United States

Environmental Protection

Agency

Air and Radiation EPA420-R-98-002

March 1999

Benefits Estimates for

Selected TCM Programs

 Printed on Recycled Paper
EPA420-R-98-002

March 1999

Benefits Estimates for Selected TCM Programs

Regional and State Programs Division

Office of Mobile Sources

U.S. Environmental Protection Agency

Prepared for EPA by

ICF Incorporated

9300 Lee Highway

Fairfax. VA
TABLE OF CONTENTS

INTRODUCTION -iI. ANALYSIS OF SINGLE TCMs

A. Example 1: Regional Public Transportation Authority 

 Telecommuting Program in Maricopa County, Arizona

1. General Description

2. Data Sources

3. Phase 1: Travel Activity Effects

4. Phase 2: Emission Effects

1

1

1

8

B. Example 2: Atlanta/De Kalb Greenway Trails

1. General Description

2. Data Sources

3. Phase 1: Travel Activity Effects

4. Phase 2: Emission Effects

17

17

17

22

C. Example 3: Cleveland Walkway to Gateway

1. General Description

2. Data Sources

3. Phase 1: Travel Activity Effects

4. Phase 2: Emission Effects

30

30

30

34

D. Example 4: Brevard County Vanpool Service

1. General Description

2. Data Sources

3. Phase 1: Travel Activity Effects

4. Phase 2: Emission Effects

40

40

40

45

E. Example 5: Boulder HOP Shuttle Service

1. General Description

2. Data Sources

3. Phase 1: Travel Activity Effects

4. Phase 2: Emission Effects

54

54

54

59

II. ANALYSIS OF TCM PACKAGES

A. Example 6: Cornell University 

 Transportation Demand Management Program

1. General Description

2. Data Sources

3. Phase 1: Modal Choice Analysis

4. Phase 2: Travel Activity Effects

5. Phase 3: Emission Effects

67

68

69

81

84

Page
-iPhase 1: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

Phase 2: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Step 4: Summation of emission effects

BENEFITS ESTIMATES FOR

SELECTED TCM PROGRAMS

INTRODUCTION

This document presents applications of EPA’s transportation control measure (TCM) analysis

guidance, entitled Methodologies for Estimating Emission and Travel Activity Effects of TCMs, to six

actual TCM programs. The document is

intended to assist government officials,

transportation planners/analysts, and other

interested parties in using EPA’s TCM guidance

to analyze and evaluate TCM programs that have

been completed, are currently in progress, or are

proposed for future implementation.

The methodology outlined in EPA’s

guidance for estimating the effects of TCM

programs consists of two phases, each of which

is composed of a number of smaller steps. The

first phases involves estimation of the travel

activity effects of TCMs, including effects on

number of trips, vehicle miles traveled (VMT),

and vehicle speeds. In the second phase, the

effects on trips, VMT, and speeds are used to

determine effects on emissions of hydrocarbons

(HC), nitrogen oxides (NOx), and carbon

monoxide (CO). EPA’s methodology also

presents a technique for analyzing the effects of

TCM packages, which involves using data on

current mode choices, travel costs by mode, and

travel times by mode to determine which TCMs

in a package of two or more will be chosen by

target populations. This type of analysis is

important given that TCM programs

implemented in the same area tend to interact

with one another.

As noted above, this document shows

how EPA’s TCM methodology can be applied to

six TCM programs that have actually been

implemented in the U.S. These programs span a

number of the TCMs listed in the 1990 Clean Air

Act Amendments, including improved transit,

bicycle and walking paths, and ridesharing. 

Using the methodology to analyze the travel

activity and emission effects of these and other

TCMs requires a large number of individual

parameters (presented in the equations in this

document) to be estimated or assumed by the

user. The methodology also requires obtaining a
-iisubstantial amount of program-specific and region-specific data. To the extent possible, the examples

below make use of such data, although in some cases reasonable assumptions or default data based on

national figures have been used. These cases are indicated where they occur. The implication of using

assumptions or default data is that the results of the analysis will tend to be less accurate than if actual

program or regional data were used. In analyzing their own TCM programs, government officials and

transportation planners/analysts will likely have ready access to most of the program-specific and regionspecific data required by EPA’s methodology.

This document is divided into two sections. The first section presents example applications of

EPA’s TCM guidance to programs involving only one TCM. The second section presents example

applications of the guidance to TCM packages.
1

Phase 1: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

1. ANALYSIS OF SINGLE TCMs

This section uses the methodology described in Chapters 2 and 3 of EPA’s TCM guidance 

to estimate the travel activity effects and emissions effects of programs involving only one TCM. 

The TCMs addressed in these examples include telecommuting programs, walking and biking trails,

transit improvements, and rideshare programs.

Example 1: Regional Public Transportation Authority Telecommuting Program in

Maricopa County, Arizona

General Description

The Regional Public Transportation Authority (RPTA) in Maricopa County, Arizona, has

implemented a program to promote telecommuting in the Maricopa County area. The program has

developed a telecommuting training curriculum and promotional materials to provide assistance to

employers interested in developing telecommuting programs. The program began with MPO approval 

in September 1993. RPTA’s goal for this program is to attain at least a 200 percent increase in the

number of businesses and other organizations with telecommuting programs in the region.

Data Sources

& “Clean Air Campaign and Trip Reduction Survey,” prepared by West Group Marketing Research

for the Regional Public Transportation Authority, Spring 1996. (hereafter, “TRP Survey”)

& “1996 Telecommuting Survey,” prepared by West Group Marketing Research for RPTA/Valley

Metro, June 1996. (hereafter, “Telecommuting Survey”)

& Transportation Inventory & Analysis of Existing Conditions, 1996: Maricopa County.

& 1997 County and City Extra: Annual Metro, City, and County Data Book, Bernan Press, 1997.

& 1990 U.S. Census data.

& 1996 Statistical Abstract of the United

States.

Phase 1: Travel Activity Effects

Step 1 in the estimation of travel activity

effects for the RPTA program involves an

assessment of the potential trip effects from the

program. For telecommuting programs, these

potential effects are calculated using the

following formula:

PT = N * F / D * 2

& In the formula, PT is the

number of trips

potentially affected, N is
2

the number of

participants in the

telecommuting program,

F is the frequency of

participation (in days per

week), and D is the

average number of

commute days per week.

The appropriate value for N is derived by first calculating the total number of telecommuters 

in the program area, which is obtained by multiplying the total population of non-home-based employed

people in the region covered by the RPTA program (1,124,600) by the percentage of respondents in the

TRP Survey who telecommuted in 1996 (5 percent). The total number of telecommuters is then

multiplied by the percentage of telecommuting programs in the area that are attributable to the RPTA

program. Because the number of telecommuting programs in the area has increased from 57 to 260 since

the beginning of the RPTA program, and because the goal of the RPTA program is to increase the

number of telecommuting programs by 200 percent, it is reasonable to assume that 114 (or 57 times 200

percent) of the current 260 programs are attributable to the RPTA program. Thus, N = 1,124,600 * 0.05

* (114 / 260) = 24,655.

The value for F is derived from the Telecommuting Survey, which indicates that 27% of

respondents telecommute one to three days a week, 25% telecommute four or five days a week, and 16%

telecommute one to three days a month. Using average estimates for telecommute days (e.g., for

participants telecommuting four or five days a week, an average of 4.5 days is used) and assuming that

there are four five-day work weeks in a month, F = (0.27)(2) + (0.25)(4.5) + (0.16)(0.5) + (0.32)(0) 

= 1.75.

The value for D is 5, based on the fact that there are five workdays per week.

Using the data above, PT = 24,655 * 1.75 / 5 * 2 = 17,259. Thus, the potential number of trips

reduced per day by the RPTA program is 17,259.

Step 2 in the travel activity methodology involves estimating the direct work and non-work trip

reductions from the RPTA program. Whereas the potential trip reductions calculated in Step 1 represent

the total number of trips that might be reduced by a TCM program, direct trip reductions measure the

number of trips that actually are reduced and, thus, can be less than potential trip reductions (e.g., if 

a telecommuter was previously using transit to commute). Direct trip reductions are calculated using 

the following formulas:

TRIPSD =  * PT

TRIPSD,W = 7 * TRIPSD

TRIPSD,NW = (1 - 7) * TRIPSD

& In the formulas, TRIPSD is the total direct trip reduction, PT is (as above) the

potential trip reductions, TRIPSD,W is the direct work trip reduction,

TRIPSD,NW is the direct non-work trip reduction,  is the fraction of program

participants who make a direct trip change, and 7 is the fraction of trip effects

that are work-related.
3

FOCUS: FROM POTENTIAL TO ACTUAL TRIP CHANGES

The equations in Step 2 of the travel activity methodology

show how the potential trip effects -- PT -- break down

into actual reductions in work and non-work trips. The

rectangles below show how only a fraction () of potential

trip effects are realized, becoming TRIPSD. Then, a

fraction (7) of these trip reductions are reductions in work

trips, while the rest (1 - 7) are reductions in non-work

trips.

FOCUS: WHY ACTUAL TRIP CHANGES ARE LESS

THAN POTENTIAL CHANGES

In this example, the fraction of potential trip effects

that are realized () is defined as the fraction of

telecommuters who do not work in satellite offices,

divided by average vehicle occupancy. Telecommuters

who use satellite offices are excluded because they still

drive from home to the satellite offices. The remaining

fraction is divided by average vehicle occupancy

because some of the workers who become

telecommuters may have been sharing rides originally.

If, for example, two workers had been sharing one

vehicle for commuting, and each began telecommuting

(without using a satellite office), we would see a

reduction of only one trip to work. Here, AVO is 2,

and  would be (1-0)/2, or one-half. (Note: The

parameter  is actually expressed as a negative number

to reflect that TCMs are typically designed to reduce

For telecommuting,  is defined

as -(1 - SAT) / AVO, where SAT is the

fraction of telecommuters who work in

satellite offices and AVO is average

vehicle occupancy. Because the

information on the RPTA program does

not indicate that satellite offices are used,

SAT is assumed to be 0%. The value

used for AVO is based on the following

information from the TRP Survey: 76%

of work trips are in single occupancy

vehicles (SOVs) (AVO = 1), 15% of work

trips are in carpools (AVO = 2.3), 5% of

work trips are on buses (AVO assumed to

be 15), 2% of work trips are on bicycles,

and 2% of work trips are walking. Thus,

AVO = (0.76 + 0.15 + 0.05 + 0.02 + 0.02)

/ [(0.76 / 1) + (0.15 / 2.3) + (0.05 / 15)] 

= 1.21. Using the values for SAT and

AVO,  = -(1 -0) / 1.21 = -0.83.

Table 2-5 in EPA’s TCM guidance document indicates that, for telecommuting, the parameter 

7 is equal to 1. This is because telecommuting directly affects work trips only.

Using the data above, TRIPSD = -0.83 * 17,259 = -14,325, TRIPSD,W = 1 * -14,325 = -14,325,

and TRIPSD,NW = (1 - 1) * -14,325 = 0. Summarizing these results, the RPTA program is responsible

for directly reducing 14,325 trips per day, all of which are work-related.

Step 3 in the travel activity methodology

involves estimating the actual indirect trip

increases (for both work and non-work trips)

from the RPTA program. Indirect trip increases

are secondary effects that typically result when

vehicles normally used for commuting are left 

at home. These increases are calculated using 

the following formulas:

TRIPSI,W = INCW,H * -TRIPSD / 2

TRIPSI,NW = INCN,H * -TRIPSD / 2
4

FOCUS: TRIPS REDUCED HERE CAN INCREASE

TRIPS ELSEWHERE

In Step 3 of the travel activity methodology, the

concept behind the calculation of INCW,H (the increased

fraction of work trips made by other household

members) is that the availability of another car when

one person starts participating in a TCM program (e.g.,

telecommuting) will prompt other workers in the

household who previously had to share rides to work to

begin driving. To estimate how frequently this would

happen, we multiply the number of other workers in a

typical household -- (SIZE - 1) * EMP -- by the

fraction of work trips made by shared modes (SHR)

and then by the fraction of households that might not

have enough cars for every worker. The factor (SIZE

- 1) is the typical number of persons in a household

minus one, to allow for the worker who is now

participating in the TCM program. EMP is the fraction

of people who are employed, and NV is the fraction of

households that have only one vehicle (and therefore

might be more likely to have more workers than cars)

. (Note: Similar logic underlies the calculation of

INCN,H, which is the increased fraction of non-work

trips made by other household members. In this

fraction, the variable UNEMP is used to account for

unemployed drivers in the household.)

& In the formulas, TRIPSI,W is the indirect work trip increase, TRIPSI,NW is the

indirect non-work trip increase, and INCW,H and INCN,H are the rates of increased

SOV work and non-work trip making by household members of TCM

participants who leave their vehicles at home. The other parameter in the

formulas is defined in an earlier step of the methodology.

INCW,H is defined as NV * SHR * (SIZE - 1) * EMP * TGW, where NV is the fraction of the

population that does not own a vehicle (Note: This analysis interprets this parameter to mean the

percentage of drivers without a vehicle, which is estimated as the percentage of vehicle-owning

households in the program area that have only one vehicle.), SHR is the fraction of shared mode trips,

SIZE is average household size, EMP is the fraction of the population that is employed, and TGW is the

work trip generation rate for SOV users. NV is

assumed to be 42%, based on U.S. Census data

for Maricopa County. The TRP Survey

indicates that 15% of work trips are in carpools

and 5% are on buses, resulting in an SHR

estimate of 20%. (Note: It may be appropriate to

use only the transit portion of shared mode trips

for the SHR parameter.) SIZE is assumed to be

2.59, based on information reported in the 1997

County and City Extra. The value for EMP is

55% and is taken from the TRP Survey, which

indicates that 47% of the population in the

program area is employed full-time and 8% of

the population is employed part-time. The TRP

Survey also reports 1,663,200 SOV work trips

and 971,700 SOV commuters, and thus TGW =

1,663,200 / 971,700 = 1.71. Based on these

numbers, INCW,H = 0.42 * 0 .20 * (2.59 - 1) *

0.55 * 1.71 = 0.13.

INCN,H is defined as NV * SHR * (SIZE

- 1) * UNEMP * TGN, where NV, SHR, and

SIZE are as defined above, UNEMP is the

fraction of the population that is not employed,

and TGN is the non-work trip generation rate for

SOV users. UNEMP is simply (1 - EMP) and

thus equals 45%. TGN is assumed to be the same

as TGW (i.e., 1.71). Based on these numbers,

INCN,H = 0.42 * 0.20 * (2.59 - 1) * 0.45 * 1.71 = 0.10.

Using the data above, TRIPSI,W = 0.13 * -(-14,325) / 2 = 1,862, and TRIPSI,NW = 0.10 

* -(-14,325) / 2 = 1,433. Summarizing these results, the RPTA program is indirectly responsible 

for an increase of 1,862 work trips per day and 1,433 non-work trips per day.

Step 4 in EPA’s methodology for estimating travel activity effects of TCMs, which involves

determining direct peak and off-peak period trip shifts, does not apply to telecommuting programs. 

Thus, Step 4 is not relevant to the analysis of the RPTA program.
5

FOCUS: DISTRIBUTING TRIP CHANGES BY

TIME-OF-DAY

Earlier steps in the travel activity methodology have

shown that trip changes resulting from TCM

programs can be broken down into work trip changes

and non-work trip changes. As shown in Step 5,

another key distinction is between peak-period trip

changes and off-peak trip changes. The parameter

PKW accounts for work trips occurring during peak

hours (i.e., 6:00 am to 9:00 am, and 4:00 pm to 7:00

pm). Similarly, the parameter PKNW accounts for

non-work trips occurring during peak hours. 

Because most people tend to keep regular work

hours, we would generally expect PKW to be greater

than 0.5. In addition, because non-work trips are

more discretionary than work trips, we would expect

most of them to occur in off-peak periods (when

Step 5 in the travel activity methodology involves estimating the net trip changes from the RPTA

program as distributed between work and non-work trips and peak and off-peak periods. These changes

are calculated using the following formulas:

NETRPW,P = 7 * TRIPSS,P + PKW * (TRIPSD,W + TRIPSI,W)

NETRPW,OP = 7 * TRIPSS,OP + (1 - PKW) * (TRIPSD,W + TRIPSI,W)

NETRPNW,P = (1 - 7) * TRIPSS,P + PKNW * (TRIPSD,NW + TRIPSI,NW)

NETRPNW,OP = (1 - 7) * TRIPSS,OP + (1 - PKNW) * (TRIPSD,NW + TRIPSI,NW)

& In the formulas, NETRPW,P is the net work trip change in the peak period,

NETRPW,OP is net work trip change in the off-peak period, NETRPNW,P is the

net non-work trip change in the peak period, and NETRPNW,OP is the net nonwork trip change in the off-peak period. TRIPSS,P is the change in peak period

trips, and TRIPSS,OP is the change in off-peak period trips. PKW is the observed

fraction of work trips during the peak period, and PKNW is the observed fraction

of non-work trips during the peak period. The other parameters in the formulas

are defined in earlier steps of the methodology.

Because there are no trip shifts associated with telecommuting (see Step 4), TRIPSS,P and

TRIPSS,OP are each equal to 0.

The value used for PKW is 0.7, based on

data for Phoenix, Arizona presented in Appendix

B of the TCM guidance document, and assuming

that peak travel hours are from 6 a.m. to 9 a.m.

and 4 p.m. to 7 p.m. PKNW is assumed to be 0.3,

based on an example presented in the TCM

guidance document.

Using the data above, NETRPW,P = 0 

+ 0.7 * (-14,325 + 1,862) = -8,724, NETRPW,OP

= 0 + (1 - 0.7) * (-14,325 + 1,862) = -3,739,

NETRPNW,P = 0 + 0.3 * (0 + 1,433) = 430, 

and NETRPNW,OP = 0 * (1 - 0.3) * (0 + 1,433) 

= 1,003. Summarizing these results, the RPTA

program results in net decreases in peak and 

off-peak work trips of 8,724 per day and 3,739

per day, respectively. The program also results 

in increases in peak and off-peak non-work trips

of 430 per day and 1,003 per day, respectively.

Step 6 in the travel activity methodology involves estimating the peak and off-peak VMT

changes due to the trip changes from the RPTA program. These changes are calculated using the

following formulas:

VMTP = (NETRPW,P * DISTW) + (NETRPNW,P * DISTNW)

VMTOP = (NETRPW,OP * DISTW) + (NETRPNW,OP * DISTNW)

& In the formulas, VMTP is the change in peak-period VMT due to trip changes,

VMTOP is the change in off-peak VMT due to trip changes, DISTW is the

average VMT per trip for work trips, and DISTNW is the average VMT per trip
6

FOCUS: VMT IS REDUCED TWO WAYS

As shown in Step 7, in addition to reducing VMT

through trip reductions, TCM programs can also reduce

VMT by reducing the length of existing trips. For

example, telecommuters who work at satellite work

centers that are closer to home than their regular offices

(so that DISTnew < DISTW) must still drive to and from

work each day. However, because these telecommuters

have reduced the length of each trip, VMT decreases.

for non-work trips. The other parameters in the formulas are defined in earlier

steps of the methodology.

DISTW is 13.9 miles per trip, as indicated by the TRP Survey. DISTNW is assumed to be 4.7

miles, based on the average passenger vehicle trip length for Maricopa County (7.1 miles, as reported

 in Transportation Inventory & Analysis of Existing Conditions, 1996: Maricopa County) and the

percentages of total trips that are work and non-work related (as reported in the 1996 Statistical Abstract

of the United States).

Using the data above, VMTP = (-8,724 * 13.9) + (430 * 4.7) = -119,243 and VMTOP = (-3,739

* 13.9) + (1,003 * 4.7) = -47,258. Summarizing these results, the RPTA program reduces peak-period

VMT by 119,243 miles per day due to trip changes and reduces off-peak VMT by 47,258 miles per day

due to trip changes.

Step 7 in the travel activity methodology involves estimating the VMT changes due to trip length

changes resulting from the RPTA program. These changes are calculated using the following formulas:

VMTL,W =  * PT * -(DISTW - DISTnew)

VMTL,NW =  * PT * -(DISTNW - DISTnew)

& In the formulas, VMTL,W is the change in VMT due to work trip length

changes, VMTL,NW is the change in VMT due to non-work trip length changes,

 is fraction of program participants who change their trip length, and DISTnew is

the new work or non-work trip length. The other parameters in the formulas are

defined in earlier steps of the methodology.

For telecommuting, the guidance indicates that  is equal to SAT. As noted in Step 2, SAT = 0

and thus  = 0.

Because no participants in the RPTA

program are assumed to work at satellite work

centers, DISTnew = 0 for work trips (i.e., the new

work trip length is 0 because all participants work

at home). Because the RPTA program does not

directly affect non-work trips, DISTnew for nonwork trips is equal to DISTNW.

Using the data above, VMTL,W = 0 *

17,259 * -(13.9 - 0) = 0, and VMTL,NW = 0 *

17,259 * -(4.7 - 4.7) = 0. Summarizing these

results, the RPTA program does not reduce VMT

through changes in trip lengths.

Step 8 in the travel activity methodology involves estimating the total peak and off-peak VMT

changes resulting from the RPTA program. These changes are calculated using the following formulas:

NETVMTP = VMTP + PKW * VMTL,W + PKNW * VMTL,NW

NETVMTOP = VMTOP + (1 - PKW) * VMTL,W + (1 - PKNW) * VMTL,NW
7

FOCUS: HOW REDUCING VMT AFFECTS

TRAVEL SPEED

When a TCM program reduces VMT during peak

periods, we would expect to see some increase (albeit

a small one) in overall fleet speeds given that fewer

vehicles on the road generally translates into less

congestion. In off-peak periods, however, people are

typically able to travel at any speeds they choose, and

thus reducing VMT during these times is not likely to

have any noticeable effect on overall fleet speeds.

Based on these observations, it is reasonable to assume

that P < 0 and OP = 0.

& In the formulas, NETVMTP is the total change in peak period VMT, and

NETVMTOP is the total change in off-peak VMT. The other parameters in the

formulas are defined in earlier steps of the methodology.

Using the data above, NETVMTP = -119,243 + 0.7 * 0 + 0.3 * 0 = -119,243 and NETVMTOP

= -47,258 + (1 - 0.7) * 0 + (1 - 0.3) * 0 = -47,258. Summarizing these results, the RPTA program reduces

peak-period VMT by a total of 119,243 miles per day and off-peak VMT by a total of 47,258 miles per

day.

Step 9 in the travel activity methodology involves estimating peak and off-peak speed changes

resulting from the RPTA program. These changes are calculated using the following formulas:

SPDP = (NETVMTP / TOTVMTP) * P

SPDOP = (NETVMTOP / TOTVMTOP) * OP

& In the formulas, SPDP is the percentage change in peak-period speeds, SPDOP

is the change in off-peak speeds, TOTVMTP is total peak-period VMT for the

program area, TOTVMTOP is total off-peak VMT for the program area, P is the

elasticity of peak-period speed with respect to volume, and OP is the elasticity of

off-peak speed with respect to volume. The other parameters in the formulas are

defined in earlier steps of the methodology.

According to Transportation Inventory & Analysis of Existing Conditions, 1996: Maricopa

County, total VMT in Maricopa County is approximately 50 million miles per day. The TRP Survey

indicates that work-related (i.e., commuter) VMT in the program area is approximately 25 million miles

per day. Thus, VMT for non-work trips is approximately 25 million miles per day (i.e., 50 million total

minus 25 million work-related). Combining this information with the assumptions from Step 5 that 70%

of work-related trips occur in the peak period and 30% of non-work trips occur in the peak period yields

a value of 25 million miles per day for each of TOTVMTP and TOTVMTOP.

The parameter P is assumed to be -0.75,

based on an example provided in the TCM

guidance document. The parameter OP is

assumed to be 0, because changes in off-peak

VMT are not likely to affect vehicle speeds 

(i.e., due to a lack of congestion).

Using the data above, SPDP = -119,243

/ 25,000,000 * -0.75 = 0.0036 and SPDOP = 

-47,258 / 25,000,000 * 0 = 0. Summarizing these

results, the RPTA program increases peak-period

speeds by approximately 0.36% but has no effect

on off-peak speeds. (Note: Data for the

Maricopa County area indicate that P could

potentially range from -0.5 to -1.94. Using these values for P yields increases in peak-period speeds of

0.24% and 0.93%, respectively.)
8

Phase 2: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Step 4: Summation of emission effects

Phase 2: Emission Effects -- STEP 1 (Trip

Changes)

Step 1 in the estimation of the emission

effects for the RPTA program involves

calculating the effect of trip changes on

emissions. This step is broken down into seven

smaller steps (1a through 1g), which are outlined

below.

Step 1a in the emission methodology

involves estimating the distribution of trip

changes for the RPTA program. These changes

are calculated using the following formulas:

TRIP,LDGV = TRIPLDGV / (TRIPLDGV + TRIPLDGT1)

TRIP,LDGT1 = 1 - TRIP,LDGV

• In the formulas, TRIP,LDGV is the

fraction of TCM-affected trips

taken by light-duty gasoline

vehicles (LDGVs), TRIP,LDGT1

is the fraction of TCM-affected

trips taken by light-duty

gasoline trucks (LDGT1s),

TRIPLDGV is the fraction of total

trips in the region taken by

LDGVs, and TRIPLDGT1 is the

fraction of total trips in the

region taken by LDGT1s. 

(Note: Most TCMs that can be analyzed using EPA’s guidance document affect only

LDGVs or LDGT1s. 

Thus, the sum of TRIP,LDGV and TRIP,LDGT1 is typically equal to one.)

TRIPLDGV and TRIPLDGT1 are derived from MOBILE5a data for Maricopa County and are equal 

to 0.619 and 0.173, respectively.

Using the data above, TRIP,LDGV = 0.619 / (0.619 + 0.173) = 0.782 and TRIP,LDGT1 = 1 - 0.782

 = 0.218. Summarizing these results, 78.2% of the trips affected by the RPTA program are taken by

LDGVs, and 21.8% are taken by LDGT1s.

Step 1b in the emission methodology involves calculating cold-start and hot-start trip changes

for the RPTA program. These changes are calculated using the following formulas:

TRIPSCST = CST,W * (NETRPW,P + NETRPW,OP) + CST, NW * (NETRPNW,P + NETRPNW,OP)

TRIPSHST = (1 - CST,W) * (NETRPW,P + NETRPW,OP) + (1 - CST,NW) * (NETRPNW,P

+ NETRPNW,OP)

& In the formulas, TRIPSCST is the number of cold-start trip changes, TRIPSHST

is the number of hot-start trip changes, CST,W is the fraction of work trips begun

in the cold-start mode, and CST, NW is the fraction of non-work trips begun in the
9

FOCUS: EMISSION RATES BETWEEN WORK

TRIPS AND NON-WORK TRIPS CAN BE

DIFFERENT

Work trips tend to be mostly cold-start trips because

vehicles typically sit for several hours at a time before

morning and evening commutes (i.e., overnight, during

working hours). Many non-work trips, however, are

made during the day by unemployed individuals and

tend to be strung together over relatively short time

periods. Also, non-work trips are often made in the

evening by employed individuals shortly after their

evening commute trips.

cold-start mode. The other parameters in the formulas are defined in earlier

steps of the methodology.

Because work trips are mostly cold-start trips, the guidance calls for CST,W to be set equal to 1. 

The guidance also suggests that CST,NW be set equal to 0.43, which is the default fraction of cold starts

used in the Federal Test Procedure (FTP).

Using the data above, TRIPSCST

 = 1 * (-8,724 + -3,739) + 0.43 * (430 + 1,003)

 = -11,847 and TRIPSHST = (1 - 1) * (-8,724 

+ -3,739) + (1 - 0.43) * (430 + 1,003) = 817. 

Summarizing these results, the RPTA program

results in a reduction of 11,847 cold-start trips

per day and an increase of 817 hot-start trips 

per day.

Step 1c in the emission methodology

involves determining cold-start and hot-start

emission factors. These changes are calculated

for a given pollutant and vehicle class using the

following formulas:

CST = (EXH100%CST,26MPH - EXH100%STB,26MPH) * 3.59

HST = (EXH100%HST,26MPH - EXH100%STB,26MPH) * 3.59

& In the formulas, CST is the cold-start emission factor in grams per trip, HST 

is the hot-start emission factor in grams per trip, and EXH is the MOBILE

emission factor in grams per mile. The 3.59 factor is the FTP driving cycle 

trip-start miles per trip, and 26 miles per hour is the speed for the start portion 

of the FTP driving cycle. (Note: The subscripts on EXH refer to the operating

conditions and speed at which MOBILE evaluates EXH. For example,

“100%CST,26MPH” indicates 100% cold-start operating mode at 26 miles 

per hour vehicle speed.)

Using national default data from MOBILE, CSTLDGV,HC = (2.55 - 0.95) * 3.59 = 5.74 grams 

per trip, CSTLDGT1,HC = (3.59 - 1.34) * 3.59 = 8.08 grams per trip, HSTLDGV,HC = (1.35 - 0.95) * 3.59 = 1.44

grams per trip, and HSTLDGT1,HC = (1.99 - 1.34) * 3.59 = 2.33 grams per trip. (Following the same

methodology, the cold-start and hot-start emission factors can also be determined for NOx and CO.)

Step 1d in the emission methodology involves determining cold-start and hot-start emission

changes for the RPTA program. These changes are calculated using the following formulas:

HCCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,HC) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,HC)

HCHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,HC) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,HC)

NOxCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,NOx) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,NOx)

NOxHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,NOx) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,NOx)

COCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,CO) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,CO)

COHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,CO) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,CO)
10

& In the formulas, HCCST, NOxCST, and COCST are the changes in cold-start

emissions for HC, NOx, and CO, respectively; and HCHST, NOxHST, and

COHST are the changes in hot-start emissions for HC, NOx, and CO,

respectively. The other parameters in the formulas are defined in earlier steps 

of the methodology.

Using national default data from MOBILE, HCCST = (-11,847 * 0.782 * 5.74) + (-11,847 

* 0.218 * 8.08) = -74,045 and HCHST = (817 * 0.782 * 1.44) + (817 * 0.218 * 2.33) = 1,335. 

Summarizing these results, the RPTA program results in a reduction in cold-start HC emissions of 74,045

grams per day and an increase in hot-start HC emissions of 1,335 grams per day. (Following the same

methodology, the cold-start and hot-start emission changes can also be determined for NOx and CO.)

