COMMUTER Model User

Manual for Analysis of

Voluntary Mobile Source

Emission Reduction and

Commuter Choice

Incentive Programs

United States

Environmental Protection

Agency

Air and Radiation EPA420-R-00-016

October 2000
COMMUTER Model User Manual for

Analysis of Voluntary Mobile Source Emission Reduction and 

Commuter Choice Incentive Programs

prepared for:

U. S. Environmental Protection Agency

prepared by:

Thomas R. Carlson

Robert G. Dulla J. Richard Kuzmyak

Sierra Research, Inc.

1801 J Street 9509 Woodstock Court

Sacramento, CA 95814 Silver Springs, MD

(916) 444-6666 (301) 495-8814
-iCOMMUTER Model User Manual for

Analysis of Voluntary Mobile Source Emission Reduction and 

Commuter Choice Incentive Programs

Table of Contents

page

1. INTRODUCTION ..........................................................1

1.1 What is the COMMUTER model? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Who will use COMMUTER? .............................................1

1.3 Why was COMMUTER created? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.4 What programs can I evaluate with COMMUTER? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.5 What methodology does COMMUTER use? .................................2

1.6 When can I use COMMUTER and when should I not use it? ....................3

1.7 What do I need to do to get started? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.8 What other documentation is available? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. USING THE MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1 What type of computer equipment and software do I need? . . . . . . . . . . . . . . . . . . . . . . 5

2.2 How do I install and operate COMMUTER? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3 How do I begin once the program is installed? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.4 How do I input data? ....................................................9

2.5 Is there help available when inputting data? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.6 Can I save my inputs to use in another analysis? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.7 Can I use my own emission factors? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.8 How do I view the results? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.9 How do I print my data and results? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.10 Can I tell the model to remember where my files are stored? . . . . . . . . . . . . . . . . . . . . 19

2.11 What do I do when I’m finished? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3. GENERAL INPUT SCREENS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.1 Scenario Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2 Local Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.3 Edit Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
-iiTable of Contents, continued

page

4. TCM-SPECIFIC DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.1 Site Access and Transit Service Improvement Programs . . . . . . . . . . . . . . . . . . . . . . . 32

4.2 Financial Incentive and Parking Cost Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.3 Site-Specific Employer Support Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.4 Area-Wide Employer Support Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4.5 Alternative Work Schedule Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5. EMISSIONS-RELATED INPUT SCREENS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5.1 Fleet Emissions Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5.2 Other Emissions-Related Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

6. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
-iiiList of Tables

page

Table 1 Summary of COMMUTER Data Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 2 Default Speeds (mph) by Area Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

List of Figures

page

Figure 1 COMMUTER Startup Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 2 Menu Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 3 Model Layout Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 4 Sample Output Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 5 Scenario Information Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 6 Local Data Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Figure 7 Edit Coefficients Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 8 Site Access and Transit Improvements Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 9 Financial Incentives Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 10 Site-Specific Employer Support Programs Input Screen . . . . . . . . . . . . . . . . . . . . . . 38

Figure 11 Area-Wide Employer Support Programs Input Screen . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 12 Alternative Work Schedules Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 13 Fleet Emissions Information Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Figure 14 Other Emissions-Related Data Input Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
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1. INTRODUCTION

1.1 What is the COMMUTER model?

The COMMUTER model (subsequently referred to as simply “COMMUTER”) is a

spreadsheet-based computer model that estimates the travel and emissions impacts of

transportation air quality programs. The model is particularly useful for programs that fall

under the EPA’s Voluntary Mobile Source Emission Reduction Programs and for Commuter

Choice Programs.

1.2 Who will use COMMUTER?

EPA and its subcontractor Sierra Research designed COMMUTER for two types of users: 

• Metropolitan Planning Organizations (MPOs) and state Departments of

Transportation (DOTs) who are assessing emissions impacts of various

Transportation Control Measure Strategies. These impacts can be incorporated into

State Implementation Plan (SIP) analyses. 

• Individual employers who are assessing the likely effectiveness of Commuter Choice

Programs and voluntary programs in general.

MPOs and DOTs can also provide guidance and assistance to employers participating in

voluntary programs on the application of this tool. 

1.3 Why was COMMUTER created?

COMMUTER was designed to help simplify the effort required by air quality planners to

estimate travel and emission effects resulting from Transportation Control Measures. The

model can also be used to estimate the benefits of site-specific Commuter Choice (employerbased transportation) programs to assist employers in designing a program appropriate for

them.

The 1990 Clean Air Act Amendments mandated that the EPA and DOT provide guidance on

“the formulation and emission reduction potential of transportation control measures related

to criteria pollutants and their precursors” (Section 108(f)). In the early 1990s, EPA
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developed a number of tools and guidance documents to assist communities in developing

these measures and taking credit for the resulting emission reductions. Because the effects of

TCMs on travel activity and emissions can be very complex, the guidance included many

aspects of vehicle operation and other factors that affect emissions. The guidance documents

were often very detailed and difficult to use. 

COMMUTER consolidates existing TCM guidance, and is based on “state-of- practice”

methodologies and data. COMMUTER will reduce the time required to calculate the benefits

of regional and employer-based TCMs. It will also save regional government resources,

since these governments will have less need to develop their own models and tools.

1.4 What Programs can I evaluate with COMMUTER?

You can use COMMUTER to evaluate these types of programs, either on the regional scale,

or for individual employers:

• Transit fare decreases or other incentives that reduce the cost of using transit;

• Transit service improvements (faster or more frequent service);

• Ridesharing programs, in which employers support carpooling and/or vanpooling

through on-site programs, financial incentives, or preferential parking;

• Other actions, such as increased parking charges or cash-out programs, that change

the time and/or cost of traveling by any particular mode;

• Non-motorized (e.g., bicycle and pedestrian) commuting programs; 

• Alternative work schedules, including flex-time, compressed work weeks, and

staggered work hours; and

• Telecommuting.

1.5 What methodology does COMMUTER use?

COMMUTER is broken down into two components: travel impacts and emissions impacts.

The travel impacts component uses a logit mode-choice model referred to as the “pivot point”

approach. This approach allows you to analyze the effects of several strategies

simultaneously. Mode choice models have been developed for many cities and regions

nationwide, so you can often use coefficients that have already been developed to reflect local

characteristics. This component will calculate the impact of the mode share changes from

these programs and translate the mode share changes into changes in trips and vehicle miles

traveled (VMT). In addition, COMMUTER contains an input option that allows you to enter
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mode share changes directly (such as might be obtained from employee survey data) as an

alternative to the pivot point-based calculation performed internally by the model.

The emissions component is based on EPA’s MOBILE5b model. MOBILE5b emission

factors were generated and loaded into COMMUTER for several sets of local conditions. 

You can select the conditions most appropriate for your area, and the model will apply the

corresponding emission factors in calculating and outputting emission reduction impacts (in

tons of VOC, CO, and NOx per day). If you are an experienced MOBILE5b user, you can

also generate your own set of MOBILE5b emission factors (reflecting your exact local

conditions) that can be imported into COMMUTER. 

 

1.6 When can I use COMMUTER, and when should I not use it?

COMMUTER is particularly useful for smaller Transportation Control Measures that will fit

under the context of the Voluntary Measures Policy, and the model can be used for the

purpose of calculating State Implementation Plan (SIP) credit. The model will not perform as

well for larger programs, particularly those large enough to impact travel speeds throughout

an area. If your program is likely to significantly impact travel patterns and speed in your

region, you will need to perform a more complete analysis using your regional travel demand

modeling in order to claim SIP credit. You should consult with your regional EPA office if

you believe your program can have these impacts. In this case, you can still use

COMMUTER to calculate an initial estimate of a potential program. You may want to do

this to help you select a program and determine if you want to further consider particular

options. 

In some cases, you may also use COMMUTER to calculate the VMT impacts of projects for

transportation conformity. You should not use the emissions estimates of the model in this

cases. Areas that are subject to transportation conformity must estimate the VMT and

emissions impacts of the projects in their transportation plans and transportation

improvement programs. For projects that are not regionally significant (as defined in 40 CFR

93.101), you may estimate the VMT effects using off-model techniques, in accordance with

reasonable professional practice. This means you do not need to determine the VMT impacts

of the program using a travel demand network model. Through the interagency consultation

process, you can discuss whether COMMUTER is an appropriate off-model method to

estimate VMT reductions. You will still need to combine the estimated VMT impacts of the

program with the impacts of other programs to determine the overall emissions impacts in the

area.

1.7 What do I need to do to get started? 

In order to get the most accurate results with the model, you will need to gather background

information about the travel characteristics in your area. COMMUTER does have data on

national average travel patterns available as default settings. However, using local data will

yield more accurate results. This greater accuracy is required if COMMUTER results are to

be used as a part of a State Implementation Plan or other regional air quality management 
* Superscripts denote references provided in Section 6.

-4-

IMPORTANT: COMMUTER is not designed to quantify baseline

travel or emissions. Instead, its purpose is to estimate travel and

emission changes associated with specific measures, based on

inputs you provide. Thus, although COMMUTER may be used to

calculated SIP credits for these measures, the baseline travel or

emissions estimates it generates will not exactly match your

baseline SIP inventory.

plan. MPOs or Councils of Government (COGs) generally compile this information for an

area. Regional COGs are local government organizations designed to study and recommend

solutions to problems facing an individual region and to help their local government

members apply effective, coordinated regional planning. MPOs are similar organizations that

focus on transportation-related planning. 

If you are an employer or other non-MPO user of this model, you should contact the MPO or

COG in your area. The National Association of Regional Councils (NARC) maintains an

Internet website at http://www.narc.org. From the NARC home page, you can access

information about the Association of Metropolitan Planning Organizations (AMPO) and lists

of COG and MPO links by state (http://www.narc.org/links/member.html). If you are unsure

of the appropriate source, you should consult with your regional EPA office to find the

appropriate source of information. The locations of EPA regional offices can be found at

http://www.epa.gov/epahome/locate2.htm.

You will also need specific background information for your particular program. This user

manual will assist you in determining the appropriate inputs into the model. Again, if you

have any further questions, you can consult with your regional EPA office.

1.8 What other documentation is available?

This user manual presents the key instructions needed for you to effectively develop inputs

and run COMMUTER. Although it attempts to provide you with enough information to

understand how to develop inputs and operate the model, it is intentionally not exhaustive in

detail. If you are interested in further understanding the theory behind the modeling

calculations, please consult the companion document to this user manual, “Procedures

Manual for the Analysis of Voluntary Mobile Source Emission Reduction and Commuter

Choice Incentive Programs.”1* 

###
* The COMMUTER application should also be able to run under Windows NT 4.0, but it has not been

tested under that operating system.

-5-

2. USING THE MODEL

This section explains how to install COMMUTER and provides a general overview of how to

run each element of the program, as well as how to view and save your results. Further

details on the type of data required are provided in Section 3 (for general existing condition

inputs), Section 4 (TCM-specific information), and Section 5 (emissions-related

information).

2.1 What type of computer equipment and software do I need?

COMMUTER runs on personal computers using Microsoft’s Windows 95/98 or Windows

NT 3.5/4.0 operating systems.* You must also have Microsoft Excel 95 (i.e., Excel 7.0), 

Excel 97, or Excel 2000 installed. If your computer allows you to run these programs, you

can use COMMUTER. (However, if you have a Pentium-class CPU with less than 150 MHz

or a 486 CPU, moving through the input screens may be slow at times.) 

COMMUTER will work at 640 x 480, 800 x 600, and 1,024 x 768 display resolutions at both

250-color and 16-bit (Hi-Color) depths, and should run at any available video display setting.

COMMUTER requires a minimum of 2.5 MB of disk space. You must also have enough

space for saving data on different scenarios that you want to analyze and if you want to

import locally-generated emission factors into the model. You should allow 85 KB of disk

space for each scenario that you expect to save and another 500 KB if you plan to import

separate emission factors into the model. (Further details on saving scenario data and

importing emission factors will be explained in the next section.)

2.2 How do I install and operate COMMUTER?

Installing the Program

Installing COMMUTER is quite simple. The model, along with some sample files, is

contained in the COMM1.EXE self-extracting archive file (which can be downloaded from

EPA’s web site at http://www.epa.gov/otaq/transp.htm). Step-by-step installation

instructions are given as follows.
* If the Windows Explorer has been replaced by Internet Explorer (e.g., in Windows 98), Internet Explorer

can be configured to launch programs with a single mouse click instead of a double-click.

