of 9.3 tons/day from uncon-
trolled painting operations
****Emissions are estimated by EPA to increase from 1975-1977
*****An EPA estimate
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Emission Factors
1) Light and heavy duty vehicle (LDV & HDV) gasoline,
HDV diesel, and motorcycle emission factors (inclu-
ding deterioration factors where applicable), were
obtained from the following document:
Compilation of Air Pollutant Emission Factors
(AP-42) 1973 Edition
Available from:
EPA Office Technical Information & Publications,
Office of Air Programs, Research Triangle Park,
NC 27711
The emission deterioration factors in the EPA
AP-42 publication are presented as a function of
vehicle age. This analysis, however, relates the
deterioration factors to accumulated mileage. The
accumulated mileages that are associated with the
vehicle ages in AP-42, are as follows:
AP-42
Vehicle Age
1
2
3
4
5
6
7
8
9+
The emission factors presented in AP-42, are listed
for various model years in terms of grams of pollu-
tant emitted per mile traveled by the vehicle.
Vehicle
Accumulated
Mileage
17,500
33,600
46,800
58,200
69,900
79,900
90,200
98,800
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C. Vehicle Population, Age Distribution# and Mileage Data
1) Population data obtained from California Air Re-
sources Board:
a) 1972:
Statewide gasoline LDV population - 11,331,900
Statewide gasoline HDV population - 296,300
Statewide diesel HDV population - 94,800
Statewide motorcycle population - 672,000
San Diego AQCR % of statewide population is
6.08%
b) 1977:
San Diego AQCR % of statewide population is
6.52%. (This factor is used only for projecting
the AQCR 1977 motorcycle population, see Sec-
tion D.2.)
2) Vehicle Age Distribution
a) 1972 (July)
Average LDV Percent** Gasoline and Diesel**
Vehicle Age* (Yr) of Population HDV Percent of Pop.
3/8 7.8 7.6
11/4 9.3 8.0
2 1/4 9.0 8.2
3 1/4 9.8 8.6
4 1/4 8-6 6.9
5 1/4 7.4 5.7
6 1/4 7.9 6.4
7 1/4 8.2 6.9
8 1/4 7.0 6.2
9 1/4 5.7 5.3
10 1/4 4.5 4.3
11 1/4 2.9 3.1
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12 1/4 2.6 3.3
13 1/4 1.9 2.9
14 1/4 1.1 1.8
15 1/4 1.3 2.2
15 1/4+ 5.0 12.8
~The 3/8 year old vehicles are 1972 models, the 1 1/4 year
old vehicles are 1971 models, etc.
**Based on State of California Air Resources Board and Dept. of
Motor Vehicle data
b) Post 1972 (July)
Average LDV** HDV**
Vehicle Age* (yr) % of population % of Population
3/8
7.9
7.2
1 1/4
9.9
8.9
2 1/4
9.5
8.0
3 1/4
9.2
7.5
4 1/4
8.9
7.1
5 1/4
8.5
6.9
6 1/4
8.2
6.8
7 1/4
7.8
6.6
8 1/4
6.7
5.9
9 1/4
5.4
4.9
10 1/4
4.2
4.0
11 1/4
2.9
3.4
12 1/4
2.2
3.0
13 1/4
1.7
2.7
14 1/4
1.5
2.5
15 1/4
1.4
2.4
15 1/4+
4.4
12.5
*The 3/8 year old vehicles are the current year models in the
base year or strategy year, the 1 1/4 year old vehicles are
prior year models, etc.
**Based on State of California Air Resources Board and Dept.
of Motor Vehicle data.
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3) Vehicle VMT/yr rate as of July:
Average
Vehicle Age
1
2
3
4
5
6
7
3/8
1/4
1/4
1/4
1/4
1/4
1/4
1/4
8 1/4
9 1/4
10 1/4
11 1/4
12 1/4
13 1/4
14 1/4
15 1/4
15 1/4+
LDV*
VMT/yr
20,000***
16,300****
13,500
10,500
9,700
8,200
7,200
6,770
6,350
5,920
5,490
5,070
4,640
4,640
4,640
4,640
4,640
Gasoline HDV**
VMT/yr
28,000***
21,100****
17,950
17,950
13,960
13,960
11,000
11,000
8,420
8,420
4,270
4,270
4,270
4,270
4,270
4,270
4,270
Diesel HDV**
VMT/yr
128,000***
96,000****
81,600
81,600
63,600
63,600
50,200
50,200
38,400
38,400
19,440
19,440
19,440
19,440
19,440
19,440
19,440
Motorcyle VMT/yr
*****
4000
•Based primarily on California State vehicle age vs.
mileage study
**Based on U. S. Dept. of Commerce study "U. S. Truck and
Inventory Study - 1967"
***The accumulated mileage of a 3/8 yr. old vehicle is de-
termined by multiplying this number by 3/8
****The accumulated mileage of a 1 1/4 yr. old vehicle is
determined by multiplying this number by 1 1/4
*****Per EPA 1973 Edition of "Compilation of Air Pollution
Emission Factors: (AP-42)
The accumulated mileage for vehicles older than 1/4 years, is
determined by adding the accumulated mileage of a 1 1/4 year
old vehicle (see **** above) to the VMT/yr values found in the
previous table, for each vehicle age after 1 1/4, up to and
including the vehicle age of interest. This is illustrated
by the following example.
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Calculate accumulated mileage for 4 1/4 year old LDV:
mileage = 16,300 x 1 1/4 + 13,500 + 10,500 + 9.700 =
54,100
The accumulated mileage is used for determing vehicle emis-
sion deterioration factors (See Section B).
D. Growth Projections
1) EPA Stationary and mobile source growth projec-
tions , except motorcycles, are as follows for the
San Diego AQCR:
1970-72 growth factor = 1.070
1970-75 growth factor = 1.171
1970-77 growth factor = 1.242
1972-77 growth factor = 1.172
1975-77 growth factor = 1.071
The above factors are California Air Implementation
Plan growth projections and EPA interpolation of
these data, based on a California Dept. of Finance
Population Research Unit Report "Provisional Pro-
jections of California Counties To 2000" dated
September 15, 1971.
2) Motorcycle growth projections for the entire state:
Growth factors are determined using the ratio
of estimated statewide motorcycle population
projections in the California Dept. of Motor
Vehicle Report No. 31 March 1970. The motor-
cycle growth rate factors derived from Report
No. 31 are as follows:
1970-75 growth factor = 1.46
1970-80 growth factor = 1.91
E. Hydrocarbon Reactivity Factors
Per recent EPA guidelines, the following factors indi-
cate the weight fraction of total hydrocarbon emissions
that are considered to be reactive (i.e., do not con-
tain unreactive hydrocarbons, which are methane, ethane,
propane, benzene, acetylene):
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Emission Source
Weight Fraction of RHC
Gasoline LDV exhaust
Gasoline LDV exhuast after/catalyst «°4
treatment*
Gasoline HDV exhaust
Diesel HDV exhaust
2 stroke motorcycle exhaust •-J®
4 stroke motorcycle exhaust
Piston & turbine aircraft exhaust
Gasoline vapor
Crankcase emissions are estimated to consist of equal
amounts of uncombusted gasoline vapor and combustion
exhaust.
A Rule 66 chemical definition of reactivity is used
for the remaining emission sources.
*This factor is to be applied to the exhaust of emis-
sions of all 1975 and later LDV models, and to those
Pre 1975 LDV models that are to have retrofit catalyst
devices installed.
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P. Strategy Application &_ Reduction Factors
1) State and local programs in effect or committed:
Program
NOx retrofit
control
N0X retrofit
control
Crankcase (PCV)
retrofit control
Petrol. Marketing
Controls
Population Base
(Vehicle Model
Yrs. or Sources)
Affected
1955-65 LDV
Exhaust
1966-70 LDV
Exhaust
1955-62 LDV
Crankcase
Petroleum
Marketing
2) EPA programs:
Program
Annual Insp.
& maintenance
Oxidizing
Catalyst Retrofit
Oxidizing
Catalyst Retrofit
Dry Cleaning
Solvent Control
New Motorcycle
Emission standards,
1976 and later
models
Degreasing
Solvent Control
Population Base
(Vehicle Model
Yrs. or Sources)
Affected
All LDV
Exhaust
1971-74 LDV
Exhaust
1966-70 LDV
Exhaust
All RHC
Dry Clean
Sources
All Motorcycle
Emissions
All RHC Solvent
Sources
Pop.
Affected
in 72
0%
0%
93%
0%
Pop.
Affected
in 72
0%
0%
0%
0%
0%
% Pop.
Affected
in 77
67%
100% approx.
100%
100%
approx.
% Pop.
Affected
in 77
100%
75%
20%
100%
100%**
RHC Red
Factor
.25
.12
1.00
.87
RHC Red
Factor
.15
.58*
.58*
.95
.25
0%
100%
.98
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trocrram
Population Base
(Vehicle Model
Yrs. or Sources)
Affected
% Pop.
Affected
in 72
Wetal Surface
voating Control
parking surcharge
pnd review, car
?ool matching,
5us and car pool
Priority treatment,
*nd employees mass
^ansit incentives***
Gasoline rationing
All Sources 0%
Metal Coating
All gasoline 0%
LDV and petroleum
marketing emissions
All gasoline LDV
and petroleum
marketing emissions
0%
% Pop.
Affected
in 77
100%
100%
RHC Red.
Factor
.90
.11
100%
.42
*This factor accounts for a total hydrocarbon reduction factor of .5
and a lowering of the exhaust reactivity factor from .77 to .64 (See
Section E).
**While only new 1976 and later model years are affected, the entire
population is included here because the reduction factors are derived
on the basis of the total population.
***See Appendix "C" "California VMT Reductions Summary" for a discussion
of these and other VMT reduction measures.
rhe June 8, 1973 Federal Register discusses various mobile source control
Programs or tactics, and outlines the reduction factors associated with
the tactics.
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APPENDIX B
Methodology for Determining the Base Year Oxidant Level
INTRODUCTION
This paper discusses a method for selecting the maxi-
mum values used in the calculation of emission reduction
requirements.
The methodology described in this paper is neither new
nor original. Dr. R. I. Larsen, Meteorology Laboratory,
NERC, Research Triangle Park, outlined such a technique in
1967 and has published numerous papers since that time ex-
plaining the use of his model in the establishment of
standards and in relating air quality measurements to such
standards (Reference 1, 2, and 3).
The rationale for selecting this method is outlined
and some of the advantages and shortcomings are covered.
A comparison of actual measured values with model calculations
is provided.
BACKGROUND
The development of a control strategy to achieve a
National Ambient Air Quality Standard is frequently based
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pollutant in the ambient air Is linearly related to the rate at which
the pollutant is emitted in the atmosphere.
This assumption permits the use of a simple proportional (or
rollback) model to determine emission reduction requirements. Such
a model states that:
(100) aS I Standari> ¦ 10n
Current air quality is defined as the maximum measured concentration.
The development of the transportation control strategies did not
rely totally upon the rollback model. A non-linear relationship between
oxidant levels and hydrocarbon emissions developed by Schuck (See
Appendix B) was also employed. In some areas data was not available
for the verification of such a non-linear model and the simple proportional
relationship had to be applied.
Regardless of which of these models was used, the selection of an
appropriate naximum concentration was a critical factor in determining
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There are several methods that can be used to
determine the maximum value needed for these"roll-back"
calculations. Among such methods are:
a. Diffusion modeling
b. Selection of a maximum value from a base year
c. Choosing the highest value over a number of years
d. Determining a maximum value by statistical analysis
Diffusion modeling, where validated models can be ap-
plied, probably represents the best method for determining
both the concentration and the location of high pollutant
levels. Unfortunately/ a model with the required accuracy
is not yet available for determining specific oxidant
concentrations.