Step 1e in the emission methodology involves determining hot soak emission changes for the

RPTA program. These changes are calculated using the following formula:

HCHSK = (TRIPSTOTAL * TRIP,LDGV * HSKLDGV) + (TRIPSTOTAL * TRIP,LDGT1 * HSKLDGT1)

& In the formula, HCHSK is the change in hot soak emissions, TRIPSTOTAL is the

total change in trips, and HSK is the hot soak emission factor in grams per trip. 

(Note: Hot soak emissions are HC emissions only.)

TRIPSTOTAL = NETRPW,P + NETRPW,OP + NETRPNW,P + NETRPNW,OP. 

Thus, TRIPSTOTAL = -8,724 + -3,739 + 430 + 1,003 = -11,030.

Using national default data from MOBILE, HCHSK = (-11,030 * 0.782 * 3.06) + (-11,030 

* 0.218 * 3.60) = -35,050. Summarizing this result, the RPTA program results in a reduction in hot soak

emissions of 35,050 grams per day.

Step 1f in the emission methodology involves determining diurnal emission changes for the

RPTA program. These changes are calculated for a given vehicle class using the following formulas:

HCDNL,W = 0.676 * (NETRPW,P + NETRPW,OP) / TPDW * TRIP * (WDI - MDI)

HCDNL,NW = 0.676 * (NETRPNW,P + NETRPNW,OP) / TPDNW * TRIP * (WDI - MDI)

HCDNL = HCDNL,W,LDGV + HCDNL,NW,LDGV + HCDNL,W,LDGT1 + HCDNL,NW,LDGT1

& In the formulas, HCDNL,W is the change in diurnal emissions associated with

work trips, HCDNL,NW is the change in diurnal emissions associated with nonwork trips, and HCDNL is the total change in diurnal emissions. TPDW is the

number of work trips per day per vehicle, and TPDNW is the number of non-work

trips per day per vehicle. WDI is the weighted diurnal emission factor in grams,

and MDI is the multi-day diurnal emission factor in grams. The other parameters

in the formulas are defined in earlier steps of the methodology. (Note: Diurnal

emissions are HC emissions only.)

The value used for TPDW is 2, since a commuter makes typically makes two work trips per day

(i.e., one trip from home to work, one trip from work to home). TPDNW is equal to TGN from Step 3 of

the “Travel Activity Effects” section above, and thus equals 1.71.
11

FOCUS: A TCM CAN INCREASE DIURNAL

EMISSIONS FROM VEHICLES NOT IN USE

Diurnal emissions (i.e., emissions resulting from daily

temperature changes that occur while a vehicle is not in

use) occur regardless of whether a vehicle is driven.

Vehicles that are driven regularly emit more partial-day

and full-day diurnal emissions than vehicles that are

not driven regularly, which emit more multi-day diurnal

emissions. To account for this, Step 1f of the emission

methodology subtracts multi-day diurnal emissions

from weighted diurnal emissions (which account for

both partial-day and full-day diurnal emissions) in

order to obtain a “net” effect. It is interesting to note

that, although TCM programs that reduce vehicle trips

generally reduce total emissions on net, diurnal

emissions actually increase. This is because an

increase in the number of vehicles not in use leads to

an increase in multi-day diurnal emissions, which are

Using national default data from

MOBILE, HCDNL,W,LDGV = 0.676 * (-8,724 

+ -3,739) / 2 * 0.782 * (3.30 - 6.04) = 9,026,

HCDNL,NW,LDGV = 0.676 * (430 + 1,003) / 1.71 

* 0.782 * (3.30 - 6.04) = -1,214, HCDNL,W,LDGT1

= 0.676 * (-8,724 + -3,739) / 2 * 0.218 * (5.11

 - 15.33) = 9,385, HCDNL,NW,LDGT1 = 0.676 * (430

+ 1,003) / 1.71 * 0.218 * (5.11 - 15.33) = -1,262,

and HCDNL = 9,026 + -1,214 + 9,385 + -1,262 

= 15,935. Summarizing these results, the RPTA

program results in a net increase in diurnal

emissions of 15,935 grams per day.

Step 1g in the emission methodology

involves calculating the total trip-related emission

changes for the RPTA program. These changes

are calculated using the following formulas:

HCTRIP = HCCST + HCHST + HCHSK + HCDNL

NOxTRIP = NOxCST + NOxHST

COTRIP = COCST + COHST

& In the formulas, HCTRIP, NOxTRIP, and COTRIP are the total changes in HC, NOx, 

and CO emissions, respectively, due to trip changes.

Using the data above, HCTRIP = -74,045 + 1,335 + -35,050 + 15,935 = -91,825. Summarizing

this result, the RPTA program results in a net decrease in trip-related HC emissions of 91,825 grams per

day. (Following the same methodology, total trip-related emission changes can also be determined for

NOx and CO.)
12

Emission Effects -- STEP 2 (VMT Changes)

Step 2 in the estimation of the emission effects for the RPTA program involves calculating the

effect of VMT changes on emissions. This step is broken down into four smaller steps (2a through 2d),

which are outlined below.

Step 2a in the emission methodology involves estimating the distribution of VMT changes for

the RPTA program. These changes are calculated using the following formulas:

VMT,LDGV = VMTLDGV / (VMTLDGV + VMTLDGT1)

VMT,LDGT1 = 1 - VMT,LDGV

& In the formulas, VMT,LDGV is the fraction of TCM-affected VMT for light-duty

gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected VMT 

for light-duty gasoline trucks (LDGT1s), VMTLDGV is the fraction of total VMT

in the region for LDGVs, and VMTLDGT1 is the fraction of total VMT in the

region for LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s

guidance document affect only LDGVs or LDGT1s. Thus, the sum of VMT,LDGV

and VMT,LDGT1 is typically equal to one.)

VMTLDGV and VMTLDGT1 are taken from MOBILE5a data for Maricopa County and are equal 

to 0.619 and 0.173, respectively. Using the data above, VMT,LDGV = 0.619 / (0.619 + 0.173) = 0.782 and

VMT,LDGT1 = 1 - 0.782 = 0.218. Summarizing these results, 78.2% of the VMT affected by the RPTA

program is by LDGVs, and 21.8% is by LDGT1s.

Step 2b in the emission methodology involves estimating hot-stabilized exhaust emission

changes for the RPTA program. These changes are calculated using the following formulas:

HCSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,HC,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,HC,P)

HCSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,HC,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,HC,OP)

NOxSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,NOx,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,NOx,P)

NOxSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,NOx,OP) + (NETVMTOP * VMT,LDGT1 *

STBLDGT1,NOx,OP)

COSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,CO,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,CO,P)

COSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,CO,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,CO,OP)

& In the formulas, HCSTB,P, NOxSTB,P, and COSTB,P are the peak-period changes

in hot-stabilized emissions for HC, NOx, and CO, respectively; and HCSTB,OP,

NOxSTB,OP, and COSTB,OP are the off-peak changes in hot-stabilized emissions

for HC, NOx, and CO, respectively. STBP is the hot-stabilized emission factor

(in grams per mile) for each pollutant and vehicle class for the peak period

(during which average vehicle speed is assumed to be 20 miles per hour), and

STBOP is the hot-stabilized emission factor (in grams per mile) for each pollutant

and vehicle class for the off-peak period (during which average vehicle speed is

assumed to be 35 miles per hour). The other parameters in the formulas are

defined in earlier steps of the methodology.

Using national default data from MOBILE, HCSTB,P = (-119,243 * 0.782 * 1.23) + (-119,243 

* 0.218 * 1.77) = -160,706 and HCSTB,OP = (-47,258 * 0.782 * 0.69) + (-47,258 * 0.218 * 0.94) 

= -35,184. Summarizing these results, the RPTA program results in a reduction in peak-period hot-
13

FOCUS: SUMMING EVAPORATIVE EMISSIONS

In Step 2c of the emission methodology, the

evaporative emission factor (VEVP) is calculated as

the sum of running loss emissions, crankcase

emissions, and refueling emissions. The peak-period

and off-peak evaporative emission factors differ only

in the running loss component, as this is the only type

of evaporative emissions that is influenced by vehicle

speeds.

stabilized HC exhaust emissions of 160,706 grams per day and a reduction in off-peak hot-stabilized HC

exhaust emissions of 35,184 grams per day. (Following the same methodology, hot-stabilized exhaust

emission changes can also be determined for NOx and CO.)

Step 2c in the emission methodology involves estimating VMT-related evaporative emission

changes for the RPTA program. These changes are calculated using the following formulas:

HCVEVP,P = (NETVMTP * VMT,LDGV * VEVPLDGV,P) + (NETVMTP * VMT,LDGT1 * VEVPLDGT1,P)

HCVEVP,OP = (NETVMTOP * VMT,LDGV * VEVPLDGV,OP) + (NETVMTOP * VMT,LDGT1 * VEVPLDGT1,OP)

& In the formulas, HCVEVP,P is the change in peak-period evaporative emissions,

HCVEVP,OP is the change in off-peak evaporative emissions, and VEVP is the

VMT-related evaporative emission factor (in grams per mile) for each vehicle

class and time period (peak or off-peak). The other parameters in the formulas

are defined in earlier steps of the methodology. (Note: Evaporative emissions

are HC emissions only.)

Using national default data from

MOBILE, HCVEVP,P = (-119,243 * 0.782 * 0.44)

+ (-119,243 * 0.218 * 0.53) = -54,806 and

HCVEVP,OP = (-47,258 * 0.782 * 0.34) 

+ (-47,258 * 0.218 * 0.44) = -17,098. 

Summarizing these results, the RPTA program

results in a reduction in peak-period evaporative

emissions of 54,806 grams per day and a

reduction in off-peak evaporative emissions 

of 17,098 grams per day.

Step 2d in the emission methodology involves calculating the total VMT-related emission

changes for the RPTA program. These changes are calculated using the following formulas:

HCVMT = HCSTB,P + HCSTB,OP + HCVEVP,P + HCVEVP,OP

NOxVMT = NOxSTB,P + NOxSTB,OP

COVMT = COSTB,P + COSTB,OP

& In the formulas, HCVMT, NOxVMT, and COVMT are the total changes in HC,

NOx, and CO emissions, respectively, due to VMT changes.

Using the data above, HCVMT = -160,706 + -35,184 + -54,806 + -17,098 = -267,794. 

Summarizing this result, the RPTA program results in a net decrease in VMT-related HC emissions 

of 267,794 grams per day. (Following the same methodology, total VMT-related emission changes 

can also be determined for NOx and CO.)
14

Emission Effects -- STEP 3 (Speed Changes)

Step 3 in the estimation of the emission effects for the RPTA program involves calculating the

effect of speed changes on emissions. This step is broken down into four smaller steps (3a through 3d),

which are outlined below.

Step 3a in the emission methodology involves estimating the speeds associated with the RPTA

program. These speeds are calculated using the following formulas:

SPEEDP,TCM = SPEEDP,BASE * (1 + SPDP)

SPEEDOP,TCM = SPEEDOP,BASE * (1 + SPDOP)

& In the formulas, SPEEDP,TCM is the peak-period speed after implementation of the

TCM, SPEEDOP,TCM is the off-peak speed after implementation of the TCM,

SPEEDP,BASE is the peak-period speed prior to implementation of the TCM, and

SPEEDOP,BASE is the off-peak speed prior to implementation of the TCM. The

other parameters in the formulas are defined in earlier steps of the methodology.

Based on data for the national default fleet, SPEEDP,BASE is assumed to be 20 miles per hour, 

and SPEEDOP,BASE is assumed to be 35 miles per hour.

Using the data above, SPEEDP,TCM = 20 * (1 + 0.0036) = 20.07 and SPEEDOP,TCM = 35 * (1 + 0) 

= 35. Summarizing these results, peak-period speeds have slightly increased from 20 miles per hour to

20.07 miles per hour due to the RPTA program. Off-peak speeds have not changed due to the program. 

(Note: Using values of -0.5 and -1.94 for P yields new peak-period speeds of 20.05 miles per hour and

20.19 miles per hour, respectively.)

Step 3b in the emission methodology involves estimating the total VMT for the program area

after implementation of the RPTA program. These VMT figures are calculated using the following

formulas:

VMTP,TCM = TOTVMTP + NETVMTP

VMTOP,TCM = TOTVMTOP + NETVMTOP

& In the formulas, VMTP,TCM is the total peak-period VMT in the program area

after implementation of the TCM, and VMTOP,TCM is the total off-peak VMT in

the program area after implementation of the TCM. The other parameters in the

formulas are defined in earlier steps of the methodology.

Using data from Step 9 of the “Travel Activity Effects” section above, VMTP,TCM = 25,000,000 

+ -119,243 = 24,880,757 and VMTOP,TCM = 25,000,000 + -47,258 = 24,952,742. Summarizing these

results, peak-period VMT has decreased from 25,000,000 miles per day to 24,880,757 miles per day due

to the RPTA program. Off-peak VMT has decreased from 25,000,000 miles per day to 24,952,742 miles

per day due to the program.

Step 3c in the emission methodology involves estimating peak-period and off-peak emission

changes due to changes in vehicle speeds. These changes are calculated using the following formulas:

HCSPD,P = VMTP,TCM * (STBFLT,HC,P,TCM + RNLFLT,P,TCM) - VMTP,TCM * (STBFLT,HC,P,BASE + RNLFLT,P,BASE)

HCSPD,OP = VMTOP,TCM * (STBFLT,HC,OP,TCM + RNLFLT,OP,TCM) - VMTOP,TCM * (STBFLT,HC,OP,BASE + RNLFLT,OP,BASE)
15

FOCUS:FLEET-WIDE EMISSIONS FACTORS IN

THIS STEP

It is important to note that the emission factors used in

Step 3c of the emission methodology are fleet-wide.

The emission factors used throughout the remainder of

the methodology are specific to individual vehicle

classes (e.g., LDGV, LDGT).

NOxSPD,P = VMTP,TCM * (STBFLT,NOx,P,TCM - STBFLT,NOx,P,BASE)

NOxSPD,OP = VMTOP,TCM * (STBFLT,NOx,OP,TCM - STBFLT,NOx,OP,BASE)

COSPD,P = VMTP,TCM * (STBFLT,CO,P,TCM - STBFLT,CO,P,BASE)

COSPD,OP = VMTOP,TCM * (STBFLT,CO,OP,TCM - STBFLT,CO,OP,BASE)

& In the formulas, HCSPD,P, NOxSPD,P, and COSPD,P are the peak-period changes

in emissions for HC, NOx, and CO, respectively, due to a change in speeds; and

HCSPD,OP, NOxSPD,OP, and COSPD,OP are the off-peak changes in emissions for

HC, NOx, and CO, respectively, due to a change in speeds. STBFLT is the fleetwide hot-stabilized emission factor (in grams per mile) for each pollutant, time

period (i.e., peak or off-peak), and scenario (i.e., base or TCM). RNLFLT is the

fleet-wide running loss emission factor (in grams per mile) for each time period

and scenario. The other parameters in the formulas are defined in earlier steps of

the methodology.

Based on data showing the relationship between vehicle speed and emissions, this analysis

assumes that the elasticity of STBFLT with respect to speed is -1 for HC, 0 for NOx, and -1 for CO. 

Thus, a 1% increase in speed is assumed to result in a 1% decrease in HC and CO emissions (on a grams

per mile basis) and no change in NOx emissions. The elasticity of RNLFLT with respect to speed is also

assumed to be -1. 

Using national default data from

MOBILE, HCSPD,P = 24,880,757 * (1.670 

+ 0.211) - 24,880,757 * (1.676 + 0.212) 

= -174,165 and HCSPD,OP = 24,952,742 * (1.938

+ 0.120) - 24,952,742 * (1.938 + 0.120) = 0. 

Summarizing these results, the RPTA program

results in a decrease in speed-related HC

emissions of 174,165 grams per day for the peak

period but does not change speed-related HC emissions for the off-peak period. (Following the same

methodology, the peak-period and off-peak emission changes due to changes in speeds can also be

determined for NOx and CO.) (Note: Using values of -0.5 and -1.94 for P yields decreases in speedrelated HC emissions of 124,404 grams per day and 447,854 grams per day, respectively.)

Step 3d in the emission methodology involves calculating the total speed-related emission

changes for the RPTA program. These changes are calculated using the following formulas:

HCSPD = HCSPD,P + HCSPD,OP

NOxSPD = NOxSPD,P + NOxSPD,OP

COSPD = COSPD,P + COSPD,OP

& In the formulas, HCSPD, NOxSPD, and COSPD are the total changes in HC,

NOx, and CO emissions, respectively, due to speed changes.

Using the data above, HCSPD = -174,165 + 0 = -174,165. Summarizing this result, the RPTA

program results in a net decrease in speed-related HC emissions of 174,165 grams per day. (Following

the same methodology, total speed-related emission changes can also be determined for NOx and CO.) 

(Note: Using values of -0.5 and -1.94 for P yields net decreases in speed-related HC emissions of

124,404 grams per day and 447,854 grams per day, respectively.)
16

Emission Effects -- STEP 4 (Total)

Step 4 in the estimation of the emission effects for the RPTA program involves calculating the

total changes in HC, NOx, and CO emissions. These changes are calculated using the following

formulas:

 

HC = HCTRIP + HCVMT + HCSPD

NOx = NOxTRIP + NOxVMT + NOxSPD

CO = COTRIP + COVMT + COSPD

& In the formulas, HC, NOx, and CO are the total changes in HC, NOx, 

and CO emissions, respectively, due to the TCM program.

Using the data above, HC = -91,825 + -267,794 + -174,165 = -533,784. Summarizing this

result, the RPTA program results in a net decrease in HC emissions of 533,784 grams per day, 

or approximately 0.59 tons per day. (Following the same methodology, total emission changes

can also be determined for NOx and CO.) (Note: Using values of -0.5 and -1.94 for P yields

net decreases in HC emissions of 0.53 tons per day and 0.89 tons per day, respectively.)
17

Phase 1: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

Example 2: Atlanta/DeKalb Greenway Trails

General Description

In 1994, the PATH Foundation funded the construction of 20 miles of trails built adjacent 

to highways servicing downtown Atlanta. The main objective of the project was to reduce traffic

congestion by encouraging commuters to bike or walk to work rather than drive. The project also

attempted to capture trips to schools and shops. The following analysis extrapolates data available 

for the 2.5-mile Westside Trail to estimate total reductions in trips, VMT, and emissions for the 20-mile

trail network. Ultimately, the PATH Foundation expects to construct over 110 miles of trails by the year

2000. Thus, the impact the trails have on travel activity and emissions will probably be much greater in

the future than this analysis indicates.

Data Sources

& Conversations with Edwin McBrayer, Executive Director, PATH Foundation, 

March 9 and 13, 1997.

& 1990 U.S. Census data.

& 1996 Statistical Abstract of the United States.

& Texas Transportation Institute web page.

Phase 1: Travel Activity Effects

Step 1 in the estimation of travel activity

effects for the PATH project involves an

assessment of the potential trip effects from the

project. For this TCM, these potential effects 

are calculated using the following user-defined

formula:

PT = N

• In the formula, PT is the

potential effect on trips,

and N is the total number

of vehicles traveling on

roadways adjacent to

trails.

The appropriate value for N is derived using information from the Atlanta Regional Commission

(ARC) indicating that approximately 18,000 vehicles use roadways adjacent to the 2.5-mile Westside

Trail on a given day. Assuming that the remaining trails comprising the 20-mile network are built along

roads that experience similar usage, the number of vehicles using roadways adjacent to trails is 144,000. 

Thus, the potential number of trips reduced per day by the PATH project is 144,000.

Step 2 in the travel activity methodology involves estimating the direct work and non-work trip

reductions from the PATH project. Whereas the potential trip reductions calculated in Step 1 represent

the total number of trips that might be reduced by a TCM program, direct trip reductions measure the
18

number of trips that actually are reduced and, thus, can be less than potential trip reductions (i.e., not all

vehicle passengers will switch to biking or walking ). Direct trip reductions are calculated using the

following formulas:

TRIPSD =  * PT

TRIPSD,W = 7 * TRIPSD

TRIPSD,NW = (1 - 7) * TRIPSD

& In the formulas, TRIPSD is the change in total direct trips, PT is (as above) the

potential trip reductions, TRIPSD,W is the change in direct work trips,

TRIPSD,NW is the change in direct non-work trips,  is the fraction of program

participants who make a direct trip change, and 7 is the fraction of trip effects

that are work-related.

The parameter  is assumed to be -0.04, based on information provided by ARC officials.

For TCM projects that influence work and non-work travel equally (such as the PATH project),

the TCM guidance calls for the parameter 7 to be set equal to the fraction of travel that is work-related. 

Thus, 7 is assumed to be 0.3, based on information provided in the 1996 Statistical Abstract of the

United States.

Using the data above, TRIPSD = -0.04 * 144,000 = -5,760, TRIPSD,W = 0.3 * -5,760 =

-1,728, and TRIPSD,NW = (1 - 0.3) * -5,760 = -4,032. Summarizing these results, the PATH project 

is responsible for directly reducing 1,728 work trips per day and 4,032 non-work trips per day.

Step 3 in the travel activity methodology involves estimating the actual indirect trip increases

(for both work and non-work trips) from the PATH project. Indirect trip increases are secondary effects

that typically result when vehicles normally used for commuting or other trips are left at home. These

increases are calculated using the following formulas:

TRIPSI,W = INCW,H * -TRIPSD / 2

TRIPSI,NW = INCN,H * -TRIPSD / 2

& In the formulas, TRIPSI,W is the indirect work trip increase, TRIPSI,NW is the

indirect non-work trip increase, and INCW,H and INCN,H are the rates of increased

SOV work and non-work trip making by household members of TCM

participants who leave their vehicles at home. The other parameter in the

formulas is defined in an earlier step of the methodology.

INCW,H is defined as NV * SHR * (SIZE - 1) * EMP * TGW, where NV is the fraction of the

population that does not own a vehicle (Note: This analysis interprets this parameter to mean the

percentage of drivers without a vehicle, which is estimated as the percentage of vehicle-owning

households in the program area that have only one vehicle.), SHR is the fraction of shared mode trips,

SIZE is average household size, EMP is the fraction of the population that is employed, and TGW is the

work trip generation rate for SOV users. Based on 1990 U.S. Census data for DeKalb County, NV is

assumed to be 38%, SHR is assumed to be 19%, SIZE is assumed to be 2.56, and EMP is assumed to be

70%. TGW is assumed to equal 2. Based on these numbers, INCW,H = 0.38 * 0.19 * (2.56 - 1) * 0.7 * 2 =

0.16.

INCN,H = NV * SHR * (SIZE - 1) * UNEMP * TGN, where NV, SHR, and SIZE are as defined

above, UNEMP is the fraction of the population that is not employed, and TGN is the non-work trip

generation rate for SOV users. UNEMP is simply (1 - EMP) and thus equals 30%. TGN is assumed to be

the same as TGW (i.e., 2). Based on these numbers, INCN,H = 0.38 * 0.19 * (2.56 - 1) * 0.3 * 2 = 0.07.
19

Using the data above, TRIPSI,W = 0.16 * -(-5,760) / 2 = 461, and TRIPSI,NW = 0.07 * -(-5,760)

/ 2 = 202. Summarizing these results, the PATH project is indirectly responsible for an increase of 461

work trips per day and 202 non-work trips per day. Summarizing these results, the PATH project is

indirectly responsible for an increase of 461 work trips per day and 202 non work trips per day.

Step 4 in EPA’s methodology for estimating travel activity effects of TCMs, which involves

determining direct peak and off-peak period trip shifts, does not apply to walking and biking trails. 

Thus, Step 4 is not relevant to the analysis of the PATH project.

Step 5 in the travel activity methodology involves estimating the net trip changes from the PATH

project as distributed between work and non-work trips and peak and off-peak periods. These changes

are calculated using the following formulas:

NETRPW,P = 7 * TRIPSS,P + PKW * (TRIPSD,W + TRIPSI,W)

NETRPW,OP = 7 * TRIPSS,OP + (1 - PKW) * (TRIPSD,W + TRIPSI,W)

NETRPNW,P = (1 - 7) * TRIPSS,P + PKNW * (TRIPSD,NW + TRIPSI,NW)

NETRPNW,OP = (1 - 7) * TRIPSS,OP + (1 - PKNW) * (TRIPSD,NW + TRIPSI,NW)

& In the formulas, NETRPW,P is the net work trip change in the peak period,

NETRPW,OP is net work trip change in the off-peak period, NETRPNW,P is the

net non-work trip change in the peak period, and NETRPNW,OP is the net nonwork trip change in the off-peak period. TRIPSS,P is the change in peak period

trips, and TRIPSS,OP is the change in off-peak period trips. PKW is the observed

fraction of work trips during the peak period, and PKNW is the observed fraction

of non-work trips during the peak period. The other parameters in the formulas

are defined in earlier steps of the methodology.

Because there are no trip shifts associated with walking and biking trails (see Step 4), TRIPSS,P

and TRIPSS,OP are each equal to 0.

The values used for PKW and PKNW are 0.6 and 0.3, respectively, based on an example shown 

in the TCM guidance document.

Using the data above, NETRPW,P = 0 + 0.6 * (-1,728 + 461) = -760, NETRPW,OP = 0 + (1 - 0.6)

* (-1,728 + 461) = -507, NETRPNW,P = 0 + 0.3 * (-4,032 + 202) = -1,149, and NETRPNW,OP

= 0 + (1 - 0.3) * (-4,032 + 202) = -2,681. Summarizing these results, the PATH project results in net

decreases in peak and off-peak work trips of 760 per day and 507 per day, respectively. The project also

results in decreases in peak and off-peak non-work trips of 1,149 per day and 2,681 per day, respectively.

Step 6 in the travel activity methodology involves estimating the peak and off-peak VMT

changes due to the trip changes from the PATH project. These changes are calculated using the

following formulas:

VMTP = (NETRPW,P * DISTW) + (NETRPNW,P * DISTNW)

VMTOP = (NETRPW,OP * DISTW) + (NETRPNW,OP * DISTNW)

& In the formulas, VMTP is the change in peak-period VMT due to trip changes,

VMTOP is the change in off-peak VMT due to trip changes, DISTW is the

average VMT per trip for work trips, and DISTNW is the average VMT per trip

for non-work trips. The other parameters in the formulas are defined in earlier

steps of the methodology.
20

DISTW is 13 miles per trip, as estimated by ARC. DISTNW is assumed to be 8.1 miles, based on

data from the 1996 Statistical Abstract of the United States.

Using the data above, VMTP = (-760 * 13) + (-1,149 * 8.1) = -19,187 and VMTOP = (-507 *

13) + (-2,681 * 8.1) = -28,307. Summarizing these results, the PATH project reduces peak-period VMT

by 19,187 miles per day due to trip changes and reduces off-peak VMT by 28,307 miles per day due to

trip changes.

Step 7 in the travel activity methodology involves estimating the VMT changes due to trip length

changes resulting from the PATH project. These changes are calculated using the following formulas:

VMTL,W =  * PT * -(DISTW - DISTnew)

VMTL,NW =  * PT * -(DISTNW - DISTnew)

& In the formulas, VMTL,W is the change in VMT due to work trip length

changes, VMTL,NW is the change in VMT due to non-work trip length changes,

 is fraction of program participants who change their trip length, and DISTnew is

the new work or non-work trip length. The other parameters in the formulas are

defined in earlier steps of the methodology.

Although it is conceivable that trail users may drive to a trail and walk or bicycle the rest of the

way, this analysis assumes that no trail users do so. Thus, both  and DISTnew are set equal to 0.

Using the data above, VMTL,W = 0 * 144,000 * -(13 - 0) = 0, and VMTL,NW = 0 * 144,000 

* -(8.1 - 0) = 0. Summarizing these results, the PATH project does not reduce VMT through changes 

in trip lengths.

Step 8 in the travel activity methodology involves estimating the total peak and off-peak VMT

changes resulting from the PATH project. These changes are calculated using the following formulas:

NETVMTP = VMTP + PKW * VMTL,W + PKNW * VMTL,NW

NETVMTOP = VMTOP + (1 - PKW) * VMTL,W + (1 - PKNW) * VMTL,NW

& In the formulas, NETVMTP is the total change in peak period VMT, and

NETVMTOP is the total change in off-peak VMT. The other parameters in the

formulas are defined in earlier steps of the methodology.
21

Using the data above, NETVMTP = -19,187 + 0.6 * 0 + 0.3 * 0 = -19,187 and NETVMTOP 

= -28,307 + (1 - 0.6) * 0 + (1 - 0.3) * 0 = -28,307. Summarizing these results, the PATH project reduces

peak-period VMT by a total of 19,187 miles per day and off-peak VMT by a total of 28,307 miles per

day.

Step 9 in the travel activity methodology involves estimating peak and off-peak speed changes

resulting from the PATH project. These changes are calculated using the following formulas:

SPDP = (NETVMTP / TOTVMTP) * P

SPDOP = (NETVMTOP / TOTVMTOP) * OP

& In the formulas, SPDP is the percentage change in peak-period speeds, SPDOP is the

change in off-peak speeds, TOTVMTP is total peak-period VMT for the program area,

TOTVMTOP is total off-peak VMT for the program area, P is the elasticity of peakperiod speed with respect to volume, and OP is the elasticity of off-peak speed with

respect to volume. The other parameters in the formulas are defined in earlier steps 

of the methodology.

According to data from the Texas Transportation Institute, total VMT in metropolitan Atlanta 

is approximately 80 million miles per day. Based on information from a local transportation agency

indicating that 40 percent of travel occurs during peak periods and 60 percent occurs during off-peak

periods, TOTVMTP is approximately 32 million miles per day and TOTVMTOP is approximately 48

million miles per day. 

The parameter P is assumed to be -0.75, based on an example provided in the TCM guidance

document. The parameter OP is assumed to be 0, because changes in off-peak VMT are not likely to

affect vehicle speeds (i.e., due to a lack of congestion).

Using the data above, SPDP = -19,187 / 32,000,000 * -0.75 = 0.0004 and SPDOP = -28,307 /

48,000,000 * 0 = 0. Summarizing these results, the PATH project increases peak-period speeds by

approximately 0.04% but has no effect on off-peak speeds.
22

Phase 2: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Phase 2: Emission Effects -- STEP 1 (Trip Changes)

Step 1 in the estimation of the emission

effects for the PATH project involves calculating

the effect of trip changes on emissions. This step

is broken down into seven smaller steps 

(1a through 1g), which are outlined below.