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Step 1 - Create a new folder or directory on your computer where you want to install and

operate COMMUTER (e.g., C:\COMMUTER). (When you run COMMUTER, it can

create and re-use “scenario” files that store your data and assumptions for a particular

analysis case or scenario. Thus, it is highly recommended that you create a separate

folder for COMMUTER so these files don’t get mixed up with others.)

Step 2 - Download or copy the COMM1.EXE installation file to the folder or directory

you just created.

Step 3 - Execute the COMM1.EXE program (e.g., double-click the COMM1.EXE file

from the Explorer window). This executable file is a self-extracting compressed archive

that contains following files:

• COMMUTER.XLS - the COMMUTER program;

• AREAWIDE.VME - an “area-wide” sample scenario file;

• ONEEMP.VME - a single-employer sample scenario file;

• USERTMPL.INP - a sample template input file for creating local MOBILE5b

emission factors for use in COMMUTER; and

• USERTMPL.PRN - a sample MOBILE5b output file for emission factor import into

COMMUTER.

After you have run the COMM1.EXE installation program, the five files listed above

should now appear in your “COMMUTER” folder. You are now ready to run 

COMMUTER.

Running the Program

Once you have installed the program, there are several different ways that you can run the

program. These will be familiar to you if you already use Windows 95/98 or Windows NT. 

• Create and launch a shortcut to the application;

• Double-click*

 the COMMUTER.XLS file from within the Windows Explorer or

Internet Explorer window (assuming Excel has been installed and associated with

.XLS file types);

• Right-click the COMMUTER.XLS file and click “Open” from the pop-up menu; or
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Release

1.0

INPUT LEGEND

 - REQUIRED INPUT

 - OPTIONAL INPUT

 - LOCKED CELLS

 - PROGRAM-CONTROLLED CELLS

 - HELP TEXT

Figure 1

COMMUTER Startup Screen

• Click the Start button at the bottom left of Windows 95/98/NT desktop, select

“Documents” from the pop-up menu, and then click the COMMUTER.XLS file

from the pop-up list of documents. (This method will work only if you have recently

opened the COMMUTER.XLS file and it still appears in your “Recent Documents”

list.)

As the program loads, you will see a startup screen like the one shown below in Figure 1.

The startup screen includes an “input legend” showing the colors that are used to identify the

different types of cell ranges that you will see on the data entry screens. Different colors are

used to identify cells that you type inputs into and to highlight on-screen help boxes as listed

below:

• light green - required input cells;

• yellow - optional input cells;

• white - locked (i.e., non-editable) cells;

• gray - program-controlled cells; and

• red - help text boxes.
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Required inputs must be typed into all light-green cells shown in the edit screens. You can

also supply inputs in the yellow shaded cells, but the program will run if they are left blank. 

(However, it is a good idea to use these optional input cells to supply more information about

the analysis scenario you are constructing.) White and gray cells are locked from editing and

are used to display information. Finally, red cells highlight help boxes containing brief

instructions for the inputs being entered on each screen.

NOTE: When the program has finished loading, you will see a

“Ready” indicator at the bottom left of the application window.

The user interface for COMMUTER has been programmed to display on your entire screen

(i.e., in “full” screen). If you need to temporarily minimize the COMMUTER application to

the Windows taskbar (located at the bottom of the Windows desktop by default), type “Ctrlm” (i.e., hold down the Ctrl key and type “m”). To restore the COMMUTER application to

the full screen, just click its button in the Windows taskbar. 

2.3 How do I begin once the program is installed?

Once the program finishes loading, you can select from four main menus listed at the top of

the screen: the File menu, the Edit Inputs menu, the Results menu, and the Help menu. 

These menus will be available at the start of every session, and will allow you to enter data

(Edit Inputs menu), view results (Results menu), print results (File menu), get help (Help

menu), and retrieve or save data and results for a specific analysis (referred to as a “scenario”,

accessed through the File Menu). 

Figure 2 shows the structure of the main menu, which includes the “File,” “Edit Inputs,”

“Results,” and “Help” menus, and each of the sub-menu elements. 

You will generally begin an analysis by clicking through the data entry elements in the Edit

Inputs menu in the order in which they are listed in the menu. (Once you have defined an

analysis, you can later load and edit a scenario from the File menu; this will be discussed later

in Section 2.6.) Each of the elements in the Edit Inputs menu corresponds to the input

screens for entering specific data required by COMMUTER. (Detailed information on the

data required for these screens is provided in Sections 3-5.)
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File Menu Edit Inputs Menu

Results Menu Help Menu

Figure 2

Menu Structure

When the program is first loaded, some of the sub-menu elements shown in the Edit Inputs

menu will be shown as gray shaded-out text, which indicates that you have not yet selected

any TCM programs for analysis. (As explained below, you will make these selections by

using the check boxes at the bottom of the Scenario Information screen.)

2.4 How do I input data?

The Edit Inputs menu lists each of the input screens available. Some of the screens are for

inputting baseline (i.e., existing condition) information needed regardless of the type of TCM

being analyzed; others will be used only when analyzing a particular measure. 
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IMPORTANT: The program will automatically size the width of

the data entry screens to the width of your monitor. However, the

length of some of the screens will exceed the monitor’s vertical

display dimension. Therefore, for some input screens (such as the

Scenario Information and Local Data screens), you must scroll to

the bottom of the screen to complete the data entry required in that

screen by using the vertical scroll bar or the “Down Arrow” or

“Page Down” keys.

The information that must be entered in each input screen is listed in Table 1. The data

required in the first three screens (“Scenario Information,” “Local Data,” and “Edit

Coefficients”) consist of general information, background travel data, and mode-choice

coefficients. 

Table 1

Summary of COMMUTER Data Inputs

Input Screen Data Required

Scenario Information General information, including area size and scope (i.e., regional vs. sitespecific) being analyzed and the TCM programs being evaluated

Local Data

Background travel data such as existing mode shares, trip lengths,

occupancy levels, baseline vehicle miles traveled, baseline speeds, and

option to provide final mode shares (after TCMs)

Edit Coefficients Provides default mode choice coefficients as a function of the area size

entered earlier and for selected cities, which can be edited by the user

Site Access & Transit

Service Improvements

Data required for analysis of either site access or transit service

improvement TCMs, including changes in site access walk times and

employer participation rates, and transit headway and route travel time

changes 

Financial Incentives &

Parking Costs

Inputs for analysis of financial and parking incentive programs consisting

of changes in parking, transit fare, or other costs by travel mode

Site-Specific Employer

Support Programs

Parameters that specify either the program participation level or expected

mode share increase resulting from the implementation of an employer

(i.e., site) specific commuter choice program

Area-Wide Employer

Support Programs

Employer participation level inputs required for area-wide analysis of

commuter choice programs being implemented across a metropolitan area 
Table 1

Summary of COMMUTER Data Inputs

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Alternative Work

Schedules

Existing and expected eligibility or participation rates for alternative work

schedule programs being evaluated, such as flex time, compressed work

weeks, staggered hours, and telecommuting

Fleet Emissions

Information

Inputs required by the program in order to either apply a pre-generated set

of MOBILE5b fleet emission factors or to utilize locally generated

MOBILE5b emission factors imported into the model

Other Emissions-Related

Data

Fleet travel mix (e.g., fraction of travel by vehicle class) and start fraction

inputs required by the program to calculate TCM emission reductions that

are specific to the local conditions being modeled 

If you have not yet done any analyses or want to analyze a new scenario, you will start with

the Scenario Information screen to enter general background information and to select the

type(s) of TCM programs being evaluated. This selection is made by checking the

appropriate boxes shown at the bottom of the Scenario Information screen. You can enter

any non-blank character in the check boxes to activate analysis of the specific TCMs. 

Travel data should be entered using the Local Data screen, and you can use the Edit

Coefficients screen to edit the default mode choice coefficients provided with the 

program. (Images of these screens and details on the data required are provided in Section 3.) 

By default, COMMUTER calculates changes in mode share due to the types and extent of

specific TCM programs being modeled. If , however, you have estimates of changes in mode

share due to modeled programs, you can optionally enter the final mode shares (resulting

from changes to existing shares) in the Local Data screen.

Data for the specific TCM program(s) being evaluated are entered in the next five screens. 

You will have access to only those screens that were selected (checked off) for analysis in the

Scenario Information screen. Detailed information on these screens is provided in Section

4.

NOTE: If you have chosen to enter your own final mode share

estimates in the Local Data screen, you do not need to enter

information in any of the TCM-specific program screens. In this

case, the inputs in these screens are bypassed and the final mode

shares you have entered are used to compute VMT and trip impacts.
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Finally, you will enter emission-related data in the last two data screens (addressed in

Section 5). This will include either vehicle fleet parameters that allow the program to find

and apply a specific set of previously generated MOBILE5b emission factors that

approximate local conditions being modeled, or selection of MOBILE5b emission factors

that you have generated to more precisely reflect local conditions.

NOTE: You may see a “Calculate” annunciator on the status bar

at the bottom of the application window while you are entering

data. This is normal. During data entry, the program recalculates

only specific portions of the underlying spreadsheets in order to

speed up performance. Later, when you view or print results or

save the scenario data, all underlying sheets are recalculated.

If you are only interested in computing travel impacts, you do not need to enter any

emissions-related inputs in these last two screens.

2.5 Is there help available when inputting data?

From the Help menu, you can view a “Model Layout” screen that provides an overview of the

layout and data flow of COMMUTER. The Model Layout screen also identifies the input

screens that apply to specific voluntary measures and commuter choice programs. Figure 3

shows the Model Layout screen. Note that on smaller monitors, you may need to scroll down

to view the entire screen.

You can also return to the Startup screen from the Help menu. (This is handy if you need to

refer to the cell coloring conventions used to guide you in entering model inputs.)

In addition, many of the input screens offer additional guidance on the specific data that must

be entered. In some screens, explanatory notes are shown next to the input cell. In other

screens, “help boxes” displayed with light red backgrounds provide more extensive

descriptions of key data inputs.

Once you’ve finished inputting all the required data for each screen (remember that in some

cases you may need to scroll down your screen to complete data entry), that screen will

appear with a checkmark (7) beside it the next time the Edit Inputs menu is accessed. You

can use the presence or absence of checkmarks as an easy visual reference of additional data

that must still be entered.
-13-

2.6 Can I save my inputs to use in another analysis?

Saving Scenarios - To make repeated use of COMMUTER quicker and easier, you can save a

complete set of analysis inputs and re-use them later as a template for evaluating other

scenarios. This avoids having to type in complete data from scratch for each analysis, but

still allows you to modify selected data to evaluate alternatives.

After inputting data for a specific analysis case, save the information to a “scenario file”

(indicated by a “.VME” file extension). First click on the “File” menu and select “Save

Scenario.” This will bring up a dialog box that allows you to save the file to disk for later

use. Click the arrow to the right of the “Save in” box to select the directory where you want

to save the file, then type a file name for the scenario to be saved in the “File name” box,

using the .VME suffix. 