The selection of a value from a base year, where the
year is usually selected as the year of the latest emission
inventory, has the advantage of being most closely related
to the emission data. It also provides a convenient base
for comparing data at different locations. However, high
concentrations of oxidant occur under certain, as yet not
fully quantified, meteorological conditions and different
sets of these conditions may apply to the production of high
levels at different locations. Since meteorological para-
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conditions producing high levels may not always occur every
year at any given location. The data indicate that maximum
levels at a particular monitoring station may vary from year
to year by as much as a factor of two. High values within a
given region do not always occur at the same site and maxi-
mum concentrations selected from all stations within a region
may also vary considerably, although not usually by as much
as they do at a single location.
Extreme values can occur either because of unusual
meteorological conditions or because sane abnormal periods
would not necessarily be expected to occur every year but
perhaps only once in 5 or 10 years. Thus, the selection of
such an extreme value could require overly stringent control
measures. Conversely, abnormally low values could also be
selected if the data record is short.
A statistical analysis of data collected over a period
of years tends to smooth out the variations due to the
meteorology and to local anomolies. Such an analysis can
also provide a prediction with a specified probability of
occurrence and the extreme or outlying values can be weighed.
This paper compares the results obtained by applying a
particular statistical method to the calculation of maximum
oxidant levels with the actual measured maximum concentrations
at selected stations from data collected over the past three
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THE ANALYSIS
Selection of Technique:
The objective of the analysis was to find an oxidant level (con-
centration) that represented the highest level expected to be achieved
with a frequency of one hour per year. The rationale for this objective
is the National Ambient Air Quality Standards for oxidant: 160 ug/m3
(0.08 ppm) - maximum 1 hour concentration not to be exceeded more than
once per year.
Although there are a number of statistical methods that could be
applied, a technique described In the Office of Air Programs publica-
tion No. AP-89, "A Mathematical Model for Relating Air Quality Measure-
ments to Air Quality Standards" by R. I. Larsen, November, 1971, seemed
to best fit the objective. This model is based on the assumption that
the air quality data fit a log-normal distribution. There is some
disagreement about whether or not this is an appropriate assumption.
For example, Mitchiner & Brewer (5) have suggested the use of a
'double-exponential1 distribution. This is a widely known extreme
value technique. Their analysis, however, was limited to data collected
in three summer months and used only the maximum daily hour data. A
report by Mosher, Fisher, and Brunelle (6) indicates peak oxidant con-
centrations of 0.50 ppm or greater have occurred in Los Angeles County
in all months of the year except January and February. The selection of
only certain months could, therefore, tend to bias the results. Addi-
tionally, extreme value techniques seem most applicable to the selection
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concentration expected to occur once per year. However, a comparison
of the values calculated by the Mit chiner-Brewer method indicate that
they do not differ greatly from Larsen's method, at least at the one
station covered in their analysis, even though a different data set was
used.
Larsen (7) analyzed all oxidant data for all California stations
for the period 1963-1967 and presented the cumulative frequency distri-
butions and a calculated maximum concentration for each station. The
tables in that publication were used in conjunction with later available
measured data to determine the location (or areas) of the higjiest con-
centrations. Stations within those areas were then selected for further
analysis. An attempt was made to obtain a three-year period of record
for each station. It was felt that the period should be comparable to
the latest emission inventory data available (in most cases this was 1970
data) and also should contain a sufficiently long period to help over-
come the problem of meteorological variability. A period of 5 to 10
years would have been desirable, but because of the changing patterns of
emissions and changing vehicular emission factors, it was felt that a
period longer than three years would tend to introduce more emission
variability than the meteorological variability that would be factored
out. Data for 1972 were not available so the period January, 1969, through
December, 1971, was selected. Unfortunately, there were many gaps in the
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- 7 -
Fourteen stations were finally selected, for analysis and cum-
mulative frequency distributions for the selected stations for the
three-year period were then obtained. The data were analyzed according
to Larsen (4). A sarrple of the frequency distribution used is shown in
Figure 1.
CALCULATION OF MAXIMUM CONCENTRATIONS
The frequency distribution as given in Figure 1 is plotted on a
logarithmic probability graph as indicated in Figure 2. If the data
were perfectly log-normally distributed, all points on the graph would
be on a straight line. As can be seen in Figure 2, this is not the
case. However, the points in the frequency ranges from 10% to .01% do
appear to closely approximate a straight line. Since these are the
frequencies of most concern when considering very high values, only
those points are considered. To find the value that would be expected
once a year, Larsen (4) suggested using the .01 and the .10 frequency
points and extrapolating the line connecting these points to the
desired once per year frequency point. This was done for each location
for which frequency distributions were available. The extrapolation can
be done either graphically or mathematically. The mathematical method
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- 8 -
The desired frequency using this log-normal distribution is
obtained from
f = r-0.4 (100%)
n
where: r = the rank of the desired concentration if all
the concentrations were ordered from one
through the number of possible samples within
a selected time period
f = the frequency of occurrence in percent
n = total number of samples
FOR EXAMPLE: To find the frequency corresponding to the highest
one-hour average in a year, all of the 8760 one-hour averages in a year
would be listed in order from 1 (the highest) to 8760 (the lowest). The
rank order, r, then is equal to 1, n, or the total number of samples, is
8760, and
f = 1-0.4 (100%) = 0.(
w
Next, the extrapolation of the data to this desired frequency, using
the two known concentration vs. frequency points, is as follows:
The equation of a straight line passing through two known points x-jy^
and y^2$2 ^s:
y - y3 = 2Lz_£i
y2- y-L x2- Xl
this can be rearranged so that
' y = yx + y2~ (x-x^
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In this case the x and y without subscripts are the intercepts of
the unknown point on this line.
Where we are using the log-normal distribution, the y intercepts are
logarithms and the x intercepts are in terms of standard deviations from
the median. In a normal distribution each frequency can be located as a
distance (standard deviations) from the center of the profile (median).
If the y intercepts are logarithms, then the equation for the
straight line becomes:
ln£2
In y = In yx + Yt (x-o^)
(x2-Xl)
The concentration at an unknown point 'x,y' is then equal to the
anti-logarithm of
In y2
(In y2 + 7l (x-xx) )
(x2-xi)
or to put it in another form:
concentration at y = exp [ In y0+ (x-x-> ) ]
(x2-xx)
where 'exp' indicates that 'e', the base of natural logarithms, is
raised to the power in the brackets, 'e' is approximately equal to
2.71828.
Following Larsen's suggestion (8), the two known points at the .01
and the .10 percentile levels are used to define the straight line we
wish to extend. Krom a statistical table, such as is given in
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- 10 -
can be determined. In the case of a log-normal profile, the .01
percentile point is 3.72 standard deviations from the median; the
.10 percentile point is 3.09 standard deviations; and the unknown point
at .00685% is 3.81 standard deviations from the median. The y intercepts
are the concentrations at each of these percentile points. These x and y
values are then substituted into the above straight line equation and
the unknown concentration at the .00685% frequency is determined.
To illustrate the procedure, the data from Figure 1 have been
replotted on Figure 3, and the points that are used below have been
labeled.
frequency concentration standard deviations
f(%) y(ppm) x
.00685 to be determined(y) 3.81 (x)
.01 .27 (y-,) 3.72 (x,)
.10 .23 (y2) 3.09 (x£)
Substituting these values into the straight line equation:
. 23
concentration at y = exp [ In.27 + ^ (T27) (3-81-3.72) ]
(3.09-3.72)
= exp [ -1.30933 + (-0.1603*0 (0.09) 1
—C=033T
= exp [ -1.286424]
concentration at y = 0.28 ppm
From the example, a concentration of 0.28 ppm would then be the
highest concentration expected to be reached (or exceeded) once each
year.
These maximum concentrations were calculated for each of the
selected stations within each Air Quality Control Region. The results
-------
- 11 -
TABLE I. Hourly average concentrations for selected frequencies of
occurence.
LOCATION Percent of time given concentration
equaled or exceeded
0.10% 0.01# 0.00685#(Annual Maximum)
South Coast AQCR
Riverside
0.34
0.56
0.60
Azusa
0.42
0.51
0.52
Pasadena
0.39
0.51
0.53
San Diego AQCR
San Diego (8th & E)
0.16
0.23
0.24
El Cajon
0.27
0.30
0.30
Sacramento Valley AQCR
Creekside
0.18
0.24
0.25
Chico
0.14
0.15
0.15
San Joaquin Valley AQCR
Fresno (So. Cedar)
0.20
0.25
0.26
San Francisco Bay AQCR
Livermore
0.24
0.32
0.33
San Leandro
0.19
0.27
0.28
Fremont
0.22
0.27
0.28
Data used in this Table were hourly averages for the period of
-------
- 12 -
It should be noted that these calculated concentrations are not
necessarily the highest values to be expected. It Is quite possible
that this value could be nearly twice as high on an unusually "srnoggy"
day. Based on this analysis, however, such very "smoggy" days would
not normally occur every year.
COMPARISON WITH MEASURED MAXIMA
The calculated maximum values were compared with the actual maxi-
mum values that have been reported within each of the Air Quality Control
Regions since 1969. These values are shown in Table 2. In all cases
the calculated maximum concentration is within .03 ppm of the actual
measured maximum, even though an additional year of measured data was
considered and the high value for the region may have been reported at
a station other than one included in the calculations.
TABLE 2. Comparison of measured and calculated highest hour average
oxidant concentrations calculated.
Calculated
AQCR Maximum
Station
Measured
Maximum
Station
Year
South Coast
.60
Riverside
.62
Riverside
1970
San Joaquin
.26
Fresno
.2H
Modesto
1972
San Diego
.30
El Cajon
.32
Escondido
1972
S.F. Bay Area
.33
Livermore
.36
San Leandro
1971
Sacramento
.25
Creekside
ro
00
Creekside
-------
- 13 -
The number of occurrences of concentrations in excess of the cal-
culated maximum within each Air Quality Control Region was also tabulated.
For comparison, the dally maximum hourly averages from 1969-1972 were
used. The calculated maximum was equaled or exceeded three times in the
San Francisco Bay Area, once in 1969 and at two separate locations on
the same day in 1971• In the South Coast Basin the calculated concentra-
tion was exceeded once. In the San Diego Area twice, once each in 1971
and in 1972 in Sacramento once and once in the San Joaquin Air Quality
Control Region,
Again, it should be noted that the calculated value represents a
level that is expected to be reached or exceeded once per year and that
the analysis does not attempt to predict the highest possible concentra-
tion. Thus, the occurrence of a concentration greater than the predicted
value tends to verify the procedure if no other concentration measured
during the year was equal to or greater than the calculated maximum.
EVALUATION OF METHOD
The fact that the calculated values are close to the actual measured
concentrations and that the values have been reached or exceeded only
once in a given year, would tend to indicate that reliability of Larsen's
technique. There are, however, some obvious shortcomings to the analysis
presented here. A full three-year period of record was not available from
-------
- Ik -
the stations listed in Table 1. The shorter the period of record that
is available, the less reliable are the calculated values. To improve
the reliability, additional data should be analyzed and a larger sample
from each Air Quality Control Region should be selected.
Also, it was assumed that the stations selected represented the highest
concentrations within the given Air Quality Control Region. This is not
necessarily a valid assumption. Although only limited data is available,
newly established monitoring sites appear to be recording higher values
than some of the listed stations. For example, data from Escondido was
used to develop the strategy in the San Diego Air Quality Control Region.
The station was established in mid-1972 and the .32 ppm oxidant measured
there represents the highest concentration within the San Diego metro-
politan area in recent years. Agencies are usually continually expanding
their networks to include new areas of high concentrations, and additional
analyses should be performed as new data become available.