Step 1a in the emission methodology

involves estimating the distribution of trip

changes for the PATH project. These changes

are calculated using the following formulas:

TRIP,LDGV = TRIPLDGV / (TRIPLDGV + TRIPLDGT1)

TRIP,LDGT1 = 1 - TRIP,LDGV

• In the formulas, TRIP,LDGV is the

fraction of TCM-affected trips

taken by light-duty gasoline

vehicles (LDGVs), TRIP,LDGT1 

is the fraction of TCM-affected

trips taken by light-duty gasoline

trucks (LDGT1s), TRIPLDGV 

is the fraction of total trips in the

region taken by LDGVs, and

TRIPLDGT1 is the fraction of total

trips in the region taken by

LDGT1s. (Note: Most TCMs

that can be analyzed using EPA’s

guidance document affect only

LDGVs or LDGT1s. Thus, the

sum of TRIP,LDGV and TRIP,LDGT1 

is typically equal to one.)

TRIPLDGV and TRIPLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values are

based on the national average default values used in MOBILE.

Using the data above, TRIP,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and TRIP,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the trips affected by the PATH project are taken by

LDGVs, and 21.5% are taken by LDGT1s.

Step 1b in the emission methodology involves calculating cold-start and hot-start trip changes

for the PATH project. These changes are calculated using the following formulas:

TRIPSCST = CST,W * (NETRPW,P + NETRPW,OP) + CST, NW * (NETRPNW,P + NETRPNW,OP)

TRIPSHST = (1 - CST,W) * (NETRPW,P + NETRPW,OP) + (1 - CST,NW) * (NETRPNW,P +

NETRPNW,OP)

& In the formulas, TRIPSCST is the number of cold-start trip changes, TRIPSHST

is the number of hot-start trip changes, CST,W is the fraction of work trips begun

in the cold-start mode, and CST, NW is the fraction of non-work trips begun in the
23

cold-start mode. The other parameters in the formulas are defined in earlier

steps of the methodology.

Because work trips are mostly cold-start trips, the guidance calls for CST,W to be set equal to 1. 

The guidance also suggests that CST,NW be set equal to 0.43, which is the default fraction of cold starts

used in the Federal Test Procedure (FTP).

Using the data above, TRIPSCST = 1 * (-760 + -507) + 0.43 * (-1,149 + -2,681) = -2,914 and

TRIPSHST = (1 - 1) * (-760 + -507) + (1 - 0.43) * (-1,149 + -2,681) = -2,183. Summarizing these results,

the PATH project results in a reduction of 2,914 cold-start trips per day and a reduction of 2183 hot-start

trips per day.

Step 1c in the emission methodology involves determining cold-start and hot-start emission

factors. These changes are calculated for a given pollutant and vehicle class using the following

formulas:

CST = (EXH100%CST,26MPH - EXH100%STB,26MPH) * 3.59

HST = (EXH100%HST,26MPH - EXH100%STB,26MPH) * 3.59

& In the formulas, CST is the cold-start emission factor in grams per trip, HST 

is the hot-start emission factor in grams per trip, and EXH is the MOBILE

emission factor in grams per mile. The 3.59 factor is the FTP driving cycle 

trip-start miles per trip, and 26 miles per hour is the speed for the start portion 

of the FTP driving cycle. (Note: The subscripts on EXH refer to the operating

conditions and speed at which MOBILE evaluates EXH. For example,

“100%CST,26MPH” indicates 100% cold-start operating mode at 26 miles 

per hour vehicle speed.)

Using national default data from MOBILE, CSTLDGV,HC = (2.55 - 0.95) * 3.59 = 5.74 grams per

trip, CSTLDGT1,HC = (3.59 - 1.34) * 3.59 = 8.08 grams per trip, HSTLDGV,HC = (1.35 - 0.95) * 3.59 = 1.44

grams per trip, and HSTLDGT1,HC = (1.99 - 1.34) * 3.59 = 2.33 grams per trip. (Following the same

methodology, the cold-start and hot-start emission factors can also be determined for NOx and CO.)

Step 1d in the emission methodology involves determining cold-start and hot-start emission

changes for the PATH project. These changes are calculated using the following formulas:

HCCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,HC) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,HC)

HCHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,HC) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,HC)

NOxCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,NOx) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,NOx)

NOxHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,NOx) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,NOx)

COCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,CO) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,CO)

COHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,CO) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,CO)

& In the formulas, HCCST, NOxCST, and COCST are the changes in cold-start

emissions for HC, NOx, and CO, respectively; and HCHST, NOxHST, and

COHST are the changes in hot-start emissions for HC, NOx, and CO,

respectively. The other parameters in the formulas are defined in earlier steps 

of the methodology.
24

Using national default data from MOBILE, HCCST = (-2,914 * 0.785 * 5.74) + (-2,914 * 0.215 

* 8.08) = -18,192 and HCHST = (-2,183 * 0.785 * 1.44) + (-2,183 * 0.215 * 2.33) = -3,561. 

Summarizing these results, the PATH project results in a reduction in cold-start HC emissions of 18,192

grams per day and a reduction in hot-start HC emissions of 3,561 grams per day. (Following the same

methodology, the cold-start and hot-start emission changes can also be determined for NOx and CO.)

Step 1e in the emission methodology involves determining hot soak emission changes for the

PATH project. These changes are calculated using the following formula:

HCHSK = (TRIPSTOTAL * TRIP,LDGV * HSKLDGV) + (TRIPSTOTAL * TRIP,LDGT1 * HSKLDGT1)

& In the formula, HCHSK is the change in hot soak emissions, TRIPSTOTAL is the

total change in trips, and HSK is the hot soak emission factor in grams per trip. 

(Note: Hot soak emissions are HC emissions only.)

TRIPSTOTAL = NETRPW,P + NETRPW,OP + NETRPNW,P + NETRPNW,OP. Thus,

TRIPSTOTAL = -760 + -507 + -1,149 + -2,681 = -5,097.

Using national default data from MOBILE, HCHSK = (-5,097 * 0.785 * 3.06) + (-5,097 * 0.215 

* 3.60) = -16,189. Summarizing this result, the PATH project results in a reduction in hot soak emissions

of 16,189 grams per day.

Step 1f in the emission methodology involves determining diurnal emission changes for the

PATH project. These changes are calculated for a given vehicle class using the following formulas:

HCDNL,W = 0.676 * (NETRPW,P + NETRPW,OP) / TPDW * TRIP * (WDI - MDI)

HCDNL,NW = 0.676 * (NETRPNW,P + NETRPNW,OP) / TPDNW * TRIP * (WDI - MDI)

HCDNL = HCDNL,W,LDGV + HCDNL,NW,LDGV + HCDNL,W,LDGT1 + HCDNL,NW,LDGT1

& In the formulas, HCDNL,W is the change in diurnal emissions associated with

work trips, HCDNL,NW is the change in diurnal emissions associated with nonwork trips, and HCDNL is the total change in diurnal emissions. TPDW is the

number of work trips per day per vehicle, and TPDNW is the number of non-work

trips per day per vehicle. WDI is the weighted diurnal emission factor in grams,

and MDI is the multi-day diurnal emission factor in grams. The other parameters

in the formulas are defined in earlier steps of the methodology. (Note: Diurnal

emissions are HC emissions only.)

The value used for TPDW is 2, since a commuter makes typically makes two work trips per day

(i.e., one trip from home to work, one trip from work to home). TPDNW is equal to TGN from Step 3 

of the “Travel Activity Effects” section above, and thus equals 2.

Using national default data from MOBILE, HCDNL,W,LDGV = 0.676 * (-760 + -507) / 2 * 0.785 

* (3.30 - 6.04) = 921, HCDNL,NW,LDGV = 0.676 * (-1,149 + -2,681) / 2 * 0.785 * (3.30 - 6.04) = 2,784,

HCDNL,W,LDGT1 = 0.676 * (-760 + -507) / 2 * 0.215 * (5.11 - 15.33) = 941, HCDNL,NW,LDGT1 = 0.676 

* (-1,149 + -2,681) / 2 * 0.215 * (5.11 - 15.33) = 2,844, and HCDNL = 921 + 2,784 + 941 + 2,844 

= 7,490. Summarizing these results, the PATH project results in an increase in diurnal emissions 

of 7,490 grams per day.

Step 1g in the emission methodology involves calculating the total trip-related emission changes

for the PATH project. These changes are calculated using the following formulas:
25

HCTRIP = HCCST + HCHST + HCHSK + HCDNL

NOxTRIP = NOxCST + NOxHST

COTRIP = COCST + COHST

& In the formulas, HCTRIP, NOxTRIP, and COTRIP are the total changes in HC,

NOx, and CO emissions, respectively, due to trip changes.

Using the data above, HCTRIP = -18,192 + -3,561 + -16,189 + 7,490 = -30,452. Summarizing

this result, the PATH project results in a net decrease in trip-related HC emissions of 30,452 grams per

day. (Following the same methodology, total trip-related emission changes can also be determined for

NOx and CO.)

Emission Effects -- STEP 2 (VMT Changes)

Step 2 in the estimation of the emission effects for the PATH project involves calculating the

effect of VMT changes on emissions. This step is broken down into four smaller steps (2a through 2d),

which are outlined below.

Step 2a in the emission methodology involves estimating the distribution of VMT changes for

the PATH project. These changes are calculated using the following formulas:

VMT,LDGV = VMTLDGV / (VMTLDGV + VMTLDGT1)

VMT,LDGT1 = 1 - VMT,LDGV

& In the formulas, VMT,LDGV is the fraction of TCM-affected VMT for light-duty

gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected VMT for

light-duty gasoline trucks (LDGT1s), VMTLDGV is the fraction of total VMT in

the region for LDGVs, and VMTLDGT1 is the fraction of total VMT in the region

for LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s guidance

document affect only LDGVs or LDGT1s. Thus, the sum of VMT,LDGV and

VMT,LDGT1 is typically equal to one.)

VMTLDGV and VMTLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are the national average default values used in MOBILE for VMT mix.

Using the data above, VMT,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and VMT,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the VMT affected by the PATH project is by LDGVs, 

and 21.5% is by LDGT1s.

Step 2b in the emission methodology involves estimating hot-stabilized exhaust emission

changes for the PATH project. These changes are calculated using the following formulas:
26

HCSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,HC,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,HC,P)

HCSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,HC,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,HC,OP)

NOxSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,NOx,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,NOx,P)

NOxSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,NOx,OP) + (NETVMTOP * VMT,LDGT1 *

STBLDGT1,NOx,OP)

COSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,CO,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,CO,P)

COSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,CO,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,CO,OP)

& In the formulas, HCSTB,P, NOxSTB,P, and COSTB,P are the peak-period changes

in hot-stabilized emissions for HC, NOx, and CO, respectively; and HCSTB,OP,

NOxSTB,OP, and COSTB,OP are the off-peak changes in hot-stabilized emissions

for HC, NOx, and CO, respectively. STBP is the hot-stabilized emission factor

(in grams per mile) for each pollutant and vehicle class for the peak period

(during which average vehicle speed is assumed to be 20 miles per hour), and

STBOP is the hot-stabilized emission factor (in grams per mile) for each pollutant

and vehicle class for the off-peak period (during which average vehicle speed is

assumed to be 35 miles per hour). The other parameters in the formulas are

defined in earlier steps of the methodology.

Using national default data from MOBILE, HCSTB,P = (-19,187 * 0.785 * 1.23) + (-19,187 

* 0.215 * 1.77) = -25,828 and HCSTB,OP = (-28,307 * 0.785 * 0.69) + (-28,307 * 0.215 * 0.94) = -21,053. 

Summarizing these results, the PATH project results in a reduction in peak-period hot-stabilized HC

exhaust emissions of 25,828 grams per day and a reduction in off-peak hot-stabilized HC exhaust

emissions of 21,053 grams per day. (Following the same methodology, hot-stabilized exhaust emission

changes can also be determined for NOx and CO.)

Step 2c in the emission methodology involves estimating VMT-related evaporative emission

changes for the PATH project. These changes are calculated using the following formulas:

HCVEVP,P = (NETVMTP * VMT,LDGV * VEVPLDGV,P) + (NETVMTP * VMT,LDGT1 * VEVPLDGT1,P)

HCVEVP,OP = (NETVMTOP * VMT,LDGV * VEVPLDGV,OP) + (NETVMTOP * VMT,LDGT1 * VEVPLDGT1,OP)

& In the formulas, HCVEVP,P is the change in peak-period evaporative emissions,

HCVEVP,OP is the change in off-peak evaporative emissions, and VEVP is the

VMT-related evaporative emission factor (in grams per mile) for each vehicle

class and time period (peak or off-peak). The other parameters in the formulas

are defined in earlier steps of the methodology. (Note: Evaporative emissions

are HC emissions only.)

Using national default data from MOBILE, HCVEVP,P = (-19,187 * 0.785 * 0.44) + (-19,187 

* 0.215 * 0.53) = -8,814 and HCVEVP,OP = (-28,307 * 0.785 * 0.34) + (-28,307 * 0.215 * 0.44) = -10,233. 

Summarizing these results, the PATH project results in a reduction in peak-period evaporative emissions

of 8,814 grams per day and a reduction in off-peak evaporative emissions of 10,233 grams per day.

Step 2d in the emission methodology involves calculating the total VMT-related emission

changes for the PATH project. These changes are calculated using the following formulas:

HCVMT = HCSTB,P + HCSTB,OP + HCVEVP,P + HCVEVP,OP

NOxVMT = NOxSTB,P + NOxSTB,OP
27

COVMT = COSTB,P + COSTB,OP

& In the formulas, HCVMT, NOxVMT, and COVMT are the total changes in HC,

NOx, and CO emissions, respectively, due to VMT changes.

Using the data above, HCVMT = -25,828 + -21,053 + -8,814 + -10,233 = -65,928. Summarizing

this result, the PATH project results in a net decrease in VMT-related HC emissions of 65,928 grams per

day. (Following the same methodology, total VMT-related emission changes can also be determined for

NOx and CO.)

Emission Effects -- STEP 3 (Speed Changes)

Step 3 in the estimation of the emission effects for the PATH project involves calculating the

effect of speed changes on emissions. This step is broken down into four smaller steps (3a through 3d),

which are outlined below.

Step 3a in the emission methodology involves estimating the speeds associated with the PATH

project. These speeds are calculated using the following formulas:

SPEEDP,TCM = SPEEDP,BASE * (1 + SPDP)

SPEEDOP,TCM = SPEEDOP,BASE * (1 + SPDOP)

& In the formulas, SPEEDP,TCM is the peak-period speed after implementation of the

TCM, SPEEDOP,TCM is the off-peak speed after implementation of the TCM,

SPEEDP,BASE is the peak-period speed prior to implementation of the TCM, and

SPEEDOP,BASE is the off-peak speed prior to implementation of the TCM. The

other parameters in the formulas are defined in earlier steps of the methodology.

Based on data for the national default fleet, SPEEDP,BASE is assumed to be 20 miles per hour, 

and SPEEDOP,BASE is assumed to be 35 miles per hour.

Using the data above, SPEEDP,TCM = 20 * (1 + 0.0004) = 20.01 and SPEEDOP,TCM = 35 * (1 + 0) 

= 35. Summarizing these results, peak-period speeds have slightly increased from 20 miles per hour 

to 20.01 miles per hour due to the PATH project. Off-peak speeds have not changed due to the project.

Step 3b in the emission methodology involves estimating the total VMT for the program area

after implementation of the PATH project. These VMT figures are calculated using the following

formulas:

VMTP,TCM = TOTVMTP + NETVMTP

VMTOP,TCM = TOTVMTOP + NETVMTOP

& In the formulas, VMTP,TCM is the total peak-period VMT in the program area

after implementation of the TCM, and VMTOP,TCM is the total off-peak VMT in

the program area after implementation of the TCM. The other parameters in the

formulas are defined in earlier steps of the methodology.

Using data from Step 9 of the “Travel Activity Effects” section above, VMTP,TCM = 32,000,000 

+ -19,187 = 31,980,813 and VMTOP,TCM = 48,000,000 + -28,307 = 47,971,693. Summarizing these

results, peak-period VMT has decreased from 32,000,000 miles per day to 31,980,813 miles per day due
28

to the PATH project. Off-peak VMT has decreased from 48,000,000 miles per day to 47,971,693 miles

per day due to the project.

Step 3c in the emission methodology involves estimating peak-period and off-peak emission

changes due to changes in vehicle speeds. These changes are calculated using the following formulas:

HCSPD,P = VMTP,TCM * (STBFLT,HC,P,TCM + RNLFLT,P,TCM) - VMTP,TCM * (STBFLT,HC,P,BASE + RNLFLT,P,BASE)

HCSPD,OP = VMTOP,TCM * (STBFLT,HC,OP,TCM + RNLFLT,OP,TCM) - VMTOP,TCM * (STBFLT,HC,OP,BASE + RNLFLT,OP,BASE)

NOxSPD,P = VMTP,TCM * (STBFLT,NOx,P,TCM - STBFLT,NOx,P,BASE)

NOxSPD,OP = VMTOP,TCM * (STBFLT,NOx,OP,TCM - STBFLT,NOx,OP,BASE)

COSPD,P = VMTP,TCM * (STBFLT,CO,P,TCM - STBFLT,CO,P,BASE)

COSPD,OP = VMTOP,TCM * (STBFLT,CO,OP,TCM - STBFLT,CO,OP,BASE)

& In the formulas, HCSPD,P, NOxSPD,P, and COSPD,P are the peak-period changes

in emissions for HC, NOx, and CO, respectively, due to a change in speeds; and

HCSPD,OP, NOxSPD,OP, and COSPD,OP are the off-peak changes in emissions for

HC, NOx, and CO, respectively, due to a change in speeds. STBFLT is the fleetwide hot-stabilized emission factor (in grams per mile) for each pollutant, time

period (i.e., peak or off-peak), and scenario (i.e., base or TCM). RNLFLT is the

fleet-wide running loss emission factor (in grams per mile) for each time period

and scenario. The other parameters in the formulas are defined in earlier steps 

of the methodology.

Based on data showing the relationship between vehicle speed and emissions, this analysis

assumes that the elasticity of STBFLT with respect to speed is -1 for HC, 0 for NOx, and -1 for CO. 

Thus, a 1% increase in speed is assumed to result in a 1% decrease in HC and CO emissions (on a grams

per mile basis) and no change in NOx emissions. The elasticity of RNLFLT with respect to speed is also

assumed to be -1. 

Using national default data from MOBILE, HCSPD,P = 31,980,813 * (1.675 + 0.212) 

- 31,980,813 * (1.676 + 0.212) = -31,981 and HCSPD,OP = 47,971,693 * (1.938 + 0.120) - 47,971,693 

* (1.938 + 0.120) = 0. Summarizing these results, the PATH project results in a decrease in speedrelated HC emissions of 31,981 grams per day for the peak period but does not change speed-related HC

emissions for the off-peak period. (Following the same methodology, the peak-period and off-peak

emission changes due to changes in speeds can also be determined for NOx and CO.)

Step 3d in the emission methodology involves calculating the total speed-related emission

changes for the PATH project. These changes are calculated using the following formulas:

HCSPD = HCSPD,P + HCSPD,OP

NOxSPD = NOxSPD,P + NOxSPD,OP

COSPD = COSPD,P + COSPD,OP

& In the formulas, HCSPD, NOxSPD, and COSPD are the total changes in HC,

NOx, and CO emissions, respectively, due to speed changes.

Using the data above, HCSPD = -31,981 + 0 = -31,981. Summarizing this result, the PATH

project results in a net decrease in speed-related HC emissions of 31,981 grams per day. (Following the

same methodology, total speed-related emission changes can also be determined for NOx and CO.)
29

Emission Effects -- STEP 4 (Total)

Step 4 in the estimation of the emission effects for the PATH project involves calculating the

total changes in HC, NOx, and CO emissions. These changes are calculated using the following

formulas:

 

HC = HCTRIP + HCVMT + HCSPD

NOx = NOxTRIP + NOxVMT + NOxSPD

CO = COTRIP + COVMT + COSPD

& In the formulas, HC, NOx, and CO are the total changes in HC, NOx, and

CO emissions, respectively, due to the TCM program.

Using the data above, HC = -30,452 + -65,928 + -31,981 = -128,361. Summarizing this result,

the PATH project results in a net decrease in HC emissions of 128,361 grams per day, or approximately

0.14 tons per day. (Following the same methodology, total emission changes can also be determined for

NOx and CO.)
30

Phase 1: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

Example 3: Cleveland Walkway to Gateway

General Description

The Cleveland Walkway to Gateway provides a link for transit riders arriving at Tower City

Center, the main shopping and entertainment area of downtown Cleveland, to the Gateway Sports and

Entertainment Complex. The climate-controlled walkway, which is about a quarter mile long, was

designed in part to stimulate transit ridership in the metro area and relieve traffic congestion, especially

during sporting events. The Greater Cleveland Regional Transport Authority determined that about

940,000 transit riders used the walkway during the 16-month period between April 1994 and August

1995.

(Note: Because the Walkway to Gateway is intended to link downtown shopping and entertainment areas

with the Gateway complexes, which are primarily used for recreational activities (e.g., sporting events),

this analysis assumes that the walkway has no effect (either directly or indirectly) on work-related trips,

VMT, speeds, or emissions (commutes by Stadium/Arena employees are considered non-work trips for

the purpose of this analysis). In addition, because events at the Gateway complex tend to occur during

off-peak hours, the analysis assumes that the walkway has no effect on peak period trips, VMT, speeds,

or emissions. Given these assumptions, this analysis excludes several of the formulas shown in EPA’s

TCM guidance and in some cases modifies formulas to reflect the nature of the travel activity and

emissions effects from the Walkway to Gateway.)

Data Sources

& Interview with Joel Freilich, Director, Strategic Planning and Research, Greater Cleveland

Regional Transit Authority, March 6, 1997.

& 1990 U.S. Census data.

& 1996 Statistical Abstract of the United States.

& Texas Transportation Institute web page.

Phase 1: Travel Activity Effects

Step 1 in the estimation of travel activity

effects for the Walkway to Gateway involves an

assessment of the potential trip effects from the

program. For this TCM, these potential effects

are calculated using the following user-defined

formula:

PT = (N) / 487
31

& In the formula, PT is the potential effect on trips, and N is the number of transit

riders who used the walkway between April 1994 and August 1995 (a period 

of 487 days) who would not have taken transit in the absence of the walkway.

The appropriate value for N is derived by “adjusting” the number of transit riders who used the

walkway between April 1994 and August 1995 (i.e., 940,000) by the percentage of those riders who

would not have taken transit in the absence of the walkway. Assuming that 70 percent of walkway users

would not have taken transit, N = 0.70 * 940,000 = 658,000. (Note: The “70 percent” assumption for

transit use is for illustrative purposes only. A more realistic assumption could be developed using

surveys or expert judgment.) It should be noted that the Walkway is only open during events at Gateway. 

Therefore, actual emission reductions on a given day are more than the average derived here.

Using the data above, PT = (658,000) / 487 = 1,351. Thus, the potential number of trips reduced

per day by the Walkway to Gateway is 1,351.

Step 2 in the travel activity methodology involves estimating the direct work and non-work trip

reductions from the Walkway to Gateway. Whereas the potential trip reductions calculated in Step 1

represent the total number of trips that might be reduced by a TCM program, direct trip reductions

measure the number of trips that actually are reduced and, thus, can be less than potential trip reductions

(e.g., if not all walkway users formerly drove alone to the Gateway complex). Direct trip reductions for

the Walkway to Gateway are calculated using the following formulas:

TRIPSD =  * PT

TRIPSD,NW = (1 - 7) * TRIPSD

& In the formulas, TRIPSD is the total direct trip reduction, PT is (as above) the

potential trip reductions, TRIPSD,NW is the direct non-work trip reduction,  is

the fraction of program participants who make a direct trip change, and 7 is the

fraction of trip effects that are work-related.

Because all trip reductions from the walkway are assumed to be non-work related, the TCM

guidance call for the parameter 7 to be set equal to 0.

For the Walkway to Gateway,  is defined as -(1 - DRIVTRAN) / AVO, where DRIVTRAN 

is the fraction of people who drive to public transit stations and AVO is average vehicle occupancy. 

This analysis assumes that 50 percent of transit riders using the walkway drive to public transit stations,

and thus DRIVTRAN = 0.5. Average vehicle occupancy for trips to Gateway is estimated to be 1.5. 

Using these values for DRIVTRAN and AVO,  = -(1 - 0.5) / 1.5 = -0.33.

Using the data above, TRIPSD = -0.33 * 1,351 = -446 and TRIPSD,NW = (1 - 0) * -446 = -446. 

Summarizing these results, the Walkway to Gateway is responsible for directly reducing 446 trips per

day, all of which are non-work related.

Step 3 in the travel activity methodology involves estimating the actual indirect trip increases

from the Walkway to Gateway. Indirect trip increases are secondary effects that typically result when

vehicles normally used for other trips are left at home. For the Walkway to Gateway, these increases 

are calculated using the following formula:

TRIPSI,NW = INCN,H * -TRIPSD / 2
32

& In the formula, TRIPSI,NW is the indirect non-work trip increase, and INCN,H 

is the rate of increased SOV non-work trip making by household members of

TCM participants who leave their vehicles at home. The other parameter in 

the formula is defined in an earlier step of the methodology.

INCN,H is defined as NV * SHR * (SIZE - 1) * UNEMP * TGN, where NV is the fraction of the

population that does not own a vehicle (Note: This analysis interprets this parameter to mean the

percentage of drivers without a vehicle, which is estimated as the percentage of vehicle-owning

households in the program area that have only one vehicle.), SHR is the fraction of shared mode trips,

SIZE is average household size, UNEMP is the fraction of the population that is not employed, and TGN

is the non-work trip generation rate for SOV users. Based on 1990 U.S. Census data for Cuyahoga

County, NV is assumed to be 45%, SHR is assumed to be 19%, and SIZE is assumed to be 2.39. 

Because the walkway is used almost entirely during evening hours, indirect trip increases do not depend

on employment status, and thus UNEMP is set equal to 1. Finally, TGN is estimated to be 1.0, based 

on national default data indicating that the average person takes approximately 3 non-work trips per day

and assuming that D of these trips are taken during the evening hours. Based on these numbers, INCN,H

= 0.45 * 0.19 * (2.39 - 1) * 1 * 1 = 0.12.

Using the data above, TRIPSI,NW = 0.12 * -(-446) / 2 = 27. Thus, the Walkway to Gateway 

is indirectly responsible for an increase of 27 non-work trips per day.

Step 4 in EPA’s methodology for estimating travel activity effects of TCMs, which involves

determining direct peak and off-peak period trip shifts, does not apply to projects such as the Walkway 

to Gateway.

Step 5 in the travel activity methodology involves estimating the net trip changes from the

Walkway to Gateway. These changes are calculated using the following formula:

NETRPNW,OP = (1 - 7) * TRIPSS,OP + (1 - PKNW) * (TRIPSD,NW + TRIPSI,NW)

& In the formula, NETRPNW,OP is the net non-work trip change in the off-peak

period, TRIPSS,OP is the change in off-peak period trips, and PKNW is the

observed fraction of non-work trips during the peak period. The other

parameters in the formula are defined in earlier steps of the methodology.

Because there are no trip shifts associated with transit improvements (see Step 4), TRIPSS,OP 

is equal to 0. Also, because direct and indirect trip effects from the Walkway to Gateway occur only 

at off-peak periods, EPA’s TCM guidance calls for PKNW to be set equal to 0.

Using the data above, NETRPNW,OP = (1 - 0) * 0 + (1 - 0) * (-446 + 27) = -419. Thus, the

Walkway to Gateway results in a net decrease of 419 off-peak non-work trips per day.

Step 6 in the travel activity methodology involves estimating the off-peak VMT changes due 

to the trip changes from the Walkway to Gateway. These changes are calculated using the following

formula:

VMTOP = (NETRPW,OP * DISTW) + (NETRPNW,OP * DISTNW)

& In the formula, VMTOP is the change in off-peak VMT due to trip changes,

DISTW is the average VMT per trip for work trips, and DISTNW is the average
33

VMT per trip for non-work trips. The other parameters in the formula are

defined in earlier steps of the methodology.

Because the Walkway to Gateway does not affect work trips, NETRPW,OP is equal to 0. DISTNW

is assumed to be 8 miles per trip for trips to the Gateway complex (based on information about transit trip

lengths provided by the Greater Cleveland Regional Transit Authority) and 8.1 miles per trip for all other

non-work trips (based on data from the 1996 Statistical Abstract of the United States).

Using the data above, VMTOP = 0 + [(-446 * 8) + (27 * 8.1)] = -3,349. Thus, the Walkway 

to Gateway reduces off-peak VMT by 3,349 miles per day due to trip changes.

Step 7 in the travel activity methodology involves estimating the VMT changes due to trip length

changes resulting from the Walkway to Gateway. These changes are calculated using the following

formula:

VMTL,NW =  * PT * -(DISTNW - DISTnew)

& In the formula, VMTL,NW is the change in VMT due to trip length changes,  is

the fraction of program participants who change their trip length, DISTNW is the

average length of a trip to the Gateway complex, and DISTnew is the new trip

length. The other parameters in the formula are defined in earlier steps of the

methodology.

Based on information in Table 2-10 of the TCM guidance,  is set equal to DRIVTRAN. 

As noted in Step 2 above, DRIVTRAN = 0.5, and thus  = 0.5.

As noted in Step 6 above, DISTNW for transit trips to Gateway is 8 miles. That is, transit reduces

VMT by 8 miles per trip because transit stations tend to be located along the route from homes to

downtown Cleveland. Therefore, regardless of the driving distance to transit stops, DISTNW - DISTnew 

= 8 miles.

Using the data above, VMTL,NW = 0.5 * 1,351 * -(8) = -5,404. Thus, the Walkway to Gateway

reduces VMT by 5,404 miles per day due to trip length changes.

Step 8 in the travel activity methodology involves estimating the total off-peak VMT changes

resulting from the Walkway to Gateway. These changes are calculated using the following formula:

NETVMTOP = VMTOP + (1 - PKNW) * VMTL,NW

& In the formula, NETVMTOP is the total change in off-peak VMT. The other

parameters in the formula are defined in earlier steps of the methodology.