Loading Saved Scenarios - When you want to load and re-use a saved scenario file, click the

“Load Scenario” item from the File menu. Then, select the directory and the specific

scenario file you saved earlier to be loaded into the application. Re-using existing scenarios

and making minor changes to their inputs is a more efficient way to create a series of related

scenarios than typing in all the data for each scenario.
-14-

COMMUTER MODEL DATA LAYOUT

(SCROLL DOWN TO VIEW ENTIRE LAYOUT SCREEN)

GENERAL INPUT SCREENS

SCENARIO INFORMATION LOCAL DATA MODE CHOICE MODEL COEFFICIENTS

General Information Existing Mode Shares Choice of:

Analysis Area Definition Existing Trip Length Defaults by Area Size

Analysis Area Employment Existing Occupancy City-Specific Defaults

TCM Programs Being Analyzed Peak Period Info User-Specified

 Observed Mode Shifts

 from TCMs (optional)

TCM PROGRAM-RELATED INPUT SCREENS

SITE-SPECIFIC PROGRAMS AREA-WIDE PROGRAMS

SITE ACCESS IMPROVEMENTS (NO TRANSIT) SITE ACCESS & TRANSIT SERVICE IMPROVEMENTS

Preferential Parking Preferential Parking

Bicycle Lockers Bicycle Lockers

New Transit Stops New Transit Stops

More Frequent Transit Service

Faster Transit Service

FINANCIAL INCENTIVES & PARKING COSTS FINANCIAL INCENTIVES & PARKING COSTS

Parking Cash-Out Parking Cash-Out

Differential Parking Charges Differential Parking Charges

Transit Incentives Transit Incentives

SITE-SPECIFIC EMPLOYER SUPPORT PROGRAMS AREA-WIDE EMPLOYER SUPPORT PROGRAMS

On-site Transportation Coordinator On-site Transportation Coordinator

Ridematching Ridematching

Outreach and Promotion to Employees Outreach and Promotion to Employees

Outreach and Promotion to Employers

ALTERNATIVE WORK SCHEDULES ALTERNATIVE WORK SCHEDULES

Flex-time Flex-time

Compressed Schedules Compressed Schedules

Staggered Hours Staggered Hours

Telework Telework

EMISSIONS-RELATED INPUT SCREENS

FLEET EMISSIONS INFORMATION (Optional) OTHER EMISSIONS-RELATED DATA (Optional)

 Inputs for Pre-Loaded MOBILE Factors Vehicle Fleet Mix

 Inputs for User-Supplied MOBILE Factors Affected Vehicle Speeds

 Cold Start Percentages

RESULTS SCREEN

RESULTS

Mode Shares & Changes

Trip Changes

VMT Changes

Emission Reductions:

HC (as VOCs)

CO

NOx

CO2

Figure 3

Model Layout Screen

Clearing Scenarios - If for some reason you have loaded a scenario or have typed in data for

all the input cells and want to delete the data from all the input cells and start over, you can

click the “Clear Scenario” item on the File menu. This initializes the program by erasing the

data currently contained in the input cells if you want to start re-entering all new data without
-15-

having to exit and reload COMMUTER. It does not delete saved scenario files from your

hard disk.

2.7 Can I use my own emission factors?

COMMUTER has been pre-loaded with 24 sets of MOBILE5b emission factors that

encompass a range of input conditions reflecting “typical” summer and winter conditions

throughout the country. Each of these pre-loaded sets contains emission factors for five

specific calendar years: 2000, 2002, 2005, 2010, and 2020. Under general circumstances

when COMMUTER is used as a screening model, selecting the set of pre-loaded emission

factors that best matches your local conditions is adequate. However, if you want to use

COMMUTER to produce SIP-consistent emission reductions and are an experienced

MOBILE5b user, you can use your own locally generated MOBILE5b emission factors to

calculate emission reductions in COMMUTER. The steps for using your own emission

factors are explained below.

Step 1 - Create Properly Formatted Emission Factor Output File - Although you can

specify your exact local input conditions, your MOBILE5b output emission factors must

be generated in a specific format expected by COMMUTER. The sample MOBILE5b

template input file USERTMPL.INP, which was installed in your “COMMUTER”

directory, identifies how specific program control flags in the MOBILE5b input file must

be set to produce output emission factors in this COMMUTER-required format. In

addition, it contains a series of 55 “Scenario Descriptive” records that produce emission

factors over a range of speeds and operating mode fractions expected by COMMUTER. 

These scenario records can be edited to reflect the altitude, calendar year, local ambient

temperature and season of interest. However, if you change the speed or operating mode

input values in these scenario records, the resulting output emission factors will not work

properly with COMMUTER.

IMPORTANT: Once you’ve edited the 55 scenario records to

reflect your own altitude, temperature, and season inputs, you can

copy and paste this block of records to create emission factors for

multiple calendar years.

Depending on your local conditions, you may also need to create additional scenario

records, inserting one after each of the 55 Scenario Descriptive records, to model a LowEmission Vehicles (LEV) program.

You cannot assemble a series of separate MOBILE5b emission factor runs in a single

input file (e.g., containing separate sets of program control flag and scenario records). 
-16-

Although this is allowed by MOBILE5b, these types of embedded runs cannot be read

correctly by COMMUTER. If you need to model different sets of local conditions (e.g.,

two levels of an inspection and maintenance program), you will need to create a separate

MOBILE5b input file.

Once you have set up your MOBILE5b input file as described above and in accordance

with the required program control flag values listed in the USERTMPL.INP file, run

MOBILE5b. You can name the MOBILE5b input and output files as you choose.

Step 2 - Import Emission Factors - Once you’ve created your properly formatted

MOBILE5b emission factor output file(s), they can be imported into COMMUTER. This

is done by clicking “Import Emission Factors” from the File menu. A window will be

displayed that allows you to point to and open a specific file. You will then choose the

output, or .PRN file resulting from running MOBILE5b with the input file you created. It

may take a minute of two for COMMUTER to incorporate the new output file into its

data structure. A message will appear telling you the file has been successfully copied

when it is done. If you have not set up your input file formatting properly as described in

Step 1, an error message will be displayed when you try to import the resulting

MOBILE5b output file. In this case, carefully check and edit your MOBILE5b input file

in accordance with the guidance in Step 1 and re-run MOBILE5b.

Step 3 - Activate User-Supplied Emission Factors Option - After you’ve successfully

imported your own emission factors into COMMUTER, you can direct the model to use

them in the emission reduction calculations by marking the “User-Supplied Emission

Factors” box (with an “X”) near the bottom of the “Fleet Emissions Information” screen

and entering the specific calendar year of interest below that box. (Further details on

information entered in the Fleet Emissions Information screen are provided in Section

5.1.)

Once you have imported your own emission factors into COMMUTER, they are internally

saved and made available each time you launch the COMMUTER program or until you

import a different set of factors as described in Step 2 above. If you import a set of emission

factors for a large number of calendar years (e.g., each year from 2000 to 2020), the size of

the COMMUTER program will become much larger than 2.5 MB. If you are short on disk

space, the “Empty Emission Factors” command from the File menu can be used to delete

your internally stored local emission factors until you need to use them again. (At that time,

you can simply re-import them.)

2.8 How do I view the results?

Once you have provided all of the required inputs (or selected default values), COMMUTER

will automatically calculate TCM travel impacts and, if you’ve entered emission factor

inputs, emission reductions. To view the results, all you need to do is simply click either of

the two command items on the Results menu. “View Travel Results” displays travel impacts
-17-

only. “View Travel and Emission Results” shows both travel impacts and emission

reductions (assuming you’ve entered emission factor inputs). You can then scroll down the

tabular summary to see the calculated results. Key outputs include the following:

• Baseline and final mode shares for each mode, including percent of trips eliminated

and change in mode share (final minus baseline);

• Percent of trips shifted from the peak to off-peak period;

• Baseline and final peak, off-peak and daily VMT;

• Baseline and final peak, off-peak and daily vehicle trips; and

• Change in total daily emissions for each criteria pollutant, HC (as VOC), CO and

NOx (in tons) and CO2 (in metric tons).

NOTE: If you did not enter all of the necessary input data, an

“Incomplete or Inconsistent Input” message box will be displayed

when the View Travel Results or View Travel and Emission Results

buttons are clicked. The message box indicates which data must

still be entered. If you click the OK button in the message box, the

program will activate the first entry screen and cell for which

missing or invalid data were detected.

To return to an input screen after viewing the results calculated by COMMUTER, simply

click the appropriate item in the Edit Inputs menu at the top of the application window.

2.9 How do I print my data and results?

For each scenario you evaluate, you can print both the detailed input data and the tabulated

emission reductions. To do this, click the File menu. Then select “Print Inputs” from the

drop-down menu to print a detailed listing of all program inputs. Select either “Print Travel

Results” or “Print Travel and Emission Results” from the File menu to print a one-page

output report showing travel impacts or travel impacts and emission reductions, respectively.

Figure 4 shows the layout of a sample output report. General scenario information and the

specific TCMs evaluated are listed at the top of the report. Included in these items are boxes

that indicate whether you have supplied your own final mode shares and emission factors. 

Below these items, summaries of the combined mode share impacts and travel and emission
* 1 short ton = 2,000 lbs.

** 1 metric ton = 2,205 lbs.

-18-

COMMUTER MODEL RESULTS

SCENARIO INFORMATION PROGRAMS EVALUATED

Description Area-Wide Example Scenario X Site Walk Access Improvements

Scenario Filename AREAWIDE.VME X Transit Service Improvements

Emission Factor File X Financial Incentives

Performing Agency EPA X Employer Support Programs

Analyst John Doe X Alternative Work Schedules

Metropolitan Area Anywhere, USA

Area Size 1 - Large (over 2 million)

Analysis Scope 1 - Area-Wide (e.g., MSA, county) User-Supplied Final Mode Shares

Analysis Area/Site Downtown

Total Employment 300,000

MODE SHARE IMPACTS TRAVEL IMPACTS (relative to affected employment)

Mode Baseline Final %Change Quantity Peak Off-Peak Total

Drive Alone 75.4% 71.8% -3.6% Baseline VMT 3,565,457 2,241,476 5,806,934

Carpool 13.2% 14.3% +1.0% Final VMT 3,419,176 2,188,857 5,608,033

Vanpool 0.5% 0.8% +0.3% VMT Reduction 146,281 52,619 198,900

Transit 5.3% 6.3% +1.1% % VMT Reduction 4.1% 2.3% 3.4%

Bicycle 0.4% 0.5% +0.1%

Pedestrian 4.0% 4.3% +0.3% Baseline Trips 300,044 188,627 488,672

Other 1.1% 1.2% +0.1% Final Trips 286,334 183,695 470,029

No Trip - 0.8% +0.8% Trip Reduction 13,711 4,932 18,643

Total 100.0% 100.0% - % Trip Reduction 4.6% 2.6% 3.8%

Shifted from Peak to Off-Peak 0.5%

EMISSION REDUCTIONS (tons/day except CO2 in metric tons/day, positive values are decreases)

Pollutant Peak Off-Peak Total

HC 0.139 0.044 0.183

CO 1.214 0.371 1.585

NOx 0.221 0.084 0.305

CO2 60.3 20.7 81.0

Figure 4

Sample Output Report

reductions from baseline levels for all the TCMs selected are presented. As noted in the table

headers, travel and emission reductions are shown as positive numbers.

Again, note that the output units for the emission reductions are different. HC, CO, and NOx

reductions are given in (short*

) tons per day; CO2 reductions are in metric** tons per day.
-19-

CAUTION: The program allows you to set up a scenario and

produce results for an individual TCM (as opposed to a

combination of measures). However, summing the results for

measures evaluated individually will not give you an accurate

representation of the true impact of a combination of measures.

2.10 Can I tell the model to remember where my files are stored?

Depending on how you launch COMMUTER (see Section 2.2), your “default” directory (the

directory pointed to when you open or save files) may not be the same as the directory that

the model and scenario files are stored in. You can tell the model where to look for your

scenario (and emission factor) files so you don’t have to click out of the “system” default

directory (e.g., C:\My Documents) each time you want to open or save a scenario. 

To set your default or “working” directory when you’re running COMMUTER, click “Set

Working Directory” from the File menu. The first time you do this, COMMUTER will

report that the working directory is blank as shown below.

This is normal. Simply click the “Yes” button. Another window, shown below, will be

displayed that then allows you to enter the disk drive and directory path where you’ve

installed COMMUTER (e.g., C:\COMMUTER).
-20-

Once you have set the working directory, COMMUTER remembers that location and uses it

each time you open or save scenario files or import your own emission factors, even if you

exit and then re-run the model.

2.11 What do I do when I’m finished?

Before exiting COMMUTER, be sure you have saved the current inputs in a scenario file, as

described above, if you plan to re-use them later. When you have completed your analysis

session and want to exit COMMUTER, click “Exit Program” from the File menu. The

application will then close and exit. 

###
-21-

3. GENERAL INPUT SCREENS

This and the following two sections guide you step-by-step through the data that must be

provided in each of the input screens. This section covers the first three screens, which you

use to input general information; Section 4 explains the five input screens that are specific to

individual TCMs being analyzed; and Section 5 discusses the two screens you will use to

enter information required to calculate emission reductions. Each subsection within these

sections corresponds to one of the program’s ten input screens. These have been ordered in

the sequence in which you would generally enter data for an analysis. To make it easier to

find information on specific data inputs, fields have been noted in bold, underlined text.