The calculations were based on the data measured during the years
1969-1971. They reflect only the emissions during that period of time.
Assuming no changes in emission patterns or emission controls at the
source, these values could be used to predict future air quality. However,
none of the areas considered are static with respect to growth, or to
the numbers and ages of motor vehicles in operation, or even with respect
to the numbers of and outputs from stationary sources. Some care should
be exercised in attempting to relate the concentrations to emissions in
-------
- 15 -
The oxidant data do not exactly fit a long-normal distribution and
the degree of fit varies at different locations. Thus, use of this
method may result in more reliable results in some areas than in others.
Also, the calculated maximum is quite sensitive to the selection of the
percentile points used in the calculations especially where the log-normal
fit is poor. Larsen (4) has suggested the use of the concentrations at
the .01 and .1 percent frequencies as being most representative of the
distribution of the higher concentrations. In seme instances it appears
that the point at the .01 percentile fits the overall log-normal
distribution least well. The problem is particularly evident when a
short period of record is used. In most of the data examined, use of
the .1 and the 1 or the 10 percentile points would result in higher
maximum levels than when the .01 percentile is included. This would
indicate that for some reason, probably meteorological, the maximum
possible values are not achieved. In other cases the .01 percentile
value seems too high. A study of the individual days could perhaps
provide an answer to the reasons why some of the high values seem out
of line.
The calculation of the maximum value is quite simple, but it does
require the preparation of cumulative frequency distributions. These
distributions are best processed by computer because of the large amounts
of data required. Once they are available, several other analyses can be
performed (see Larsen, 3). Additionally, a comparison of the different
yearly and three-year distributions suggests a possible method for trend
-------
- 16 -
suMiytARy
Air quality data for a number of California air monitoring stations
were reviewed and analyzed according to a method suggested by Larsen.
The objective of the analysis was to determine a maximum oxidant concen-
tration for certain Mr Quality Control Regions that could be related to
the available emission data and used to determine the emission reductions
needed to achieve the National .Ambient Air Quality Standards.
Because of the variability of concentrations from year to year, at
least a three-year period of record would appear to be required for
analysis. This limits the selection of maximum concentrations to these
stations where data have been collected over that long a period and
could eliminate areas where higher concentrations are possible.
Although values obtained in this analysis compare favorably with
measured conentrations ^ other statistical approaches may provide equally
meaningful solutions and should be compared with this method. The method
outlined in this paper, however, is relatively simple and well documented
and is applicable to all pollutants. The use of some statistical approach
is certainly less arbitrary than the selection of one particular measured
concentration.
ACKNOWLEDGEMENTS
The author is indebted to Dr. R. I. Larsen of the Meteorology
Laboratory for his assistance and Mr. Don Worley of the Data Systems
-------
- 17 -
REFERENCES
(1) LARSEN, R. I. (1967) "Determining Reduced Emission Goals Needed to
Achieve Air Quality Goals - A Hypothetical Case," YAPCA 17, pp. 823-829
(2) LARSEN, R. I. (1969) "A New Mathematical Model of Air Pollutant
Concentration, Averaging Time and Frequency," YAPCA 19, pp. 24-30
(3) LARSEN, R. I. (1971) "A Mathematical Model for Relating Air Quality
Measurements to Air Quality Standards," Publication AP-89, U. S.
Environmental Protection Agency, Research Triangle Park, NC 27711
(4) LARSEN, R. I. (1973) "An Air Quality Data Analysis System for Interrelating
Effects Standards, and Needed Source Reductions," presented at WMQ-WHO
Technical Conference on Observation and Measurement of Atmosphere Pollution,
Helsinki, Finland, July 30 to August 4, 1973
(5) MITCHINER, T. L., and BREWER, J. W., "A Comment on the Method Used by
EPA to Calculate Required Reductions in Emissions," University of California
at Davis, unpublished
(6) MOSHER, T. C., FISHER, E. L., and BRUNELLE, M. F. (1972) "Ozone Alerts in
Los Angeles County," Air Pollution Control District, County of Los Angeles, CA
(7) LARSEN, R. I. (1971) "Air Pollution Concentrations as a Function of
Averaging Time and Frequency
-------
— CONCENTRAf I ON Avfei^SlNG TIME AND FREQUENCY FOR"
OXIDANT (PPM1S LOS ANGELES, S. SAN PEORO ST. STATION 001
' "" JANUARY "I, I960 TO DEC. 31 V 1971
_ PERCENT OF TIME CONCENTRATION IS EQUALED OR^EXCEEDED
AVERAGING " 0.001 " ~ 99.999
TIME HFAN MAX HIN PERCENT O.Ol 0.1 1 10 20 30 40 50 60 70 80 90 99 99.99 99.999
5 min ooo~ooor~ooo. "ooo. oioo 0.00" 0.00~0i00 0.00 0.00~0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
,0 000. 000. 000. 000. 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
,5 "000."000.*000. boo." 0.00 0.00 0.00 oioo o.oo oVoo 0.00 0.00 0.00 0.00 0.00'0.00 0.00 0.00 0.00 0.00 0.00 0.00
10 _ 000. 000. ooo. oOo. 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
1 HOUR 0.03 0.33 0.01 069. 0.33 0.27 0.23 0.16 0.07 0.04 0.03 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
3 0.03 0.27 O.Ol 072. 0.27 0.27 0.21 0.15 0.07 0.04 0.03 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 O.Ol 0.01
3 6-9 AM 0.01 0.05 0.01 073. 0.05 0.05 0.04 0.03 0.02 0.01 O.Ol O.Ol O.Ol 0.01 0.01 0.01 0.01 O.Ol 0.01 O.Ol 0.01 O.Ol
8 0.03 0.21 O.Ol 073. 0.21 0.21 0.18 0.13 0.07 0.04 0.03 0.02 0.02 0.01 0.01 0.01 0.01 O.Ol 0.01 O.Ol O.Ol O.Ol
[2"" 0.03"'0.12 0.01 073. 0.12" 0.12 O.lOO.08 0.05 0.04 0.03 0.03 0.02 0.02 0.02 0.01 0.01 0.01 O.Ol 0.01 0.01 0,01
1 OAY 0.03 0.10 0.01 074. 0.10 0.10 0.09 0.07 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 O.Ol
2 0.03 0.09 0.01 074. 0.09 0.09 0.09 0.07 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.02 O.Ol O.Ol 0.01 0.01 O.Ol O.Ol
4 0.03 0.07 0.01 075. 0.07 0.07 0.07 0.06 0.05 0.04 0.03 0.03 0.03 0.02 0.02 0.02 O.Ol 0.01 0.01 O.Ol 0.01 C.01
7" 0.03 0.06 0.01 075. 0.06 0.06 0.06 0.06 "0.04 0.04 0.03 0.03 0.03 0.02 0.02 0.02 O.Ol O.Ol 0.01 O.Ol O.Ol 0.01
4 0.03 0.06 0.01 075. 0.06 0.06 0.06 0.06 0.04 0.04 0.03 0.030.03 0.02 0.02 0.02 0.01 0.01 0.01 O.Ol O.Ol 0.01
1 "MONTH 0.03 0.05 0.01 075." 0.05 0.05 0.05 0.0$ 0.04" 0.04 0.03 0.03 0.03 0.03 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01
2 0.03 0.05 O.Ol 075. 0.05 0.05 0.05 0.05 0.04 0.04 0.03 0.03 0.03 0.03 0.02 0.02 0.01 O.Ol 0.01 0.01 0.01 0,01
3 0.03 0.04 0.02 075.0.04 0.04 0.04 0.040.04 0.04 0.03 0.03 0.03 0.02 0.02 0.02 0-02 0.02 0.02 0.02 0.02 0.02
6 0.03 0.03 0.02 075. 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02
1"YEAR "0.03 "0.03 0.02 075. 0.03 0.03 "0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02
2 0.03 0.03 0.03 050. 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03
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Appendix C
CALIFORNIA VMT REDUCTION SUMMARY:
Presentation of Analytic Basis
for
-------
SUMMARY
Purpose
It is the purpose of this paper to summarize recent
studies relating various transportation control measures such
as car pooling, bus lanes, gasoline sales limitations, etc.,
to VMT reductions. In particular, the paper includes those
measures proposed for California Transportation Control Plan
(TCP) .
Concentrating on the measures proposed by EPA and local
AQCR task forces, the paper shows the range of VMT reductions
that can be expected from the TCP measures individually and
combined in a complementary strategy for each AQCR. Deter-
minations of the effective range of VMT reductions achieveable
are based on application of various transportation modal split
models developed for the purpose of predicting commuter trans-
portation patterns.
Most of the effects of measures promulgated by EPA are
predictable within a range of certainty. Results of pilot
studies'and public reaction attitude surveys have been used
as inputs to the data base. Measures that can not be assessed
quantitively at this time or that have delayed effects and are
unable to effect air quality fast enough for the Clean Air Act
standards are not included in EPA promulgation. However, many
of these measures have future short and long-term potential.
EPA encourages local proposal and implementation of these
measures.
Although the socio-economic impact of VMT reduction
measures is important, the scope of this analysis is limited
to the technical effects. Many of the studies done for EPA
have addressed the socio-economic questions.
I. INTRODUCTION
THE ROLE OP VMT MEASURES
In the majority of air quality control regions requiring
additional controls, the combined impact of stricter controls
-------
-2-
and maintenance system will not provide emission reductions
adequate to achieve the air quality standards by 1975. Conse-
quently, EPA has promulgated a variety of measures to reduce
vehicle miles traveled in these regions. In several urban
areas a shift from present reliance on automobiles occupied by
one or two persons to a greater reliance on other forms of
transit is essential to the achievement of the air quality
standards. Significant reductions in vehicle miles traveled
can also be accomplished within a limited time span.
The States have had practically no experience with trans-
portation control measures as a means of dealing with air quality
problems and the success of particular VMT reduction measures
is difficult to predict. However, recent developments involving
bus lanes, mass transit improvements, carpool programs, bikeways,
and other innovations indicate that many VMT reduction measures
are available and feasible. Furthermore, attitude surveys show
that the public in many of our urban areas recognizes the need
to place less emphasis on the automobile for urban mobility and
is already encouraging the implementation of steps to develop
alternative forms of transit.
Some of the regulations being promulgated will have signif-
icant effects on the future development of urban transportation
in the major cities of this country. A clear implication of
these air plans is that future augmentation of mass transit must
focus not only on the center city streets but also on urban/sub-
urban routes. It is expected that the regulations will lead
not only to substantial reductions in air pollution, noise,
congestion, and energy comsumption, but to the development of
more mass/rapid transit to serve the growing urban and suburban
regions of the nation. The need, desirability, and feasibility
of reducing urban auto use are no longer issues. The problem
is determining the degree to which VMT reductions can be
reasonably implemented within the limited time frames.
The amount of VMT reduction that can be considered "rea-
sonably available" varies greatly according to a city's indi-
vidual characteristics and the ability of other modes of trans-
portation to absorb the demand that would be created by a
significant VMT reduction. A measure cannot be considered
"reasonably available" if putting it into effect would cause
severe economic and social disruption. Although some reduc-
tion in personal travel could certainly be absorbed without
disruption, to achieve a significant VMT reduction, the bulk
of the travel displaced from single-passenger automobiles
must be absorbed by such other modes of transportation as
-------
-3-
The significant expansion of public transit facilities
that can be accomplished by 1975 depends on the upgrading and
expansion of bus service. Much can be done in this regard.
Scheduling and service can be improved. Individual lanes of
freeways and other major roads can be set aside for the exclu-
sive use of buses. Significant numbers of new buses can be
purchasds and put into service by 1975; according to the
Department of Transportation figures, 2,500 transit buses were
sold in this country in 1972, but there is considerable poten-
tial for expansion of the transit industry's production by
two or three-fold. Foreign sources of supply could provide
additional resources.