Using the data above, NETVMTOP = -3,349 + (1 - 0) * -5,404 = -8,753. Thus, the Walkway 

to Gateway reduces off-peak VMT by a total of 8,753 miles per day.

Step 9 in the travel activity methodology involves estimating off-peak speed changes resulting

from the Walkway to Gateway. These changes are calculated using the following formula:

SPDOP = (NETVMTOP / TOTVMTOP) * OP
34

Phase 2: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Step 4: Summation of emission effects

& In the formula, SPDOP is the change in off-peak speeds, TOTVMTOP is total

off-peak VMT for the program area, and OP is the elasticity of off-peak speed

with respect to volume. The other parameter in the formula is defined in an

earlier step of the methodology.

According to data from the Texas Transportation Institute, total VMT in metropolitan Cleveland

is approximately 36 million miles per day. Assuming that 50 percent of travel activity occurs during 

off-peak periods, TOTVMTOP is approximately 18 million miles per day.

Post-event traffic is less congested as a result of increased tranit use. However, sufficient data 

is not available. Therefore, the parameter OP is assumed to be 0, because changes in off-peak VMT 

do not usually affect vehicle speeds (i.e., due to a lack of congestion).

Using the data above, SPDOP = (-8,753 / 18,000,000) * 0 = 0. Summarizing this result, the

Walkway to Gateway has no effect on off-peak period speeds.

Phase 2: Emission Effects -- STEP 1 (Trip

Changes)

Step 1 in the estimation of the emission

effects for the Walkway to Gateway involves

calculating the effect of trip changes on

emissions. This step is broken down into seven

smaller steps (1a through 1g), which are outlined

below.

Step 1a in the emission methodology

involves estimating the distribution of trip

changes for the Walkway to Gateway. These

changes are calculated using the following

formulas:

TRIP,LDGV = TRIPLDGV / (TRIPLDGV + TRIPLDGT1)

TRIP,LDGT1 = 1 - TRIP,LDGV
35

& In the formulas, TRIP,LDGV is the fraction of TCM-affected trips taken by lightduty gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected trips

taken by light-duty gasoline trucks (LDGT1s), TRIPLDGV is the fraction of total

trips in the region taken by LDGVs, and TRIPLDGT1 is the fraction of total trips 

in the region taken by LDGT1s. (Note: Most TCMs that can be analyzed using

EPA’s guidance document affect only LDGVs or LDGT1s. Thus, the sum of

TRIP,LDGV and TRIP,LDGT1 is typically equal to one.)

TRIPLDGV and TRIPLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are based on the national average default values used in MOBILE.

Using the data above, TRIP,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and TRIP,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the trips affected by the Walkway to Gateway are taken 

by LDGVs, and 21.5% are taken by LDGT1s.

Step 1b in the emission methodology involves calculating cold-start and hot-start trip changes

for the Walkway to Gateway. These changes are calculated using the following formulas:

TRIPSCST = CST,W * (NETRPW,P + NETRPW,OP) + CST, NW * (NETRPNW,P + NETRPNW,OP)

TRIPSHST = (1 - CST,W) * (NETRPW,P + NETRPW,OP) + (1 - CST,NW) * (NETRPNW,P +

NETRPNW,OP)

& In the formulas, TRIPSCST is the number of cold-start trip changes, TRIPSHST

is the number of hot-start trip changes, CST,W is the fraction of work trips begun

in the cold-start mode, and CST, NW is the fraction of non-work trips begun in the

cold-start mode. The other parameters in the formulas are defined in earlier

steps of the methodology.

Because work trips are mostly cold-start trips, the guidance calls for CST,W to be set equal to 1. 

The guidance also suggests that CST,NW be set equal to 0.43, which is the default fraction of cold starts

used in the Federal Test Procedure (FTP).

Using the data above, TRIPSCST = 1 * (0 + 0) + 0.43 * (0 + -419) = -180 and TRIPSHST 

= (1 - 1) * (0 + 0) + (1 - 0.43) * (0 + -419) = -239. Summarizing these results, the Walkway to Gateway

results in a reduction of 180 cold-start trips per day and a reduction of 239 hot-start trips per day.

Step 1c in the emission methodology involves determining cold-start and hot-start emission

factors. These changes are calculated for a given pollutant and vehicle class using the following

formulas:

CST = (EXH100%CST,26MPH - EXH100%STB,26MPH) * 3.59

HST = (EXH100%HST,26MPH - EXH100%STB,26MPH) * 3.59

& In the formulas, CST is the cold-start emission factor in grams per trip, HST 

is the hot-start emission factor in grams per trip, and EXH is the MOBILE

emission factor in grams per mile. The 3.59 factor is the FTP driving cycle 

trip-start miles per trip, and 26 miles per hour is the speed for the start portion 

of the FTP driving cycle. (Note: The subscripts on EXH refer to the operating

conditions and speed at which MOBILE evaluates EXH. For example,

“100%CST,26MPH” indicates 100% cold-start operating mode at 26 miles 

per hour vehicle speed.)
36

Using national default data from MOBILE, CSTLDGV,HC = (2.55 - 0.95) * 3.59 = 5.74 grams per

trip, CSTLDGT1,HC = (3.59 - 1.34) * 3.59 = 8.08 grams per trip, HSTLDGV,HC = (1.35 - 0.95) * 3.59 = 1.44

grams per trip, and HSTLDGT1,HC = (1.99 - 1.34) * 3.59 = 2.33 grams per trip. (Following the same

methodology, the cold-start and hot-start emission factors can also be determined for NOx and CO.)

Step 1d in the emission methodology involves determining cold-start and hot-start emission

changes for the Walkway to Gateway. These changes are calculated using the following formulas:

HCCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,HC) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,HC)

HCHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,HC) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,HC)

NOxCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,NOx) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,NOx)

NOxHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,NOx) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,NOx)

COCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,CO) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,CO)

COHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,CO) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,CO)

& In the formulas, HCCST, NOxCST, and COCST are the changes in cold-start

emissions for HC, NOx, and CO, respectively; and HCHST, NOxHST, and

COHST are the changes in hot-start emissions for HC, NOx, and CO,

respectively. The other parameters in the formulas are defined in earlier steps 

of the methodology.

Using national default data from MOBILE, HCCST = (-180 * 0.785 * 5.74) + (-180 * 0.215 

* 8.08) = -1,124 and HCHST = (-239 * 0.785 * 1.44) + (-239 * 0.215 * 2.33) = -390. Summarizing these

results, the Walkway to Gateway results in a reduction in cold-start HC emissions of 1,124 grams per day

and a reduction in hot-start HC emissions of 390 grams per day. (Following the same methodology, 

the cold-start and hot-start emission changes can also be determined for NOx and CO.)

Step 1e in the emission methodology involves determining hot soak emission changes for the

Walkway to Gateway. These changes are calculated using the following formula:

HCHSK = (TRIPSTOTAL * TRIP,LDGV * HSKLDGV) + (TRIPSTOTAL * TRIP,LDGT1 * HSKLDGT1)

& In the formula, HCHSK is the change in hot soak emissions, TRIPSTOTAL is the

total change in trips, and HSK is the hot soak emission factor in grams per trip. 

(Note: Hot soak emissions are HC emissions only.)

TRIPSTOTAL = NETRPW,P + NETRPW,OP + NETRPNW,P + NETRPNW,OP. 

Thus, TRIPSTOTAL = 0 + 0 + 0 + -419 = -419.

Using national default data from MOBILE, HCHSK = (-419 * 0.785 * 3.06) + (-419 * 0.215 

* 3.60) = -1,331. Summarizing this result, the Walkway to Gateway results in a reduction in hot soak

emissions of 1,331 grams per day.

Step 1f in the emission methodology involves determining diurnal emission changes for the

Walkway to Gateway. These changes are calculated for a given vehicle class using the following

formulas:

HCDNL,NW = 0.676 * (NETRPNW,P + NETRPNW,OP) / TPDNW * TRIP * (WDI - MDI)
37

HCDNL = HCDNL,W,LDGV + HCDNL,NW,LDGV + HCDNL,W,LDGT1 + HCDNL,NW,LDGT1

& In the formulas, HCDNL,NW is the change in diurnal emissions associated with

non-work trips, and HCDNL is the total change in diurnal emissions. TPDNW 

is the number of non-work trips per day per vehicle. WDI is the weighted

diurnal emission factor in grams, and MDI is the multi-day diurnal emission

factor in grams. The other parameters in the formulas are defined in earlier steps

of the methodology. (Note: Diurnal emissions are HC emissions only.)

TPDNW is assumed to equal to TGN from Step 3 of the “Travel Activity Effects” section above,

and thus equals 1.0.

Using national default data from MOBILE, HCDNL,NW,LDGV = 0.676 * (0 + -419) / 1 * 0.785 

* (3.30 - 6.04) = 609, HCDNL,NW,LDGT1 = 0.676 * (0 + -419) / 1 * 0.215 * (5.11 - 15.33) = 622, and

HCDNL = 0 + 609 + 0 + 622 = 1,231. Summarizing these results, the Walkway to Gateway results in 

a net increase in diurnal emissions of 1,231 grams per day.

Step 1g in the emission methodology involves calculating the total trip-related emission changes

for the Walkway to Gateway. These changes are calculated using the following formulas:

HCTRIP = HCCST + HCHST + HCHSK + HCDNL

NOxTRIP = NOxCST + NOxHST

COTRIP = COCST + COHST

& In the formulas, HCTRIP, NOxTRIP, and COTRIP are the total changes in HC,

NOx, and CO emissions, respectively, due to trip changes.

Using the data above, HCTRIP = -1,124 + -390 + -1,331 + 1,231 = -1,614. Summarizing this

result, the Walkway to Gateway results in a net decrease in trip-related HC emissions of 1,614 grams per

day. (Following the same methodology, total trip-related emission changes can also be determined for

NOx and CO.)

Emission Effects -- STEP 2 (VMT Changes)

Step 2 in the estimation of the emission effects for the Walkway to Gateway involves calculating

the effect of VMT changes on emissions. This step is broken down into four smaller steps (2a through

2d), which are outlined below.

Step 2a in the emission methodology involves estimating the distribution of VMT changes for

the Walkway to Gateway. These changes are calculated using the following formulas:

VMT,LDGV = VMTLDGV / (VMTLDGV + VMTLDGT1)

VMT,LDGT1 = 1 - VMT,LDGV

& In the formulas, VMT,LDGV is the fraction of TCM-affected VMT for light-duty

gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected VMT 

for light-duty gasoline trucks (LDGT1s), VMTLDGV is the fraction of total VMT 

in the region for LDGVs, and VMTLDGT1 is the fraction of total VMT in the

region for LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s

guidance document affect only LDGVs or LDGT1s. Thus, the sum of VMT,LDGV

and VMT,LDGT1 is typically equal to one.)
38

VMTLDGV and VMTLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are the national average default values used in MOBILE for VMT mix.

Using the data above, VMT,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and VMT,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the VMT affected by the Walkway to Gateway 

is by LDGVs, and 21.5% is by LDGT1s.

Step 2b in the emission methodology involves estimating hot-stabilized exhaust emission

changes for the Walkway to Gateway. These changes are calculated using the following formulas:

HCSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,HC,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,HC,OP)

NOxSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,NOx,OP) + (NETVMTOP * VMT,LDGT1 *

STBLDGT1,NOx,OP)

COSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,CO,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,CO,OP)

& In the formulas, HCSTB,OP, NOxSTB,OP, and COSTB,OP are the off-peak changes

in hot-stabilized emissions for HC, NOx, and CO, respectively. STBOP is the

hot-stabilized emission factor (in grams per mile) for each pollutant and vehicle

class for the off-peak period (during which average vehicle speed is assumed to

be 35 miles per hour). The other parameters in the formulas are defined in

earlier steps of the methodology.

Using national default data from MOBILE, HCSTB,OP = (-8,753 * 0.785 * 0.69) + (-8,753 

* 0.215 * 0.94) = -6,510. Summarizing this result, the Walkway to Gateway results in a reduction 

in off-peak hot-stabilized HC exhaust emissions of 6,510 grams per day. (Following the same

methodology, hot-stabilized exhaust emission changes can also be determined for NOx and CO.)

Step 2c in the emission methodology involves estimating VMT-related evaporative emission

changes for the Walkway to Gateway. These changes are calculated using the following formula:

HCVEVP,OP = (NETVMTOP * VMT,LDGV * VEVPLDGV,OP) + (NETVMTOP * VMT,LDGT1 * VEVPLDGT1,OP)

& In the formula, HCVEVP,OP is the change in off-peak evaporative emissions, and

VEVP is the VMT-related evaporative emission factor (in grams per mile) for

each vehicle class. The other parameters in the formula are defined in earlier

steps of the methodology. (Note: Evaporative emissions are HC emissions only.)

Using national default data from MOBILE, HCVEVP,OP = (-8,753 * 0.785 * 0.34) + (-8,753 

* 0.215 * 0.44) = -3,164. Summarizing this result, the Walkway to Gateway results in a reduction 

in off-peak evaporative emissions of 3,164 grams per day.

Step 2d in the emission methodology involves calculating the total VMT-related emission

changes for the Walkway to Gateway. These changes are calculated using the following formulas:

HCVMT = HCSTB,P + HCSTB,OP + HCVEVP,P + HCVEVP,OP

NOxVMT = NOxSTB,P + NOxSTB,OP

COVMT = COSTB,P + COSTB,OP

& In the formulas, HCVMT, NOxVMT, and COVMT are the total changes in HC,

NOx, and CO emissions, respectively, due to VMT changes.
39

Using the data above, HCVMT = 0 + -6,510 + 0 + -3,164 = -9,674. Summarizing this result, 

the Walkway to Gateway results in a net decrease in VMT-related HC emissions of 9,674 grams per day. 

(Following the same methodology, total VMT-related emission changes can also be determined for NOx

and CO.)

Emission Effects -- STEP 3 (Speed Changes)

Step 3 in the estimation of the emission effects for the Walkway to Gateway involves calculating

the effect of speed changes on emissions. This step is not necessary because, as estimated in Step 9

above, the Walkway to Gateway has no effect on vehicle speeds.

Emission Effects -- STEP 4 (Total)

Step 4 in the estimation of the emission effects for the Walkway to Gateway involves calculating

the total changes in HC, NOx, and CO emissions. These changes are calculated using the following

formulas:

 

HC = HCTRIP + HCVMT + HCSPD

NOx = NOxTRIP + NOxVMT + NOxSPD

CO = COTRIP + COVMT + COSPD

& In the formulas, HC, NOx, and CO are the total changes in HC, NOx, 

and CO emissions, respectively, due to the TCM program.

Using the data above, HC = -1,614 + -9,674 + 0 = -11,288. Summarizing this result, 

the Walkway to Gateway results in a net decrease in HC emissions of 11,288 grams per day, 

or approximately 0.011 tons per day. (Following the same methodology, total emission changes 

can also be determined for NOx and CO.)
40

Phase 1: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

Example 4: Brevard County Vanpool Service

General Description

Brevard County, located along the eastern Florida coastline, has been operating an innovative

vanpool program for more than 14 years. The vanpool program, which provides commuter services 

and social service agency transportation needs to area residents, began in 1983 with six vans and by 1996

had grown to a total of 95 vans (44 of which are used for commuting). The program is administered by

Space Coast Area Transit (SCAT), in conjunction with a private, for-profit company called VPSI, Inc.

Data Sources

& Interview with Jim Leisenfelt, Program Director, SCAT, February 20, 1997.

& Interview with George Gaudy, VPSI, Inc., Brevard County, February 21, 1997.

& 1990 U.S. Census data.

& 1996 Statistical Abstract of the United States.

& Texas Transportation Institute web page.

Phase 1: Travel Activity Effects

Step 1 in the estimation of travel activity

effects for the Brevard County Vanpool Service

involves an assessment of the potential trip

effects from the program. For ridesharing

programs, these potential effects are calculated

using the following formula:

PT = N * F / D * 2

& In the formula, PT is the

potential effect on trips,

N is the number of

participants in the

ridesharing program, 

F is the frequency of

participation (in days per

week), and D is the

average number of

commute days per week.

The appropriate value for N is determined from data obtained from interviews with program

officials. A total of 44 vans are leased to commuters, and each van seats 11 people (1 driver and 10

passengers). Thus, the greatest number of participants in the program at any one time is equal to 484

(i.e., 44 * 11).

This analysis assumes that participants use the vanpools for transportation to work every day. 

Thus, the value of F is assumed to be 5.
41

The value for D is 5, based on the fact that there are five workdays per week.

Using the data above, PT = 484 * 5 / 5 * 2 = 968. Thus, the potential number of trips reduced

per day by the Brevard County Vanpool Service is 968.

Step 2 in the travel activity methodology involves estimating the direct work and non-work trip

reductions from the Brevard County Vanpool Service. Whereas the potential trip reductions calculated

in Step 1 represent the total number of trips that might be reduced by a TCM program, direct trip

reductions measure the number of trips that actually are reduced and, thus, can be less than potential trip

reductions (e.g., if a participant in the program was previously part of a carpool). Direct trip reductions

are calculated using the following formulas:

TRIPSD =  * PT

TRIPSD,W = 7 * TRIPSD

TRIPSD,NW = (1 - 7) * TRIPSD

& In the formulas, TRIPSD is the total direct trip reduction, PT is (as above) the

potential trip reductions, TRIPSD,W is the direct work trip reduction,

TRIPSD,NW is the direct non-work trip reduction,  is the fraction of program

participants who make a direct trip change, and 7 is the fraction of trip effects

that are work-related.

For ridesharing,  is defined as -[NOLD + NEW * (NCAR - 1) / NCAR] / AVO, where NOLD 

is the fraction of vanpoolers who join an existing vanpool and do not drive to a park and ride lot, NEW 

is the fraction of vanpoolers who form new vanpools and do not drive to a park and ride lot, NCAR is the

average number of people in a vanpool, and AVO is average vehicle occupancy. Assuming that each

vanpool is started by one person, all vans are full, and 5% of vanpoolers drive to park and ride lots,

NOLD and NEW values are 0.864 and 0.086, respectively. NCAR is 11, which includes 1 driver and 

10 passengers.

The value used for AVO is based on the following information from 1990 U.S. Census data for

Brevard County: approximately 83% of work trips are in single occupancy vehicles (SOVs) (AVO = 1),

approximately 13% of work trips are in carpools (AVO = 2.28), 2% of work trips are walking, 0.1% use

buses (AVO assumed to be 15), and less than 2% of work trips are made using motorcycles, bicycles, and

taxicabs combined. Thus, AVO = (0.83 + 0.13 + 0.02 + 0.001 + 0.02 ) / [(0.83 / 1) + (0.13 / 2.28) 

+ (0.001 / 15)] = 1.13. Using the values for NOLD, NEW, NCAR, and AVO,  = -[0.864 + 0.086 

* (11 - 1) / 11] / 1.13 = -0.83.

Table 2-5 in EPA’s TCM guidance document indicates that, for ridesharing, the parameter 7 

is equal to 1. This is because ridesharing directly affects work trips only.

Using the data above, TRIPSD = -0.83 * 968 = -803, TRIPSD,W = 1 * -803 = -803 and

TRIPSD,NW = (1 - 1) * -803 = 0. Summarizing these results, the Brevard County Vanpool Service 

is responsible for directly reducing 803 trips per day, all of which are work-related.

Step 3 in the travel activity methodology involves estimating the actual indirect trip increases

(for both work and non-work trips) from the Brevard County Vanpool Service. Indirect trip increases 

are secondary effects that typically result when vehicles normally used for commuting are left at home. 

These increases are calculated using the following formulas:

TRIPSI,W = INCW,H * -TRIPSD / 2
42

TRIPSI,NW = INCN,H * -TRIPSD / 2

& In the formulas, TRIPSI,W is the indirect work trip increase, TRIPSI,NW is the

indirect non-work trip increase, and INCW,H and INCN,H are the rates of increased

SOV work and non-work trip making by household members of TCM

participants who leave their vehicles at home. The other parameter in the

formulas is defined in an earlier step of the methodology.

INCW,H is defined as NV * SHR * (SIZE - 1) * EMP * TGW, where NV is the fraction of the

population that does not own a vehicle (Note: This analysis interprets this parameter to mean the

percentage of drivers without a vehicle, which is estimated as the percentage of vehicle-owning

households in the program area that have only one vehicle.), SHR is the fraction of shared mode trips,

SIZE is average household size, EMP is the fraction of the population that is employed, and TGW is the

work trip generation rate for SOV users. Based on 1990 U.S. Census data for Brevard County, NV 

is assumed to be 41%, SHR is assumed to be 14%, SIZE is assumed to be 2.43, and EMP is assumed 

to be 58%. TGW is assumed to equal 2. Based on these numbers, INCW,H = 0.41 * 0.14 * (2.43 - 1) * 0.58

* 2 = 0.10.

INCN,H = NV * SHR * (SIZE - 1) * UNEMP * TGN, where NV, SHR, and SIZE are as defined

above, UNEMP is the fraction of the population that is not employed, and TGN is the non-work trip

generation rate for SOV users. UNEMP is simply (1 - EMP) and thus equals 42%. TGN is assumed to 

be the same as TGW (i.e., 2). Based on these numbers, INCN,H = 0.41 * 0.14 * (2.43 - 1) * 0.42 * 2 = 0.07.

Using the data above, TRIPSI,W = 0.10 * -(-803) / 2 = 40, and TRIPSI,NW = 0.07 * -(-803) / 2 

= 28. Summarizing these results, the Brevard County Vanpool Service is indirectly responsible for an

increase of 40 work trips per day and 28 non-work trips per day.

Step 4 in EPA’s methodology for estimating travel activity effects of TCMs, which involves

determining direct peak and off-peak period trip shifts, does not apply to ridesharing programs. 

Thus, Step 4 is not relevant to the analysis of the Brevard County Vanpool Service.

Step 5 in the travel activity methodology involves estimating the net trip changes from the

Brevard County Vanpool Service as distributed between work and non-work trips and peak and off-peak

periods. These changes are calculated using the following formulas:

NETRPW,P = 7 * TRIPSS,P + PKW * (TRIPSD,W + TRIPSI,W)

NETRPW,OP = 7 * TRIPSS,OP + (1 - PKW) * (TRIPSD,W + TRIPSI,W)

NETRPNW,P = (1 - 7) * TRIPSS,P + PKNW * (TRIPSD,NW + TRIPSI,NW)

NETRPNW,OP = (1 - 7) * TRIPSS,OP + (1 - PKNW) * (TRIPSD,NW + TRIPSI,NW)

& In the formulas, NETRPW,P is the net work trip change in the peak period,

NETRPW,OP is net work trip change in the off-peak period, NETRPNW,P is the

net non-work trip change in the peak period, and NETRPNW,OP is the net nonwork trip change in the off-peak period. TRIPSS,P is the change in peak period

trips, and TRIPSS,OP is the change in off-peak period trips. PKW is the observed

fraction of work trips during the peak period, and PKNW is the observed fraction

of non-work trips during the peak period. The other parameters in the formulas

are defined in earlier steps of the methodology.

Because there are no trip shifts associated with ridesharing (see Step 4), TRIPSS,P and

TRIPSS,OP are each equal to 0.
43

The values used for PKW and PKNW are 0.6 and 0.3, respectively, based on an example shown 

in the TCM guidance document.

Using the data above, NETRPW,P = 0 + 0.6 * (-803 + 40) = -458, NETRPW,OP = 0 + (1 - 0.6) 

* (-803 + 40) = -305, NETRPNW,P = 0 + 0.3 * (0 + 28) = 8, and NETRPNW,OP = 0 * (1 - 0.3) * (0 + 28)

= 20. Summarizing these results, the Brevard County Vanpool Service results in net decreases in peak

and off-peak work trips of 458 per day and 305 per day, respectively. The program also results in

increases in peak and off-peak non-work trips of 8 per day and 20 per day, respectively.

Step 6 in the travel activity methodology involves estimating the peak and off-peak VMT

changes due to the trip changes from the Brevard County Vanpool Service. These changes are calculated

using the following formulas:

VMTP = (NETRPW,P * DISTW) + (NETRPNW,P * DISTNW)

VMTOP = (NETRPW,OP * DISTW) + (NETRPNW,OP * DISTNW)

& In the formulas, VMTP is the change in peak-period VMT due to trip changes,

VMTOP is the change in off-peak VMT due to trip changes, DISTW is the

average VMT per trip for work trips, and DISTNW is the average VMT per trip

for non-work trips. The other parameters in the formulas are defined in earlier

steps of the methodology.

DISTW is 50 miles per trip, as estimated by a vanpool service official. DISTNW is assumed 

to be 8.1 miles, based on data from the 1996 Statistical Abstract of the United States.

Using the data above, VMTP = (-458 * 50) + (8 * 8.1) = -22,835 and VMTOP = (-305 * 50) 

+ (20 * 8.1) = -15,088. Summarizing these results, the Brevard County Vanpool Service reduces peakperiod VMT by 22,835 miles per day due to trip changes and reduces off-peak VMT by 15,088 miles per

day due to trip changes.

Step 7 in the travel activity methodology involves estimating the VMT changes due to trip length

changes resulting from the Brevard County Vanpool Service. These changes are calculated using the

following formula:

VMTL,W =  * PT * -(DISTW - DISTnew)

VMTL,NW =  * PT * -(DISTNW - DISTnew)

& In the formulas, VMTL,W is the change in VMT due to work trip length

changes, VMTL,NW is the change in VMT due to non-work trip length changes,

 is fraction of program participants who change their trip length, and DISTnew 

is the new work or non-work trip length. The other parameters in the formulas

are defined in earlier steps of the methodology.

For ridesharing, the TCM guidance indicates that  is equal to 1 - NOLD - NEW. As noted 

in Step 2 above, NOLD and NEW are 0.864 and 0.086, respectively. Thus,  = 1 - 0.864 - 0.086 = 0.05.

DISTnew for work trips is assumed to be 5 miles. Because the Brevard County Vanpool Service

does not directly affect non-work trips, DISTnew for non-work trips is equal to DISTNW.

Using the data above, VMTL,W = 0.05 * 968 * -(50 - 5) = -2,178, and VMTL,NW = 0.05 * 968 
44

* -(8.1 - 8.1) = 0. Summarizing these results, the Brevard County Vanpool Service reduces work-related

VMT by 2,178 miles per day due to trip length changes but does not reduce non-work VMT due to trip

length changes.

Step 8 in the travel activity methodology involves estimating the total peak and off-peak VMT

changes resulting from the Brevard County Vanpool Service. These changes are calculated using the

following formulas:

NETVMTP = VMTP + PKW * VMTL,W + PKNW * VMTL,NW

NETVMTOP = VMTOP + (1 - PKW) * VMTL,W + (1 - PKNW) * VMTL,NW

& In the formulas, NETVMTP is the total change in peak period VMT, and

NETVMTOP is the total change in off-peak VMT. The other parameters in the

formulas are defined in earlier steps of the methodology.

Using the data above, NETVMTP = -22,835 + 0.6 * -2,178 + 0.3 * 0 = -24,142 and

NETVMTOP = -15,088 + (1 - 0.6) * -2,178 + (1 - 0.3) * 0 = -15,959. Summarizing these results, 

the Brevard County Vanpool Service reduces peak-period VMT by a total of 24,142 miles per day 

and off-peak VMT by a total of 15,959 miles per day.

Step 9 in the travel activity methodology involves estimating peak and off-peak speed changes

resulting from the Brevard County Vanpool Service. These changes are calculated using the following

formulas:

SPDP = (NETVMTP / TOTVMTP) * P

SPDOP = (NETVMTOP / TOTVMTOP) * OP

& In the formulas, SPDP is the percentage change in peak-period speeds, SPDOP

is the change in off-peak speeds, TOTVMTP is total peak-period VMT for the

program area, TOTVMTOP is total off-peak VMT for the program area, P is the

elasticity of peak-period speed with respect to volume, and OP is the elasticity 

of off-peak speed with respect to volume. The other parameters in the formulas

are defined in earlier steps of the methodology.

Total VMT for Brevard County is assumed to be approximately 12 million miles per day. 

This assumption is derived using data from the Texas Transportation Institute on VMT in the

nearby Orlando area. Assuming that 50 percent of travel activity occurs during peak periods and 50

percent occurs during off-peak periods, TOTVMTP and TOTVMTOP are each approximately 6 million

miles per day.

The parameter P is assumed to be -0.75, based on an example provided in the TCM guidance

document. The parameter OP is assumed to be 0, because changes in off-peak VMT are not likely 

to affect vehicle speeds (i.e., due to a lack of congestion).

Using the data above, SPDP = -24,142 / 6,000,000 * -0.75 = 0.003 and SPDOP = -15,959 

/ 6,000,000 * 0 = 0. Summarizing these results, the Brevard County Vanpool Service increases 

peak-period speeds by approximately 0.3% but has no effect on off-peak speeds.
45

Phase 2: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Step 4: Summation of emission effects

Phase 2: Emission Effects -- STEP 1 (Trip

Changes)

Step 1 in the estimation of the emission

effects for the Brevard County Vanpool Service

involves calculating the effect of trip changes on

emissions. This step is broken down into seven

smaller steps (1a through 1g), which are outlined

below.

Step 1a in the emission methodology

involves estimating the distribution of trip

changes for the Brevard County Vanpool

Service. These changes are calculated using the

following formulas:

TRIP,LDGV = TRIPLDGV / (TRIPLDGV + TRIPLDGT1)

TRIP,LDGT1 = 1 - TRIP,LDGV

• In the formulas, TRIP,LDGV 

is the fraction of TCM-affected

trips taken by light-duty gasoline

vehicles (LDGVs), TRIP,LDGT1 

is the fraction of TCM-affected

trips taken by light-duty gasoline

trucks (LDGT1s), TRIPLDGV 

is the fraction of total trips in 

the region taken by LDGVs, 

and TRIPLDGT1 is the fraction 

of total trips in the region taken

by LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s guidance document

affect only LDGVs or LDGT1s. Thus, the sum of TRIP,LDGV and TRIP,LDGT1 is typically

equal to one.)

TRIPLDGV and TRIPLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are based on the national average default values used in MOBILE.

Using the data above, TRIP,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and TRIP,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the trips affected by the Brevard County Vanpool Service

are taken by LDGVs, and 21.5% are taken by LDGT1s.