3.1 Scenario Information

Scenario information describes the area you are analyzing and the broad types of commuter

choice programs to be analyzed. Figure 5 displays the layout of the Scenario Information

screen. Key data items are explained below.

Metropolitan Area Size - This is where you define the size of the metropolitan area you are

analyzing, using the following categories:

& Large - more than 2,000,000 in population;

& Medium - 750,000 to 2,000,000 in population; and

& Small - less than 750,000 in population.

Based on the area size you select, the program will retrieve default mode-choice model

coefficients. Coefficients have also been developed for selected individual cities and are

more accurate than the default coefficients. As discussed later in Section 3.3, you have the

option to override the area size default mode choice coefficients in the “Edit Coefficients”

screen with either the city-specific defaults supplied in the program or updated values you

obtain for your city.

Analysis Scope - The actual analysis can apply to any geographic level. However, you must

define the scope of your analysis as being area-wide (“1”) or site-specific (“2”). 
-22-

SCENARIO INFORMATION

Field Data Notes

Scenario Information

Scenario Filename Filename of scenario stored on disk

User EFs Filename User-supplied MOBILE emission factors (if used)

Description Title to further identify the scenario (optional)

General Information

Performing Agency Name of your organization (optional)

Address Address of your organization (optional)

Analyst Your name (optional)

Metropolitan Area Name of city/area being modeled (optional)

Metropolitan Area Size 1 = Large (Over 2 million) 2 = Medium (750,000 

to 2 million) 3 = Small (Under 750,000)

Definition of Analysis Area

Analysis Scope 1 = Area-Wide (Metropolitan Area, County, etc) 

2 = Site or Employer-Based

Analysis Area/Site Name of analysis area evaluated (optional)

Analysis Area Type 1 = CBD (Central Business District) 2 = Other 

High-Density Commercial 3 = Other 

Employment in Analysis Area

Office Employment Refers to "traditional" professional office space 

employment

Non-Office Employment

Manufacturing, warehousing, retail, medical, 

educational, entertainment and other 

employment-generating land uses

Total Employment - 

Programs (Mark All Programs Being Analyzed with an "X")

 1. Site Walk Access Improvements Includes preferential parking, improved access to 

transit

 2. Transit Service Improvements Includes more frequent and/or faster transit 

service

 3. Financial Incentives Includes parking costs, transit fare/pass 

subsidies, or other financial incentives

 4. Employer Support Programs Includes support programs for carpooling, 

vanpooling, transit, and/or bicycling

 5. Alternative Work Schedules Includes flex time, telecommuting, staggered 

work hours, and/or compressed work weeks

The COMMUTER model may generate abnormally large mode shifts under a regional or area-wide analysis 

scenario if realistic limits are not applied in estimating the affected employment input above. For site-specific 

analysis, enter the employment of the workplace being analyzed. For area-wide analysis, the user is encouraged to 

consult Section 3.1 of the COMMUTER Model User Manual for more detailed guidance on estimating affected 

employment inputs for region being modeled.

Metropolitan Area Size is a required input. The program retrieves default mode choice model coefficients for the 

area size input by the user. However, these defaults for Large, Medium and Small metropolitan areas are not as 

accurate as the coefficients developed for individual cities that are displayed in Tables A-1, A-2 and A-3 in the 

appendix to the COMMUTER Model User Manual. These default mode coefficients can be overridden in the "Edit 

Coefficients" screen and the user is encouraged to refer to these tables and to use local coefficients for the specific 

city being modeled. See the help box in the Edit Coefficients screen and the COMMUTER Model User Manual for 

additional guidance on supplying local model coefficients.

The COMMUTER model can be used to evaluate commuter choice programs on both an urban area-wide and 

individual employer (or site-specific) basis. The Analysis Scope input controls whether the model calculates areawide or site-specific impacts of commuter choice programs.

Figure 5

Scenario Information Input Screen
-23-

An area-wide analysis evaluates TCM programs for a geographic area such as traffic

corridors, subareas (for example, the central business district), activity centers (for example, a

large office park complex), or the entire metropolitan region. A site-specific analysis

evaluates TCM programs applied only to a single business or employer location. This option

can be used when considering either a single place of business for a given employer or a

mixed use or multi-purpose place of business for a given employer or employers. If you are

an individual employer using this model to evaluate a company employer support program,

you should use the “site-specific” analysis.

As discussed in Sections 4.3 and 4.4, you will later be asked for further data that are related

to the scope you select. For example, if you specify “area-wide,” some screens will ask you

to specify the percentage of employers in the area participating in the program. If “sitespecific” is specified, this percentage will be assumed to be 100 percent. (See Sections 4.3

and 4.4 for detailed instructions for inputting data for both area-wide and site-specific

analysis.)

Affected Employment in Analysis Area - The impact or applicability of various programs

and strategies is affected by type of employees in an area, which COMMUTER defines

according to the land use category of the employer. “Office” employees are those working in

land use categories that include traditional professional office space. “Non-office”

employees include those working in manufacturing, warehousing, retail, medical,

educational, entertainment, and other employment-generating land use activities. 

You will be asked to enter both the number of office and non-office employees in the area or

at the target site that can be affected by the TCM programs being modeled. “Affected” is the

keyword in understanding what employment levels you should input here and depends on

whether you are performing a site-specific or area-wide analysis, as explained below.

Site-Specific Affected Employment - If you are performing a site-specific or “single

employer” analysis (specified by choosing “2” for Analysis Scope), the employment levels

you enter should be the total of all employees that are eligible for, or exposed to, any or all of

the TCM programs you are evaluating. Most of the time, site-specific affected employment

will be the total employment level at the site. In rare cases where employer support, financial

incentive, or alternate work schedule programs being evaluated would only be made available

to a portion of all employees, enter that portion as the affected employment.

Area-Wide Affected Employment - In an area-wide analysis, affected employment should not

be entered as the total employment in the area being considered. You must estimate that

subset of the total area employment that will be potentially affected by any or all of the

specific TCM programs you are evaluating.
-24-

CAUTION: For area-wide analysis, you should not enter the total

employment in the analysis area. You do not want to base the

analysis on the total employment in the analysis area because

COMMUTER will then generate unrealistically high results for

regional scenarios. For example, the number of trips being shifted

from one mode of travel to another if all employees for a given

region are assumed to participate in a voluntary program would be

too high.

Steps to help you calculate the number of employees that can be affected by the TCM

programs you are evaluating under an area-wide analysis are listed below.

1. First, identify the portion of regional employers (and number of employees) that are

currently participating in existing programs, and therefore should be excluded from the

analysis. You can obtain the percentages of employers (by size and type) from the MPO

responsible for transportation and emissions planning in the region. Using the total

number of employees for a region is not realistic.

2. Finally, determine that portion of employers of a specific size (based on their number of

employees) that will be subjected to, or encouraged to implement, the voluntary programs

being evaluated. This percentage will vary by MPO region and could include either

office or non-office employers with 1,000, 500, 250, or 100 employees. 

3. Next, estimate the portion of employers of each type (office and non-office) who will

agree to participate in any of the TCM programs you are evaluating, which will largely be

voluntary in nature. This percentage will vary by MPO region and could include office

employers only or a combination of office and non-office employers. 

The following example is provided to demonstrate how you should use this process to

determine the employment levels you need to enter under an area-wide analysis.

Assume total employees for Region X: 1,000,000 employees

1. Estimate portion of total employees currently

participating in existing TCM programs: 20% -200,000 employees

800,000 employees

2. Estimate portion of remaining employees by size of 

employer targeted by your voluntary programs, using

employers of 500+ employees in this example:

Office (500+ employers): 250,000 employees
-25-

Non-office (500+ employers): 50,000 employees

3. Determine portion of remaining employees based on

estimated percentage of employers willing to 

participate in any of the modeled programs:

(In this example we’ll assume 30% office and 

10% non-office employer participation)

Office - 30% participation: 75,000 employees

Non-Office - 10% participation: 5,000 employees

Using this example, you would enter inputs of 75,000 and 5,000 employees for affected

office and non-office employment, respectively.

You should be careful in making assumptions about the number of affected employees in

each region. Each region is likely to be significantly different based on the current

participation in voluntary programs, employer and employee participation rates, and regional

employment characteristics.

As these steps and the example indicate, when inputting the “affected” employment under an

area-wide analysis, you should supply estimates of the number of office and non-office

employees that are eligible for participation in any of the specific TCM programs you are

evaluating. 

NOTE: If you are evaluating a scenario that packages multiple

programs (e.g., site access improvements, transit improvements,

and financial incentives), individual “program” participation rates

can also be specified in subsequent input screens for each program.

You should not confuse these program-specific participation rates

with the employer participation percentage in any program used to

estimate affected employment inputs. The program-specific

participation rates in subsequently discussed input screens provide

you with a means to “weight” the participation of all affected

employees within individual programs when analyzing scenarios

that combine multiple programs.

Programs - In this section, you simply check off which types of TCM strategies or programs

are to be considered in the scenario being analyzed. There are five possible choices,

described below. You simply mark (with an “X”) all of the programs being analyzed; you do

not have to select only one.
-26-

1. Site Walk Access Improvements - Includes preferential parking for employees using

carpool and/or vanpool programs and improved access to transit systems.

2. Transit Service Improvements - Includes more frequent and/or faster transit service.

3. Financial Incentives - Includes any project or program that changes the out-of-pocket

cost of alternative travel modes relative to automobile travel. Examples include

transit fare/pass subsidies, parking costs, or other financial incentives.

4. Employer Support Programs - Includes support programs for carpooling, vanpooling,

transit, and/or bicycling that do not result in any changes in direct travel time or cost

changes. For example, employers might provide information about ridesharing and

transit opportunities, match employees with carpools or vanpools, and offer

guaranteed ride home programs.

5. Alternative Work Schedules - Includes flex time, telecommuting, staggered work

hours, and/or compressed work weeks.

NOTE: If you are planning to enter your own estimate of final mode

shares as described in the Local Data inputs in Section 3.2,

COMMUTER will ignore any TCM programs you have selected on

the Scenario Information Input screen and will delete your

checkmarks from those selection boxes. By inputting your own final

mode shares, you are bypassing COMMUTER’s final mode share

calculations that are based on TCM screen inputs.

3.2 Local Data

Once you have provided the general information on the scenario you are analyzing, you need

to provide data on the existing travel behavior and characteristics of the area or site. Because

travel characteristics such as mode shares (for example, transit users) and average travel

distances can vary a great deal within a region, you should define separate geographic areas

that have distinct and more or less homogenous characteristics for analysis. For example,

you may wish to conduct separate analyses for the central business district (CBD) and for the

non-CBD portions of a city. 

Baseline (i.e., existing) travel data for the region of interest are entered in the Local Data

input screen, shown in Figure 6. Each of the data elements in this screen is discussed

following Figure 6.
-27-

LOCAL DATA

Use

Baseline (Existing) 

Data

Default Local Default

Work-Trip Mode Shares Supply Final Mode Shares?

Auto - Drive Alone 75.4%

Auto - Carpool 13.2%

Vanpool 0.5%

Transit 5.3%

Bicycle 0.4%

Walk 4.0%

Other 1.1%

Total 0.0% 100.0%

Work Trip Length (mi)

Average person-trip length 11.4

Average trip length -- vanpool 17.7

Average trip length -- bicycle 1.8

Average trip length -- walk 1.0

Vehicle Occupancy

Average Carpool Occupancy 2.2

Average Vanpool Occupancy 6.0

Length of Peak Period (hours) 3.0

Percent of Work Trips in Peak Periods 61.4%

Baseline mode share, trip length, average occupancy and peak period data representing local conditions are entered in this 

input screen. From these inputs and data entered in the "Mode Choice Model Coefficients" screen, the COMMUTER model 

internally calculates final mode shares and travel changes resulting from TCM programs selected. If you want to supply your 

own estimates of final mode shares (such as might be obtained from employee survey data), mark the box labeled "Supply 

Final Mode Shares" (with an "X"). When this option is selected, the COMMUTER model displays an additional series of input 

cells below the box where final mode share inputs can be entered. Remember, these final mode shares should reflect worktrip mode choice after implementation of the TCM programs you're currently analyzing and override the mode share 

calculations made by the model.