The Environmental Protection Agency is working with the
Department of Transportation to assure increased Federal sup-
port for short-term augmentation of mass transit capacity and
appropriate modifications of highway facilities to permit
increased utilization of mass transit.
In addition to public transit, part of the transportation
demand created by VMT reductions can be absorbed by carpools.
Private automobiles, which are designed to carry four to six
persons, carry an average of 1.1 to 1.4 persons per trip for
work trips in major urban areas, and thus represent the largest
unused pool of transportation capacity presently available.
The measures mentioned above are primarily concerned with
providing an alternative to low-occupancy use of private auto-
mobiles. Although measures such as buying more buses and
improving bus service, providing for carpool programs, building
bicycle paths, and (possibly in the long run) building new
rapid transit systems increase the availability and attrac-
tiveness of alternative transit forms, VMT reductions will not
necessarily be achieved unless disincentive restrictions are
placed on the use of automobiles.
The applicability of both measures—incentives such as bus
lanes that increase the attractiveness of alternative transit
forms and disincentives such as parking limitations that dis-
courage the low-occupancy use of private automobiles—varies
according the the conditions in the individual urban area.
For example, bus lanes are a more appropriate strategy in
Washington, D.C. than certain other areas. Similarly,
parking restrictions are more applicable to a major center
like Boston than to a small city with few transit alterna-
tives like Fairbanks, Alaska.
After consideration of the already available transit
alternatives, the city's local conditions, and the applica-
-------
-4-
EPA has determined that varying degrees of VMT reduction
are feasible in particular areas. The Agency believes a 3
to 10 percent VMT reduction can be achieved in some of the
regions by 1975. Since the Clean Air Act specified that
all reasonable available measures be instituted before any
time extension is granted, the Administrator is taking into
consideration all VMT-related measures presently being
implemented by a municipality and augmenting those measures
with methods that are available, applicable, and adoptable
in the individual area by 1975.
Through studies and the public hearing process, the
Agency has also determined that it may be unrealistic to
expect reductions in auto use greater than 10 to 20 percent
by 1977. Generally, reductions beyond 10 to 20 percent
would require a special and, in most cases, unreasonable
effort unless driving is to be cut without a corresponding
increase in mass transit. Achievement of even the levels
provided for in these plans will require a strong commitment
by local areas to implement strict disincentive programs,
improve mass transit, and make carpooling or other programs
work.
EPA has promulgated a number of measures designed both
to increase the attractiveness of alternative forms of transit
and to discourage the low-occupancy use of automobiles. The
measures include: regulatory fees for mass transit augmenta-
tion, bus/carpool lanes, carpool matching systems, and carpool
programs stressing preferential treatment. Local task forces
have proposed additional measures, applicable to their par-
ticular regions, that will be implemented along with EPA
strategies. These measures include: traffic flow improve-
ments, ramp metering, fringe parking for park and ride, dial-
a-ride service, bicycle lanes and facilities, reduced transit
fares, four day work weeks, and taxation and pricing measures.
State, Local, and Federal Implementation of Control Measures
In order to preserve the intent of the Clean Air Act
that pollution problems be dealt with primarily at the local
level, the Agency is requiring that State and local govern-
ments take action wherever possible and will involve the
Federal Government only in the direct implementation of some
programs. State and/or locally enforced, Federal promulgated
requirements are: retrofit programs; parking supply and sur-
charge; bus and carpool lanes; inspection and maintenance;
and stationary source controls. Federally operated programs
will be: motorcycle controls, gasoline limitation, and a
-------
-5-
DESCRIPTION OF EPA PROMULGATED VMT REDUCTION MEASURES
Bus Lanes
Bus priority treatment consists of allocating highway
facilities preferentially to buses for the purpose of improving
the quality of bus service. Methods of effecting bus priority
treatment in the transportation plans include reserved lanes
for buses (and/or carpools), preferential access for buses at
metered freeway ramps, and certain traffic engineering improve-
ments. The forms of bus lanes set forth in either the plans
proposed or approved by the States or promulgated by EPA in-
clude normal bus flow lanes, and contra-flow lanes. In Cali-
fornia, the Department of Transportation suggested that only
certain freeways or major roads be dedicated to the bus lane
concept and EPA agreement with this suggestion is reflected in
these promulgations. The method of selecting the lanes has
been changed from one based on the number of lanes in the road
to one looking to the establishment of a coherent network of
such lanes along transportation corridors. In some regions,
pilot programs will be conducted to discover the best way to
implement a full-scale program. In some cases, measures such
as the conversion of entire streets to bus and carpool use may
prove preferable to limited lanes.
The use of bus (and/or carpool) lanes has been observed
to increase mass transit freeway speeds by a factor of two or
more. Through the elimination of congestion problems, bus
service dependability is increased as late arrivals are sig-
nificantly reduced. Furthermore, bus ridership will increase,
and the fares may eventually be reduced. Because of these
factors, the regulations set forth for bus lanes are expected
to be a positive inducement to increased bus patronage. The
timetables for implementation of bus lanes will vary according
to regional situations.
Carpool Systems
Experience to date with carpool programs suggests that
policies to encourage carpooling might double auto occupancy
rates for downtown peak period work trips. If a 10 to 50
percent increase in auto occupancy is adopted as a realistic
range of possible effects, the net effect of carpool policies
on total urban area auto use might be a 5 to 10 percent re-
duction .
EPA is promulgating measures that provide computerized
-------
-6-
programs. The matching program provides for the formation
of carpools and the preferential treatment programs provide
incentives such as free parking to encourage carpools. Under
the measures included in some plans, disincentives such as
parking space reduction or paid, rather than free parking,
are included to discourage single occupancy on commuter trips.
In all Regions EPA is requiring the establishment of
carpool matching systems to enable persons with similiar daily
travel patterns to make contact with each other and arrange
carpools. In some regions, pilot programs will be established
prior to establishment of the system throughout the region.
Such a measure is necessary if the restraints on individual
vehicle use contained in this plan are to have the desired
effect of reducing VMT.
The EPA Regional Office in San Francisco has contacted
various Federal agencies in order to facilitate the implemen-
tation of the pilot programs called for in the regulation.
The Regional Office has experienced initial success in its
first contacts, and this effort is continuing. A detailed
guide for the operation of a bus/carpool matching program,
along with a discussion of a number of successful programs
in operation in many areas of the country is found in a U. S.
Department of Transportation Federal Highway Administration
Publication "Carpool and Buspool Matching Guide (Second
Edition)", May 1973. This report discusses the considera-
tions involved in a successful program such as public infor-
mation, incentives, data processing, and a continuing updating
of the service, and is an excellent guide and reference for
conducting such a program.
The EPA believes that this approach to reducing vehicle
miles traveled is an excellent short-term strategy, it
involves a minimum investment and deserves the active promo-
tion and support of government and industry.
Employer Provisions for Mass Transit Priority Incentives
As was pointed out in the public hearings by some of
those testifying, employer-paid privileges for employees tend
to encourage employees to drive to their place of employment
rather than use carpools or mass transit. The promulgated
regulation therefore, provides for employer-paid mass transit
fares and special parking privileges to those who travel in a
carpool. It also requires that individuals who drive may not
be provided with free unlimited parking, but must pay the
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This regulation will be implemented in stages, the first
stage applicable to employers of 700 or more employees, and
the second to employers of 70 or more.
The purpose of this regulation is to effect sizeable
reductions in VMT caused by commuting, with appears to be the
mode of travel most easily diverted to mass transit and car-
pools .
Control of Existing Parking Spaces: Surcharge on Parking
The proposal that spaces in public parking facilities
be reduced by 20 percent drew almost universal adverse comment
during the rulemaking proceedings. At the same time, the use
of regulatory fees to discourage pollution-causing activities
was widely supported. In particular the use of fees to control
parking was mentioned.
EPA also believes that the use of such parking fees has
much to recommend as a matter of policy. Accordingly, EPA is
not promulgating a reduction in publicly owned parking spaces
and is instead promulgating a regulatory fee to increase the
price of parking in, and so discourage traffic to, selected
trip attraction centers in the three most heavily polluted
AQCR's. The regulation's coverage will be increased in
three phases. At least 50 percent of the revenues will be
used for mass transit.
Several of the plans call for the imposition of regulatory
fees on parking. In earlier Notices of Proposed Rulemaking,
the Agency expressed some doubt about its authority to impose
such fees. That legal question has been extensively reexamined,
and EPA has now concluded that such a step is authorized by the
statute. The transportation control measures promulgated by
EPA will require a significant change in the driving habits of
the American people. The use of fees can help to bring that
change about with a minimum of social disruption of the wide
latitude they leave to individual choice. Those whose needs or
preferences are strongly in favor of using the single-passenger
automobile may continue to do so, although at a somewhat higher
cost; those who can easily adapt to the use of other modes of
transportation have a financial incentive to do so. Many public
comments supported the adoption of such fees. In addition, the
enforcement of such fees will be less difficult than some other
Measures. Finally, such fees will be used to support mass
transit. Expansion of mass transit is essential if the disin-
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plans are to have the desired effect. Such a use of the proceeds
will also greatly mitigate the potentially regressive nature of
such fees.
In requiring the States and EPA to impose transportation
controls where they are needed to meet air quality standards,
the Congress imposed a regulatory task whose difficulty and
complexity are virtually unparalleled. The legislative history
shows that Congress fully recognized the magnitude of the
problem. At the same time, the statute's description of the
exact types of measures that may be imposed is extremely broad
and general. In the face of this broad language, the Adminis-
trator concluded that the Congress intended him to impose the
method of control that he determined was best able to achieve
the purposes of the statute.
Parking Management Program
The proposal for review of new commercial parking facil-
ities has been modified, from an earlier proposal, to allow
a wider range of variables to be considered. In essence, the
regulation promulgated today would forbid the construction of
any facility that could be expected to lead to a VMT increase
unless either (1) the application retired from service or
caused the retirement from service of an equal number of
spaces elsewhere in the AQCR, or (2) the applicant could show
in a separate hearing devoted only to that question that the
impact of the proposed facility on VMT, and thus air quality,
would be insignificant.
The promulgated regulations will require that the appro-
priate local government submit to the Administrator a plan
outlining the locally planned expansion of parking facilities
for the next five years. If a submittal is not made that
shows to the satisfaction of the EPA that such planned parking
expansion does not conflict with the California State Imple-
mentation Plan, the EPA will review each proposed new parking
facility individually. Such review by either the State or
EPA will be consistent with the previously discussed complex
sources regulations to be promulgated shortly.
Motorcycle Controls
In the July 16, 1973, proposal, regulations were included
that would have restricted 2-stroke motorcycle operations during
the "smog season" in California. This action was taken due to
the very high pollution potential of the 2-stroke motorcycle.
The average 2-stoke motorcycle emits approximately 31 times as
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automobile will emit. Consequently, prevention of increases
in the number of motorcycles was proposed to prevent counter-
productive shifts from automobiles to motorcycle as a result
of other elements of the control strategy. The Agency has
evaluated the feasibility of establishing emission standards
for new motorcycles and is currently evaluating the availability
of motorcycle emission control technology for existing motor-
cycles to reduce emissions.
Based upon testimony presented by motorcycle manufacturers,
testimony presented by motorcycle trade associations, and an
independent analysis by the Environmental Protection Agency, it
appears that significant reductions in the emissions from new
motorcycles can be achieved.