Step 1b in the emission methodology involves calculating cold-start and hot-start trip changes

for the Brevard County Vanpool Service. These changes are calculated using the following formulas:

TRIPSCST = CST,W * (NETRPW,P + NETRPW,OP) + CST, NW * (NETRPNW,P + NETRPNW,OP)

TRIPSHST = (1 - CST,W) * (NETRPW,P + NETRPW,OP) + (1 - CST,NW) * (NETRPNW,P +

NETRPNW,OP)

& In the formulas, TRIPSCST is the number of cold-start trip changes, TRIPSHST

is the number of hot-start trip changes, CST,W is the fraction of work trips begun

in the cold-start mode, and CST, NW is the fraction of non-work trips begun in the
46

cold-start mode. The other parameters in the formulas are defined in earlier

steps of the methodology.

Because work trips are mostly cold-start trips, the guidance calls for CST,W to be set equal to 1. 

The guidance also suggests that CST,NW be set equal to 0.43, which is the default fraction of cold starts

used in the Federal Test Procedure (FTP).

Using the data above, TRIPSCST = 1 * (-458 + -305) + 0.43 * (8 + 20) = -751 and TRIPSHST

= (1 - 1) * (-458 + -305) + (1 - 0.43) * (8 + 20) = 16. Summarizing these results, the Brevard County

Vanpool Service results in a reduction of 751 cold-start trips per day and an increase of 16 hot-start trips

per day.

Step 1c in the emission methodology involves determining cold-start and hot-start emission

factors. These changes are calculated for a given pollutant and vehicle class using the following

formulas:

CST = (EXH100%CST,26MPH - EXH100%STB,26MPH) * 3.59

HST = (EXH100%HST,26MPH - EXH100%STB,26MPH) * 3.59

& In the formulas, CST is the cold-start emission factor in grams per trip, HST 

is the hot-start emission factor in grams per trip, and EXH is the MOBILE

emission factor in grams per mile. The 3.59 factor is the FTP driving cycle 

trip-start miles per trip, and 26 miles per hour is the speed for the start portion 

of the FTP driving cycle. (Note: The subscripts on EXH refer to the operating

conditions and speed at which MOBILE evaluates EXH. For example,

“100%CST,26MPH” indicates 100% cold-start operating mode at 26 miles 

per hour vehicle speed.)

Using national default data from MOBILE, CSTLDGV,HC = (2.55 - 0.95) * 3.59 = 5.74 grams per

trip, CSTLDGT1,HC = (3.59 - 1.34) * 3.59 = 8.08 grams per trip, HSTLDGV,HC = (1.35 - 0.95) * 3.59 = 1.44

grams per trip, and HSTLDGT1,HC = (1.99 - 1.34) * 3.59 = 2.33 grams per trip. (Following the same

methodology, the cold-start and hot-start emission factors can also be determined for NOx and CO.)

Step 1d in the emission methodology involves determining cold-start and hot-start emission

changes for the Brevard County Vanpool Service. These changes are calculated using the following

formulas:

HCCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,HC) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,HC)

HCHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,HC) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,HC)

NOxCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,NOx) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,NOx)

NOxHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,NOx) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,NOx)

COCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,CO) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,CO)

COHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,CO) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,CO)

& In the formulas, HCCST, NOxCST, and COCST are the changes in cold-start

emissions for HC, NOx, and CO, respectively; and HCHST, NOxHST, and

COHST are the changes in hot-start emissions for HC, NOx, and CO,

respectively. The other parameters in the formulas are defined in earlier steps of

the methodology.
47

Using national default data from MOBILE, HCCST = (-751 * 0.785 * 5.74) + (-751 * 0.215 

* 8.08) = -4,689 and HCHST = (16 * 0.785 * 1.44) + (16 * 0.215 * 2.33) = 26. Summarizing these

results, the Brevard County Vanpool Service results in a reduction in cold-start HC emissions of 4,689

grams per day and an increase in hot-start HC emissions of 26 grams per day. (Following the same

methodology, the cold-start and hot-start emission changes can also be determined for NOx and CO.)

Step 1e in the emission methodology involves determining hot soak emission changes for the

Brevard County Vanpool Service. These changes are calculated using the following formula:

HCHSK = (TRIPSTOTAL * TRIP,LDGV * HSKLDGV) + (TRIPSTOTAL * TRIP,LDGT1 * HSKLDGT1)

& In the formula, HCHSK is the change in hot soak emissions, TRIPSTOTAL is the

total change in trips, and HSK is the hot soak emission factor in grams per trip. 

(Note: Hot soak emissions are HC emissions only.)

TRIPSTOTAL = NETRPW,P + NETRPW,OP + NETRPNW,P + NETRPNW,OP. 

Thus, TRIPSTOTAL = -458 + -305 + 8 + 20 = -735.

Using national default data from MOBILE, HCHSK = (-735 * 0.785 * 3.06) + (-735 * 0.215 

* 3.60) = -2,334. Summarizing this result, the Brevard County Vanpool Service results in a reduction 

in hot soak emissions of 2,334 grams per day.

Step 1f in the emission methodology involves determining diurnal emission changes for the

Brevard County Vanpool Service. These changes are calculated for a given vehicle class using the

following formulas:

HCDNL,W = 0.676 * (NETRPW,P + NETRPW,OP) / TPDW * TRIP * (WDI - MDI)

HCDNL,NW = 0.676 * (NETRPNW,P + NETRPNW,OP) / TPDNW * TRIP * (WDI - MDI)

HCDNL = HCDNL,W,LDGV + HCDNL,NW,LDGV + HCDNL,W,LDGT1 + HCDNL,NW,LDGT1

& In the formulas, HCDNL,W is the change in diurnal emissions associated with

work trips, HCDNL,NW is the change in diurnal emissions associated with nonwork trips, and HCDNL is the total change in diurnal emissions. TPDW is the

number of work trips per day per vehicle, and TPDNW is the number of non-work

trips per day per vehicle. WDI is the weighted diurnal emission factor in grams,

and MDI is the multi-day diurnal emission factor in grams. The other parameters

in the formulas are defined in earlier steps of the methodology. (Note: Diurnal

emissions are HC emissions only.)

The value used for TPDW is 2, since a commuter makes typically makes two work trips per day

(i.e., one trip from home to work, one trip from work to home). TPDNW is equal to TGN from Step 3 

of the “Travel Activity Effects” section above, and thus equals 2.

Using national default data from MOBILE, HCDNL,W,LDGV = 0.676 * (-458 + -305) / 2 * 0.785 

* (3.30 - 6.04) = 555, HCDNL,NW,LDGV = 0.676 * (8 + 20) / 2 * 0.785 * (3.30 - 6.04) = -20, HCDNL,W,LDGT1

= 0.676 * (-458 + -305) / 2 * 0.215 * (5.11 - 15.33) = 567, HCDNL,NW,LDGT1 = 0.676 * (8 + 20) / 2 * 0.215

* (5.11 - 15.33) = -21, and HCDNL = 555 + -20 + 567 + -21 = 1,081. Summarizing these results, the

Brevard County Vanpool Service results in an increase in diurnal emissions of 1,081 grams per day.
48

Step 1g in the emission methodology involves calculating the total trip-related emission changes

for the Brevard County Vanpool Service. These changes are calculated using the following formulas:

HCTRIP = HCCST + HCHST + HCHSK + HCDNL

NOxTRIP = NOxCST + NOxHST

COTRIP = COCST + COHST

& In the formulas, HCTRIP, NOxTRIP, and COTRIP are the total changes in HC,

NOx, and CO emissions, respectively, due to trip changes.

Using the data above, HCTRIP = -4,689 + 26 + -2,334 + 1,081 = -5,916. Summarizing this result,

the Brevard County Vanpool Service results in a net decrease in trip-related HC emissions of 5,916

grams per day. (Following the same methodology, total trip-related emission changes can also be

determined for NOx and CO.)

Emission Effects -- STEP 2 (VMT Changes)

Step 2 in the estimation of the emission effects for the Brevard County Vanpool Service involves

calculating the effect of VMT changes on emissions. This step is broken down into four smaller steps

(2a through 2d), which are outlined below.

Step 2a in the emission methodology involves estimating the distribution of VMT changes for

the Brevard County Vanpool Service. These changes are calculated using the following formulas:

VMT,LDGV = VMTLDGV / (VMTLDGV + VMTLDGT1)

VMT,LDGT1 = 1 - VMT,LDGV
49

& In the formulas, VMT,LDGV is the fraction of TCM-affected VMT for light-duty

gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected VMT 

for light-duty gasoline trucks (LDGT1s), VMTLDGV is the fraction of total VMT

in the region for LDGVs, and VMTLDGT1 is the fraction of total VMT in the

region for LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s

guidance document affect only LDGVs or LDGT1s. Thus, the sum of VMT,LDGV

and VMT,LDGT1 is typically equal to one.)

VMTLDGV and VMTLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are the national average default values used in MOBILE for VMT mix.

Using the data above, VMT,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and VMT,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the VMT affected by the Brevard County Vanpool Service

is by LDGVs, and 21.5% is by LDGT1s.

Step 2b in the emission methodology involves estimating hot-stabilized exhaust emission

changes for the Brevard County Vanpool Service. These changes are calculated using the following

formulas:

HCSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,HC,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,HC,P)

HCSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,HC,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,HC,OP)

NOxSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,NOx,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,NOx,P)

NOxSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,NOx,OP) + (NETVMTOP * VMT,LDGT1 *

STBLDGT1,NOx,OP)

COSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,CO,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,CO,P)

COSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,CO,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,CO,OP)

& In the formulas, HCSTB,P, NOxSTB,P, and COSTB,P are the peak-period changes

in hot-stabilized emissions for HC, NOx, and CO, respectively; and HCSTB,OP,

NOxSTB,OP, and COSTB,OP are the off-peak changes in hot-stabilized emissions

for HC, NOx, and CO, respectively. STBP is the hot-stabilized emission factor

(in grams per mile) for each pollutant and vehicle class for the peak period

(during which average vehicle speed is assumed to be 20 miles per hour), 

and STBOP is the hot-stabilized emission factor (in grams per mile) for each

pollutant and vehicle class for the off-peak period (during which average vehicle

speed is assumed to be 35 miles per hour). The other parameters in the formulas

are defined in earlier steps of the methodology.

Using national default data from MOBILE, HCSTB,P = (-24,142 * 0.785 * 1.23) + (-24,142 

* 0.215 * 1.77) = -32,498 and HCSTB,OP = (-15,959 * 0.785 * 0.69) + (-15,959 * 0.215 * 0.94) = -11,870. 

Summarizing these results, the Brevard County Vanpool Service results in a reduction in peak-period

hot-stabilized HC exhaust emissions of 32,498 grams per day and a reduction in off-peak hot-stabilized

HC exhaust emissions of 11,870 grams per day. (Following the same methodology, hot-stabilized

exhaust emission changes can also be determined for NOx and CO.)

Step 2c in the emission methodology involves estimating VMT-related evaporative emission

changes for the Brevard County Vanpool Service. These changes are calculated using the following

formulas:

HCVEVP,P = (NETVMTP * VMT,LDGV * VEVPLDGV,P) + (NETVMTP * VMT,LDGT1 * VEVPLDGT1,P)
50

HCVEVP,OP = (NETVMTOP * VMT,LDGV * VEVPLDGV,OP) + (NETVMTOP * VMT,LDGT1 * VEVPLDGT1,OP)

& In the formulas, HCVEVP,P is the change in peak-period evaporative emissions,

HCVEVP,OP is the change in off-peak evaporative emissions, and VEVP is the

VMT-related evaporative emission factor (in grams per mile) for each vehicle

class and time period (peak or off-peak). The other parameters in the formulas

are defined in earlier steps of the methodology. (Note: Evaporative emissions

are HC emissions only.)

Using national default data from MOBILE, HCVEVP,P = (-24,142 * 0.785 * 0.44) + (-24,142 

* 0.215 * 0.53) = -11,090 and HCVEVP,OP = (-15,959 * 0.785 * 0.34) + (-15,959 * 0.215 * 0.44) = -5,769. 

Summarizing these results, the Brevard County Vanpool Service results in a reduction in peak-period

evaporative emissions of 11,090 grams per day and a reduction in off-peak evaporative emissions of

5,769 grams per day.

Step 2d in the emission methodology involves calculating the total VMT-related emission

changes for the Brevard County Vanpool Service. These changes are calculated using the following

formulas:

HCVMT = HCSTB,P + HCSTB,OP + HCVEVP,P + HCVEVP,OP

NOxVMT = NOxSTB,P + NOxSTB,OP

COVMT = COSTB,P + COSTB,OP

& In the formulas, HCVMT, NOxVMT, and COVMT are the total changes in HC,

NOx, and CO emissions, respectively, due to VMT changes.

Using the data above, HCVMT = -32,498 + -11,870 + -11,090 + -5,769 = -61,227. Summarizing

this result, the Brevard County Vanpool Service results in a net decrease in VMT-related HC emissions

of 61,227 grams per day. (Following the same methodology, total VMT-related emission changes can

also be determined for NOx and CO.)

Emission Effects -- STEP 3 (Speed Changes)

Step 3 in the estimation of the emission effects for the Brevard County Vanpool Service involves

calculating the effect of speed changes on emissions. This step is broken down into four smaller steps

(3a through 3d), which are outlined below.

Step 3a in the emission methodology involves estimating the speeds associated with the Brevard

County Vanpool Service. These speeds are calculated using the following formulas:

SPEEDP,TCM = SPEEDP,BASE * (1 + SPDP)

SPEEDOP,TCM = SPEEDOP,BASE * (1 + SPDOP)

& In the formulas, SPEEDP,TCM is the peak-period speed after implementation of the

TCM, SPEEDOP,TCM is the off-peak speed after implementation of the TCM,

SPEEDP,BASE is the peak-period speed prior to implementation of the TCM, and

SPEEDOP,BASE is the off-peak speed prior to implementation of the TCM. The

other parameters in the formulas are defined in earlier steps of the methodology.

Based on data for the national default fleet, SPEEDP,BASE is assumed to be 20 miles per hour, 

and SPEEDOP,BASE is assumed to be 35 miles per hour. (Note: These default assumptions for speeds 
51

are likely to be unrealistic for Brevard County. The analysis might be similar, however, if more realistic

values were used.)

Using the data above, SPEEDP,TCM = 20 * (1 + 0.003) = 20.06 and SPEEDOP,TCM = 35 * (1 + 0) 

= 35. Summarizing these results, peak-period speeds have slightly increased from 20 miles per hour 

to 20.06 miles per hour due to the Brevard County Vanpool Service. Off-peak speeds have not changed

due to the service.

Step 3b in the emission methodology involves estimating the total VMT for the program area

after implementation of the Brevard County Vanpool Service. These VMT figures are calculated using

the following formulas:

VMTP,TCM = TOTVMTP + NETVMTP

VMTOP,TCM = TOTVMTOP + NETVMTOP

& In the formulas, VMTP,TCM is the total peak-period VMT in the program area

after implementation of the TCM, and VMTOP,TCM is the total off-peak VMT 

in the program area after implementation of the TCM. The other parameters 

in the formulas are defined in earlier steps of the methodology.

Using data from Step 9 of the “Travel Activity Effects” section above, VMTP,TCM = 6,000,000 

+ -24,142 = 5,975,858 and VMTOP,TCM = 6,000,000 + -15,959 = 5,984,041. Summarizing these results,

peak-period VMT has decreased from 6,000,000 miles per day to 5,975,858 miles per day due 

to the Brevard County Vanpool Service. Off-peak VMT has decreased from 6,000,000 miles per day 

to 5,984,041 miles per day due to the service.

Step 3c in the emission methodology involves estimating peak-period and off-peak emission

changes due to changes in vehicle speeds. These changes are calculated using the following formulas:

HCSPD,P = VMTP,TCM * (STBFLT,HC,P,TCM + RNLFLT,P,TCM) - VMTP,TCM * (STBFLT,HC,P,BASE + RNLFLT,P,BASE)

HCSPD,OP = VMTOP,TCM * (STBFLT,HC,OP,TCM + RNLFLT,OP,TCM) - VMTOP,TCM * (STBFLT,HC,OP,BASE + RNLFLT,OP,BASE)

NOxSPD,P = VMTP,TCM * (STBFLT,NOx,P,TCM - STBFLT,NOx,P,BASE)

NOxSPD,OP = VMTOP,TCM * (STBFLT,NOx,OP,TCM - STBFLT,NOx,OP,BASE)

COSPD,P = VMTP,TCM * (STBFLT,CO,P,TCM - STBFLT,CO,P,BASE)

COSPD,OP = VMTOP,TCM * (STBFLT,CO,OP,TCM - STBFLT,CO,OP,BASE)
52

& In the formulas, HCSPD,P, NOxSPD,P, and COSPD,P are the peak-period changes

in emissions for HC, NOx, and CO, respectively, due to a change in speeds; and

HCSPD,OP, NOxSPD,OP, and COSPD,OP are the off-peak changes in emissions for

HC, NOx, and CO, respectively, due to a change in speeds. STBFLT is the fleetwide hot-stabilized emission factor (in grams per mile) for each pollutant, time

period (i.e., peak or off-peak), and scenario (i.e., base or TCM). RNLFLT is the

fleet-wide running loss emission factor (in grams per mile) for each time period

and scenario. The other parameters in the formulas are defined in earlier steps 

of the methodology.

Based on data showing the relationship between vehicle speed and emissions, this analysis

assumes that the elasticity of STBFLT with respect to speed is -1 for HC, 0 for NOx, and -1 for CO. 

Thus, a 1% increase in speed is assumed to result in a 1% decrease in HC and CO emissions (on a grams

per mile basis) and no change in NOx emissions. The elasticity of RNLFLT with respect to speed is also

assumed to be -1. 

Using national default data from MOBILE, HCSPD,P = 5,975,858 * (1.671 + 0.211) - 5,975,858 

* (1.676 + 0.212) = -35,855 and HCSPD,OP = 5,984,041 * (1.938 + 0.120) - 5,984,041 * (1.938 + 0.120)

 = 0. Summarizing these results, the Brevard County Vanpool Service results in a decrease in speedrelated HC emissions of 35,855 grams per day for the peak period but does not change speed-related HC

emissions for the off-peak period. (Following the same methodology, the peak-period and off-peak

emission changes due to changes in speeds can also be determined for NOx and CO.)

Step 3d in the emission methodology involves calculating the total speed-related emission

changes for the Brevard County Vanpool Service. These changes are calculated using the following

formulas:

HCSPD = HCSPD,P + HCSPD,OP

NOxSPD = NOxSPD,P + NOxSPD,OP

COSPD = COSPD,P + COSPD,OP

& In the formulas, HCSPD, NOxSPD, and COSPD are the total changes in HC,

NOx, and CO emissions, respectively, due to speed changes.

Using the data above, HCSPD = -35,855 + 0 = -35,855. Summarizing this result, the Brevard

County Vanpool Service results in a net decrease in speed-related HC emissions of 35,855 grams per day. 

(Following the same methodology, total speed-related emission changes can also be determined for NOx

and CO.)

Emission Effects -- STEP 4 (Total)

Step 4 in the estimation of the emission effects for the Brevard County Vanpool Service involves

calculating the total changes in HC, NOx, and CO emissions. These changes are calculated using the

following formulas:

 

HC = HCTRIP + HCVMT + HCSPD

NOx = NOxTRIP + NOxVMT + NOxSPD

CO = COTRIP + COVMT + COSPD

& In the formulas, HC, NOx, and CO are the total changes in HC, NOx, and

CO emissions, respectively, due to the TCM program.
53

Using the data above, HC = -5,916 + -61,227 + -35,855 = -102,998. Summarizing this result,

the Brevard County Vanpool Service results in a net decrease in HC emissions of 102,998 grams per day,

or approximately 0.11 tons per day. (Following the same methodology, total emission changes can also

be determined for NOx and CO.)
54

Phase 1: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

Example 5: Boulder HOP Shuttle Service

General Description

In 1989, transportation planners in Boulder, Colorado designed the HOP shuttle service in

response to commercial growth and the influx of traffic associated with the expansion. The goal of the

program was to provide an alternative to SOV driving, and therefore preserve the quality of the air and

prevent the construction of new roadways. The service was called the “HOP” because the name indicates

the ease with which a passenger may “hop” around Boulder to meetings, school, shopping centers, etc. 

The service consists of six medium-size buses that circulate in two directions on a loop connecting the

University of Colorado campus and retail district with downtown employment and retail areas and the

Crossroads Mall area.

(Note: This analysis excludes the extra trips caused by the HOP shuttle buses themselves. Thus, the net

effects on trips, VMT, speeds, and emissions will be smaller than shown here.)

Data Sources

& Interview with Penny Puskarich, Program Administrator, City of Boulder/Go Boulder, March 8,

1997.

& “HOP Shuttle Service Profile,” prepared by City of Boulder, Colorado, June 25, 1996.

& 1990 U.S. Census data.

& 1996 Statistical Abstract of the United States.

Phase 1: Travel Activity Effects

Step 1 in the estimation of travel activity

effects for the HOP service involves an

assessment of the potential trip effects from the

program. For this TCM, these potential effects

are calculated using the following user-defined

formula:

PT = N

& In the formula, 

PT is the potential effect

on trips per day, 

and N is the number 

of TCM participants.

The appropriate value of N is derived by dividing the number of people who use the HOP shuttle

service each year by 307, the number of days per year the HOP Shuttle Service operates (it does not

operate on Sundays and holidays). According to the “HOP Shuttle Service Profile,” approximately 

1.1 million riders used the service in 1996. Thus, PT = N = 1,100,000 / 307 = 3,583. Summarizing 

this result, the potential number of trips reduced per day by the HOP service is 3,583.

Step 2 in the travel activity methodology involves estimating the direct work and non-work trip

reductions from the HOP service. Whereas the potential trip reductions calculated in Step 1 represent 
55

the total number of trips that might be reduced by a TCM program, direct trip reductions measure the

number of trips that actually are reduced and, thus, can be less than potential trip reductions (e.g., if 

a HOP rider was previously walking to his or her HOP destination). Direct trip reductions are calculated

using the following formulas:

TRIPSD =  * PT

TRIPSD,W = 7 * TRIPSD

TRIPSD,NW = (1 - 7) * TRIPSD

& In the formulas, TRIPSD is the total direct trip reduction, PT is (as above) 

the potential trip reductions, TRIPSD,W is the direct work trip reduction,

TRIPSD,NW is the direct non-work trip reduction,  is the fraction of program

participants who make a direct trip change, and 7 is the fraction of trip effects

that are work-related.

For transit improvements,  is defined as -1 / AVO, where AVO is average vehicle occupancy. 

Assuming average vehicle occupancy for non-work trips is the same as work trips, the value used for

AVO is based on the following information from 1990 U.S. Census data for the City of Boulder: 

approximately 65% of work trips are in single occupancy vehicles (SOVs) (AVO = 1), approximately

10% of work trips are in carpools (AVO = 2.3), 11% of work trips are walking, 6% use buses (AVO

assumed to be 15), and less than 8% of work trips are made using other means. Thus, AVO = (0.65

 + 0.1 + 0.11 + 0.06 + 0.08 ) / [(0.65 / 1) + (0.1 / 2.3) + (0.06 / 15)] = 1.43. Using this value for AVO, 

 = -1 / 1.43 = -0.7.

Based on survey results from the “HOP Shuttle Service Profile,” approximately 20% of HOP

riders use the service for work travel. Thus, the parameter 7 is equal to 0.2. 

Using the data above, TRIPSD = -0.7 * 3,583 = -2,508, TRIPSD,W = 0.2 * -2,508 = -502, 

and TRIPSD,NW = (1 - 0.2) * -2,508 = -2,006. Summarizing these results, the HOP service is responsible

for directly reducing 502 work trips per day and 2,006 non-work trips per day.

Step 3 in the travel activity methodology involves estimating the actual indirect trip increases

(for both work and non-work trips) from the HOP service. Indirect trip increases are secondary effects

that typically result when vehicles normally used for commuting are left at home. These increases are

calculated using the following formulas:

TRIPSI,W = INCW,H * -TRIPSD / 2

TRIPSI,NW = INCN,H * -TRIPSD / 2

& In the formulas, TRIPSI,W is the indirect work trip increase, TRIPSI,NW is the

indirect non-work trip increase, and INCW,H and INCN,H are the rates of increased

SOV work and non-work trip making by household members of TCM

participants who leave their vehicles at home. The other parameter in the

formulas is defined in an earlier step of the methodology.

INCW,H is defined as NV * SHR * (SIZE - 1) * EMP * TGW, where NV is the fraction of the

population that does not own a vehicle (Note: This analysis interprets this parameter to mean the

percentage of drivers without a vehicle, which is estimated as the percentage of vehicle-owning

households in the program area that have only one vehicle.), SHR is the fraction of shared mode trips,

SIZE is average household size, EMP is the fraction of the population that is employed, and TGW is the

work trip generation rate for SOV users. Based on 1990 U.S. Census data for the City of Boulder, NV 
56

is assumed to be 34%, SHR is assumed to be 16%, SIZE is assumed to be 2.45, and EMP is assumed to

be 70%. TGW is assumed to equal 2. Based on these numbers, INCW,H = 0.34 * 0 .16 * (2.45 - 1) * 0.7 

* 2 = 0.11.

INCN,H = NV * SHR * (SIZE - 1) * UNEMP * TGN, where NV, SHR, and SIZE are as defined

above, UNEMP is the fraction of the population that is not employed, and TGN is the non-work trip

generation rate for SOV users. UNEMP is simply (1 - EMP) and thus equals 30%. TGN is assumed to 

be the same as TGW (i.e., 2). Based on these numbers, INCN,H = 0.34 * 0.16 * (2.45 - 1) * 0.3 * 2 = 0.05.

Using the data above, TRIPSI,W = 0.11* -(-2,508) / 2 = 138, and TRIPSI,NW = 0.05 * -(-2,508) 

/ 2 = 63. Summarizing these results, the HOP service is indirectly responsible for an increase of 138

work trips per day and 63 non-work trips per day.

Step 4 in EPA’s methodology for estimating travel activity effects of TCMs, which involves

determining direct peak and off-peak period trip shifts, does not apply to transit improvements. 

Thus, Step 4 is not relevant to the analysis of the HOP service.

Step 5 in the travel activity methodology involves estimating the net trip changes from the HOP

service as distributed between work and non-work trips and peak and off-peak periods. These changes

are calculated using the following formulas:

NETRPW,P = 7 * TRIPSS,P + PKW * (TRIPSD,W + TRIPSI,W)

NETRPW,OP = 7 * TRIPSS,OP + (1 - PKW) * (TRIPSD,W + TRIPSI,W)

NETRPNW,P = (1 - 7) * TRIPSS,P + PKNW * (TRIPSD,NW + TRIPSI,NW)

NETRPNW,OP = (1 - 7) * TRIPSS,OP + (1 - PKNW) * (TRIPSD,NW + TRIPSI,NW)

& In the formulas, NETRPW,P is the net work trip change in the peak period,

NETRPW,OP is net work trip change in the off-peak period, NETRPNW,P 

is the net non-work trip change in the peak period, and NETRPNW,OP is the net

non-work trip change in the off-peak period. TRIPSS,P is the change in peak

period trips, and TRIPSS,OP is the change in off-peak period trips. PKW is the

observed fraction of work trips during the peak period, and PKNW is the observed

fraction of non-work trips during the peak period. The other parameters in the

formulas are defined in earlier steps of the methodology.

Because there are no trip shifts associated with transit improvements (see Step 4), TRIPSS,P

and TRIPSS,OP are each equal to 0.

The values used for PKW and PKNW are 0.6 and 0.3, respectively, based on an example shown 

in the TCM guidance document.

Using the data above, NETRPW,P = 0 + 0.6 * (-502 + 138) = -218, NETRPW,OP = 0 + (1 - 0.6) 

* (-502 + 138) = -146, NETRPNW,P = 0 + 0.3 * (-2,006 + 63) = -583, and NETRPNW,OP = 0 * (1 - 0.3) 

* (-2,006 + 63) = -1,360. Summarizing these results, the HOP service results in net decreases in peak 

and off-peak work trips of 218 per day and 146 per day, respectively. The service also results 

in decreases in peak and off-peak non-work trips of 583 per day and 1,360 per day, respectively.

Step 6 in the travel activity methodology involves estimating the peak and off-peak VMT

changes due to the trip changes from the HOP service. These changes are calculated using the following

formulas:
57

VMTP = (NETRPW,P * DISTW) + (NETRPNW,P * DISTNW)

VMTOP = (NETRPW,OP * DISTW) + (NETRPNW,OP * DISTNW)

& In the formulas, VMTP is the change in peak-period VMT due to trip changes,

VMTOP is the change in off-peak VMT due to trip changes, DISTW is the

average VMT per trip for work trips, and DISTNW is the average VMT per trip

for non-work trips. The other parameters in the formulas are defined in earlier

steps of the methodology.

The total length of the Hop Shuttle Service route is six miles. The average trip, according 

to Go Boulder officials is two miles. Hence, both DISTW and DISTNW are assumed to be 2 miles.

Using the data above, VMTP = (-218 * 2) + (-583 * 2) = -1,602 and VMTOP = (-146 * 2) 

+ (-1,360 * 2) = -3,012. Summarizing these results, the HOP service reduces peak-period VMT by 1,602

miles per day due to trip changes and reduces off-peak VMT by 3,012 miles per day due to trip changes.

Step 7 in the travel activity methodology involves estimating the VMT changes due to trip length

changes resulting from the HOP service. These changes are calculated using the following formulas:

VMTL,W =  * PT * -(DISTW - DISTnew)

VMTL,NW =  * PT * -(DISTNW - DISTnew)

& In the formulas, VMTL,W is the change in VMT due to work trip length

changes, VMTL,NW is the change in VMT due to non-work trip length changes,

 is fraction of program participants who change their trip length, and DISTnew 

is the new work or non-work trip length. The other parameters in the formulas

are defined in earlier steps of the methodology.

Although it is conceivable that people may drive to a HOP stop to access the shuttle, this analysis

assumes that no HOP users do so. Thus, both  and DISTnew are set equal to 0.

Using the data above, VMTL,W = 0 * 3,583 * -(2 - 0) = 0, and VMTL,NW = 0 * 3,583 * -(2 - 0)

= 0. Summarizing these results, the HOP service does not reduce VMT through changes in trip lengths.