The peak period includes the morning and evening time periods when highways are most congested. These periods may be 

defined differently in different areas. For the default "percent of work trips in peak period" provided, the AM peak is defined as 

6:00 to 9:00 AM and the PM peak as 4:00 to 7:00 PM. The same peak period should be used for reporting percent of work 

trips in peak period and affected vehicle speeds (which are entered later in the "Other Emissions-Related Data" screen). 

"Length of peak period" refers to the length (in hours) of the AM or PM peak period. If the AM and PM peak periods are 

different lengths, this can be an average of the two lengths.

"Percent of work trips in peak period" should also be reported as an average for the AM and PM peak periods combined. For 

example, assume there are 200,000 and 300,000 total vehicle trips in the AM and PM peak periods, respectively. If the 

number of work trips are 150,000 in the AM peak and 250,000 in the PM peak, then the percentage of work trips in peak period 

is (150,000 + 250,000) / (200,000 + 300,000) = 80%.

Figure 6

Local Data Input Screen

Existing Mode Shares, Trip Length, and Occupancy - If you are conducting a site-specific

analysis, you may be able to obtain data on existing employee mode shares from employee

surveys, if such surveys have been conducted. You can also enter local data on trip lengths

and average vehicle occupancy for carpools and vanpools if such data are available. 
-28-

If you do not have specific data available, you should be able to obtain transportation data for

the city, metropolitan area as a whole, or other area of analysis from the regional

transportation planning agency. You should work with local or regional transportation

planners to identify the most appropriate data for the analysis. 

If local data are not available, you may use the default parameters provided in the model. 

These are shown in Figure 6 under the “Defaults” column. You should indicate which

default values to use by checking the appropriate box(es) on this screen. 

User-Supplied Final Mode Shares - If you are performing an analysis where you have

estimates of “final” mode shares (after implementation of the TCMs being modeled), you can

enter these final mode share estimates in the Local Data screen. Under most circumstances,

you’ll want to let COMMUTER calculate final mode shares based on the inputs you supply

in the TCM screens using the pivot-point methodology discussed in Section 1.5. There may

be certain situations where you want to enter your own estimate of final mode shares, rather

than using COMMUTER’s calculations. For example, when you are performing a sitespecific analysis for a company, you may have employee survey data available that estimate

how mode choice would change in response to a particular program or programs.

For these situations, mark the “Supply Final Mode Shares?” box at the upper right of the

Local Data input screen. When you do, a series of cells appears below this box, allowing you

to enter final mode shares, reflecting changes from existing shares due to the TCM programs

you’re modeling. 

For example, suppose under existing conditions that “Company A” work-trip mode shares

were split at 80% Auto-Drive Alone and 20% Transit. Company A is considering a program

in which employees are offered a cash incentive to ride the bus and, from an employee

survey, determines that an additional 5% would accept the incentive and ride the bus. The

final mode shares are thus split as 75% Auto-Drive Alone and 25% Transit. These values

would be entered in the final mode share cells after you marked the “Supply Final Mode

Shares?” box.

NOTE: When you enter your own final mode shares in the Local

Data input screen as explained above, any TCM programs that

you’ve checked at the bottom of the Scenario Information screen are

removed and inputs you’ve entered in those TCM-specific screens

are ignored. By entering your own final mode shares, you’re telling

COMMUTER not to use the TCM inputs to calculate final mode

shares.
-29-

150 000 250 000

200 000 300 000 80% , ,, ,

+

+ =

Under most circumstances, you won’t know what the final mode shares will be as a result of

the TCM programs that you are analyzing. In these cases, leave the “Supply Final Mode

Shares?” box blank and allow COMMUTER to calculate final mode share from the TCM

program inputs you’ll enter in subsequent input screens.

Length of Peak Period - The “peak period” includes the morning and evening time periods

when highways are most congested. These periods may be defined differently in different

areas. You should use the same peak period definition when reporting the percent of work

trips in a peak period that you use when reporting baseline travel speeds (see below). You

can obtain information on the peak period definition from transportation planning staff at

your regional transportation planning agency.

“Length of peak period” refers to the length (in hours) of the AM or PM peak period. If the

AM and PM peak periods are different lengths, you should use the average of the two.

Percent of Work Trips in Peak Periods - You need to enter the percent of trips during the

peak periods that are work-related, averaging the totals for the AM and PM peak periods

combined. For example, assume there are 200,000 and 300,000 total vehicle trips in the AM

and PM peak periods, respectively. If the number of work trips are 150,000 in the AM peak

and 250,000 in the PM peak, then the percentage of work trips in the peak period is

calculated as follows:

You should enter local or site-specific data if it is available, instead of relying on the default

value. The default value provided is based on the national percentage of all work trips that

occur in both the AM and PM peak periods. In this program, the default AM peak is defined

as 6:00 to 9:00 AM and the default PM peak as 4:00 to 7:00 PM.

3.3 Edit Coefficients

This screen allows you to enter locally available values for mode-choice travel time and cost

coefficients, rather than use the default values provided by the model. Figure 7 illustrates the

layout of the Edit Coefficients screen.

Mode-choice coefficients are used within COMMUTER to compute changes in travel of each

commute mode (e.g., drive-alone, carpool, transit, walk, etc.) under Site Access or Transit

Improvement programs and Financial Incentive programs. These coefficients are used in

transportation models referred to as “logit mode-choice” models to represent the willingness

of commuters to use alternate modes of travel to driving alone when faced with changes in

travel time or cost. (Please refer to the accompanying COMMUTER Model Procedures

Manual for detailed information on how mode-choice coefficients are developed, tested and

applied in transportation modeling.)
-30-

MODE CHOICE MODEL COEFFICIENTS

Check here to apply local coefficients entered below in "User-Specified" row

DEFAULTS BY AREA SIZE IVTT (min) OVTT (min) Cost (cents)

Metro Area Size All Modes Walk Time

Transit -- 

Wait

Auto - 

Parking

Transit - 

Fare

Large - more than 2,000,000 -0.0281 -0.0521 -0.0584 -0.0094 -0.0065

Medium - 750,000 to 2,000,000 -0.0241 -0.0472 -0.0468 -0.0071 -0.0064

Small - less than 750,000 -0.0207 -0.0373 -0.0563 -0.0065 -0.0038

User-Specified

Coefficients Used: User-Specified

CITY-SPECIFIC DEFAULTS IVTT OVTT Cost

Check

City Area Size Year All Modes Walk Time

Transit -- 

Wait

Auto - 

Parking

Transit - 

Fare

Albuquerque Small 1992 -0.0209 -0.0219 -0.0978 -0.0031 -0.0031

Boston Large 1991 -0.0314 -0.0330 -0.0550 -0.0173 -0.0083

Chicago Large 1990 -0.0282 -0.0440 -0.0960 -0.0021 -0.0008

Cincinnati Medium 1978 -0.0190 -0.0280 -0.0280 -0.0050 -0.0050

Cleveland Large 1994 -0.0178 -0.0444 -0.0378 -0.0034 -0.0024

Dallas Large 1984 -0.0297 -0.0552 -0.0552 -0.0116 -0.0046

Denver Medium 1985 -0.0180 -0.0540 -0.0282 -0.0095 -0.0044

Detroit Large 1965 -0.0457 -0.0641 -0.1165 -0.0065 -0.0065

Houston Large 1994 -0.0220 -0.0568 -0.0568 -0.0154 -0.0061

Los Angeles Large 1991 -0.0210 -0.0530 -0.0530 -0.0030 -0.0030

Milwaukee Medium 1991 -0.0160 -0.0410 -0.0410 -0.0045 -0.0045

Minneapolis Large 1970 -0.0310 -0.0440 -0.0300 -0.0140 -0.0140

New Orleans Medium 1960 -0.0150 -0.0330 -0.0770 -0.0080 -0.0080

Philadelphia Large 1986 -0.0420 -0.0320 -0.0510 -0.0026 -0.0012

Phoenix Large 1997 -0.0195 -0.0257 -0.0308 -0.0111 -0.0055

Pittsburg Large 1978 -0.0632 -0.1507 -0.1507 -0.0210 -0.0210

Portland Medium 1985 -0.0390 -0.0650 -0.0400 -0.0135 -0.0135

Reno Small 1991 -0.0275 -0.0550 -0.0550 -0.0167 -0.0067

Sacramento Medium 1991 -0.0250 -0.0380 -0.0380 -0.0028 -0.0028

San Francisco Large 1990 -0.0333 -0.0931 -0.0523 -0.0021 -0.0021

San Juan Medium 1990 -0.0366 -0.0717 -0.0752 -0.0066 -0.0066

Santa Cruz Small 1990 -0.0163 -0.0325 -0.0325 -0.0045 -0.0036

St Louis Large 1965 -0.0228 -0.0570 -0.0570 -0.0117 -0.0117

Tucson Small 1993 -0.0180 -0.0400 -0.0400 -0.0018 -0.0018

Wash DC Large 1980 -0.0170 -0.0580 -0.0580 -0.0094 -0.0044

Mode choice model coefficients are entered in this screen. The program retrieves default coefficients for the metropolitan area 

size input in the Scenario Information screen. However, these defaults for Large, Medium and Small metropolitan areas are not 

as accurate as city-specific coefficients developed for many communities across the country. City-specific coefficients for a 

number of cities based on a review of current literature and existing travel demand models are provided for use within the 

model and can be viewed by scrolling down below this help box. The user is encouraged to utilize these local coefficients for 

the specific city being modeled (if available) in lieu of the area size defaults by simply checking the box next to the appropriate 

city. The user is also encouraged to contact their local transportation planning agency to ensure the values cited are up-to-date 

or to obtain coefficients for cities not listed in these tables. 

When applying user-specified values, be aware that most models generally use input travel/wait time coefficients in MINUTES 

and cost-related coefficients in CENTS. Mode choice models such as the TDM model then internally convert the values of 

these coefficients to match the units of the travel/wait time or cost inputs. The COMMUTER model has also been programmed 

to apply a conversion factor to the Auto Parking and Transit Fare cost coefficients (in cents) when used with financial incentive 

inputs in units of DOLLARS per vehicle per day. When inputting your own coefficients, make sure the travel/wait time 

coefficients are in MINUTES and the cost-related coefficients are in CENTS.

Figure 7

Edit Coefficients Input Screen
-31-

The travel and emission impacts calculated by COMMUTER are highly sensitive to the

values of these coefficients, especially the cost coefficients. It is recommended that you use

local coefficients for mode choice, if they are available and up-to-date. Coefficients have

been estimated in many urban areas by the regional transportation planning agency (usually

MPOs, Councils of Government, or Associations of Governments). Values of travel time

and cost coefficients for many individual cities are incorporated into COMMUTER at the

bottom of this input screen. The values of these mode-choice coefficients are based on the

travel models currently used by regional transportation planning agencies. You are

encouraged to contact your local transportation planning agency to ensure the values cited are

up-to-date or to obtain coefficients for cities not listed in the table at the bottom of the input

screen. In cases where the survey data underlying the coefficients are more than ten years

old, it is recommended that you use the default coefficients for your area size for estimating

purposes and consult your local planning agency before using the city-specific coefficients.

###
* As noted in Section 2, however, you will not obtain accurate results by analyzing individual measures

and then summing the results. Measures that may be implemented together should be analyzed together.

-32-

4. TCM-SPECIFIC DATA

This section discusses the input screens that are used to enter TCM-specific data for each of

five different types of programs, with each program having its own input screen. As

explained in Section 2, programs can be analyzed individually or in combination.*

 At this

stage, you can edit any of the programs checked under “Programs Analyzed” on the

“Scenario Information” screen. (Remember, however, that if you did not select a program

from the Scenario Information screen, you will not have access to the data entry screen for

that program.) 

4.1 Site Access and Transit Service Improvement Programs

This section describes the Site Access and Transit Service Improvement program inputs.

Figure 8 shows the single input screen used for these programs.

Site Access Improvements

Site access improvements include such things as preferential parking policies for carpools

and vanpools or improvements to the work site or area that make access to transit easier. For

example, parking spaces in close proximity to both office building locations and transit

station/transit center locations could be provided for ease of access and reduced travel times

for carpool and vanpool vehicles. These programs also include improved pedestrian and

bicycle infrastructure at transit locations to encourage transit usage. Along with preferential

parking spaces, infrastructure improvements could include secure lockers and showers for

pedestrians and bicyclists and improved access to transit facilities from the adjacent roadway

system.