Accordingly, the EPA is no longer requiring an uncondi-
tional ban on motorcycle operations. Instead, the ban regula-
tion has been rewritten to provide that it will not go into
effect in the event that nationally applicable Federal regula-
tions are promulgated that require at least a 50 percent reduc-
tion of 2-stroke motorcycle emissions by 1976 and conformity
with the 1976 automobile standards by 1979. Comparable emission
reductions will be required of 4-stroke motorcycles.
Vehicle Free Zones - Not Promulgated
Traffic free zones are primarily promulgated to control
local carbon monoxide problems. The zones are necessarily
restricted in size (approximately ten blocks or less) in order
to provide foot access. Consequently, the zones can be put
into effect by 1975 since no additional transit facilities
are required. Although increasing the size of the vehicle
free zone tends to increase the potential air quality im-
provements , such action also increases the problems of access,
circulation, and peripheral congestion and pollution.
Selective Vehicle Use Prohibitions - Not Promulgated
In several regions, EPA proposed a regulation under which
the vehicle population would have been divided into five cate-
gories . Each category of vehicles would have been required to
display prominently a tag of distinctive color; on one day of
each working week vehicles marked with one such color would
have been forbidden to operate.
Testimony at all the public hearings indicated that
measures of this type so far proposed would be unenforceable
because of their severeness and arbitrary nature. In addition,
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implement such a program would then have been so great as to
preclude the reasonable availability of this measure. Were
they to be implemented, many very workable methods of evading
the requirements would doubtless be devised.
Gasoline Supply Limitations
The proposed transportation controls included measures
to limit the gasoline supply in certain areas in order to
reduce vehicle miles traveled. The measure included two types
of regulations: (1) a gasoline supply lid that would become
effective in 1974 to limit the quantity of gasoline sold to
fiscal 1973 levels; and (2) a regulation to be implemented on
May 31, 1977, to reduce an area's gasoline supply, and thus
VMT, to the extent necessary to achieve the standards.
The gasoline supply requirement has been dropped as a
primary measure. The Act requires that all "reasonably avail-
able" measures must be implemented by May 31, 1975, before
granting an extension. Based upon the comments received at
the public hearings on this measure and the Agency's evalua-
tion of the feasibility of implementing and administering
successful gasoline supply limitations, the Administrator has
determined that a gasoline supply lid cannot be considered
"reasonably available." The possibilities of evasion, the
likelihood of noncompliance, and the difficulty of enforce-
ment are too great to make this measure practicable at this
time.
The gasoline supply reduction regulation to be implemented
on May 31, 1977, however, has been retained in several plans.
As was noted above, the Clean Air Act required air quality
standards to be achieved by 1977 without regard to cost or
social disorganization that may result as a by-product of
achievement. If gasoline supply limitations are needed to
achieve the standard, the "reasonableness" criteria is not a
determining factor. Accordingly, the Administrator was obli-
gated to use gasoline supply limitations as a final resort
measure in certain areas with severe air pollution problems.
Most of these areas required reductions in vehicle miles,
traveled far in excess of 10 to 20 percent. In some regions,
however, the required VMT reductions may well be accomplished
through the specified VMT reduction measures. Gasoline supply
limitations were required in these areas only to assure the
attainment of the standards by 1977. If a review of air
quality data and VMT reduction monitoring information prior
to 1977 indicates that the gasoline reduction measure is not
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ADDITIONAL VMT REDUCTION MEASURES - LOCAL PROPOSALS
State/Local Task Forces
State/local task forces have been formed in all AQCRs
(except the Southeast Desert) covered by this promulgation to
develop alternatives to the EPA-proposed control measures,
with the goal of developing draft plans by mid-October 1973.
Meetings were held between the task force and EPA representa-
tives to discuss potential alternatives for inclusion in the
EPA control plan promulgated for each AQCR. Although the
EPA promulgations are not wholly comprised of recommendations
of the task forces, EPA hopes that they will more properly
reflect reasonable and locally acceptable measures to improve
air quality in each AQCR. EPA also hopes that the recommended
alternative plans being developed by the task forces later
this fall will be approvable by EPA and will allow EPA to
rescind its regulations.
The membership of the task forces follows:
Los Angeles: District VII Cal/Trans, California Air
Resources Board, City and County of Los Angeles,
California Highway Patrol, Southern California
Association of Governments, Los Angeles County Air
Pollution Control District, Southern California Rapid
Transit District, South Coast Air Basin Coordinating
Council, the League of California Cities.
San Francisco: District IV Cal/Trans, California Air
Resources Board, San Francisco Bay Area Metropolitan
Transportation Commission, Association of Bay Area
Governments, and the Bay Area Pollution Control
District.
San Diego: District XI Cal/Trans, California Air
Resources Board, San Diego Comprehensive Planning
Organization (CPO), San Diego County Office of
Environmental Management, San Diego County Pollution
Control District, City of San Diego, the San Diego
Unified Port District, and San Diego Rapid Transit
District.
San Joaquin Valley: Cal/Trans, California Air Resources
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local transit officials, and county, city, and govern-
mental bodies including the Fresno County Air Pollution
Control District.
Sacramento Valley: Cal/Trans, California Air Resources
Board, Sacramento Regional Area Planning Commission,
county, city and regional governmental bodies, and
the Sacramento Regional Transit District.
Four-Day Work Week Schedule
The four-day week would reduce VMT generated in work
commute travel. Like staggered work hours, this would be a
useful measure if there were a localized, temporal problem in
employment concentration areas. However, indications are that
increased recreational and other non-work travel will fully
replace if not exceed the reductions in VMT resulting from
decreased work commuting. Thus, this measure does not respond
well to hydrocarbon emission problems.
Staggered Work Hours
Changes in work schedule by staggering work hours have
been proposed as a control measure in some cities as they
tend to produce some flow improvements by reducing commute
period traffic congestion. This measure, however, would
produce only marginal reduction in emissions.
Staggered work hours do not decrease total daily VMT but
simply spreads the time of VM^' generation. Such a strategy is
most applicable when the problem is a short duration, localized
concentration of pollutant, which results from temporal con-
centration of traffic flow. High concentrations of carbon
monoxide are most typical of this type of problem. Staggered
work hours, however, also tend to reduce the potential for car
pooling, a measure which relates well to hydrocarbon emission
reduction, since it tends to directly reduce VMT.
Traffic Flow Improvements
Measures to achieve emission reductions through improved
traffic flow fall into two categories: construction of new
major traffic facilities (freeways, expressways and major
arterial linkages); and operational improvements to existing
streets and highways. The emission reductions are brought
about by increases in vehicle speeds, reduced idling, and a
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Major facility construction normally enables significant
increases in vehicle travel speed in the corridors affected
but also tends to activate latent travel demand. In the long
run this reinforces auto dependence and increases vehicle miles
traveled. Over the short-range time frame of primary concern
in this study, the air quality impacts of new traffic facil-
ities can be assumed positive.
Operational improvements to existing streets and highways
cover a broad range of programs. These include freeway improve-
ments such as ramp metering and removal of bottlenecks; and
surface street improvements such as area wide signal system
integration, intersection channelization, minor widening of
streets and intersection approaches, institution of one-way
street systems, and the like. Because they do not produce
dramatic shifts in accessibility, operation improvements gener-
ally do not lead to activation of latent travel demand and their
^ear-term impact on emissions and air quality is assessed as
positive but their specific contribution to areawide emission
deduction is small and difficult to quantify. At best, the
planned operational improvements can be expected to accommodate
an ever increasing amount of travel without decrease in the
level of service.
Ramp Metering
Ramp metering is used to optimize the efficiency of traf-
fic movement in a freeway corridor. Metering also has potential
utility for shutting down the freeway for episode control,
and as a means to provide preferential entry for vehicles
that have a higher utilization (car pools, buses).
Mass Transit Improvements
Since personal travel requirements cannot be diminished,
some form of transportation alternatives must be provided if
vehicle use is to be reduced, particularly if vehicle re-
straints are implemented. One form for these alternatives
is public transit.
Improvements to public transit systems include both
extensions and/or upgrading of bus systems and provision of
fapid transit on separate rights-of-way. In conventional
bus operation, improvements include level of service (area
of coverage, headway, etc.) betterment and amenity promotions
(air conditioning, bus stop shelters, etc.). Most of the
u*ban areas already have or are in the process of setting up
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could result in significant patronage increases, but it is
unlikely that such improvements would induce major shifts of
choice riders from auto to transit without a system of con-
current disincentives for single occupancy use of the auto-
mobile .
Fringe Parking, Dial-A-Ride, Jitneys
Fringe park and ride facilities could allow suburban
commuters to park their cars on the peripheries of urban areas
and then take either mass transit or carpools into the central
business district. To have significant impact on lowering
emissions, local meterological conditions in a specific geo-
graphical area would have to be suitable. For instance, if
such a facility were in a basin, the amount of pollution
reduced would be diminished. Dial-a-ride and jitney service
could serve as feeders to either mass transit or carpool
rendezvous points, in addition to serving as a primary means
of transit.
Network of Bicycle Paths and Facilities
Greater use of bicycles could be encouraged through
designation and protection of bicycle lanes and incorporating
bike/pedestrian paths in new developments. A recent EPA
study suggested that increased use of bicycles in urban com-
muting could reduce auto vehicle miles traveled by as much
as three percent in some areas particularly amenable to
bicycle travel.
Imposition of restraints on auto usage, particularly
measures like gas pricing and rationing, could be expected
to encourage bicycle use. The greatest increase in bicycle
ridership would probable occur for children in getting to
school, recreation, etc., as parents pre-empt the car for
more essential functions. Work trips by bicycle could be
encouraged by providing exclusive bike lanes in city
streets and a carefully laid out bicycle grid system.
Free or Lower Transit Fares
Lowering the fare is one of the more effective means
of improving the competitive position of transit vis a vis
the automobile, particularly for intercity travel. However,
very little travel diversion from auto could be expected from
short trips, or from longer trips where time is valued over
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Accompanied by auto use time penalty strategies or mass
transit time savings measures, lower fares could play a more
important role in reducing VMT.
Tax Disincentives
A "pollution" tax could be charged in direct ratio to
the emission rate and mileage of each motor vehicle or to
increase the tax on gasoline (consumption varies directly to
mileage). Schemes to reduce vehicle mileage through gasoline
pricing may be very effective if prices are set high enough.
If imposed indiscriminately on all segments of society, the
largest impact is felt by limited income groups.
Various taxes on automobiles have been proposed. Low
fees are not effective in reducing VMT and high fees are
extremely regressive. Substantial registration fees on second
or third family autos might provide reductions in VMT and still
avoid some of the more regressive elements of this type of
taxation.
Tolls
The imposition of tolls on freeways is a potential method
of regulating road use. It is possible, however, that a high
percentage of those priced off the freeways by tolls may drive
on surface streets rather than shifting to car pools or transit.
This could produce increased emissions as a result of reduced
travel speed and idling on surface streets. Tolls also tend
to be regressive since many of those priced off the roads will
be low income persons.
Gasoline Limitation
Recent increasing fuel demands and the predicted fuel
shortages may cause some gas rationing in the near future,
and therefore result in a VMT reduction. However, this
would be a by-product, and not a TCP stragegy. Administrator
Train recently announced a decision not to use gasoline
limitation as a TCP strategy, if possible. Studies have been
done evaluating the impact of schemes to raise the price of
gasoline and thus reduce consumption. The use of gasoline is
inelastic in lower price ranges and more elastic with higher
prices with increased effects if accompanied by a range of
other VMT reduction incentives. Experience in European
countries shows that even when a gallon of gasoline is priced
as high as $1.50 a gallon, VMT rates continue to grow. TRW
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the effects of raising the price of gasoline. However, a gas
tax accompanied by other pricing penalties on private use of
the automobile - parking surcharge, tolls, high registration
fees on second and third cars, emission taxes - would help
decrease VMT as well as contribute funds to mass transit.