Step 8 in the travel activity methodology involves estimating the total peak and off-peak VMT

changes resulting from the HOP service. These changes are calculated using the following formulas:

NETVMTP = VMTP + PKW * VMTL,W + PKNW * VMTL,NW

NETVMTOP = VMTOP + (1 - PKW) * VMTL,W + (1 - PKNW) * VMTL,NW

& In the formulas, NETVMTP is the total change in peak period VMT, and

NETVMTOP is the total change in off-peak VMT. The other parameters in the

formulas are defined in earlier steps of the methodology.

Using the data above, NETVMTP = -1,602 + 0.6 * 0 + 0.3 * 0 = -1,602 and NETVMTOP

= -3,012 + (1 - 0.6) * 0 + (1 - 0.3) * 0 = -3,012. Summarizing these results, the HOP service reduces

peak-period VMT by a total of 1,602 miles per day and off-peak VMT by a total of 3,012 miles per day.

Step 9 in the travel activity methodology involves estimating peak and off-peak speed changes

resulting from the HOP service. These changes are calculated using the following formulas:
58

SPDP = (NETVMTP / TOTVMTP) * P

SPDOP = (NETVMTOP / TOTVMTOP) * OP

& In the formulas, SPDP is the percentage change in peak-period speeds, SPDOP

is the change in off-peak speeds, TOTVMTP is total peak-period VMT for the

program area, TOTVMTOP is total off-peak VMT for the program area, P is the

elasticity of peak-period speed with respect to volume, and OP is the elasticity of

off-peak speed with respect to volume. The other parameters in the formulas are

defined in earlier steps of the methodology.

Total VMT for the City of Boulder is assumed to be approximately 2 million miles per day. 

This assumption is derived using data from the Texas Transportation Institute on VMT in the nearby

Denver area. Assuming that 50 percent of travel activity occurs during peak periods and 50 percent

occurs during off-peak periods, TOTVMTP and TOTVMTOP are each approximately 1 million miles 

per day.

The parameter P is assumed to be -0.75, based on an example provided in the TCM guidance

document. The parameter OP is assumed to be 0, because changes in off-peak VMT are not likely 

to affect vehicle speeds (i.e., due to a lack of congestion).

Using the data above, SPDP = -1,602 / 1,000,000 * -0.75 = 0.001 and SPDOP = -3,012 

/1,000,000 * 0 = 0. Summarizing these results, the HOP service increases peak-period speeds 

by approximately 0.1% but has no effect on off-peak speeds.
59

Phase 2: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Step 4: Summation of emission effects

Phase 2: Emission Effects -- STEP 1 (Trip Changes)

Step 1 in the estimation of the emission

effects for the HOP service involves calculating

the effect of trip changes on emissions. This step

is broken down into seven smaller steps 

(1a through 1g), which are outlined below.

Step 1a in the emission methodology

involves estimating the distribution of trip

changes for the HOP service. These changes 

are calculated using the following formulas:

TRIP,LDGV = TRIPLDGV / (TRIPLDGV + TRIPLDGT1)

TRIP,LDGT1 = 1 - TRIP,LDGV

• In the formulas, TRIP,LDGV 

is the fraction of TCM-affected

trips taken by light-duty gasoline

vehicles (LDGVs), TRIP,LDGT1 

is the fraction of TCM-affected

trips taken by light-duty gasoline

trucks (LDGT1s), TRIPLDGV 

is the fraction of total trips in 

the region taken by LDGVs, 

and TRIPLDGT1 is the fraction 

of total trips in the region taken

by LDGT1s. (Note: Most TCMs

that can be analyzed using EPA’s

guidance document affect only

LDGVs or LDGT1s. Thus, the

sum of TRIP,LDGV and TRIP,LDGT1

is typically equal to one.)

TRIPLDGV and TRIPLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are based on the national average default values used in MOBILE.

Using the data above, TRIP,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and TRIP,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the trips affected by the HOP service are taken by LDGVs,

and 21.5% are taken by LDGT1s.

Step 1b in the emission methodology involves calculating cold-start and hot-start trip changes

for the HOP service. These changes are calculated using the following formulas:

TRIPSCST = CST,W * (NETRPW,P + NETRPW,OP) + CST, NW * (NETRPNW,P + NETRPNW,OP)

TRIPSHST = (1 - CST,W) * (NETRPW,P + NETRPW,OP) + (1 - CST,NW) * (NETRPNW,P +

NETRPNW,OP)

& In the formulas, TRIPSCST is the number of cold-start trip changes, TRIPSHST

is the number of hot-start trip changes, CST,W is the fraction of work trips begun

in the cold-start mode, and CST, NW is the fraction of non-work trips begun in the
60

cold-start mode. The other parameters in the formulas are defined in earlier

steps of the methodology.

Because work trips are mostly cold-start trips, the guidance calls for CST,W to be set equal to 1. 

The guidance also suggests that CST,NW be set equal to 0.43, which is the default fraction of cold starts

used in the Federal Test Procedure (FTP).

Using the data above, TRIPSCST = 1 * (-218 + -146) + 0.43 * (-583 + -1,360) = -1,200 and

TRIPSHST = (1 - 1) * (-218 + -146) + (1 - 0.43) * (-583 + -1,360) = -1,108. Summarizing these results,

the HOP service results in a reduction of 1,200 cold-start trips per day and a reduction of 1,108 hot-start

trips per day.

Step 1c in the emission methodology involves determining cold-start and hot-start emission

factors. These changes are calculated for a given pollutant and vehicle class using the following

formulas:

CST = (EXH100%CST,26MPH - EXH100%STB,26MPH) * 3.59

HST = (EXH100%HST,26MPH - EXH100%STB,26MPH) * 3.59

& In the formulas, CST is the cold-start emission factor in grams per trip, HST 

is the hot-start emission factor in grams per trip, and EXH is the MOBILE

emission factor in grams per mile. The 3.59 factor is the FTP driving cycle 

trip-start miles per trip, and 26 miles per hour is the speed for the start portion 

of the FTP driving cycle. (Note: The subscripts on EXH refer to the operating

conditions and speed at which MOBILE evaluates EXH. For example,

“100%CST,26MPH” indicates 100% cold-start operating mode at 26 miles 

per hour vehicle speed. While “100%STB,26MPH” indicates 100% hot- or 

cold-stabilized operating mode at 26 mph vehicle speed.)

Using national default data from MOBILE, CSTLDGV,HC = (2.55 - 0.95) * 3.59 = 5.74 grams per

trip, CSTLDGT1,HC = (3.59 - 1.34) * 3.59 = 8.08 grams per trip, HSTLDGV,HC = (1.35 - 0.95) * 3.59 = 1.44

grams per trip, and HSTLDGT1,HC = (1.99 - 1.34) * 3.59 = 2.33 grams per trip. (Following the same

methodology, the cold-start and hot-start emission factors can also be determined for NOx and CO.)

Step 1d in the emission methodology involves determining cold-start and hot-start emission

changes for the HOP service. These changes are calculated using the following formulas:

HCCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,HC) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,HC)

HCHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,HC) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,HC)

NOxCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,NOx) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,NOx)

NOxHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,NOx) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,NOx)

COCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,CO) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,CO)

COHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,CO) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,CO)

& In the formulas, HCCST, NOxCST, and COCST are the changes in cold-start

emissions for HC, NOx, and CO, respectively; and HCHST, NOxHST, 

and COHST are the changes in hot-start emissions for HC, NOx, and CO,

respectively. The other parameters in the formulas are defined in earlier steps 

of the methodology.
61

Using national default data from MOBILE, HCCST = (-1,200 * 0.785 * 5.74) + (-1,200 * 0.215 

* 8.08) = -7,492 and HCHST = (-1,108 * 0.785 * 1.44) + (-1,108 * 0.215 * 2.33) = -1,808. Summarizing

these results, the HOP service results in a reduction in cold-start HC emissions of 7,492 grams per day

and a reduction in hot-start HC emissions of 1,808 grams per day. (Following the same methodology, 

the cold-start and hot-start emission changes can also be determined for NOx and CO.)

Step 1e in the emission methodology involves determining hot soak emission changes for the

HOP service. These changes are calculated using the following formula:

HCHSK = (TRIPSTOTAL * TRIP,LDGV * HSKLDGV) + (TRIPSTOTAL * TRIP,LDGT1 * HSKLDGT1)

& In the formula, HCHSK is the change in hot soak emissions, TRIPSTOTAL is the

total change in trips, and HSK is the hot soak emission factor in grams per trip. 

(Note: Hot soak emissions are HC emissions only.)

TRIPSTOTAL = NETRPW,P + NETRPW,OP + NETRPNW,P + NETRPNW,OP. 

Thus, TRIPSTOTAL = -218 + -146 + -583 + -1,360 = -2,307.

Using national default data from MOBILE, HCHSK = (-2,307 * 0.785 * 3.06) + (-2,307 * 0.215 

* 3.60) = -7,327. Summarizing this result, the HOP service results in a reduction in hot soak emissions 

of 7,327 grams per day.

Step 1f in the emission methodology involves determining diurnal emission changes for the HOP

service. These changes are calculated for a given vehicle class using the following formulas:

HCDNL,W = 0.676 * (NETRPW,P + NETRPW,OP) / TPDW * TRIP * (WDI - MDI)

HCDNL,NW = 0.676 * (NETRPNW,P + NETRPNW,OP) / TPDNW * TRIP * (WDI - MDI)

HCDNL = HCDNL,W,LDGV + HCDNL,NW,LDGV + HCDNL,W,LDGT1 + HCDNL,NW,LDGT1

& In the formulas, HCDNL,W is the change in diurnal emissions associated with

work trips, HCDNL,NW is the change in diurnal emissions associated with 

non-work trips, and HCDNL is the total change in diurnal emissions. TPDW 

is the number of work trips per day per vehicle, and TPDNW is the number of

non-work trips per day per vehicle. WDI is the weighted diurnal emission factor

in grams, and MDI is the multi-day diurnal emission factor in grams. The other

parameters in the formulas are defined in earlier steps of the methodology. 

(Note: Diurnal emissions are HC emissions only.)

The value used for TPDW is 2, since a commuter typically makes two work trips per day 

(i.e., one trip from home to work, one trip from work to home). TPDNW is equal to TGN from Step 3 

of the “Travel Activity Effects” section above, and thus equals 2.

Using national default data from MOBILE, HCDNL,W,LDGV = 0.676 * (-218 + -146) / 2 * 0.785 

* (3.30 - 6.04) = 265, HCDNL,NW,LDGV = 0.676 * (-583 + -1,360) / 2 * 0.785 * (3.30 - 6.04) = 1,413,

HCDNL,W,LDGT1 = 0.676 * (-218 + -146) / 2 * 0.215 * (5.11 - 15.33) = 270, HCDNL,NW,LDGT1 = 0.676 

* (-583 + -1,360) / 2 * 0.215 * (5.11 - 15.33) = 1,443, and HCDNL = 265 + 1,413 + 270 + 1,443 = 3,391. 

Summarizing these results, the HOP service results in an increase in diurnal emissions of 3,391 grams 

per day.
62

Step 1g in the emission methodology involves calculating the total trip-related emission changes

for the HOP service. These changes are calculated using the following formulas:

HCTRIP = HCCST + HCHST + HCHSK + HCDNL

NOxTRIP = NOxCST + NOxHST

COTRIP = COCST + COHST

& In the formulas, HCTRIP, NOxTRIP, and COTRIP are the total changes in HC,

NOx, and CO emissions, respectively, due to trip changes.

Using the data above, HCTRIP = -7,492 + -1,808 + -7,327 + 3,390 = -13,237. Summarizing this

result, the HOP service results in a net decrease in trip-related HC emissions of 13,237 grams per day. 

(Following the same methodology, total trip-related emission changes can also be determined for NOx

and CO.)

Emission Effects -- STEP 2 (VMT Changes)

Step 2 in the estimation of the emission effects for the HOP service involves calculating the

effect of VMT changes on emissions. This step is broken down into four smaller steps (2a through 2d),

which are outlined below.

Step 2a in the emission methodology involves estimating the distribution of VMT changes 

for the HOP service. These changes are calculated using the following formulas:

VMT,LDGV = VMTLDGV / (VMTLDGV + VMTLDGT1)

VMT,LDGT1 = 1 - VMT,LDGV

& In the formulas, VMT,LDGV is the fraction of TCM-affected VMT for light-duty

gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected VMT 

for light-duty gasoline trucks (LDGT1s), VMTLDGV is the fraction of total VMT

in the region for LDGVs, and VMTLDGT1 is the fraction of total VMT in the

region for LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s

guidance document affect only LDGVs or LDGT1s. Thus, the sum of VMT,LDGV

and VMT,LDGT1 is typically equal to one.)

VMTLDGV and VMTLDGT1 are assumed to equal 0.626 and 0.171, respectively. These values 

are the national average default values used in MOBILE for VMT mix.

Using the data above, VMT,LDGV = 0.626 / (0.626 + 0.171) = 0.785 and VMT,LDGT1 = 1 - 0.785 

= 0.215. Summarizing these results, 78.5% of the VMT affected by the HOP service is by LDGVs, 

and 21.5% is by LDGT1s.

Step 2b in the emission methodology involves estimating hot-stabilized exhaust emission

changes for the HOP service. These changes are calculated using the following formulas:

HCSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,HC,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,HC,P)

HCSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,HC,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,HC,OP)

NOxSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,NOx,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,NOx,P)
63

NOxSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,NOx,OP) + (NETVMTOP * VMT,LDGT1 *

STBLDGT1,NOx,OP)

COSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,CO,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,CO,P)

COSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,CO,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,CO,OP)

& In the formulas, HCSTB,P, NOxSTB,P, and COSTB,P are the peak-period changes

in hot-stabilized emissions for HC, NOx, and CO, respectively; and HCSTB,OP,

NOxSTB,OP, and COSTB,OP are the off-peak changes in hot-stabilized emissions

for HC, NOx, and CO, respectively. STBP is the hot-stabilized emission factor

(in grams per mile) for each pollutant and vehicle class for the peak period

(during which average vehicle speed is assumed to be 20 miles per hour), 

and STBOP is the hot-stabilized emission factor (in grams per mile) for each

pollutant and vehicle class for the off-peak period (during which average vehicle

speed is assumed to be 35 miles per hour). The other parameters in the formulas

are defined in earlier steps of the methodology.

Using national default data from MOBILE, HCSTB,P = (-1,602 * 0.785 * 1.23) + (-1,602 * 0.215

* 1.77) = -2,156 and HCSTB,OP = (-3,012 * 0.785 * 0.69) + (-3,012 * 0.215 * 0.94) = -2,240. 

Summarizing these results, the HOP service results in a reduction in peak-period hot-stabilized HC

exhaust emissions of 2,156 grams per day and a reduction in off-peak hot-stabilized HC exhaust

emissions of 2,240 grams per day. (Following the same methodology, hot-stabilized exhaust emission

changes can also be determined for NOx and CO.)

Step 2c in the emission methodology involves estimating VMT-related evaporative emission

changes for the HOP service. These changes are calculated using the following formulas:

HCVEVP,P = (NETVMTP * VMT,LDGV * VEVPLDGV,P) + (NETVMTP * VMT,LDGT1 * VEVPLDGT1,P)

HCVEVP,OP = (NETVMTOP * VMT,LDGV * VEVPLDGV,OP) + (NETVMTOP * VMT,LDGT1 * VEVPLDGT1,OP)

& In the formulas, HCVEVP,P is the change in peak-period evaporative emissions,

HCVEVP,OP is the change in off-peak evaporative emissions, and VEVP is the

VMT-related evaporative emission factor (in grams per mile) for each vehicle

class and time period (peak or off-peak). The other parameters in the formulas

are defined in earlier steps of the methodology. (Note: Evaporative emissions

are HC emissions only.)

Using national default data from MOBILE, HCVEVP,P = (-1,602 * 0.785 * 0.44) + (-1,602 

* 0.215 * 0.53) = -736 and HCVEVP,OP = (-3,012 * 0.785 * 0.34) + (-3,012 * 0.215 * 0.44) = -1,089. 

Summarizing these results, the HOP service results in a reduction in peak-period evaporative emissions

of -736 grams per day and a reduction in off-peak evaporative emissions of 1,089 grams per day.

Step 2d in the emission methodology involves calculating the total VMT-related emission

changes for the HOP service. These changes are calculated using the following formulas:

HCVMT = HCSTB,P + HCSTB,OP + HCVEVP,P + HCVEVP,OP

NOxVMT = NOxSTB,P + NOxSTB,OP

COVMT = COSTB,P + COSTB,OP

& In the formulas, HCVMT, NOxVMT, and COVMT are the total changes in HC,

NOx, and CO emissions, respectively, due to VMT changes.
64

Using the data above, HCVMT = -2,156 + -2,240 + -736 + -1,089 = -6,221. Summarizing this

result, the HOP service results in a net decrease in VMT-related HC emissions of 6,221 grams per day. 

(Following the same methodology, total VMT-related emission changes can also be determined for NOx

and CO.)

Emission Effects -- STEP 3 (Speed Changes)

Step 3 in the estimation of the emission effects for the HOP service involves calculating the

effect of speed changes on emissions. This step is broken down into four smaller steps (3a through 3d),

which are outlined below.

Step 3a in the emission methodology involves estimating the speeds associated with the HOP

service. These speeds are calculated using the following formulas:

SPEEDP,TCM = SPEEDP,BASE * (1 + SPDP)

SPEEDOP,TCM = SPEEDOP,BASE * (1 + SPDOP)

& In the formulas, SPEEDP,TCM is the peak-period speed after implementation of the

TCM, SPEEDOP,TCM is the off-peak speed after implementation of the TCM,

SPEEDP,BASE is the peak-period speed prior to implementation of the TCM, 

and SPEEDOP,BASE is the off-peak speed prior to implementation of the TCM. 

The other parameters in the formulas are defined in earlier steps of the

methodology.

Based on data for the national default fleet, SPEEDP,BASE is assumed to be 20 miles per hour, 

and SPEEDOP,BASE is assumed to be 35 miles per hour.

Using the data above, SPEEDP,TCM = 20 * (1 + 0.004) = 20.08 and SPEEDOP,TCM = 35 * (1 + 0) 

= 35. Summarizing these results, peak-period speeds have slightly increased from 20 miles per hour 

to 20.08 miles per hour due to the HOP service. Off-peak speeds have not changed due to the service.

Step 3b in the emission methodology involves estimating the total VMT for the program area

after implementation of the HOP service. These VMT figures are calculated using the following

formulas:

VMTP,TCM = TOTVMTP + NETVMTP

VMTOP,TCM = TOTVMTOP + NETVMTOP

& In the formulas, VMTP,TCM is the total peak-period VMT in the program area

after implementation of the TCM, and VMTOP,TCM is the total off-peak VMT 

in the program area after implementation of the TCM. The other parameters 

in the formulas are defined in earlier steps of the methodology.

Using data from Step 9 of the “Travel Activity Effects” section above, VMTP,TCM = 1,000,000 

+ -1,602 = 998,398 and VMTOP,TCM = 1,000,000 + -3,012 = 996,988. Summarizing these results, 

peak-period VMT has decreased from 1,000,000 miles per day to 998,398 miles per day due to the HOP

service. Off-peak VMT has decreased from 1,000,000 miles per day to 996,988 miles per day due to the

service.
65

Step 3c in the emission methodology involves estimating peak-period and off-peak emission

changes due to changes in vehicle speeds. These changes are calculated using the following formulas:

HCSPD,P = VMTP,TCM * (STBFLT,HC,P,TCM + RNLFLT,P,TCM) - VMTP,TCM * (STBFLT,HC,P,BASE + RNLFLT,P,BASE)

HCSPD,OP = VMTOP,TCM * (STBFLT,HC,OP,TCM + RNLFLT,OP,TCM) - VMTOP,TCM * (STBFLT,HC,OP,BASE + RNLFLT,OP,BASE)

NOxSPD,P = VMTP,TCM * (STBFLT,NOx,P,TCM - STBFLT,NOx,P,BASE)

NOxSPD,OP = VMTOP,TCM * (STBFLT,NOx,OP,TCM - STBFLT,NOx,OP,BASE)

COSPD,P = VMTP,TCM * (STBFLT,CO,P,TCM - STBFLT,CO,P,BASE)

COSPD,OP = VMTOP,TCM * (STBFLT,CO,OP,TCM - STBFLT,CO,OP,BASE)

& In the formulas, HCSPD,P, NOxSPD,P, and COSPD,P are the peak-period changes

in emissions for HC, NOx, and CO, respectively, due to a change in speeds; 

and HCSPD,OP, NOxSPD,OP, and COSPD,OP are the off-peak changes in emissions

for HC, NOx, and CO, respectively, due to a change in speeds. STBFLT is the

fleet-wide hot-stabilized emission factor (in grams per mile) for each pollutant,

time period (i.e., peak or off-peak), and scenario (i.e., base or TCM). RNLFLT 

is the fleet-wide running loss emission factor (in grams per mile) for each time

period and scenario. The other parameters in the formulas are defined in earlier

steps of the methodology.

Based on data showing the relationship between vehicle speed and emissions, this analysis

assumes that the elasticity of STBFLT with respect to speed is -1 for HC, 0 for NOx, and -1 for CO. 

Thus, a 1% increase in speed is assumed to result in a 1% decrease in HC and CO emissions (on a grams

per mile basis) and no change in NOx emissions. The elasticity of RNLFLT with respect to speed is also

assumed to be -1. 

Using national default data from MOBILE, HCSPD,P = 998,398 * (1.669 + 0.211) - 998,398 

* (1.676 + 0.212) = -0 and HCSPD,OP = 996,988 * (1.938 + 0.120) - 996,988 * (1.938 + 0.120) = 0. 

Summarizing these results, the HOP service changes neither speed-related HC emissions per day for the

peak period nor speed-related HC emissions for the off-peak period. (Following the same methodology,

the peak-period and off-peak emission changes due to changes in speeds can also be determined for NOx

and CO.)

Step 3d in the emission methodology involves calculating the total speed-related emission

changes for the HOP service. These changes are calculated using the following formulas:

HCSPD = HCSPD,P + HCSPD,OP

NOxSPD = NOxSPD,P + NOxSPD,OP

COSPD = COSPD,P + COSPD,OP

& In the formulas, HCSPD, NOxSPD, and COSPD are the total changes in HC,

NOx, and CO emissions, respectively, due to speed changes.

Using the data above, HCSPD = 0 + 0 = 0. Summarizing this result, the HOP service results 

in no net change in speed-related HC emissions per day. (Following the same methodology, total 

speed-related emission changes can also be determined for NOx and CO.)

Emission Effects -- STEP 4 (Total)
66

Step 4 in the estimation of the emission effects for the HOP service involves calculating the total

changes in HC, NOx, and CO emissions. These changes are calculated using the following formulas:

 

HC = HCTRIP + HCVMT + HCSPD

NOx = NOxTRIP + NOxVMT + NOxSPD

CO = COTRIP + COVMT + COSPD

& In the formulas, HC, NOx, and CO are the total changes in HC, NOx, 

and CO emissions, respectively, due to the TCM program.

Using the data above, HC = -13,236 + -6,221 + 0 = -19,457. Summarizing this result, the HOP

service results in a net decrease in HC emissions of 19,457 grams per day, or approximately 0.019 tons

per day. (Following the same methodology, total emission changes can also be determined for NOx 

and CO.)
67

2. ANALYSIS OF TCM PACKAGES

This section uses the methodology outlined in Chapters 2, 3, and 4 of EPA’s TCM guidance 

to estimate the travel activity effects and emissions effects of programs involving TCM packages. 

The key distinction between the analysis presented in this section and the analysis in Section 1 

is the need to first consider modal choice.

People tend to base their travel mode decisions on the attributes of each travel mode. The time 

it takes to get to a destination by a certain mode, the cost of a mode, the convenience of a particular

mode, and mode reliability are the four characteristics people primarily consider when deciding on travel

methods. EPA’s methodology for TCM packages uses these attribute characteristics in a particular study

area to determine the probability that a representative person in the affected community will choose 

a particular mode. These probabilities for a representative individual are then extrapolated to the whole

study area population. When the characteristics of travel modes suddenly change (i.e. after TCM

implementation), travel attributes change, and therefore mode choice probabilities for the representative

individual and the entire study area also change. The TCM modeler can now compare the “pre-TCM”

mode splits with the “post-TCM” splits to determine mode choice change due to the introduction of the

TCM package.

Two analyses need to be conducted under the TCM package methodology before travel activity

and emission changes can be determined. The first involves establishing the travel attribute

characteristics and travel mode profiles that existed before introduction of the TCM package 

(i.e., a “base case”). The second analysis predicts travel choices after TCM implementation by plugging

the new travel conditions into the base case framework. In other words, by multiplying the new travel

attributes by preferences established in the base case, a new travel mode profile can be obtained.

Example 6: Cornell University Transportation Demand Management Program

General Description

The Cornell University Transportation Demand Management Program (TDMP) was instituted 

by the University in the early 1990s to combat significant traffic congestion near and on the Ithaca

campus. Realizing that a parking pricing scheme alone would not be sufficient to alter faculty and staff

work travel habits, the University’s Office of Transportation Services (OTS) developed a transportation

management package that, along with parking fees, included subsidized transit and rideshare measures.

The TDMP introduced several measures to encourage transit and carpooling. First, all but one

campus parking lot began to charge single occupancy vehicles (SOVs). Second, a program called

RideShare was established with a number of features, some key ones are a rideshare parking fee schedule

that includes rebates in particular instances, a listing of people looking for others with whom to rideshare

to help match people interested in carpooling, and emergency ride services to staff members who become

stranded on campus due to missing their carpool rides. Finally, a program called OmniRide was

developed. This program provides Cornell employees who do not participate in the RideShare program

with free transit passes that can be used for work as well as leisure.

The Cornell TDMP has been quite successful, not only at reducing vehicle emissions as shown 

in the analysis below, but at saving large amounts of money for the university by enabling it to forgo

large expenses for additional parking facilities that would have been needed otherwise. The university

estimates that, without TDMP, construction of additional parking structures offering a total of 3,100
68

Phase 1: Mode Choice Analysis

Step 1: Base case (before TCM implementation)

cost, time, convenience and reliability for

each mode

Step 2: Highest and lowest possible values for time

and cost among all modes

Step 3: Scale base-case cost, time, convenience,

and reliability values for each mode on a

“best-to-worst” scale

Step 4: Weight factors for cost, time, convenience

and reliability

Step 5: Base case utilities for each travel mode

(scale values times weight factors)

Step 6: Percentage of time in the base case a person

will travel by each mode

Step 7: Percentage of time after TCM

implementation a person will travel by each

mode. This involves redoing steps 1

through 6 with values reflecting the TCM.

parking spaces would have been needed since 1991, when the program started. With TDMP the

university has added a total of 350 parking spaces in that time period. Total cost savings to date from 

the forgone construction are estimated at $13 million.

A key factor in the success of the program has been the measures taken to provide backups, 

when needed, for commuters participating in the RideShare and OmniRide programs. Guaranteed rides

home are available when program participants need them due to unforeseen circumstances. Participants

also each receive a book of ten 1-day parking permits enabling them to drive alone on the occassional

days when circumstances require them to have their cars at work. In special circumstances, such as the

need to provide care to a family member for an extended period of time, participants may obtain

additional books of permits.

Program officials also point to their outreach efforts as a key to their success. One tangible result

is that they have gotten agreements from churches, town halls, grocery stores, and other facilites with

parking lots that are not heavily used during weekday working hours, to allow RideShare participants 

to use their lots as park-and-ride lots.

Data Sources

& “Commuting Solutions Summary of Transportation Demand Management Program (TDMP),”

Office of Transportation Services, June 1996.

& Cornell Commuter Report, Spring 1996.

& “Patterns and Trends: New York State Energy Profiles, 1981-1995,” prepared by the New York

State Energy Research and Development Authority.

& Personal Interview with David Lieb, Communications Manager, Office of Transportation and

Mail Services, March 12, 1997, March 13, 1997, and March 17, 1997.

& Personal Interview with Lois Chaplin, University Bike Safety Specialist, March 12, 1997.

& Personal Interview with Nate Earlbomb,

New York Department of Transportation,

December 5, 1997.

& “Report on Reducing Oregon’s

Greenhouse Gas Emissions,” prepared by

the Oregon Office of Energy.

& “TCAT Service and Fare Consolidation

Project: Tompkins Consolidated Area

Transit, Ithaca, New York.”

& Texas Transportation Institute web page.

& 1990 U.S. Census data.

& 1996 Statistical Abstract of the United

States.

Phase 1: Modal Choice Analysis
69

FOCUS: COMPONENTS OF TRAVEL COST BY MODE

Relevant costs for each travel mode are listed in the boxes

below. While an SOV and a carpool vehicle encounter similar

costs, total carpool costs need to be divided by average carpool

vehicle occupancy (CVO) in order to determine cost per

carpooler. (Note: This analysis is conducted from the

perspective of an individual making a commuting decision, 

and thus costs need to be calculated on an individual basis.) 

Transit costs must include the costs incurred by the fraction 

of commuters who drive or get a ride to a transit stop. 

Finally, this analysis assumes that the walk/bike travel mode

poses no cost to a commuter.

Fuel

Prices

Fuel

Efficiency

Parking

Fees

Tolls

Fuel Prices

Fuel Efficiency

Parking Fees

Tolls

Note: Total cost

needs to be divided

by CVO to obtain

cost faced by each

individual.

Transit Fees

Note: Mode cost

must incorporate

the costs to transit

riders who drive

to a transit stop,

including fuel

prices, fuel

efficiency, parking

fees, and tolls.

SOV Carpool Transit

Step 1 of the modal choice analysis for the TDMP involves determining the base case (i.e., prior

to implementation of the TCM package) cost, time, convenience, and reliability for each mode of travel.

Cost

Relevant costs include parking fees, tolls, gasoline, and transit fees, although not every travel

mode incurs all four costs. (For example, SOV travelers do not incur transit fees. Transit users,

however, could face all four costs if they drive via a toll road to a transit station that charges for parkand-ride services.) Data needed to determine travel mode costs in the study area include the average

distance to work for each mode, the fuel economy of passenger vehicles, gasoline prices, toll prices,

parking prices, and transit prices.