 

Walk-Access Time - You will need to specify the change in “walk access time,” which is the

time required to walk from the parking space or transit stop to the work site. A decrease in

walk access time for any particular travel mode is represented as a negative value. 
-33-

SITE ACCESS & TRANSIT SERVICE IMPROVEMENTS

I. Site Access Improvements

Mode:

Change in 

Walk Access 

Time (min)

Drive Alone

Carpool

Vanpool

Transit

Bicycle

Pedestrian

Employer Participation Rate:

II. Transit Service Improvements

IIa. More Frequent Service

Change in avg. headway (min)

Employment Served

IIb. Faster Service 

Change in route travel time (min)

Employment Served

Transit Operating Data

Increase in daily VMT by Transit 

Vehicles

Average speed of affected transit 

vehicles (mph)

Default average speed 19.6

Check here to use default transit 

speed

"Change in Walk Access Time" represents the difference in walking time associated with travel to or from the workplace 

as a result of worksite access changes. Walking time includes the time taken to walk from a parking lot or a bus stop to 

the actual worksite. Walk access time can be affected through policies such as preferential parking for carpools and 

vanpools or through improvements to the worksite or area which make access to transit easier. A decrease in walk 

access time for any particular mode should be entered as a negative value. 

"Employer participation rate" refers to the percent of employers in the analysis area implementing the walk access 

improvements. (This option is not necessary for site-specific analysis because the "participation rate" is 100%.) 

"Change in average headway" refers to the average change in frequency of service for transit service to the employment 

center or analysis area. An increase in service frequency is entered as a negative number. For example, if peak period 

transit service frequency increases from 20-minute to 15-minute intervals, the change in average headway would be 

entered as "-5.0". 

"Change in route travel time" refers to the average change in total route travel time for all transit service to the area. A 

decrease in travel time is entered as a negative number. For example, if new express bus service decreases the overall 

route travel time by 5 minutes, this would be entered as "-5.0".

"Employment served" refers to the percent of employment in the analysis area which is served by the improved transit 

service. (This option is not available for site-specific analysis). 

"Increase in daily VMT by transit vehicles" refers to the additional transit vehicle-miles of travel as a result of the 

improved transit service. Refer to Section 4.1 of the COMMUTER Model User Manual for guidance on how to calculate 

this parameter.

Figure 8

Site Access & Transit Improvements Input Screen
-34-

Employer Participation Rate - If you specified an area-wide analysis scope, you will also

need to specify the percent of employers in the analysis area implementing the walk-access

improvements. 

Remember, as discussed in Section 3.1, that there are two types of participation rates you

need to consider in setting up the inputs to COMMUTER. The first type is used in estimating

the affected employment inputs and refers to participation in any of the TCM programs being

modeled. The second type, the individual program participation rates, are actual model

inputs, and are used to further restrict the “eligibility” of all affected employment to

individual programs, such as Site Access Improvement programs. Thus, in an area-wide

analysis assuming 100,000 affected employees, a 15% Employer Participation Rate for Site

Access Improvement programs instructs COMMUTER that 15,000 employees (100,000 ×

15%) are eligible or affected by site access improvement strategies. (Note that the model

assumes a proportional ratio of employers to employees in determining affected employment

for individual programs.) 

The employer participation rate is not used in site-specific analysis because it is assumed to

be 100%.

Transit Service Improvements

Transit service improvements may include providing more frequent bus or shuttle service to

work sites, as well as providing faster transit service through express routes or operational

improvements. These improvements may also include implementing new route services

resulting from the transit planning process.

If you are analyzing improvements that lead to more frequent service, you will need to enter

the “Change in Average Headway.” This refers to the average change in the frequency of

transit service to the employment center or analysis area. An increase in service frequency is

entered as a negative number. For example, if peak period transit service frequency increases

from every 20 minutes to every 15 minutes, the change in average headway would be

represented as -5.0 minutes. 

“Employment Served” refers to the percent of employment in the analysis area that is served

by the improved transit service. As with the Employment Participation Rate input for Site

Access Improvement programs, Employment Served should reflect the fraction of all affected

employment that are exposed to the transit improvements. As an example, expanding transit

service along a single network corridor would affect only the fraction of employment served

by this transit corridor. Again, you do not need to enter this input if you are conducting a

site-specific analysis.

If you are evaluating faster service improvements, you will need to enter the “Change in

Route Travel Time.” This refers to the average change in the time required to travel the

total route for all transit service to the area. A decrease in travel time is represented as a
-35-

negative number. For example, if new express bus service decreases the overall route travel

time by 5 minutes, this would be represented as -5.0 minutes.

If transit service improvements are implemented, the change in daily transit vehicle-miles as

a result of increased service must also be considered. For this, you will need to estimate the

following items:

& The number of additional daily bus-trips on each route, for routes on which service is

increased; and

& The total round-trip route length for each route on which service is increased. 

You should be able to obtain information on route-mileage increases from the local transit

agency or you can develop estimates from operating plans for the proposed transit service. 

Estimates of daily mileage increases should take into consideration the distance traveled to

and from the storage/maintenance facility to the beginning/end of the route. 

In addition, an average travel speed for the affected transit service should be estimated. 

This can be done by dividing the total length of each affected route by the time taken to

complete the route.

If transit service improvements are implemented, the change in daily transit vehicle-miles as

a result of increased service must also be considered. This requires estimating the following

items:

& The number of additional daily bus-trips on each route, for routes on which service is

increased; and

& The total round-trip route length for each route on which service is increased. 

Information on route-mileage increases can be obtained from the local transit agency or can

be estimated from operating plans for the proposed transit service. Estimates of daily

mileage increases should take into consideration the distance traveled to and from the

storage/maintenance facility to the beginning/end of the route. 

In addition, an average travel speed for the affected transit service should be estimated. This

can be done by dividing the total length of each affected route by the time taken to complete

the route.

4.2 Financial Incentive and Parking Cost Programs

Financial incentives include any policies that affect how much it costs to travel via a

particular mode. Some examples of financial incentives are listed below.
-36-

FINANCIAL INCENTIVES AND PARKING COSTS

Change In Daily Cost:

Mode:

Parking Cost 

($/vehicle)

Fare Cost ($/ 

person/RT)

Other 

Financial 

Cost ($/ 

person/RT)

Total Change 

($/ 

person/RT)

Drive Alone - $ 

Carpool - $ 

Vanpool - $ 

Transit - $ 

Bicycle - $ 

Pedestrian - $ 

Employer 

Participation Rate:

"Financial incentives and parking costs" may include higher parking charges for single-occupant vehicles, reduced 

parking fees for carpools or vanpools, transit subsidies such as free monthly passes, or other financial incentives for 

specific modes. A decrease in cost is entered as a negative number. For example, provision of a transit pass valued 

at $30 a month would be entered as a change in fare cost of -$1.50 ($30 / 20 days). The cost change inputs are 

entered on a daily basis.

"Employer participation rate" refers to the percent of employers in the analysis area offering these incentives to their 

employees. (This option is not required for site-specific analysis because the "participation rate" is 100%.)

Figure 9

Financial Incentives Input Screen

& Increased parking charges, especially for single-occupant vehicles.

& Reduced parking fees for carpools and vanpools.

& Transit subsidies such as free monthly passes.

& Parking cash-out programs.

The Financial Incentive and Parking Cost program input screen is shown in Figure 9. A

decrease in cost (i.e., an incentive) is entered as a negative number. Changes in parking cost

are entered on a per-vehicle basis. Changes in other fare costs and other financial costs are

entered based on the change in cost per person per day (i.e., round trip transit fare).

As in other screens, “Employer Participation Rate” refers to the fraction of all affected

employees being offered financial incentives on a percent-of-employers basis. Like the other

program-specific “employer participation rate” inputs, COMMUTER applies the proportion

of participating employers to determine the fraction of all affected employees being offered

financial incentives. It is not used for site-specific analysis.
-37-

Two examples are provided below to illustrate how the financial costs should be calculated

and entered.

Sample Calculations for Financial Incentives and Parking Cost Programs:

& If parking costs are increased by $2.00 per day for all types of vehicles, you would

enter +$2.00 for Auto-Drive Alone, Carpool, and Vanpool. (The model will convert

the costs per vehicle to the costs per person by dividing by the assumed average

vehicle occupancy as identified in “Local Data.”)

& If a transit pass worth $30 per month is provided, you would enter a change in fare

cost of -$1.50 ($30 divided by 20 days per month).

Note that you enter these cost inputs in dollars per vehicle per day. COMMUTER internally

converts the Parking Cost and Transit Fare mode-choice coefficients that you entered in units

of cents in the “Edit Coefficients” screen into dollar units before combining them with the

cost inputs entered in this screen in the mode share calculations.

Parking Cash-Out Programs - Parking cash-out programs are modeled in this input screen by

treating the cash-out payment as a “subsidy” for use of eligible alternative modes. For

example, if the cash value of the parking subsidy were $60 per month or $2 per day, a current

Single Occupant Vehicle (SOV) user would see no difference in his/her cost to drive (park),

but the transit user would suddenly find it $2 per day cheaper to use transit. The same logic

applies to all modes that are eligible alternatives, i.e., bike, walk, or ridesharing (if there is no

problem with the cash-out recipient still parking at the site as a carpooler/vanpooler). In this

example, you would enter -$2 in the “Transit” row and “Parking Cost” column.

So to handle cash-out programs in COMMUTER, you enter nothing for the SOV mode

parking cost, and enter a subsidy for each of the eligible alternative modes. Note that in the

rideshare case, each passenger receives the full value of the subsidy, unlike where you give a

parking discount to carpools and the savings is split among the number of occupants.

4.3 Site-Specific Employer Support Programs

There are a number of strategies that employers can use that reduce the number of people

commuting to work in single-occupancy vehicles (SOVs), but do not result in measurable

changes in the time or cost of traveling to work. Research suggests that such “soft”

incentives or support programs can change travel behavior by providing encouragement to

use other modes of travel, informing travelers of alternatives, or removing impediments. 

Examples of this type of strategy include selling transit passes at the work site, providing

rideshare matches, marketing and promoting alternative modes, providing a guaranteed ride

home program, forming and supporting a vanpool, and providing preferential parking for

carpools. (Note that these types of programs also apply for an area-wide analysis, discussed

in Section 4.4.)
-38-

EMPLOYER SUPPORT PROGRAMS FOR ALTERNATIVE MODES

SITE-SPECIFIC ANALYSIS

Entry Format (check one only):

Specify Program Level

Specify Mode Share Increase

Specify Program Level:

Program Existing New

Carpool

Vanpool

Transit

Bicycle

Specify Mode Share Increase:

Program Existing Increase New

Carpool 0.0% 0.0%

Vanpool 0.0% 0.0%

Transit 0.0% 0.0%

Bicycle 0.0% 0.0%

"Employer Support Programs" include programs such as provision for an on-site transportation coordinator, ridematching, 

transit information, and other actions aside from time and cost incentives which encourage employees to utilize 

alternative modes. Two entry options are available for site-specific analysis:

(1) Specify existing and new program levels for Carpool, Vanpool, Transit, and Bicycle program support. A program level 

of "0" represents no program. Program levels of "1" through "4" indicate varying levels of effort for the programs. These 

program levels are described in Section 4.3 of the COMMUTER Model User Manual.

(2) Specify an expected mode share increase for each mode. This increase is added to the baseline mode share as 

specified in the input data.

IMPORTANT: This entry option should not be utilized unless the user has definitive data indicating a likely mode share 

increase as a result of proposed programs. If a mode share increase is specified, the user should document existing 

support programs and programs to be implemented, along with survey or other data indicating the basis for the mode 

share increase estimates.

"Program Level" and "Mode Share Increase" input options are mutually 

exclusive. You enter input data for either one or the other based on which 

Entry Format box you check to the left. See the help box below for an 

explanation of each input.

Figure 10

Site-Specific Employer Support Programs Input Screen

Figure 10 shows the input screen for site-specific analysis of employer support programs. As

shown in the figure, the first thing you need to do is specify the entry format, which refers to

the type of data you will be entering.

For a site-based analysis, it is recommended that you specify existing and proposed program

levels. These refer to the general level of effort spent on the program (which affects its

effectiveness) and are explained below, along with the codes used for data entry. They are

defined separately for carpooling, vanpooling, transit, and bicycle commuting.
-39-

As an alternative, you can specify the expected mode share increase. This expected increase

in each mode of travel is added to the baseline mode share that was specified in the input

data.