II. ANALYTIC BASIS OF VMT REDUCTION ESTIMATES
To evaluate the relative effectiveness of various VMT
reduction strategies, it is necessary to have analytical
methodology which can predict the potential transit rider-
ship of average automobile occupancy rates for a set of
critical variables. Unfortunately, it is very difficult
to quantitate the factors people use to rate the attrac-
tiveness of car pools relative to driving alone or riding
in a bus. Many of the measures EPA and the local task
forces have designed to reduce VMT are untried. EPA has
gathered the available data and studies that analyze the
range of VMT reductions possible from various transportation
controls. Analysis has included surveys to measure public
attitude and anticipated behavior, pilot studies conducted
in specific areas to gain better understanding of carpool
modal splits, and modeling to estimate the proportion of
total trips between two geographical locations that will be
made via mass transit (see Appendix 1 for listing of studies).
A Federal Department of Transportation draft report indi-
cated some important relationships between increased use of
mass transit and total auto travel.1 The following quotes
from that study illustrate the difficulties in achieving
shifts away from personal use of the car by only providing
improved transit incentives:
"(a) The price elasticity of demand for transit work
trips is only -0.19. This means that a one percent
change in price will only result in .19 percent change
in demand for transit work trips. Therefore, a 20 per-
cent decrease in transit fares would only increase
transit ridership by 3.8 percent."
"(b) The price elasticity or demand for transit shopping
trips is only -.323. Therefore, a 20 percent reduction
in price will result in an increase in shopping trip
ridership of 6.5 percent."
!/Alternative Transportation Investments and/or Controls for
Reduction of Air Pollution in Major Metropolitan Areas,
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"(c) The time elasticity of demand for transit work
trips is -.709. Therefore, a 20 percent decrease in
travel time will increase the work trip ridership by 14
percent. (Note that time elasticity of demand is about
3.7 times the price elasticity.)"
M(d) The time elasticity of demand for transit shopping
trips is -.593. Therefore, a 20 percent reduction in
transit time will increase ridership by about 12 percent.
(Note that time elasticity of demand for shopping is
about twice as responsive to changes in travel time as
it is to changes in fare: -.593 compared to -.323.)"
In addition, the cross elasticity for mass transit may be
low without accompanying disincentives and penalties on per-
sonal use of the automobile.
EPA has funded studies to assess the possible impact of
a range of incentives and disincentives to achieve VMT reduc-
tions in five of the California AQCR's. TRW has conducted
studies for the Los Angeles Basin, San Francisco Bay Area,
San Joaquin and Sacramento Valley. A joint IREM/Rand project
[Ref. 12, 14] studied San Diego. Each region's transportation
patterns can be applied to a model that can reasonably esti-
mate the proportion of total trips between two geographical
locations that will be made via alternate means other than
private automobile when different incentives or disincentives
are applied (Appendix 2 displays the various models and cal-
culations used to arrive at the VMT reduction estimates).
The model that has been applied to most of the California
transportation studies was developed by Alan M. Voorhees and
Associates (San Francisco).
The Voorhees Model
1. A "marginal utility" function is calculated for a
typical trip between the two sub-areas between which projec-
tions are being made. "Marginal utility" is defined as a
measure of the advantages of the private automobile over
public transit. Therefore, higher marginal utilities will
result in lower levels of transit ridership and vice versa.
2. Diversion curves are developed empirically for each
regional area, which specifically relate transit ridership to
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3. The diversion curves are used to predict the expected
transit ridership for any calculated marginal utility. It is
important to remember that the utility curves were derived
empirically, and hence subject to uncertainties. It would be
a mistake to view the model as an absolute predictor. Since
the model has inherent uncertainties, any values calculated
have the same uncertainties plus the additional uncertainties
associated with various assumptions made.
There are a number of variables which can be used to
measure the relative advantage the private auto has over
public transit. Voorhees related marginal utility to nine
variables, which fall into two classes - time and money.
Within the group of nine variables used to formulate the
marginal utility function, certain variables are more sus-
ceptible to change than others. Variables which are sus-
ceptible to change in the direction of decreasing marginal
utility are the ones which hold most potential for decreasing
VMT. Appendix 2 includes tables of the nine parameters and
some implications associated with changing their marginal
utility.
Theoretically, some or all of the nine parameters can be
modified in hopes of affecting increases in transit ridership.
Application of the model invariably shows that demand for pub-
lic transit will increase if the marginal utility of the auto-
mobile is decreased.
4. Transit ridership estimates are extrapolated for
different marginal utilities. They reflect three levels of
optimism for what transit ridership might become under rather
ideal conditions. The patronage level of forecast used
depends on the transportation characteristics of the region
in which the model is applied.
5. Within the defined patronage level of a region, the
Voorhees curves are drawn for three different levels of income.
Various income groups will exhibit different responses to, or
perceive differing marginal utility changes to a uniform change
in actual conditions. This is explained by the differing
values placed on time and money within each economic class.
Low income drivers will probably divert to public transit more
rapidly than middle income drivers in the event a substantially
increased cost penalty is associated with driving. However,
since more low income people ride transit now, the percentage
increase in transit ridership within each income level could
be about the same. Appendix 2 shows the expected changes in
transit ridership for various parameters as a function of
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For each region in which the model is used data is col-
lected and typical values assumed for each parameter needed
to simulate conditions experienced during a commute type trip.
Using the assumed values and the variables curves can be gen-
erated for estimating the percent transit ridership as a
function of each of the variables. Marginal utility is deter-
mined by holding all but one of the variables constant as one
is allowed to change.
Conclusions From Applied Model
In comparison to transit variables, controls aimed at
penalizing the automobile, are more effective. Theoretically,
if the penalty placed on the auto is severe enough, high
transit ridership and therefore, large VMT reductions are
possible. However, the measures necessary to achieve large
VMT reductions have to be very drastic.
A fairly consistent finding is that the private auto
user is more affected by time loss and inconvenience than by
monetary considerations. To achieve large VMT reduction by
economic means alone would necessitate severe economic pen-
alties for private auto use. The impact would be very in-
equitable affecting the lower classes the most.
An example from the TRW study for the L.A. Basin shows
the degree of impedence necessary in money or time to achieve
a VMT reduction response. Assuming no transit operation
improvement, the combined vehicle operating and parking cost
would have to be raised to approximately $4.00 per day ($2.00
per trip), an increase of 14 cents per mile in order to get
to the saddle-point of the curve that separates the flat por-
tion from the steeper, more responsive section. Similarly,
if varied alone, the automobile travel time would have to be
lengthened to more than 80 minutes (an average speed of
approximately eight miles per hour) or the parking terminal
time lengthened to 30 minutes to reach the same saddle point
(present commute time is 23 minutes).
Unfortunately, attempts to use time to penalize the
private auto are often counterproductive to reducing pollution.
It has been shown that cars tend to emit less hydrocarbons and
carbon monoxide at higher levels of speed than when idling or
crawling in congested traffic. Therefore, the closest alter-
native is to implement measures that achieve great time savings
for modes of travel (bus or carpool) other than the auto. Even
this incentive does not achieve the same level of possible VMT
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To lenghten the parking terminal time implies the need to elim-
inate present parking spaces, a measure that is considered
infeasible in light of public testimony and comment received.*
However, parking management will control the growth of avail-
able spaces and impose time penalties if there is a growth in
private car VMT.
A combination of adequately severe economic disincentives
and of improved mass transit incentives has been promulgated
for the regions in California requiring VMT reduction measures.
Estimates of the expected VMT reductions achievable have been
made based on the best available data and its application to
the Voorhees model, or, in the case of San Francisco, to a
modified BATSC/MTC** model.
* Periphery parking cannot be expected to cause significant
increases in parking terminal time, since one would be able
to take advantage of improved local transit or minibus to
get into the CBD.
**Model designed by Bay Area Transportation Study Commission
(BATSC) to estimate transportation modal choice in Bay Area.
The Metropolitan Transit Commission (MTC) updated this modal
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III. ESTIMATED IMPACT OP VMT REDUCTION MEASURES
C. San Diego AQCR
A study has recently been completed in the San Diego Region
to determine strategies for meeting the national ambient air
quality standards. The study was conducted by Rand Corporation
of Santa Monica, California, and was part of the San Diego Clean
Air Project, "Regional Analysis for Meeting Air Quality Standards",
being performed by the Integrated Environmental Development Agency
under contract number 6704-0270-E. The Clean Air Project is sup-
ported by a grant to San Diego County from the Environmental Pro-
tection Agency and by a matching contribution from local sources.
The preliminary results of this study were presented at the EPA
public hearing on the San Diego plan and were carefully evaluated
in developing the promulgation of the final EPA plan for the San
Diego Region. Table C shows the VMT reduction control measures
that are to be implemented, and their expected achievable reduc-
tions . Appendix 2 contains a sample of the model the Rand/Irem
project used to project the expected VMT reductions for the region.
The proposal to require a bus/car pool computer matching and
promotion system by March 1974 has been modified to require that
such a system be initially established at the U.S. Navy Elec-
tronics Laboratory and the U.S. Navy Underwater Systems Center
in San Diego. Upon evaluation, the system will likely be expanded
to cover major private employers and governmental agencies. The
Cal/Trans task force estimates a 4.2 percent reduction in VMT by
1977 if one half of the employees use the three-phase volunteer
car pool system. Total cost of implementing this measure is
$175,000. Finally, approximately 10 miles of freeway will be
given preferential bus/car pool treatment through ramp meter-
ing with bus/car pool bypass lanes, and a major downtown San
Diego street, Broadway, will be converted to exclusive bus
usage as the first phase of a program to examine preferential
treatment for mass transit.
Locally Implemented Proposals—
Major improvements to the mass transit system in San Diego
have occurred during the past year and are expected to be
expanded as additional funds become available for these pur-
poses. San Diego Transit initiated a 25€, all destinations,
fare in August 1972 and bus ridership has doubled since that
time. Three express bus routes to outlying areas of the metro-
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more will be in operation by the end of 1977. This part of the
system will require at least 125 new buses with an additional
175 feeder and local, off-peak buses to serve the express routes.
Also, it is planned that 30 buses be added to the North County
system. Fringe parking lots will be established along these
routes as well as at major regional shopping centers. Approxi-
mately 20 fringe parking lots are planned to serve the expanded
mass transit system with a pilot project planned at Miramar for
1975. There are plans to place bicycle protection facilities
at these fringe parking lots to allow nearby residents to
bicycle to the bus stops. Ridership incentive programs are
being planned through an extensive public information program.
Dial-A-Bus and subscription bus service will also be carefully
examined. The Cal/Trans task force estimates a 5 percent reduc-
tion in VMT by 1977 through implementation of these measures.
The City of San Diego has a $125,000 regional bikeway plan
under consideration, consisting of 30 local bikepath proposals.
Additionally, Cal/Trans is examining at least two bike routes to
parallel portions of proposed freeway improvements.
Various traffic flow improvement programs are either under-
way or proposed for the next 4 years in the San Diego Region.
These include a major synchronized traffic signal system for
major arterials, easing of traffic bottlenecks, and additional
ramp metering. City officials are examining the possibility of
fringe parking facilities on the perimeter of the central busi-
ness district with a system of people-movers and automobile bans
in the same area.