Data on the average round-trip work travel distance for each travel mode in Tompkins County

were not available from any consulted data sources. However, by cross-referencing the average trip

length and time for all American

workers (obtained from the 1996

Statistical Abstract of the United States)

with average work trip time information

for Tompkins County (obtained from

1990 U.S. Census data), the average

one-way trip length in Tompkins

County is determined to be 8.83 miles. 

Because the majority of trips to the

Cornell campus before TCM

implementation were made by SOVs

(75%), this one-way trip length is

assigned to the SOV mode. 

This analysis also assumes that carpool

vehicles would need to travel an extra 

2 miles on a one-way work trip to pick

up passengers. Average transit distances

and walk/bile distances in this particular

case are relatively small.

Fuel economy for the Tompkins

County area was derived using data from

an Oregon Greenhouse Gas study, which

reported that the average fuel economy

for a passenger vehicle in 1991 (the year 

of TDMP implementation) was 20.1

miles per gallon (mpg). SOV fuel

economy is increased to 20.3 mpg to

account for the fact that most SOVs are

passenger cars. Also, fuel economy for

carpool vehicles 

is lowered to 19.9 to account for the greater use of larger vehicles (e.g., mini-vans) and slower speeds.

Due to the lack of parking fees on the Cornell campus prior to TCM implementation and the 

non-existence of toll roads in Tompkins County, costs for SOV and carpool use are simply the price of

gasoline consumed. (According to the NYSERDA, the average gasoline price in New York in 1991 was

$1.33 per gallon.) This analysis assumes that the cost of gasoline is distributed evenly among all carpool
70

FOCUS: COMPONENTS OF TRAVEL TIME BY MODE

The factors that determine travel time for each mode are listed 

in the boxes below. SOV travel time is calculated by dividing

travel distance by average vehicle speed. Carpool travel time 

is calculated in the same manner. However, it is important 

to note that carpool vehicles generally go slower and travel

longer distances than SOVs due to passenger pick-up stops. 

In the TDMP base case, carpool vehicles are assumed to travel

four miles more than SOVs and travel at a speed 3 miles per

hour slower than SOVs. In addition to travel distance and

vehicle speed, transit commute time is augmented by time spent

waiting for transportation and time spent reaching the transit

stop. Walk/bike commute time is calculated in the same manner

as the SOV and carpool modes.

Travel

Distance

Vehicle

Speed

Travel

Distance

Vehicle

Speed

Note: Travel

distance will be

affected by the

number of

carpool

participants,

and vehicle

speed will be

less than SOV

speed due to

multiple stops

for passenger

pickup.

Travel

Distance

Vehicle

Speed

Time Spent

Waiting at

Transit Stop

Time Spent

Traveling to

and from

Transit Stop

Travel

Distance

Mode

Speed

SOV Carpool Transit Walk/Bike

passengers (including the driver). Therefore, the cost of gasoline consumed for an individual in a carpool

is determined by dividing the cost of gasoline by the average number of passengers in a carpool (2.18 in

Tompkins County, as reported in 1990 U.S. Census data).

Based on the data above, 

the cost of SOV travel is calculated 

as follows: 17.67 miles (round trip) 

* $1.33 per gallon / 20.3 mpg = $1.16. The cost of carpool travel is calculated as follows: 22 miles

(round trip) 

* $1.33 per gallon / 19.9 mpg / 2.18 

= $0.67.

Total transit costs are the sum of two components. The first component, the price of using

transit, 

is assumed to be $0.50, based on fee information found on the TCAT web site. The second component

accounts for transit users who drive to a transit stop. Assuming that 30% of transit users drive to their

stop, the average one-way distance to

the park-and-ride stop is 1.5 miles, and

average vehicle occupancy reflects

county averages (1.21 according to

1990 U.S. Census data), the average

one-way transit cost is calculated as

follows: $0.50 + 0.3 

* (1.5 miles * $1.33 per gallon / 20.1

mpg / 1.21) = $0.525. Multiplying this

figure by 2 yields a round-trip cost 

of $1.05.

Time

For SOVs and carpools, round

trip travel time is determined by

dividing round trip travel distance by

average speed. Speed data for SOVs

and carpools is based on the national

average for travel on principle arterial

streets during peak hours. (Note: This

analysis assumes most work trips take

place during peak periods.) Because

Tompkins County is largely rural and

is not located near any major highway

infrastructure, this analysis assumes

that most travel is done on arterial

roads. Carpool vehicles travel 

at slightly lower speeds due to the slow

speeds involved when traveling in

residential areas to pick up passengers. 

For walkers and bikers, the analysis

assumes that the average speed is 5

miles per hour.
71

To calculate travel time for transit, this analysis assumes that the average speed of a transit

vehicle is 20 miles per hour. With a round trip of 13 miles, travel time is calculated to be 0.65 hours. 

EPA’s TCM guidance suggests that walking and waiting time for transit amounts to approximately 8.76

minutes. This is multiplied by 2 to generate round-trip walking and waiting time for transit. Finally,

there is additional driving time for the fraction of individuals who drive to park-and-ride lots. This is

calculated by dividing the average round-trip distance for park-and-ride users by vehicle speed (assumed

to be 30 miles per hour) and multiplying by the fraction of transit riders who use park-and-ride lots (0.3).

Based on the information above, the travel time for SOVs is 17.67 miles (round trip) / 30 miles

per hour = 0.59 hours. The travel time for carpools is 22 miles (round trip) / 27 miles per hour = 0.81

hours. The travel time for transit is 13 miles (round trip) / 20 miles per hour + ((8.76 / 60) * 2) + (0.3 

* (3 miles / 30 miles per hour)) = 0.97 hours. The travel time for walkers/bikers is 4.5 miles (round trip)

/ 5 miles per hour = 0.90 hours.

The costs and travel times associated with SOV travel, carpool travel, transit, and walking/biking

for the base case are summarized below in Table 1.

Table 1: Average Travel Cost and Time for the Base Case

Travel Mode

Total

Daily

Work

Trip

Length

Average

Peak

Period

Speed

Hours of

Daily Work

Travel

Time

Fuel

Economy Dollars per

Gallon Parking Fee Transit Cost (one way) Total Cost

Walk/Bike 4.5 5 0.9 N/A N/A N/A N/A -

Transit 13 20 0.97 20.1 $1.33 N/A $0.52 $1.05

Carpool 22 27 0.81 19.9 $1.33 N/A N/A $0.67

SOV 17.67 30 0.59 20.3 $1.33 N/A N/A $1.16

Note: This methodology does not include the costs of wear-and-tear on privately-owned vehicles and thus may undervalue the true costs faced 

by SOV and carpool users. Nevertheless, wear-and-tear is an indirect cost that vehicle owners rarely account for in their work travel choices.

Convenience

Determining the convenience value for each travel mode primarily involves a qualitative

analysis. Due to a lack of information on Tompkins County and the area around Cornell’s campus, the

convenience factors used on this analysis are based on factors shown in the TCM guidance for the San

Francisco area, with a few minor adjustments. (Note: A convenience value of 0 indicates that an option

is totally inconvenient, and a convenience value of 1 indicates that an option is totally convenient.)

& The convenience of SOV travel in Tompkins County is given a value 0.9. While

the guidance gives SOVs a value of 0.8, the lack of a transit system in Tompkins

County similar to BART and the relative spread of development in Tompkins

County when compared to the density of San Francisco would seem to encourage

SOV use in Tompkins County to a greater extent.

& The convenience of transit in Tompkins County is given a value of 0.2. 

The TCM guidance gives transit a value of 0.4 for San Francisco. However, 

the Bay Area’s extensive transit system is much more comprehensive than the

system serving Tompkins County.
72

FOCUS: ASSESSING CONVENIENCE OF EACH MODE

The convenience of a particular mode is largely determined by three factors -- comfort, safety, and

flexibility. If a mode provides physical comfort, is relatively non-stressful, and does not prevent

commuters from indulging in their favorite travel habits, such as listening to the radio or drinking coffee,

its convenience value will be fairly high. Convenience value will also be enhanced by feelings of safety. 

(For example, many observers partially attribute the recent popularity of sport utility vehicles to the feeling

of safety these vehicles provide.) If a transportation choice allows the commuter to complete errands

before and after work and provides flexibility in departure time, convenience value for that particular mode

will be relatively high. Conversely, a transportation choice that makes commuting taxing and stressful,

provides little transportation flexibility, and is prone more than any other mode to cause physical injury will

be relatively inconvenient and an unpopular modal choice.

Comfort Safety Flexibility

Aesthetic value is high, 1.0 Risk of personal 1.0 Can complete other trips, range

transportation is easily accessible 0.9 injury is low 0.9 of start-end times, immediate

0.8 0.8 access to transportation

0.7 0.7

0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3

Aesthetic value is low, difficult and 0.2 0.2 Cannot complete other trips, no range

time-consuming to access 0.1 Risk of personal 0.1 of start-end times, difficult to

transportation 0.0 injury is high 0.0 access transportation immediately

& The convenience of carpool travel in Tompkins County is given a value of 0.2. 

While ridesharing in San Francisco is given a convenience value of 0.3, the lack

of congestion and spread of development in Tompkins County makes ridesharing

less convenient than it is in San Francisco.

& The convenience of walking/biking in Tompkins County is given a value of 0.1. 

While walking and biking can be very convenient for some people, for many 

it is not a viable option.

Reliability

Like convenience value, reliability can only be determined by a qualitative assessment. 

(Note: A reliability value of 0 indicates that an option is totally unreliable, and a reliability value 

of 1 indicates that an option is totally reliable.)

& The reliability of SOV travel is given a value of 0.9. This is based on the fact

that (1) the vehicle is immediately available, (2) travel does not depend on

anyone else, and (3) there is a slight chance that a vehicle will experience

mechanical failure. 
73

FOCUS: ASSESSING RELIABILITY OF EACH MODE

The reliability of a particular mode is largely determined by two factors -- availability and

predictability. If a particular transportation mode is immediately available and can deliver the user 

to his/her destination of choice in a timely manner, reliability will be high. The reliability attribute of

a particular mode will be strengthened if the mode is also predictable. For example, if a car has just

been serviced, it is very likely to run with few problems, and performance predictability will be high. 

Conversely, if a bus route is scheduled to run infrequently or is always late, predictability will be low.

Availability Predictability

Transportation is always 1.0 It is known exactly when

available for immediate use 0.9 transportation will be needed and

0.8 when it will be available

0.7

0.6

0.5

0.4

0.3 It is very difficult to

0.2 determine when transportation

Transportation is rarely 0.1 will be needed and if it

immediately available 0.0 will be available when wanted

& The reliability of walking/biking is given a value of 0.4. This is based on that

fact that (1) travel does not depend on anyone else, (2) immobility is generally

not a problem, and (3) inclement weather can make this option intolerable.

& The reliability of carpool travel is given a value of 0.2. This is based on that fact

that ridesharers depend on the cooperation of others.

& The reliability of transit is given a value of 0.2. This is based on that fact that 

(1) transit riders often experience delays, and (2) transit systems sometimes

experience mechanical failures.

Step 2 of the modal choice analysis for the TDMP involves determining the best and worst limits

of the cost and travel time profiles for the base case.

The best cost is the lowest cost among the four modes. Based on an example shown in the TCM

guidance document, the worst cost limit is derived by multiplying the highest cost among the four modes

by a factor of approximately 1.8. Therefore, the best cost is $0, and the worst cost is $2.08 (i.e., 1.8 

* $1.16).

The best travel time involves no travel at all. For example, a faculty member who lives 

in a dormitory experiences virtually no travel time. On the other hand, for people who commute over

long distances, travel time can easily extend over an hour. Therefore, the best travel time is assumed 

to be 0, and the worst travel time is assumed to be 1.5 hours.
74

FOCUS: COMPARING COST ACROSS MODES

To normalize the range of mode costs on a scale of 0 to 1 (highest commute cost to lowest commute cost), 

the highest and lowest possible costs a commuter could encounter need to be determined. In the TDMP base

case, the lowest possible cost is $0 (for walkers and bikers) and the highest possible cost $2.08 (for SOV users

who have a particularly long commute or face an extra toll). Normalized costs in the TDMP base case are

0.444 for an SOV commute, 0.497 for a transit commute, 0.676 for a carpool commute, and 1.000 for 

a walk/bike commute.

0 (Highest) 0.5 (Lowest) 1

SOV Transit Carpool Walk/Bike

FOCUS: COMPARING TIME ACROSS MODES

To normalize the range of travel times on a scale of 0 to 1 (longest commute time to shortest commute time),

the longest and shortest possible travel times a commuter could encounter need to be determined. In the TDMP

base case, the shortest possible commute time is 0 hours (for people who live next to their offices) and the

longest possible commute time is 1.5 hours (for SOV users who have a particularly long commute). 

Normalized travel times in the TDMP base case are 0.607 for an SOV commute, 0.352 for a transit commute,

0.457 for a carpool commute, and 0.400 for a walk/bike commute.

0 (Longest) 0.5 (Shortest) 1

Transit Walk/Bike Carpool SOV

Step 3 of the modal choice analysis for the TDMP involves scaling the base case cost, time,

convenience, and reliability of each travel mode on a “best-to-worst” scale. To scale the cost and time 

of each mode on a best-to-worst scale (1 representing the best value and 0 the worst value), the following

formulas are used:

COSTVALk = (worst cost - COSTk) / (worst cost - best cost)

TIMEVALk = (worst time - TIMEk) / (worst time - best time)

& In the formulas, COSTVALk is the cost value for travel mode k, TIMEVALk 

is the time value of travel mode k, COSTk is the cost of mode k, and TIMEk 

is the travel time of mode k.

Based on the analysis above, COSTVALWalk/Bike = (2.08 - 0) / (2.08 - 0) = 1, COSTVALTransit
75

FOCUS: COMPARING CONVENIENCE ACROSS MODES

While SOVs may exhibit the worst safety record of the four modes, the great flexibility and comfort they

provide gives this mode a convenience factor of 0.9 in the TDMP base case. Transit scores very low on

flexibility and comfort and is given an overall value of 0.2 in the base case. Carpools are similarly limited in

the comfort and flexibility categories, resulting in an overall convenience score of 0.2 in the base case. Finally,

walking/biking scores well in the safety and flexibility categories. However, since walking/biking is not a

viable option for commuters who live several miles from their work sites, the overall convenience score of this

mode must be adjusted downward. In the base case, walking/biking is assigned a convenience value of 0.1.

Comfort

0 (Worst) 0.5 (Best) 1

Transit Carpool Walk/

Bike* SOV

Safety

0 (Worst) 0.5 (Best) 1

SOV Carpool Transit Walk/

Bike*

Flexibility

0 (Worst) 0.5 (Best) 1

Transit Carpool Walk/

Bike* SOV

* These scores only apply to commuters who live close enough to their work sites to make this mode a viable option. FOCUS: SOME FACTORS MATTER MORE

THAN OTHERS

How much does the average member of the

TCM program area value cost in comparison

with convenience? What weight should be

attached to reliability? The answers to these

questions will help determine the relative

importance of the four travel attributes for the

region being studied. This relative importance

is reflected in the “weight profile.” For

example, if cost is valued more than time in a

particular community, any TCM that decreases

cost will have a greater chance of affecting

behavior than a TCM that modifies travel time. 

The TCM guidance suggests an initial weight

profile. However, analysts will need to make

appropriate judgements to determine the weight

profile of the particular area being studied.

FOCUS: COMPARING RELIABILITY ACROSS MODES

The availability and predictability of SOV use is very high, although congestion can serve to reduce the

reliability of SOVs. SOV use is given a reliability factor of 0.9 in the TDMP base case. Transit scores very

low on availability and predictability and is given an overall value of 0.2 in the base case. Carpools are

similarly limited in the availability and predictability categories, resulting in an overall convenience score 

of 0.2 in the base case. Finally, walking/biking is a readily available and predictable mode during good

weather. However, during inclement weather, the reliability and predictability of this mode is low. In addition,

since walking/biking is not a viable option for commuters who live several miles from their work sites, the

overall reliability score of this mode must be adjusted downward. In the base case, walking/biking is assigned

a reliability value of 0.4.

Availability

0 (Worst) 0.5 (Best) 1

Carpool Transit Walk/

Bike* SOV

Predictability

0 (Worst) 0.5 (Best) 1

Transit Carpool Walk/

Bike* SOV

* These scores only apply to commuters who live close enough to their work sites to make this mode a viable option.

= (2.08 - 1.05) / (2.08 - 0) = 0.497, COSTVALCarpool = (2.08 - 0.67) / (2.08 - 0) = 0.676, 

and COSTVALSOV = (2.08 - 1.16) / (2.08 - 0) = 0.444. Also, TIMEVALWalk/Bike = (1.5 - 0.9) / (1.5 - 0) 

= 0.400, TIMEVALTransit = (1.5 - 0.97) / (1.5 - 0) = 0.352, TIMEVALCarpool = (1.5 - 0.81) / (1.5 - 0)

 = 0.457, and TIMEVALSOV = (1.5 - 0.59) / (1.5 - 0) = 0.607. (Note: The values for convenience and

reliability are assumed to be the same as those calculated in Step 1 above.)

Step 4 of the modal choice analysis for the

TDMP involves determining a base case weight

profile for the population of the program area. This

step involves assigning the relative importance of each

attribute from the perspective of the average member

of the study population. The “weight profile” must

sum to one (i.e., 100% of the travel decision process is

affected by these four attributes). The TCM guidance

suggests initial relative weights of 0.3 for cost, 0.3 for

travel time, 0.2 for convenience, and 0.2 for reliability. 

Based on survey data for the TDMP and calculations

performed under Steps 5 and 6 below, the relative

weights ultimately used in this analysis for cost, time,

convenience, and reliability are 0.3, 0.19, 0.3, and

0.21, respectively.
76

Step 5 of the modal choice analysis for the TDMP involves calculating the total utilities of each

mode of travel for the base case. These utilities are determined for each travel mode using the following

formula:

TUk = COSTVALk * 1 + CONVVALk * 2 + TIMVALk * 3 + RELVALk * 4

& In the formula, TUk is the total utility of travel mode k, COSTVALk is the cost

value of mode k, CONVVALk is the convenience value of mode k, TIMVALk 

is the time value of mode k, and RELVALk is the reliability value of mode k. 

1 is the relative weight on cost, 2 is the relative weight on convenience, 

3 is the relative weight on time, and 4 is the relative weight on reliability.

Based on the analysis above, TUWalk/Bike = 1 * 0.3 + 0.1 * 0.3 + 0.4 * 0.19 + 0.4 * 0.21 = 0.49,

TUTransit = 0.497 * 0.3 + 0.2 * 0.3 + 0.352 * 0.19 + 0.2 * 0.21 = 0.32, TUCarpool = 0.676 * 0.3 + 0.2 * 0.3 +

0.457 * 0.19 + 0.2 * 0.21 = 0.39, and TUSOV = 0.444 * 0.3 + 0.9 * 0.3 + 0.607 * 0.19 + 0.9 * 0.21 = 0.71.

Step 6 of the modal choice analysis for the TDMP involves estimating the percentage of time

(i.e., probability) that a person from the program area will travel via a given mode of travel in the base

case. This percentage is calculated for each travel mode using the following formula:

Pk = e6.5TU

k / Nj=1 e6.5TUj

& In the formula, Pk is the probability that a person from the program area will

travel via mode k relative to the N modes examined.

Table 2 below presents the results of Step 6 for the base case. As can be seen from the table, the

estimated probabilities correspond closely to actual mode splits.

Table 2: Travel Mode Choice for the Base Case

Mode Split SOV Carpool Transit Walk/Bike

Actual 74.9 4.4 4.4 16.4

Projected 68.9 8.8 5.5 16.8

Step 7 of the modal choice analysis for the TDMP involves estimating the percentage of time

(i.e., probability) that a person from the program area will travel via a given mode of travel after

implementation of the TCM package. This requires repeating Steps 1 through 6 above using data and

assumptions applicable to the TCM package (see Steps 7a through 7f below).

Step 7a of the modal choice analysis for the TDMP involves determining the TCM-adjusted cost,

time, convenience, and reliability for each mode of travel.

Cost

For SOVs, the weighted average price for parking due to the TCM is calculated to be $0.83. 

The parking fee for carpools is calculated to be $0.12 and includes both fees and rebates. Rebates are

offered to cars with three or more people that park in specific lots. Based on 1990 U.S. Census data 
77

for Tompkins County, this analysis assumes that 86.4% of carpools contain 2 people, 10.6% contain 3

people, and 3% have 4 or more people. The analysis also assumes that an even distribution of carpool

vehicles use the four campus carpool lots. Both carpools and SOVs incur gasoline costs, which are

added to the parking fees. Based on this information, the total costs for SOVs and carpools are estimated

to be $1.99 and $0.79, respectively. 

The only cost for transit is the gasoline used by park-and-ride participants. As in Step 1 above,

this step assumes that 30% of the people who use transit drive to the transit station and that these vehicles

on average contain 1.21 people. The cost of using transit is estimated to be $0.05 after implmentation 

of the TCM.

Time

The time attributes for each travel mode do not change due to the TCM package, given no

significant change in average speeds. In addition, congestion would be reduced equally for every mode

of travel (except for walking and biking).

The costs and travel times associated with SOV travel, carpool travel, transit, and walking/biking

for the TCM case are summarized below in Table 3.

Table 3: Average Travel Cost and Time After Implementation of the TCM

Travel Mode

Total

Daily

Work

Trip

Length

Average

Peak

Period

Speed

Hours of

Daily Work

Travel

Time

Fuel

Economy Dollars per

Gallon Parking Fee Transit Cost (one way) Total Cost

Walk/Bike 4.5 5 0.9 N/A N/A N/A N/A -

Transit 13 20 0.97 20.1 $1.33 N/A $0.02 $0.05

Carpool 22 27 0.81 19.9 $1.33 $0.12 N/A $0.79

SOV 17.67 30 0.59 20.3 $1.33 $0.83 N/A $1.99

Note: This methodology does not include the costs of wear-and-tear on privately-owned vehicles and thus may undervalue the true costs faced 

by SOV and carpool users. Nevertheless, wear-and-tear is an indirect cost that vehicle owners rarely account for in their work travel choices.

Convenience

After implementation of the TCM, the convenience of SOV travel does not change, as nothing 

is done to make SOV use more or less convenient. Due to the improvements resulting from the TCM,

however, the convenience of transit use is assumed to increase from 0.2 to 0.25. Similarly, the

convenience of carpooling is assumed to increase from 0.2 to 0.35, and the convenience of walking/

biking is assumed to increase from 0.1 to 0.2.

Reliability

After implementation of the TCM, the reliability of SOV travel does not change, as nothing 

is done to make SOV use more or less reliable. Due to the improvements resulting from the TCM,

however, the reliability of transit use is assumed to increase from 0.2 to 0.25. Similarly, the reliability 

of carpooling is assumed to increase from 0.2 to 0.3, and the reliability of walking/biking is assumed 

to increase from 0.4 to 0.45.
78

Step 7b of the modal choice analysis for the TDMP involves determining the best and worst

limits of the cost and travel time profiles for the TCM case.

The best cost is the lowest cost among the four modes. Based on an example shown in the

guidance document, the worst cost limit is derived by multiplying the highest cost among the four modes

by a factor of approximately 1.8. Therefore, the best cost is $0, and the worst cost is $3.58 (i.e., 1.8 

* $1.99).

The best and worst travel times for the TCM case are assumed to be the same as in the base case. 

Thus, the best travel time is 0, and the worst travel time is 1.5 hours.

Step 7c of the modal choice analysis for the TDMP involves scaling the TCM-adjusted cost,

time, convenience, and reliability of each travel mode on a “best-to-worst” scale using the formulas

shown in Step 3 above. Based on the analysis above, COSTVALWalk/Bike = (3.58 - 0) / (3.58 - 0) = 1,

COSTVALTransit = (3.58 - 0.05) / (3.58 - 0) = 0.986, COSTVALCarpool = (3.58 - 0.79) / (3.58 - 0) = 0.779,

and COSTVALSOV = (3.58 - 1.99) / (3.58 - 0) = 0.444. Also, TIMEVALWalk/Bike = (1.5 - 0.9) / (1.5 - 0) 

= 0.400, TIMEVALTransit = (1.5 - 0.97) / (1.5 - 0) = 0.352, TIMEVALCarpool = (1.5 - 0.81) / (1.5 - 0) 

= 0.457, and TIMEVALSOV = (1.5 - 0.59) / (1.5 - 0) = 0.607. (Note: The values for convenience and

reliability are assumed to be the same as those calculated in Step 7a above.)

Step 7d of the modal choice analysis for the TDMP involves determining a weight profile for 

the population of the program area after implementation of the TCM. The TCM guidance calls for this

profile to be the same as the profile determined in the base case. Thus, the relative weights for cost, time,

convenience, and reliability are 0.3, 0.19, 0.3, and 0.21, respectively.

Step 7e of the modal choice analysis for the TDMP involves calculating the total utilities of each

mode of travel for the TCM case. These utilities are determined for each travel mode using the formula

shown in Step 5 above. Based on the analysis above, TUWalk/Bike = 1 * 0.3 + 0.2 * 0.3 + 0.4 * 0.19 + 0.45

* 0.21 = 0.53, TUTransit = 0.986 * 0.3 + 0.3 * 0.3 + 0.352 * 0.19 + 0.25 * 0.21 = 0.51, TUCarpool = 0.779 

* 0.3 + 0.35 * 0.3 + 0.457 * 0.19 + 0.3 * 0.21 = 0.49, and TUSOV = 0.444 * 0.3 + 0.9 * 0.3 + 0.607 * 0.19

+ 0.9 * 0.21 = 0.71.

Step 7f of the modal choice analysis for the TDMP involves estimating the percentage of time

(i.e., probability) that a person from the program area will travel via a given mode of travel after

implementation of the TCM. This percentage is calculated for each travel mode using the formula shown

in Step 6 above. Table 4 below presents the mode splits estimated under the TCM case, along with the

mode splits estimated for the base case.

Table 4: Travel Mode Choice Before and After Implementation of the TCM

Mode Split SOV Carpool Transit Walk/Bike

Base Case 68.9 8.8 5.5 16.8

TCM Case 54.8 13.2 14.7 17.3

Step 8 of the modal choice analysis for the TDMP involves estimating the daily changes in the

number of work trips made using each mode of travel. These changes are derived using the changes in

the number of Cornell faculty and staff who use each mode, as shown in Table 5 below. 
79

Table 5: Change in Number of People Using Each Mode Per Day (N = 11,481)

SOV Carpool Transit Walk/Bike

Projected Before TCM Implementation 7,916 1,015 628 1,923

Projected After TCM Implementation 6,293 1,512 1,688 1,989

Change in Mode Choice (Number of People) -1,623 497 1,060 66

The changes shown in Table 5 are converted into work trip changes as follows:

& For the SOV mode, 1,623 cars are now left at home. This number is multiplied by 2 to reflect

that work trips involve a return trip, thus yielding a total of 3,246 trips reduced per day.

& After TCM implementation, there are 497 additional carpoolers. An example in the TCM

guidance indicates that 33% of new carpoolers join existing carpools, 62% of new carpoolers

form new carpools that do not drive to park-and-ride lots, and 5% of new carpoolers form new

carpools that drive to park-and-ride lots. Based on these percentages, the total trip increase 

by new carpools is estimated to be 285.

& Of the 1,060 new transit users, this analysis assumes that 30%, or 318, drive to park-and-ride

lots. This number is divided by average vehicle occupancy for Tompkins County, yielding an

additional 263 vehicles (not including carpool park-and-ride vehicles) making trips to park-andride lots. Multiplying this figure by 2 (to account for return trips) yields 526 additional trips.

As shown in Table 6 below, summing the change in trips for each category (SOV, carpool, 

and transit) yields a net reduction of 2,435 trips per day for the TDMP.

Table 6: Work Trip Changes Per Day 

Transit 526

New Carpools 282

New Carpools with Park-and-Ride 3 (equivalent carpool trips)

Drive Alone -3,246

Total Trip Change -2,435
80

Phase 2: Effects on Travel Activity

Step 1: Potential trip effects

Step 2: Direct work and non-work trip reductions

Step 3: Indirect work and non-work trip increases

Step 4: Peak and off-peak trip shifts

Step 5: Summation of distribution of trip effects

among work peak, work off-peak, nonwork peak, and non-work off-peak trips

Step 6: Peak and off-peak VMT changes due to

reduced number of trips

Step 7: VMT changes due to reduced trip lengths

Step 8: Net VMT changes

Step 9: Peak and off-peak speed changes

Phase 2: Travel Activity Effects

Step 1 in the estimation of travel activity

effects, which involves an assessment of the

potential trip effects from the TCM program, 

is not applicable in this case.

Step 2 in the travel activity methodology

involves estimating the direct work and non-work

trip reductions from the TDMP. Direct trip

reductions are calculated using the following

formulas:

TRIPSD,W = 7 * TRIPSD

TRIPSD,NW = (1 - 7) * TRIPSD

& In the formulas, TRIPSD is the total direct trip reduction, TRIPSD,W is the

direct work trip reduction, TRIPSD,NW is the direct non-work trip reduction, 

and 7 is the fraction of trip effects that are work-related.

TRIPSD is calculated in Table 6 above to be -2,435 trips per day.

Due to the fact that TDMP is assumed to affect only work-related trips, the parameter 7 is set

equal to 1.

Using the data above, TRIPSD,W = 1 * -2,435 = -2,435, and TRIPSD,NW = (1 - 1) * -2,435 = 0. 

Summarizing these results, the TDMP is responsible for directly reducing 2,435 trips per day, all of

which are work-related.

Step 3 in the travel activity methodology involves estimating the actual indirect trip increases

(for both work and non-work trips) from the TDMP. Indirect trip increases are secondary effects that

typically result when vehicles normally used for commuting are left at home. These increases are

calculated using the following formulas:

TRIPSI,W = INCW,H * -TRIPSD / 2

TRIPSI,NW = INCN,H * -TRIPSD / 2

& In the formulas, TRIPSI,W is the indirect work trip increase, TRIPSI,NW is the

indirect non-work trip increase, and INCW,H and INCN,H are the rates of increased

SOV work and non-work trip making by household members of TCM

participants who leave their vehicles at home. The other parameter in the

formulas is defined in an earlier step of the methodology.