CAUTION: You should not use this alternative entry option unless

you have good data indicating that a proposed program will lead

to a likely mode share increase. If you do specify a mode share

increase, you should document existing support programs and the

programs to be implemented, along with survey or other data that

were used to estimate the mode share increase.

Definition of Program Levels

The impact of employer support programs and strategies varies depending on the level of

effort expended on the program. The level of program effort is a particularly important data

input because it defines what is actually meant by, for example, a “carpool support” program. 

The program level can vary from 0 to 4, with 0 representing no program and 4 representing a

program of maximum effort. (These program level definitions will also apply for area-wide

analyses, as discussed in Section 4.4.) The following program level descriptions are not

requirements for each level, but are intended as suggested guidelines to help you assign a

level designation to the support activities you are trying to model. Note that preferential

parking or financial incentives offered as part of a support program should be captured on the

Site Access and Transit Service Improvement input screen, and the Financial Incentives and

Parking Costs input screen, respectively.

Carpool Support Programs

Level 0 - no program

Level 1 - includes carpool information activities (tied in with area-wide matching)

and a quarter-time transportation coordinator.

Level 2 - includes an in-house carpool matching service and/or personalized carpool

candidate get-togethers (including information activities) and a quarter-time

transportation coordinator.
* Flexible work schedules as defined under these support programs refers to providing latitude to

employees to accommodate slight variations in arrival/departure to participate in these programs. This

differs from a formal Flex-Time policy, which is defined and discussed later in Section 4.5.

-40-

Level 3 - includes in-house carpool matching and information services, a policy of

flexible work schedules* to accommodate carpools, and a half-time transportation

coordinator.

Level 4 - includes in-house carpool matching and information, flexible work

schedules, and a full-time transportation coordinator.

Vanpool Support Programs

Level 0 - no program

Level 1 - includes vanpool information activities (tied in with area-wide vanpool

matching and/or third-part vanpool programs), plus a quarter-time

transportation coordinator.

Level 2 - includes in-house vanpool matching services and/or personalized vanpool

candidate get-togethers, and non-monetary vanpool development, plus a

quarter-time transportation coordinator and a policy of flexible work

schedules.

Level 3 - includes in-house vanpool matching services; vanpool development and

operating assistance, including financial assistance, such as vanpool purchase

loan guarantees, consolidated purchase of insurance, and a startup subsidy

(note that such assistance is different from offering financial incentives to use

vanpools); and additional services such as van washing, plus a half-time

transportation coordinator.

Level 4 - includes in-house vanpool matching services; vanpool development and

operating assistance, including major financial assistance, such as employer

purchase of vans with favorable leaseback (or alternative continuing subsidy,

such as free maintenance, free insurance) in addition to startup subsidy;

several additional incentives such as van washing, guaranteed ride home, and

a full-time transportation coordinator and/or personalized vanpool candidate

get-togethers.

Transit Support Programs

Level 0 - no program
-41-

Level 1 - includes a transit information center plus a quarter-time transportation

coordinator.

Level 2 - includes a transit information center and a policy of work hours flexibility to

accommodate transit schedules/delays, plus a quarter-time transportation

coordinator.

Level 3 - includes a transit information center and a policy of work hours flexibility,

on-site transit pass sales, plus a half-time transportation coordinator.

Level 4 - includes a transit information center and a policy of work hours flexibility,

on-site transit pass sales, guaranteed ride home, and a full-time transportation

coordinator.

Bicycle Support Programs

Level 0 - no program

Level 1 - providing on-site bicycle parking (racks or lockers). 

Level 2 - providing bicycle parking (racks or lockers) and shower facilities.

Level 3 - providing secure bicycle parking (storage lockers or indoor storage) and

shower facilities, in conjunction with local infrastructure conducive to

bicycling. This includes the presence of (a) off-street bike paths, (b) on-street

bike lanes, and/or (c) local streets with light traffic by which cyclists can

access the workplace. 

Level 4 - providing parking, shower, and infrastructure conditions as for Level 3, and

also sponsoring workplace promotional activities. These activities should

include promoting bicycle commuting, identifying the availability and

location of parking and shower facilities, and providing local bicycle route

maps, along with other activities to encourage bicycle commuting.

Some employer support programs may have combinations of characteristics different than

those shown here. In this case, you should choose the program level that most closely

represents the actual program being implemented. 

If there is no program level that you feel most closely represents the combination program

being offered, you can specify “combinations” of program levels by running the program for

an area-wide rather than site-specific analysis. For example, if a carpool program includes all

the elements of a Level 3 program except for flexible work schedules, you may want to

model this program as halfway between Level 2 and Level 3 in terms of effectiveness. You

can do this by setting the analysis scope to “Area-Wide” and specifying that 50 percent of
-42-

EMPLOYER SUPPORT PROGRAMS FOR ALTERNATIVE MODES

AREA-WIDE ANALYSIS

Percent of Employers Participating -- Existing

Program Level

Program None 1 2 3 4 Total

Carpool 100% 100%

Vanpool 100% 100%

Transit 100% 100%

Bicycle 100% 100%

Percent of Employers Participating -- New

Program Level

Program None 1 2 3 4 Total

Carpool 100% 100%

Vanpool 100% 100%

Transit 100% 100%

Bicycle 100% 100%

"Employer Support Programs" include programs such as provision of an on-site transportation coordinator, 

ridematching, transit information, and other actions aside from time and cost incentives which encourage employees to 

utilize alternative modes. 

For an area-wide analysis, the analyst should specify both existing and new (expected) participation rates (percent of 

employers participating) by program level for each mode. Program levels of "1" through "4" indicate varying levels of 

effort for the programs which are described in Section 4.4 of the COMMUTER Model User Manual.

Figure 11

Area-Wide Employer Support Programs Input Screen

employers have a Level 2 program and 50 percent have a Level 3 program. Note that if you

set the employer participation rate at 100 percent for every program being tested, the areawide and site-specific analyses will give identical results.

4.4 Area-Wide Employer Support Programs

The discussion in Section 4.3 of the types of employer support programs that may be offered

also applies here. Although different input formats are used for site-specific and area-wide

employer support programs, the data elements themselves are similar. Figure 11 shows the

input screen for area-wide analysis of employer support programs.

You should use the definitions of support program levels given in Section 4.3 for area-wide

analyses also. Be sure to read these definitions before proceeding.

For area-wide analysis of employer support programs, you must specify the percent of

employers participating in each of the program levels and modes. For each mode (carpool,

vanpool, transit, and bicycle), you need to enter the percent of employers in the area

participating at each program level. The sum of Levels 0 through 4 for each mode should

equal 100%. Employers who are not participating in any program would be included in the
* For an area-wide analysis, this will be the percent in the area-wide employment base; for a sitespecific (single employer) analysis, it will be the percent of employees within the firm.

-43-

“Level 0” program level. Participation rates should be specified for both the base case

(existing conditions) and the proposed program levels being evaluated.

4.5 Alternative Work Schedule Programs

This class of commuter-related TCM strategies is aimed at reducing how often commute trips

are made or shifting the timing of the trip out of the peak hour. For example, flex-time and

staggered work hour strategies have the effect of merely shifting commute travel to a lesscongested time period. These strategies will not affect the number of overall trips or the

amount of VMT, but they will change the distribution of trips, VMT, and emissions between

the peak and off-peak time periods. They may also affect overall emissions slightly by

affecting the average speed in the peak and off-peak periods. Definitions of the various work

schedule programs and their likely impacts are discussed later in this section.

Figure 12 shows the input screen for entering information on alternative work schedules and

telecommuting programs. As shown, you will first need to choose an entry format option,

as explained below:

& Eligibility Rate - This indicates the percent of all employees in the analysis system*

who are offered the program. The model then applies an assumed participation rate

to the total number of employees that are eligible. Note that the employees eligible

for each alternative work schedule and those not eligible for any strategy must sum

to 100 percent. In other words, only one alternative work schedule strategy may be

offered to an employee at a time. This simplifying assumption is used in the manual

and spreadsheet model because employees are unlikely to combine more than one

alternative work strategy at a time (for example, those employees working a

compressed work week are unlikely to be allowed to telecommute on regularly

scheduled work days). This parameter relates mainly to the logic of applying this

strategy to different employment segments. For example, manufacturing or retail

employees are not reasonable candidates for participation in telecommuting

programs. You should consider the characteristics of the employment base you are

analyzing when determining the value to use for this parameter.

& Participation Rate - As an alternative, you can specify existing and expected actual

participation rates for each program. 
-44-

CAUTION: You should not use the “Participation Rate” entry

option unless you have definitive data on the likely participation

rate as a result of proposed programs. If you do specify the

participation rates, you should document the existing support

programs and the programs to be implemented, along with the

survey or other data that formed the basis for the participation rate

estimates.
-45-

ALTERNATIVE WORK SCHEDULES

Use Data

Default Local Default

Alternative Work Schedule Parameters

Telecommute: Avg. Days/Week 1.8

Flex Time/Staggered Hours: Percent of trips 

shifted from peak period

Participation Entry Format (check one only):

Specify Eligibility for Participation

Specify Before/After Participation Rates

A. Eligibility for Participation

% Eligible

Program Existing New

Flex Time

Compressed 4/40

Compressed 9/80

Staggered Hours

Telecommute

Not Eligible 100% 100%

Total 100% 100%

B. Participation Rates

% Participating

Program Existing New

Flex Time

Compressed 4/40

Compressed 9/80

Staggered Hours

Telecommute

Not Participating 100% 100%

Total 100% 100%

"Alternative Work Schedules" include the option to allow employees to utilize flex time, compressed work weeks, staggered work hours, or 

telecommuting. Flex time and staggered hours will have the effect of shifting some trips outside of the peak period, while compressed 

work weeks and telecommuting will have the effect of eliminating some work trips. Two program entry options are available:

(1) The user can specify the percentage of employees eligible for each program. Both existing and new levels of eligibility should be 

specified.

(2) The user can specify existing and expected participation rates for each program.

To accomodate instances where employees are eligible for, or participate in multiple programs, the model allows the user to enter rates 

that exceed 100% when summed across all alternative programs. The model then internally normalizes the rates before using them in 

the travel calculations. Section 4.5 of the COMMUTER Model User Manual presents an example for this situtation.

IMPORTANT: Entry option (2) should not be utilized unless the user has definitive data indicating a likely participation rate as a result of 

proposed programs. If participation rates are specified, the employer/analyst should document existing support programs and programs 

to be implemented, along with survey or other data indicating the basis for the participation rate estimates.

Figure 12

Alternative Work Schedules Input Screen

Definition of Alternative Work Schedule Strategies

Flex-Time - In this policy, employees can adjust their work schedule (based on when they

arrive at and depart from the work site) in order to travel during the off-peak hours, when

there should be less traffic congestion. COMMUTER assumes a formal Flex-Time policy
-46-

rather than flexible work schedules. Flexible work schedules are seen as simply allowing

employees who would carpool or take transit to arrive or leave with slight variations in order

to be compatible with the pool/bus schedule. In contrast, a Flex-Time policy involves

formally moving the time of arrival or departure to a set of consistent work hours that are

different from the employer’s official hours. This type of policy may actually detract from

employees’ incentive to carpool or take transit as a means of avoiding traffic congestion. The

only assumed effect of this strategy is to shift the time of the trips, no vehicle trips are

eliminated.

Staggered Work Hours - Under this strategy, employers establish different starting times for

groups of employees in order to avoid having the entire workforce arrive or leave at the same

time. Some work sites have a large number of employees arriving within a very narrow time

period, so staggering starting hours can help reduce localized traffic problems. This strategy

is also assumed to affect only the timing of the trips, not the number of vehicle trips.

Compressed Work Week - Under this strategy, employees are allowed to reduce the number

of work trips made by working longer hours on fewer days per week. Options include the

4/40 schedule where 40 hours are worked in 4 days with the fifth day off and the 9/80

schedule where 80 hours are worked in 9 days with the tenth day off. COMMUTER

assumes that the 4/40 schedule eliminates one round-trip a week (1/5 of a daily trip) and that

the 9/80 schedule eliminates one round-trip every two weeks (1/10 of a daily trip) for each

participating employee. 