A final measure that will likely be the subject of further
consideration and experimentation in the next few years will be
the variation of the work week to four 10-hour days and other
combinations to determine the effects of such variations on air
quality and VMT. Governmental agencies will likely be early
-------
- 23 -
TABLE C
SAN DIEGO - VMT REDUCTION MEASURES
Estimated Percent
Reduction in Daily
Vehicle Miles
Traveled - DVMT
G
o
+j -rH
O C +»
-) di to
a> a
a) res
0
1 0
\ on
> >1
¦p ^
£ X} E tP-P
1
c
k +j o a c
< P
d ¦a
« •.-» U -rH o
CU -P
o c
H £ 4-J Q u
W M
CJ (0
2-4
6-10
8-10
1. Exclusive Bus/Car Pool Lanes X
Bus/Car Pool Matching (not X
additive with measure 1)
Parking Supply Management X
Mass Transit Incentives for X
Employees
Parking Surcharge X
VMT/Air Quality Improvement X
Monitoring Program
Gasoline Limitations X
Bus System Improvements
Bikeways and Bike Lanes
4-Day Work Week
Taxation and Pricing Measures X
(includes parking surcharge)
X
(Bus only
Ltd. use)
xi/
4.2
8-10
1-2—^
1-2—/
X
X
4-10
4/
X-'
X
X
2/
5
1
0-2.5
-------
- 24 -
1/ - Car pool matching programs accompanied by employer promotional
Incentive and disincentive programs are aimed at achieving a fifty
percent rate of employee car pools.
2/ - In addition to more new buses, better scheduling, fare reductions
and express bus routes, the local plan includes selective exclusive bus
bypass projects, express bus stops at freeway ramp on Route 15 with
fringe parking which are part of the "Improved Road Systems" strategy
proposed by the local task force. An improved road systems plan that
eases congestion is not included in the VMT reduction because reduc-
tion of traffic congestion may encourage the latent demand for use of
the automobile, and thereby increase VMT counteracting whatever gains
had been anticipated by easing congestion and thus any emissions reduc-
tion achieved.
3/ - Estimate by EPA, Region IX
-------
APPENDIX I
References
TRW, Transporation Control Strategy Development for the
Metropoliton Los Angeles Region, December 1972
TRW, Transportation Control Strategy Development for
Sacramento Valley
TRW, for San Joaquin
TRW, for San Francisco
TRW, Air Quality Implementation Plan Development for Central
California Regions: Summary Report July 19 73
State of California, Department of Public Works, for Air
Resources Board, Can Vehicle Travel Be Reduced 20% in South
Air Basin? January 1973. "
California Institute of Technology, EQL, SMOG:
A Report to the People of the South Coast Air Basin,
January 19 72
DOT, a Computer Simulation Model for Evaluating Priority
Operations on Freeways June 1973.
Alan M. Voorhees and Associates, for Department of
Transportation(DOT), Summary Report:
Feasibility and Evaluation Study of Reserved Freeway
Lanes for Buses and Car Pools, January 1971.
MTC, Proposed Regional Transportation Plan and Revisions:
Improvement Proposals, June 1973.
Local Agencies Plan for LA Basin,
-------
- 26 -
12. San Diego Air Pollution Control Task Force Report, Local
Transporation Control Plan for the San Diego Basin,
October 5, 1973.
13. San Diego Air Pollution Control Task Force, Evaluation of EPA1 a
Proposed Air Pollution Control Plan with Alternatively '
14. Rand Corporation, A Policy Oriented Urban Transportation
Model: Notes on the Rand Approvals, March 9, 1973.
15. TRW, Report on the IREM/RAND Clean Air Project.
16. EPA Region IX, Technical Support Document for LA Basin,
July 31, 1573
17. Federal Register, Proposed Regulations for California Air
Quality Control Districts, Vol. 38, No. 126, Monday,
July 2, 1973
18. Federal Register, Promulgation for Transportation Control
Plans for California, Vol. 38, No. 217, Part I,
-------
- 27 -
APPENDIX 2a
VOORHEES MODEL
Marginal utility = U = 2.5 (Ta + Tw) + Tr-(2.5 At + Ar) + F-(Ao + Ap) (1)
0.251
there : Ta = transit access time in minutes (i.e. the time to walk
to the bus stop)
Tw = transit wait time in minutes
Tr = transit riding time in minutes
At = automobile parking access time in minutes (i.e., the
time necessary to find parking and walk to destination)
Ar = automobile riding time in minutes
F = transit fare in cents
Ao = automobile operating costs in cents (excluding
depreciation and insurance)
Ap = automobile parking cost in cents (averaged over the
round trip)
-------
- 28 -
TABLE 7.4
Control of Marginal Utility Parameters
Marginal Utility Potential Example(s) of Control Aimed
Parameter a for Control at Decreasing Marginal Utility
Ta Low More bus stops and/or routes
Tw Medium Improved frequency of service
Tr Medium Exclusive busways for freeway lanes
At Low Peripheral parking, auto free zones
Ar High Ramp metering
F High Lowered fares
Ao High Gasoline tax, "smog" tax, tolls
Ap Medium Increased parking costs
I Very low Lower personal income levels
-------
- 29 -
TABLE 7.5
ASSUMED VALUES OP MARGINAL UTILITY PARAMETERS
FOR A TYPICAL COMMUTE TRIP
Trip Length
Ta
rw
fr
Assumed Value
10.5 miles
5 minutes
7 minutes
48 minutes
38 cents
50 cents
2.5 cents
8.3 cents/minute
2 minutes
23 minutes
Source
Table 5.4 (EPA publication APTD-1372)
Generally accepted value
15 minute headway, no transfer
LARTS, 1971 Travel Time Study
30C basic fare + 8C for one
additional zone
4.8C per mile - assumed by Voorhees
90C per day for estimated 5.8
percent who pay See Table 7.7.
$10,000 per year
A. M. Voorhees & Associates
Table 5.4 (EPA publication No.
-------
TABLE 7.6
MARGINAL UTILITY PARAMETER COMBINATIONS
Marginal Utility Variables Symbol
Transit fare (one way) F
Transit access and waiting time Ta+Tw
Transit riding time
Auto operating and parking
cost (one way)
Auto riding time
Auto terminal time
Tr
A0+Ap
Ar
At
Potential
for Control
High
Medium
Medium
Medium
Medium
LOW
Relative
Effectiveness^
Low
Medium
High
High
Low
Low
NOTE: Income is considered a constant throughout, primarily because
-------
ex
oc.
<_>
Currently .38
.90
.60
1.20
1.50
.30
0
F - Dollars
Figure 7.3. Transit Fare (One Way) vs. Per Cent Transit R1dersh1p.
-------
- 32 -
20.0
Q.
SZ
t/1
>.
01
T»
OC
•M
C
QJ
t_)
I.
at
a.
Currently 12
20
5
7.5
17.5
10
15
12.5
Tfl + Tw - Minutes
Figure 7.4. Transit Access and Waiting Time vs. Per Cent Transit R1dersh1p.
Source: Developed from the Los Angeles Metropolitan
-------
- 33 -
20
18
16
Q.
£ 14
tfl 1 ^
(-
-------
- 31* -
40
-C
\A
i-
01
T3
£ 30
c
a>
<_>
u
«
a.
20
10
Currently .52
0 .50 1.00 1.50 2.00 2.50
A + A - Dollars
o p
Figure 7.6. Automobile Operating and Parking Cost
(One Way) vs. Per Cent Transit Rldership.
-------
- 35 -
40
Q.
u>
30
¦a
a:
U>
U
10
Currently 23
0
10
110
90
30
50
70
Ap - Minutes
Figure 7.7. Automobile Riding Time vs. Per Cent Transit R1dersh1p.
-------
- 36 -
Currently 2
Minutes
Figure 7.8. Automobile Terminal Parking Time vs. Per Cent Transit R1dersh1p.
-------
Sample Calculation #9
Impact of Exclusive Bus-Carpool Lane
- 37 -
Assumptions:
1) "Trip length = 10.1 miles
2) 20 minute travel time
advantage for users of the
lane
3) Values of Voorhees parameters
T, = 2 minutes
a
Tw = 3 minutes
F = 46*
AQ = 48* (or 78*)
Ap - 2.5*
At
rr-Ar
i
2 minutes
20 minutes
8.3*/m1nute
U =¦ 2.5 (Ta+Tw) ~ Tr
(2.5At+Ar)
Source
See Appendix 6, Table G-8.
(Trip to freeway is excluded.)
San Bernardino Busway will have
18 minute advantage; Shirley Highway
Busway has 30 minute advantage.
Assumed
5 minute headway for correct bus
Basic 30* fare + 2 zones
4.8* per mile (+3* per mile "tax")
Assumed
See Reference E-5
20 minute time advantage
$10,000 per year
- (vy
0.25 I
U = -15 (-29 with 3* per mile "tax")
Based on the above assumptions and Figure 7.2, the estimated transit
patronage 1s approximately 15 percent without the tax and 20 percent with
-------
Sample Calculation #9 (Cont'd) - 38 -
0CB(1-Ft) + 0CA(Ft)
( 0CB(1-Ft) + 0CA(Ft) |
\ 0CB(1-Ft )+ 0CA(Ft
(Eq.(7).Sample
Calculation #1)
% VMT Reduction » 100-100
f uuo\
0 0
The percentage of total commute VMT which is travelled on the freeway system
In the*Basin 1s approximately 17 percent (see Appendix G, Table.G-8); therefore,
% VMT Reduction » .17
100-100
0CB(1-Ft) + 0CA(Ft)
0CB(1-Ft )+ 0CA(Ft )
o J
Assume:
1) OCB = 50 persons per bus
2) OCA »1.1 persons per car
negligible on freeways presently
4) Fy = .15 (.20 with "tax")
3) F =
o
% VMT Reduction =2.5 (or 3.2 with "tax")
To achieve an occupancy of 1.5
Assume:
1) During conmute periods, average volume per lane of traffic
of 1500 vehicles per hour
2) Carpool is three or more people per automobile
3) Negligible carpooling on the freeway presently
4) Eight lane freeway (four in each direction)
5) Capacity of freeway lanes is 1800 vehicles per hour
6) Ho diversion to transit
-------
Sample Calculation §9 (Cont'd)
- 39 -
Let N » Number of cars in carpool lane (three persons per car) when
all other lanes are at capacity and the resultant average
automobile occupancy is 1.5 persons per vehicle.
Then * (3)(1800 veh./ln-hr)(l.1 persons/veh.) + N(3 persons/veh.) ^
(3)(1800) + N veh./ln-hr
-*• N ¦ 1440 veh./ln-hr
Persons diverting to carpools = 1440 x 3 » 4320
Total number of person trips = (3)(1800)(1.1) + (1440)(3) = 11,340
% of freeway commuters shifting to car pools n ^ ^q- ® 38%
Impact of Shifts in Carpools
Assume occupancy can be Increased to 1.5 persons per vehicle.
From Sample Calculation #2 for commute periods periods,
1.21
% VMT Reduction = 32.4
1-
0CA
This strategy impacts 72.5 percent of the commute VMT (see Appendix G,
Table 6-8).
X VMT Reduction = .725(32.4)(1 - lj|^)
= 23.5 (1- ly^)
-------
Figure 1
TMAMSPORTAT so m model
DEMAND GEHERATOR AND MObAL jSPLIT
BAR&AIMINO CONTROL
SUPPLY MODEL
v
BUS
NETWORK LOADING
• SY STEM
• ASSIGNMENT
• SYSTEM
DESIGN
DESI6M
o CONGEST 1 ON
• TOTAL
TOTAL
COST
o TIME
COST
>
TJ
TJ
X
r\j
cr
M
O
H
M
8
§
-Cr
O
-------
SYS?