INCW,H is defined as NV * SHR * (SIZE - 1) * EMP * TGW, where NV is the fraction of the

population that does not own a vehicle (Note: This analysis interprets this parameter to mean the

percentage of drivers without a vehicle, which is estimated as the percentage of vehicle-owning

households in the program area that have only one vehicle.), SHR is the fraction of shared mode trips,

SIZE is average household size, EMP is the fraction of the population that is employed, and TGW is the

work trip generation rate for SOV users. NV is assumed to be 44%, based on U.S. Census data for

Tompkins County. The TDMP data indicate that 13.2% of work trips are in carpools and 14.7% are on

buses, resulting in an SHR estimate of 27.9%. (Note: This variable uses estimates generated after TCM
81

introduction.) SIZE is assumed to be 2.46, based on 1990 U.S. Census data. The value for EMP is 59%

and is taken from 1990 U.S. Census data. Based on an example in the TCM guidance, TGW is assumed

to equal 1.71. Based on these numbers, INCW,H = 0.44 * 0 .279 * (2.46 - 1) * 0.59 * 1.71 = 0.18.

INCN,H is defined as NV * SHR * (SIZE - 1) * UNEMP * TGN, where NV, SHR, and SIZE are as

defined above, UNEMP is the fraction of the population that is not employed, and TGN is the non-work

trip generation rate for SOV users. UNEMP is simply (1 - EMP) and thus equals 41%. TGN is assumed

to be the same as TGW (i.e., 1.71). Based on these numbers, INCN,H = 0.44 * 0.279 * (2.46 - 1) * 0.41 

* 1.71 = 0.13.

Using the data above, TRIPSI,W = 0.18 * -(-2,435) / 2 = 219, and TRIPSI,NW = 0.13 * -(-2,435)

/ 2 = 158. Summarizing these results, the TDMP is indirectly responsible for an increase of 219 work

trips per day and 158 non-work trips per day.

Step 4 in EPA’s methodology for estimating travel activity effects of TCMs, which involves

determining direct peak and off-peak period trip shifts, is not relevant to the analysis of the TDMP.

Step 5 in the travel activity methodology involves estimating the net trip changes from the

TDMP as distributed between work and non-work trips and peak and off-peak periods. These changes

are calculated using the following formulas:

NETRPW,P = 7 * TRIPSS,P + PKW * (TRIPSD,W + TRIPSI,W)

NETRPW,OP = 7 * TRIPSS,OP + (1 - PKW) * (TRIPSD,W + TRIPSI,W)

NETRPNW,P = (1 - 7) * TRIPSS,P + PKNW * (TRIPSD,NW + TRIPSI,NW)

NETRPNW,OP = (1 - 7) * TRIPSS,OP + (1 - PKNW) * (TRIPSD,NW + TRIPSI,NW)

& In the formulas, NETRPW,P is the net work trip change in the peak period,

NETRPW,OP is net work trip change in the off-peak period, NETRPNW,P is the

net non-work trip change in the peak period, and NETRPNW,OP is the net 

non-work trip change in the off-peak period. TRIPSS,P is the change in peak

period trips, and TRIPSS,OP is the change in off-peak period trips. PKW is the

observed fraction of work trips during the peak period, and PKNW is the observed

fraction of non-work trips during the peak period. The other parameters in the

formulas are defined in earlier steps of the methodology.

Because there are no trip shifts associated with the TDMP (see Step 4), TRIPSS,P and

TRIPSS,OP are each equal to 0.

The values used for PKW and PKNW are 0.7 and 0.3, respectively, based on an example in the

TCM guidance and assuming that peak travel hours are from 6 a.m. to 9 a.m. and 4 p.m. to 7 p.m.

Using the data above, NETRPW,P = 0 + 0.7 * (-2,435 + 219) = -1,551, NETRPW,OP = 0 + (1 -

0.7) * (-2,435 + 219) = -665, NETRPNW,P = 0 + 0.3 * (0 + 158) = 47, and NETRPNW,OP = 0 * (1 - 0.3) 

* (0 + 158) = 107. Summarizing these results, the TDMP results in net decreases in peak and off-peak

work trips of 1,551 per day and 665 per day, respectively. The program also results in increases in peak

and off-peak non-work trips of 47 per day and 107 per day, respectively.

Step 6 in the travel activity methodology involves estimating the peak and off-peak VMT

changes due to the trip changes from the TDMP. These changes are calculated using the following

formulas:
82

VMTP = (NETRPW,P * DISTW) + (NETRPNW,P * DISTNW)

VMTOP = (NETRPW,OP * DISTW) + (NETRPNW,OP * DISTNW)

& In the formulas, VMTP is the change in peak-period VMT due to trip changes,

VMTOP is the change in off-peak VMT due to trip changes, DISTW is the

average VMT per trip for work trips, and DISTNW is the average VMT per trip

for non-work trips. The other parameters in the formulas are defined in earlier

steps of the methodology.

DISTW is derived to be 8.51 miles per trip based on the analysis of modal choice. DISTNW is

assumed to be 6.3 miles, based on work trip data for Tompkins County and data on work and non-work

trip distances reported in the 1996 Statistical Abstract of the United States.

Using the data above, VMTP = (-1,551 * 8.51) + (47 * 6.3) = -12,903 and VMTOP = (-665 *

8.51) + (107 * 6.3) = -4,978. Summarizing these results, the TDMP reduces peak-period VMT by 12,903

miles per day due to trip changes and reduces off-peak VMT by 4,978 miles per day due to trip changes.

Step 7 in the travel activity methodology involves estimating the VMT changes due to trip length

changes resulting from the TDMP. This step is not necessary, as it has been accounted for in the

estimation of TRIPSD.

Step 8 in the travel activity methodology involves estimating the total peak and off-peak VMT

changes resulting from the TDMP. These changes are calculated using the following formulas:

NETVMTP = VMTP + PKW * VMTL,W + PKNW * VMTL,NW

NETVMTOP = VMTOP + (1 - PKW) * VMTL,W + (1 - PKNW) * VMTL,NW

& In the formulas, NETVMTP is the total change in peak period VMT, and

NETVMTOP is the total change in off-peak VMT. The other parameters in the

formulas are defined in earlier steps of the methodology.

Because VMT changes due to trip length changes have already been accounted for in the

analysis, VMTL,W and VMTL,NW are each set equal to 0.

Using the data above, NETVMTP = -12,903 + 0.7 * 0 + 0.3 * 0 = -12,903 and NETVMTOP 

= -4,978 + (1 - 0.7) * 0 + (1 - 0.3) * 0 = -4,978. Summarizing these results, the TDMP reduces peakperiod VMT by a total of 12,903 miles per day and off-peak VMT by a total of 4,978 miles per day.

Step 9 in the travel activity methodology involves estimating peak and off-peak speed changes

resulting from the TDMP. These changes are calculated using the following formulas:

SPDP = (NETVMTP / TOTVMTP) * P

SPDOP = (NETVMTOP / TOTVMTOP) * OP

& In the formulas, SPDP is the percentage change in peak-period speeds, SPDOP

is the change in off-peak speeds, TOTVMTP is total peak-period VMT for the

program area, TOTVMTOP is total off-peak VMT for the program area, P is the

elasticity of peak-period speed with respect to volume, and OP is the elasticity 

of off-peak speed with respect to volume. The other parameters in the formulas

are defined in earlier steps of the methodology.
83

Phase 3: Effects on Emissions

Step 1: Effect of trip changes on emissions

1a: Distribution of trip changes among vehicle

types

1b: Changes in cold-start and hot-start trips

1c: Cold-start and hot-start emission factors by

pollutant and vehicle type

1d: Cold-start and hot-start emission changes

for the project

1e: Hot-soak emission changes

1f: Diurnal changes by vehicle type

1g: Summation of trip related emission changes

Step 2: Effect of VMT changes on emissions

2a: Distribution of VMT changes among

vehicle types

2b: Hot-stabilized exhaust emission changes by

vehicle type

2c: VMT-related evaporative emission changes

2d: Summation of VMT-related emission

changes

Step 3: Emission effects due to speed changes

3a: Peak and off-peak speed after

implementation

3b: Peak and off-peak VMT after

implementation

3c: Peak and off-peak emissions changes due

to changes in speeds

3d: Summation of speed related changes

Step 4: Summation of emission effects

Total VMT in Tompkins County is approximately 1,662,000 miles per day. This analysis

assumes that half of this VMT is work-related. Combining this information with the assumptions from

Step 5 that 70% of work-related trips occur in the peak period and 30% of non-work trips occur in the

peak period yields a value of 831,000 miles per day for each of TOTVMTP and TOTVMTOP.

The parameter P is assumed to be -0.75, based on an example provided in the TCM guidance

document. The parameter OP is assumed to be 0, because changes in off-peak VMT are not likely to

affect vehicle speeds (i.e., due to a lack of congestion).

Using the data above, SPDP = -12,903 

/ 831,000 * -0.75 = 0.0116 and SPDOP = -4,978 

/ 831,000 * 0 = 0. Summarizing these results, 

the TDMP increases peak-period speeds by approximately 1.16% but has no effect on 

off-peak speeds.

Phase 3: Emission Effects -- STEP 1 (Trip Changes)

Step 1 in the estimation of the emission

effects for the TDMP involves calculating the

effect of trip changes on emissions. This step 

is broken down into seven smaller steps 

(1a through 1g), which are outlined below.

Step 1a in the emission methodology

involves estimating the distribution of trip

changes for the TDMP. These changes are

calculated using the following formulas:

TRIP,LDGV = TRIPLDGV / (TRIPLDGV + TRIPLDGT1)

TRIP,LDGT1 = 1 - TRIP,LDGV
84

& In the formulas, TRIP,LDGV is the fraction of TCM-affected trips taken by lightduty gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected trips

taken by light-duty gasoline trucks (LDGT1s), TRIPLDGV is the fraction of total

trips in the region taken by LDGVs, and TRIPLDGT1 is the fraction of total trips in

the region taken by LDGT1s. (Note: Most TCMs that can be analyzed using

EPA’s guidance document affect only LDGVs or LDGT1s. Thus, the sum of

TRIP,LDGV and TRIP,LDGT1 is typically equal to one.)

According to a study on the TDMP, TRIPLDGV and TRIPLDGT1 for the program area are equal 

to 0.86 and 0.14, respectively.

Using the data above, TRIP,LDGV = 0.86 / (0.86 + 0.14) = 0.86 and TRIP,LDGT1 = 1 - 0.86 = 0.14. 

Summarizing these results, 86% of the trips affected by the TDMP are taken by LDGVs, and 14% are

taken by LDGT1s.

Step 1b in the emission methodology involves calculating cold-start and hot-start trip changes

for the TDMP. These changes are calculated using the following formulas:

TRIPSCST = CST,W * (NETRPW,P + NETRPW,OP) + CST, NW * (NETRPNW,P + NETRPNW,OP)

TRIPSHST = (1 - CST,W) * (NETRPW,P + NETRPW,OP) + (1 - CST,NW) * (NETRPNW,P +

NETRPNW,OP)

& In the formulas, TRIPSCST is the number of cold-start trip changes, TRIPSHST

is the number of hot-start trip changes, CST,W is the fraction of work trips begun

in the cold-start mode, and CST, NW is the fraction of non-work trips begun in the

cold-start mode. The other parameters in the formulas are defined in earlier

steps of the methodology.

Because work trips are mostly cold-start trips, the guidance calls for CST,W to be set equal to 1. 

The guidance also suggests that CST,NW be set equal to 0.43, which is the default fraction of cold starts

used in the Federal Test Procedure (FTP).

Using the data above, TRIPSCST = 1 * (-1,551 + -665) + 0.43 * (47 + 107) = -2,150 and

TRIPSHST = (1 - 1) * (-1,551 + -665) + (1 - 0.43) * (47 + 107) = 88. Summarizing these results, the

TDMP results in a reduction of 2,150 cold-start trips per day and an increase of 88 hot-start trips per day.

Step 1c in the emission methodology involves determining cold-start and hot-start emission

factors. These changes are calculated for a given pollutant and vehicle class using the following

formulas:

CST = (EXH100%CST,26MPH - EXH100%STB,26MPH) * 3.59

HST = (EXH100%HST,26MPH - EXH100%STB,26MPH) * 3.59

& In the formulas, CST is the cold-start emission factor in grams per trip, HST 

is the hot-start emission factor in grams per trip, and EXH is the MOBILE

emission factor in grams per mile. The 3.59 factor is the FTP driving cycle 

trip-start miles per trip, and 26 miles per hour is the speed for the start portion 

of the FTP driving cycle. (Note: The subscripts on EXH refer to the operating

conditions and speed at which MOBILE evaluates EXH. For example,

“100%CST,26MPH” indicates 100% cold-start operating mode at 26 miles per

hour vehicle speed.)
85

Using national default data from MOBILE, CSTLDGV,HC = (2.55 - 0.95) * 3.59 = 5.74 grams per

trip, CSTLDGT1,HC = (3.59 - 1.34) * 3.59 = 8.08 grams per trip, HSTLDGV,HC = (1.35 - 0.95) * 3.59 = 1.44

grams per trip, and HSTLDGT1,HC = (1.99 - 1.34) * 3.59 = 2.33 grams per trip. (Following the same

methodology, the cold-start and hot-start emission factors can also be determined for NOx and CO.)

Step 1d in the emission methodology involves determining cold-start and hot-start emission

changes for the TDMP. These changes are calculated using the following formulas:

HCCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,HC) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,HC)

HCHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,HC) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,HC)

NOxCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,NOx) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,NOx)

NOxHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,NOx) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,NOx)

COCST = (TRIPSCST * TRIP,LDGV * CSTLDGV,CO) + (TRIPSCST * TRIP,LDGT1 * CSTLDGT1,CO)

COHST = (TRIPSHST * TRIP,LDGT1 * HSTLDGV,CO) + (TRIPSHST * TRIP,LDGT1 * HSTLDGT1,CO)

& In the formulas, HCCST, NOxCST, and COCST are the changes in cold-start

emissions for HC, NOx, and CO, respectively; and HCHST, NOxHST, and

COHST are the changes in hot-start emissions for HC, NOx, and CO,

respectively. The other parameters in the formulas are defined in earlier steps 

of the methodology.

Using national default data from MOBILE, HCCST = (-2,150 * 0.86 * 5.74) + (-2,150 * 0.14 

* 8.08) = -13,045 and HCHST = (88 * 0.86 * 1.44) + (88 * 0.14 * 2.33) = 138. Summarizing these

results, the TDMP results in a reduction in cold-start HC emissions of 13,045 grams per day and an

increase in hot-start HC emissions of 138 grams per day. (Following the same methodology, the coldstart and hot-start emission changes can also be determined for NOx and CO.)

Step 1e in the emission methodology involves determining hot soak emission changes for the

TDMP. These changes are calculated using the following formula:

HCHSK = (TRIPSTOTAL * TRIP,LDGV * HSKLDGV) + (TRIPSTOTAL * TRIP,LDGT1 * HSKLDGT1)

& In the formula, HCHSK is the change in hot soak emissions, TRIPSTOTAL is the

total change in trips, and HSK is the hot soak emission factor in grams per trip. 

(Note: Hot soak emissions are HC emissions only.)

TRIPSTOTAL = NETRPW,P + NETRPW,OP + NETRPNW,P + NETRPNW,OP. 

Thus, TRIPSTOTAL = -1,551 + -665 + 47 + 107 = -2,062.

Using national default data from MOBILE, HCHSK = (-2,062 * 0.86 * 3.06) + (-2,062 * 0.14 

* 3.60) = -6,466. Summarizing this result, the TDMP results in a reduction in hot soak emissions of

6,466 grams per day.

Step 1f in the emission methodology involves determining diurnal emission changes for 

the TDMP. These changes are calculated for a given vehicle class using the following formulas:

HCDNL,W = 0.676 * (NETRPW,P + NETRPW,OP) / TPDW * TRIP * (WDI - MDI)

HCDNL,NW = 0.676 * (NETRPNW,P + NETRPNW,OP) / TPDNW * TRIP * (WDI - MDI)
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HCDNL = HCDNL,W,LDGV + HCDNL,NW,LDGV + HCDNL,W,LDGT1 + HCDNL,NW,LDGT1

& In the formulas, HCDNL,W is the change in diurnal emissions associated with

work trips, HCDNL,NW is the change in diurnal emissions associated with nonwork trips, and HCDNL is the total change in diurnal emissions. TPDW is the

number of work trips per day per vehicle, and TPDNW is the number of non-work

trips per day per vehicle. WDI is the weighted diurnal emission factor in grams,

and MDI is the multi-day diurnal emission factor in grams. The other parameters

in the formulas are defined in earlier steps of the methodology. (Note: Diurnal

emissions are HC emissions only.)

The value used for TPDW is 2, since a commuter makes typically makes two work trips per day

(i.e., one trip from home to work, one trip from work to home). TPDNW is equal to TGN from Step 3 of

the “Travel Activity Effects” section above, and thus equals 1.71.

Using national default data from MOBILE, HCDNL,W,LDGV = 0.676 * (-1,551 + -665) / 2 * 0.86 

* (3.30 - 6.04) = 1,765, HCDNL,NW,LDGV = 0.676 * (47 + 107) / 1.71 * 0.86 * (3.30 - 6.04) = -143,

HCDNL,W,LDGT1 = 0.676 * (-1,551 + -665) / 2 * 0.14 * (5.11 - 15.33) = 1,072, HCDNL,NW,LDGT1 = 0.676 

* (47 + 107) / 1.71 * 0.14 * (5.11 - 15.33) = -87, and HCDNL = 1,765 + -143 + 1,072 + -87 = 2607. 

Summarizing these results, the TDMP results in a net increase in diurnal emissions of 2,607 grams 

per day.

Step 1g in the emission methodology involves calculating the total trip-related emission changes

for the TDMP. These changes are calculated using the following formulas:

HCTRIP = HCCST + HCHST + HCHSK + HCDNL

NOxTRIP = NOxCST + NOxHST

COTRIP = COCST + COHST

& In the formulas, HCTRIP, NOxTRIP, and COTRIP are the total changes in HC,

NOx, and CO emissions, respectively, due to trip changes.

Using the data above, HCTRIP = -13,045 + 138 + -6,466 + 2,607 = -16,766. Summarizing this

result, the TDMP results in a net decrease in trip-related HC emissions of 16,766 grams per day. 

(Following the same methodology, total trip-related emission changes can also be determined for NOx

and CO.)

Emission Effects -- STEP 2 (VMT Changes)

Step 2 in the estimation of the emission effects for the TDMP involves calculating the effect 

of VMT changes on emissions. This step is broken down into four smaller steps (2a through 2d), which

are outlined below.

Step 2a in the emission methodology involves estimating the distribution of VMT changes for

the TDMP. These changes are calculated using the following formulas:

VMT,LDGV = VMTLDGV / (VMTLDGV + VMTLDGT1)

VMT,LDGT1 = 1 - VMT,LDGV

& In the formulas, VMT,LDGV is the fraction of TCM-affected VMT for light-duty

gasoline vehicles (LDGVs), TRIP,LDGT1 is the fraction of TCM-affected VMT 
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for light-duty gasoline trucks (LDGT1s), VMTLDGV is the fraction of total VMT

in the region for LDGVs, and VMTLDGT1 is the fraction of total VMT in the

region for LDGT1s. (Note: Most TCMs that can be analyzed using EPA’s

guidance document affect only LDGVs or LDGT1s. Thus, the sum of VMT,LDGV

and VMT,LDGT1 is typically equal to one.)

According to a study on the TDMP, VMTLDGV and VMTLDGT1 for the program area are equal 

to 0.86 and 0.14, respectively.

Using the data above, VMT,LDGV = 0.86 / (0.86 + 0.14) = 0.86 and VMT,LDGT1 = 1 - 0.86 = 0.14. 

Summarizing these results, 86% of the VMT affected by the TDMP is by LDGVs, and 14% is by

LDGT1s.

Step 2b in the emission methodology involves estimating hot-stabilized exhaust emission

changes for the TDMP. These changes are calculated using the following formulas:

HCSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,HC,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,HC,P)

HCSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,HC,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,HC,OP)

NOxSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,NOx,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,NOx,P)

NOxSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,NOx,OP) + (NETVMTOP * VMT,LDGT1 *

STBLDGT1,NOx,OP)

COSTB,P = (NETVMTP * VMT,LDGV * STBLDGV,CO,P) + (NETVMTP * VMT,LDGT1 * STBLDGT1,CO,P)

COSTB,OP = (NETVMTOP * VMT,LDGV * STBLDGV,CO,OP) + (NETVMTOP * VMT,LDGT1 * STBLDGT1,CO,OP)

& In the formulas, HCSTB,P, NOxSTB,P, and COSTB,P are the peak-period changes

in hot-stabilized emissions for HC, NOx, and CO, respectively; and HCSTB,OP,

NOxSTB,OP, and COSTB,OP are the off-peak changes in hot-stabilized emissions

for HC, NOx, and CO, respectively. STBP is the hot-stabilized emission factor

(in grams per mile) for each pollutant and vehicle class for the peak period

(during which average vehicle speed is assumed to be 20 miles per hour), 

and STBOP is the hot-stabilized emission factor (in grams per mile) for each

pollutant and vehicle class for the off-peak period (during which average vehicle

speed is assumed to be 35 miles per hour). The other parameters in the formulas

are defined in earlier steps of the methodology.

Using national default data from MOBILE, HCSTB,P = (-12,903 * 0.86 * 1.23) + (-12,903 * 0.14

* 1.77) = -16,846 and HCSTB,OP = (-4,978 * 0.86 * 0.69) + (-4,978 * 0.14 * 0.94) = -3,609. Summarizing

these results, the TDMP results in a reduction in peak-period hot-stabilized HC exhaust emissions 

of 16,846 grams per day and a reduction in off-peak hot-stabilized HC exhaust emissions of 3,609 grams

per day. (Following the same methodology, hot-stabilized exhaust emission changes can also be

determined for NOx and CO.)

Step 2c in the emission methodology involves estimating VMT-related evaporative emission

changes for the TDMP. These changes are calculated using the following formulas:

HCVEVP,P = (NETVMTP * VMT,LDGV * VEVPLDGV,P) + (NETVMTP * VMT,LDGT1 * VEVPLDGT1,P)

HCVEVP,OP = (NETVMTOP * VMT,LDGV * VEVPLDGV,OP) + (NETVMTOP * VMT,LDGT1 * VEVPLDGT1,OP)
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& In the formulas, HCVEVP,P is the change in peak-period evaporative emissions,

HCVEVP,OP is the change in off-peak evaporative emissions, and VEVP is the

VMT-related evaporative emission factor (in grams per mile) for each vehicle

class and time period (peak or off-peak). The other parameters in the formulas

are defined in earlier steps of the methodology. (Note: Evaporative emissions

are HC emissions only.)

Using national default data from MOBILE, HCVEVP,P = (-12,903 * 0.86 * 0.44) + (-12,903 

* 0.14 * 0.53) = -5,840 and HCVEVP,OP = (-4,978 * 0.86 * 0.34) + (-4,978 * 0.14 * 0.44) = -1,762. 

Summarizing these results, the TDMP results in a reduction in peak-period evaporative emissions 

of 5,840 grams per day and a reduction in off-peak evaporative emissions of 1,762 grams per day.

Step 2d in the emission methodology involves calculating the total VMT-related emission

changes for the TDMP. These changes are calculated using the following formulas:

HCVMT = HCSTB,P + HCSTB,OP + HCVEVP,P + HCVEVP,OP

NOxVMT = NOxSTB,P + NOxSTB,OP

COVMT = COSTB,P + COSTB,OP

& In the formulas, HCVMT, NOxVMT, and COVMT are the total changes in HC,

NOx, and CO emissions, respectively, due to VMT changes.

Using the data above, HCVMT = -16,846 + -3,609 + -5,840 + -1,762 = -28,057. Summarizing

this result, the TDMP results in a net decrease in VMT-related HC emissions of 28,057 grams per day. 

(Following the same methodology, total VMT-related emission changes can also be determined for NOx

and CO.)

Emission Effects -- STEP 3 (Speed Changes)

Step 3 in the estimation of the emission effects for the TDMP involves calculating the effect 

of speed changes on emissions. This step is broken down into four smaller steps (3a through 3d), which

are outlined below.

Step 3a in the emission methodology involves estimating the speeds associated with the TDMP. 

These speeds are calculated using the following formulas:

SPEEDP,TCM = SPEEDP,BASE * (1 + SPDP)

SPEEDOP,TCM = SPEEDOP,BASE * (1 + SPDOP)

& In the formulas, SPEEDP,TCM is the peak-period speed after implementation of the

TCM, SPEEDOP,TCM is the off-peak speed after implementation of the TCM,

SPEEDP,BASE is the peak-period speed prior to implementation of the TCM, 

and SPEEDOP,BASE is the off-peak speed prior to implementation of the TCM. 

The other parameters in the formulas are defined in earlier steps of the

methodology.

For this analysis, SPEEDP,BASE is assumed to be 30 miles per hour, and SPEEDOP,BASE is assumed

to be 35 miles per hour.

Using the data above, SPEEDP,TCM = 30 * (1 + 0.0116) = 30.35 and SPEEDOP,TCM = 35 * (1 + 0) 

= 35. Summarizing these results, peak-period speeds have slightly increased from 30 miles per hour 
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to 30.35 miles per hour due to the TDMP. Off-peak speeds have not changed due to the program.

Step 3b in the emission methodology involves estimating the total VMT for the program area

after implementation of the TDMP. These VMT figures are calculated using the following formulas:

VMTP,TCM = TOTVMTP + NETVMTP

VMTOP,TCM = TOTVMTOP + NETVMTOP

& In the formulas, VMTP,TCM is the total peak-period VMT in the program area

after implementation of the TCM, and VMTOP,TCM is the total off-peak VMT 

in the program area after implementation of the TCM. The other parameters 

in the formulas are defined in earlier steps of the methodology.

Using data from Step 9 of the “Travel Activity Effects” section above, VMTP,TCM = 831,000

 + -12,903 = 818,097 and VMTOP,TCM = 831,000 + -4,978 = 826,022. Summarizing these results, 

peak-period VMT has decreased from 831,000 miles per day to 818,097 miles per day due to the TDMP. 

Off-peak VMT has decreased from 831,000 miles per day to 826,022 miles per day due to the program.

Step 3c in the emission methodology involves estimating peak-period and off-peak emission

changes due to changes in vehicle speeds. These changes are calculated using the following formulas:

HCSPD,P = VMTP,TCM * (STBFLT,HC,P,TCM + RNLFLT,P,TCM) - VMTP,TCM * (STBFLT,HC,P,BASE + RNLFLT,P,BASE)

HCSPD,OP = VMTOP,TCM * (STBFLT,HC,OP,TCM + RNLFLT,OP,TCM) - VMTOP,TCM * (STBFLT,HC,OP,BASE + RNLFLT,OP,BASE)

NOxSPD,P = VMTP,TCM * (STBFLT,NOx,P,TCM - STBFLT,NOx,P,BASE)

NOxSPD,OP = VMTOP,TCM * (STBFLT,NOx,OP,TCM - STBFLT,NOx,OP,BASE)

COSPD,P = VMTP,TCM * (STBFLT,CO,P,TCM - STBFLT,CO,P,BASE)

COSPD,OP = VMTOP,TCM * (STBFLT,CO,OP,TCM - STBFLT,CO,OP,BASE)

& In the formulas, HCSPD,P, NOxSPD,P, and COSPD,P are the peak-period changes

in emissions for HC, NOx, and CO, respectively, due to a change in speeds; 

and HCSPD,OP, NOxSPD,OP, and COSPD,OP are the off-peak changes in emissions

for HC, NOx, and CO, respectively, due to a change in speeds. STBFLT is the

fleet-wide hot-stabilized emission factor (in grams per mile) for each pollutant,

time period (i.e., peak or off-peak), and scenario (i.e., base or TCM). RNLFLT 

is the fleet-wide running loss emission factor (in grams per mile) for each time

period and scenario. The other parameters in the formulas are defined in earlier

steps of the methodology.

Based on data showing the relationship between vehicle speed and emissions, this analysis

assumes that the elasticity of STBFLT with respect to speed is -1 for HC, 0 for NOx, and -1 for CO. 

Thus, a 1% increase in speed is assumed to result in a 1% decrease in HC and CO emissions (on a grams

per mile basis) and no change in NOx emissions. The elasticity of RNLFLT with respect to speed is also

assumed to be -1. 

Using national default data from MOBILE, HCSPD,P = 818,097 * (1.916 + 0.119) - 818,097 

* (1.938 + 0.120) = -18,816 and HCSPD,OP = 826,022 * (1.938 + 0.120) - 826,022 * (1.938 + 0.120) = 0. 

Summarizing these results, the TDMP results in a decrease in speed-related HC emissions of 18,816

grams per day for the peak period but does not change speed-related HC emissions for the off-peak
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period. (Following the same methodology, the peak-period and off-peak emission changes due to

changes in speeds can also be determined for NOx and CO.)

Step 3d in the emission methodology involves calculating the total speed-related emission

changes for the TDMP. These changes are calculated using the following formulas:

HCSPD = HCSPD,P + HCSPD,OP

NOxSPD = NOxSPD,P + NOxSPD,OP

COSPD = COSPD,P + COSPD,OP

& In the formulas, HCSPD, NOxSPD, and COSPD are the total changes in HC,

NOx, and CO emissions, respectively, due to speed changes.

Using the data above, HCSPD = -18,816 + 0 = -18,816. Summarizing this result, the TDMP

results in a net decrease in speed-related HC emissions of 18,816 grams per day. (Following the same

methodology, total speed-related emission changes can also be determined for NOx and CO.)

Emission Effects -- STEP 4 (Total)

Step 4 in the estimation of the emission effects for the TDMP involves calculating the total

changes in HC, NOx, and CO emissions. These changes are calculated using the following formulas:

 

HC = HCTRIP + HCVMT + HCSPD

NOx = NOxTRIP + NOxVMT + NOxSPD

CO = COTRIP + COVMT + COSPD

& In the formulas, HC, NOx, and CO are the total changes in HC, NOx, 

and CO emissions, respectively, due to the TCM program.

Using the data above, HC = -16,766 + -28,057 + -18,816 = -63,639. Summarizing this result,

the TDMP results in a net decrease in HC emissions of 63,639 grams per day, or approximately 0.07 tons

per day. (Following the same methodology, total emission changes can also be determined for NOx 

and CO.)