TRANSLATOR
Design Param-
eters into
Service
Characteris-
tics
-by mode
-by period
-by traveller
income
REFERENCE
TRIP TABLES
V
DEMAND
GENERATION
AMD
MODAL SPLIT
Predicts
Travellers
Desires
-by O-D pair
(each direc-
tion)
-by mode
-by purpose
-by period
-by traveller
income
NETWORK(S)
-connections
-capacities
-priorities
V
SUPPLY
"Load Travel-
lers onto
Modes
°Load Modal
Vehicles
onto Net-
work (s)
"Estimate
Congestion
"Estimate
Times
"Estimate
Costs
Pernand
No
It
-------
Compute
Evaluation
Indices
and
Sensi tivities
- r.obility
- costs
- congestion
~ emissions
NO
Return
to
Start
Calculate
Vehicle Miles
in Grid Cells
Su.TuT.ary
Calculation
by vehicle
type
by perjod
Service
Data
File
Cost
Social impacts
Pollution
-------
EXAMPLES Of TRANSLATOR OPERATION
. Describe Policies in Natural Terms
— Parking availability and cost, by area
— Motor Vehicle Emission Control Device Policy
— Specify 0-D pairs with duitcJ: !:us service
— Specify hsadwa.ys
-- Priority and nonpriority capacities by link
— Minimum priority-eligible caroool size
— Taxes, license fees, parking fet:s
, Special Models Translate Policy to Service Characteristics
— Parking availability implies delay
— Motor Vehicle Emission Controls contribute to auto operating cost
-------
DEMAND GENERATION AND MODAL SPLIT
USES EXISTING OR FORECAST TRIP TAliLES AS STARTER
- e.g., 1970 actual ;
- e.g., 1975 San Diego forecast from California Highway Department
PERTURBS THESE TO ESTIMATE DEMAND
INCLUDES INDUCED DEMAND FROM SERVICE IMPROVEMENTS
- predicts upper and lower bound as well as intermediate value
USES MODIFIED VERSION OF EXISTING, CALIBRATED SAN DIEGO MODAL SPLIT MOD
I t
- considers service characteristics for each mode
- considers income distribution of travelers
SERVICE CHARACTERISTICS CONSIDERED INCLUDE:
- in-vehicle time
- excess time (wait, walk, etc.)
- user cost
Service characteristics may differ with income group
I
DEMAND IS DISTINGUISHED ,
• t
- by mode
»
- by purpose '
- by period of day (AM-peak, PM-peak, off-peak) .
-------
SUPPLY: LOADING the modes
° AUTOMOBILE MODES INCLUDE: personal auto, car pool auto
° BUSSES INCLUDE: regular,, mini, or aial-a-bus
° BUS COVERAGE: line-haul., low- or high-density area coverage
° BUS ROUTE: fined or demand responsive (dial-a-bus)
0 BUS ACCESS/EGRESS: walking, bus, auto park—or kics-and-ride
° SEPARATE SUPPLY MODELS FOR EACH MODE
p GIVEN BUS DEMAND, AMONG ORIGINS AND DESTINATIONS ^
i
ITERATIVELY DETERMINE LEAST COSTLY ROUTE STRUCTURE
-------
SUPPLY: LOADING THE NETWORK(S)
USES DETAILED, REALISTIC NETVJORK
- e.g., Division of Highways: 7000 links, 2300 nodes
CONSIDERS ACTUAL LINK CAPACITIES
PRIORITIES MAY BE SPECIFIED BY LINK, BY MODE, BY PERIOD
- Link A for bus only
- Link B for bus and car pools (e.g., 3 or more people)
LOADS NETWORKS WITH VEHICLES, CONSIDERING' PRIORITY A^D CAPACITY
CALCULATES CONGESTION - BY LINK, BY PERIOD
CALCULATES TRAVEL TIMES AND COSTS BY O-D PAIR AND DIRECTION, MODE,
PERIOD, PURPOSE
-------
OUTPUT OF TRANSPORTATION MODEL
. Person-Trips -- Volume, including indtc.ed
— By O-D pair, purpose, mode, period of day, traveler income group, traveler residence
— Highlights differences in travel behavior by different social groups
. Service Characteristics - User Time(s), Cost(s), Frequency
-- By 0-D pair, mods, period of cl.iy, traveler income
-- Predicts accessibility to work, nonwork destinations
. Traffic Volumes
— By network link, mode, traveler income, period of day, speed
— Used with motor vehicle emission control model to obtain emissions
. To Distribute Impacts by Social Group
— Predict ir.pacts by income and residence group ^
"S3
— Apportion the impact for a particular income-residence group among it s ccrripontrjt ,
-------
- 1)8 -
III. MODEL PIPrOSE, MErHOD OF OPERATION, AND SOURCES OF EFFICIENCY
PURPOSE
The purpose of the set of models described in this note
is to predict a number of important potential. impacts of a
wide variety of transportation-related policies. The
policies include any blend of the following:
° adjust parking price
° adjust parking availability
° priority routes for designated vehicles
° taxes and liscense fees
° fixed-route or demand responsive public transit
and many others. Impacts include;
° cost irapetcts
° economic impacts (e.g., employment)
0 service impacts (e.g., mobility)
° environmental impacts (e.g. , air quality)
The distribution of most impacts among socio-economic strata
is also accomplished.
iiLOD of o?eratio>:--ce>:eral
The straightforv.'ard method for accomplishing those purposes
(and in part our method) is to follow these steps:
1. Partition the study region into a number of areas.
Each area is to be treated as a single point, to
and from vhi.ch trips are made.
2. Specify the transportation policy, including technical
-------
- 49 -
3. Translate the policy variables into the trans-
portation service characteristics perceived
by the traveller.
4. On"the basis of the service characteristics,
predict the demand for travel from each area to
every other area. Predictions are made for each
mode, for various periods in the day, and for
various trip purposes. Demand is also stratified
by traveller characteristics (e.g.income).
5. Load the predicted demand onto the transportation
systems provided. This is a process involving
several steps.
a) put tine preitic Leu coructi'iu——x. <». , person
trips—in the appropriate modal vehicles.
For example, put bus riders on busses
following the appropriate routes.
b) Load the modal vehicles on the appropriate
networks of roadways and/or guideways.
c) Examine the traffic flows on links of the
network to determine congestion. If
travel times are altered due to traffic
volumes, re-load the networks. Repeat
until no one can improve his service by
-------
- 50 -
d) Compare each traveller's new service
characteristics with those from which
demand was predicted. If there has
been any significant change, return to
step 4, and obtain a new prediction of
demand. Otherwise {i.e., if service
has not changed significantly), we say
that demand and supply are "balanced,"
and we continue.
Evaluate the policy that was input at step 2. This
requires cex'tain criteria, against which one tests
the policy's performance. These criteria should
include:
a) Mobility—how easily may members of dif-
ferent social groups get around?
b) Costs—e.g., are there certain bus routes
that cost a great deal and serve very
little demand?
c) Congestion--how much time is lost per
day by travellers due to congestion?
d) Emissions—does this policy reduce emis-
sions as much as desired?
Also compute the sensitivities of these indices
(mobility, cost, etc.) to changes in selected policy
variables. If the policy is satisfactory—that is,
-------
- 51 -
these sensitivities will indicate what changes
in policy variables must take place in order to
more nearly satisfy the criteria. We then make
the indicated changes, and re-enter at step 2
-------
?KXANp_ AND MODAL SPLIT :
WE TSlfPS 7"??Rr^\CH"
In transportation modelling, one usually predicts total
demand for trips first, and later apportions the trips among
the different modes of travel (e.g., bus, auto). Depending
on the model used, the total demand will depend on such
things as population, per capita income, and. amount of em-
ployment. The fraction of trips using each mode (called the
modal split) will depend upon the service characteristics
provided by that mode (e.g., trip time, cost, frequency of
service). The function describing this dependence is called
the conductance of the mode.
Clearly, this separation of a total demand prediction
from the modal split operation is artificial. Moreover,
for our purposes, (designing measures to reduce air pollu-
tion), it is not even approximately right. For this separa-
tion assumes that total demand is independent of the con-
ductances, or service characteristics, of the different
modes, and one possible measure for reducing emissions of
air pollutants is to raise the price of travel, thus caus-
ing people to forego some trips.
On the other hand, ve have no need to predict changes
in total demand in response to changes in income or popula-
-------
- 53 -
having dene so, combine it: with the modal split step. We
call our method the "potential trips approach".
VJe assume that no matter how good (within reason) the
service becomes, there will still be a limit to the number
of trips that will be taken. Call this limit T. Vie also
know that in the nominal case, the numbers of trips actually
taken by each mode are T* (for auto) and Tg (for bus), total tn<
(The superscript * will always refer to the value of a quan-
tity in the nominal case.) Then we define the number of
trips foregone in the nominal case, T-\, by the equation:
(1) T* + Tg + T*. = 7.
One may think of T* as the potential latent demand that may
be realized by a sufficiently great improvement in, for
example, the bus system.
We let con^actances for auto and bus
respectively, remembering that they are functions of the
auto and bus service characteristics respectively. Their
values in the nominal case are, of course, and W*. We
take the "conductance" W* of not making the trip to be the
constant 1.
The conductance is defined so that, if the conduccance
of a mode (say auto) is changed, then the ratio of the mean
number of trips by that mode to the old number of trips must
-------
~ -
(?•)
(3)
ta wa
^ R ' WB
Tf « w£
By analogy wc let
V W„
«> *g « i#
F F
We also require that the new trips T^, Tg and iy sura
to the maximum number of trips allowed. That is,
(5) Ta + Tb + Tf =. T.
But equations (2) - (5) are easy to solve. We obtain
WA -
T. =»
A UA WB
+ TV- .2. 4- t-a-
xhwg ^ V
-------
Two questions remain: .whc.ro does one obtain the con-
ductances; and what is the source of T? For the San Diego
transportation model, the conductances are obtained directly
from the San Diego Modal Split equation. This equation is:
(6) W = exp (c + £ a.X. )
ra L K m ^ i. inr
where the subscript m refers to mode (bus or auto), the
a. and c are calibration constants, and X. is the value
i m ' im
of the service characteristic for mode m. Service
characteristics are line-travel time, excess time, and cost.
(Actually, the San Diego modal split equation was origina lly
expressed in terms of the differences in service character-
istics between bus and auto, but the manipulations necessary
to arrive at the equivalent equation (6) are trivial.)
Recall that f was an upper limit to the number of
trips that would be taken, given the best reasonable quality
of service. In San Diego, where there is virtually no
congestion, no mode of travel is likely to provide better
service times in the foreseeable future than auto docs
today. Further*, for the very wealthy, the cost of travel
by auto is of small importance. Thus in San Diego, we may
take T to be the number cf trips that the Division of
Highways' demand model predicts would be taken if every
-------
A lower bound on T is just the trips currently being made when
service characteristics are the same as the nominal, then T* = T*
F F
In this case, our potential trips model gives answers identical to
the San Diego modal split model. Further, given a set of service
characteristics, the potential trips model will predict the same
modal split percentages among people who do travel as would the ori-
ginal San Diego model. But the number of trips will be different
when the value chosen for T is different from the nominal number of
trips taken (T*A + T*g). For example, consider the following two
scenarios:
(i) Auto service is degraded, and bus service held constant,
until the split between the modes is equal.
(ii) Bus service is improved, and auto held constant, until
the split is equal.
If T is taken to be the number of trips as If everyone were wealthy,
then under scenario (I) we would predict a decrease In the total
number of trips, while under scenario (ii) we would predict an increase.
The San Diego model (and the potential trips model with T = T*^ + T*g)
-------
- 57 -
BASIC DATA USKD IN DAILY VEHICLE MILK CA LC.'L ! >AT!.().\S
The- data are based upon 1.075 forecasts of:
1. Average auto occupancy for work trips of
1.1 persons per auto.
2. 18. 8 miles per work round trip.
3. 400, 000 daily vehicle work round trips.
4. 7. 5 million daily vehicle work trip miles.
21. 0 million total daily vehicle miles.
------- |