Telecommuting - This strategy involves allowing employees to work off-site, usually at home

via telecommunications linkups, one or more days per week. Telecommuting thus reduces

the demand for travel to the workplace. This is accounted for in COMMUTER by simply

removing person trips, along with the equivalent number of vehicle trips, from the total

amount of travel. (A more sophisticated analysis would consider how some of the commute

trips might be replaced by non-work travel.)

###
-47-

5. EMISSIONS-RELATED INPUT SCREENS

In the final two input screens, you will supply the information that COMMUTER needs to

calculate emission reductions. (If you are only interested in using COMMUTER to compute

travel impacts, you don’t need to enter any input information these two screens.)

To make this easier, a large matrix of MOBILE5b emission factors was generated for a series

of local conditions and pre-loaded into the program. (A total of 24 different sets of emission

factors are contained in COMMUTER.) To use these pre-loaded factors, all that you need to

do is supply a simple set of vehicle fleet characteristics, and COMMUTER will then look up

the appropriate set of MOBILE5b factors and use them to calculate emission reductions from

the TCM programs being evaluated. Thus, you do not have to supply detailed, locally

generated MOBILE5b emission factors.

If you are an experienced MOBILE5b user, however, and want to use emission factors that

exactly match your local conditions, you can optionally direct COMMUTER to import and

apply your locally generated factors. (Refer to Section 2.7 for step-by-step details on

generating and properly importing your own MOBILE5b emission factors into

COMMUTER.)

5.1 Fleet Emissions Information

In the first emissions-related input screen, you will provide the data needed for the program

to select the appropriate set of pre-loaded MOBILE5b emission factors or activate the UserSupplied Emission Factors” option if you want to use your own locally generated MOBILE5b

factors.

Figure 13 shows the layout of this screen. If you want to use the pre-loaded emission factors

contained in COMMUTER, follow the input requirements under “Using Pre-Loaded

Factors.” To use your own factors, see “Using Locally Generated Factors.”

Using Pre-Loaded Factors - To use pre-loaded factors, you must select from the available

fleet characteristic options in the MOBILE Scenario section at the top of the screen that best

match your local conditions. (Leave the “User-Supplied Emission Factors” and “Calendar

Year of User EFs” cells toward the bottom of the screen blank.) 
-48-

FLEET EMISSIONS INFORMATION

Field Data Notes

MOBILE Scenario Inputs

Calendar Year of Analysis Enter either 2000, 2002, 2005, 2010 or 2020

Season S = Summer, W = Winter

I/M Program Type 0 (zero) = none, 1 = Basic I/M, 2 = Enhanced I/M

Fuel Volatility Class B = Class B (Control Rgn 1), C = Class C (Control Rgn 2)

Fuel Control Program 0 = Conventional Gasoline, 1 = Reformulated Gasoline, 2 = Winter 

Oxygenated Fuel

User-Supplied MOBILE Emission Factors

 Mark the box to the left (with an "X") to compute emission reductions

User-Supplied Emission Factors using alternate MOBILE5b emissions factors instead of the

 pre-loaded factors already contained in the COMMUTER model 

Calendar Year of User EFs Select the calendar year of the user-supplied emission factors

The "MOBILE Scenario" inputs are used by the program to select a specific set of MOBILE5b emission factors from a 

series of stored tables that best represent local conditions and emission control programs being modeled. These inputs 

are familiar to MOBILE5b users. Further clarification of these inputs for users less familiar with the MOBILE5b emission 

factor model is provided below.

Calendar Year - Because new vehicle emission levels continue to decrease with the introduction of each model year, 

current and future vehicle fleet emissions will depend on the calendar year being analyzed.

Season - Enter either S for summer or W for winter.

I/M Program Type - The type of Inspection and Maintenance program, if any, being operated. Basic I/M refers to a 

program where a simple "no-load" idle or 2500 RPM test is performed. Enhanced I/M represents programs in which a 

loaded IM240 or ASM test are run on a dynamometer.

Fuel Volatility Class - Under EPA rulemaking related to fuel volatility ("Volatility Regulations for Gasoline and Alcohol 

Blends Sold in Calendar Years 1992 and Beyond, " 55 FR 23658, June 11, 1990), the U.S. has been divided into two 

VOC Control Regions. Generally speaking, Volatility Class B (Control Region 1) covers the southern U.S.; Volatility 

Class C encompasses the northern states. If in doubt, contact your EPA Regional Office to identify the correct Fuel 

Volatility Class.

Fuel Control Program - Under the 1990 amendments to the Clean Air Act, certain areas of the country must use 

reformulated gasoline (RFG) beginning in 1995. This input allows the user to specify whether RFG is being used and to 

include benefits of additional wintertime oxygenate blends beyond the level required under RFG.

NOTE TO MOBILE5b USERS: The daily temperature profile used by this program is based upon profiles developed by 

EPA as a function of season and fuel volatility class in its analysis of RFG benefits using the Complex Model. These 

profiles are as follows: Summer/Class B - 69 to 94 deg F; Summer/Class C - 72 to 92 deg F; Winter (either class) - 39 

to 57 deg F.

The COMMUTER model has been designed to use pre-loaded MOBILE5b emission factors for a defined range of input 

conditions or a set of user-supplied emission factors for specific local conditions. Before user-supplied emission factors 

can be used, they must be loaded into model using the "Import Emission Factors" command from the File menu. If the 

box above is marked and no user-supplied factors have been loaded, the model will signal an error when you try to view 

output results.

The "Calendar Year of User EFs" input identifies the specific calendar year factors from the set of user-supplied factors. 

You can load user-supplied emission factors for any number of individual calendar years. This input allows you to select 

and compute emission impacts for any one of the calendar years for which emission factors were supplied. If you enter 

a calendar year that doesn't match those in the user-supplied factors, an error is signaled.

Note: The VMT mixes (percent of travel by vehicle class) contained in the user-supplied emission factors are 

automatically loaded into the model and used in the emission calculations. If you are computing impacts with usersupplied emission factors, you cannot change the VMT mix from the "Other Emission-Related Data" input screen. When 

applying user-supplied emission factors, the VMT mix must be specified in the MOBILE5b runs. However, you must still 

supply affected vehicle speed and cold start percentage inputs in the "Other Emissions-Related Data" screen, 

regardless of whether pre-loaded or user-supplied emission factors are being used.

Figure 13

Fleet Emissions Information Input Screen
-49-

Each of these “pre-loaded” fleet characteristics inputs is explained below.

• Calendar Year - Since vehicle fleet emission levels change as new technology

improvements are introduced on newer cars, the calendar year that represents the

analysis scenario must be entered. 

You can choose either 2000, 2002, 2005, 2010, or 2020. If you are interested in an

analysis year between two of those years, the model should be run for both of the

surrounding years (for example, if you are interested in 2008, you should run

analyses for both 2005 and 2010). You will then need to interpolate the resulting

travel and emission impacts to represent impacts in the year of interest.

When you choose the year, you should keep in mind the time period when the TCM

programs being modeled will actually be implemented. For example, in evaluating

improved levels of transit service, it may take a couple of years to implement the

service improvements.

 

• Season - The choice of vehicle emission factors is affected by the ambient

temperature, and, in some areas, fuel controls that are imposed only during certain

seasons. You therefore need to enter the season for the analysis of interest, selecting

either “S” (summer) or “W” (winter). If you are an air quality planner, you will

generally select summer when evaluating ozone or particulate-related emission

reductions, and winter for carbon monoxide-triggered evaluations.

• I/M Program Type - The presence of an Inspection and Maintenance (I/M) program

will affect vehicle fleet emissions. There are three levels of I/M programs for you to

choose from: 

1. None - no I/M program operating in the region being analyzed;

2. Basic I/M - an I/M program where a simple “no-load” idle or 2500 RPM tailpipe

emissions test is performed along with a visual inspection; and

3. Enhanced I/M - I/M programs in which loaded IM240 or ASM emission tests are

conducted on a chassis dynamometer in conjunction with a visual and functional

emission control system inspection.

You should select and enter the level of I/M that most closely matches the type of

program being operated in the analysis area.

• Fuel Volatility Class - You must select either “B” or “C” to represent the gasoline

volatility class of the analysis region. These have been assigned under EPA’s final

volatility control regulations.2 Under this rulemaking, the U.S. has been divided into

two VOC (volatile organic compound) control regions, each of which has certain

specifications for reformulated gasoline.
*

Experienced MOBILE5 users should note that the combination of season and fuel volatility class

inputs is used to select the daily temperature profile upon which the emission factors are based. 

These daily temperature profiles as a function of season and volatility class are the same as those

used by EPA in its analysis of reformulated gasoline benefits using the Complex Model. These

temperature profiles are as follows:

- Summer, Class B - 69(F to 94(F;

- Summer, Class C - 72(F to 92(F; and

- Winter, either class - 39(F to 57(F.

-50-

If you are within VOC Control Region 1, you should enter “B.” If you are in an area

in VOC Control Region 2, you should enter “C.”* Generally speaking, volatility

class B (Control Region 1) covers the southern part of the U.S., and volatility class C

encompasses the northern states. If uncertain about which area the analysis region is

in, contact your EPA Regional Office.

• Fuel Control Program - Under the 1990 amendments to the Clean Air Act, certain

areas must use reformulated gasoline (RFG) beginning in 1995. This parameter

allows you to specify if RFG is being used in the analysis region and whether effects

of additional wintertime oxygenated blends should be included. You should select

and enter one of the following values:

0 - for conventional gasoline;

1 - for reformulated gasoline; or

2 - for wintertime oxygenated fuel.

Using Locally Generated Factors - Once you have successfully imported your own locally

generated MOBILE5b emission factors into COMMUTER as described in Section 2.7, you

can direct COMMUTER to apply them in the emission reduction calculations by marking the

“User-Supplied Emission Factors” box (with an “X”) toward the bottom of the screen. Once

you activate this option, you must then enter the specific calendar year of the emission factors

you’ve imported in the “Calendar Year of User EFs” input cell. (This input is used to select a

specific calendar year from a set of factors you’ve imported that may encompass multiple

calendar years. Even if you’ve only imported emission factors for a single year, you must

enter it into this input cell.)
-51-

NOTE: When you activate the “User-Supplied Emission Factors”

option, any entries you may have made in the “MOBILE Scenario

Inputs” cells at the top of the screen are ignored. In addition, the

vehicle fleet mix that you’ve specific in your locally generated

emission factors file is automatically loaded into the appropriate

cells in the “Other Emissions-Related Data” screen that follows.

5.2 Other Emissions-Related Data

In this final input screen, you will provide additional emission-related inputs that 

COMMUTER will then use in conjunction with the MOBILE5b emission factors discussed

in Section 5.1 to calculate “before TCM” (i.e., existing) and “after TCM” daily emissions for

the vehicle fleet. It will then determine the resulting emission reductions from the TCMs

being evaluated. 

Figure 14 shows the Other Emissions-Related Data input screen. Each of the inputs you will

be required to enter is described below.

Vehicle Fleet VMT Mix - The vehicle fleet is composed of eight different classes of

vehicles, which are listed on the screen. The VMT mix for the vehicle fleet refers to the

percent of the total travel (VMT) that is driven by each of the eight vehicle classes. The

emission factors in MOBILE5b are based on vehicle class. COMMUTER will calculate

emissions for the entire vehicle fleet (referred to as the fleet composite emissions) based on

the percentage of VMT in each vehicle class, by weighing the emission factors together

according to the fleet mix input.

If known, you should supply local data on fleet mix for the analysis area in the “Local”

column. Be sure that the percentages supplied sum to 100. If they do not, you will see an

error message when you attempt to view, print, or save the analysis results. 

If local data are not available, you can check the boxes in the “Use Default” column to use

the national default fleet mixes obtained from MOBILE5b. Note that the default fleet mixes

vary by calendar year and season.

As indicated in Section 5.1, if you are using your own locally generated emission factors, the

VMT mix from your MOBILE5b emission factor file is automatically loaded into these input

cells.

Affected Vehicle Speeds - The values you enter here should represent existing average

vehicle speeds in your region. You should be able to obtain data on average travel speeds

from transportation planning staff at the regional transportation planning agency. Even if you

are running a site-specific analysis, enter speeds that represent averages for your urban

region.
-52-

OTHER EMISSIONS-RELATED DATA

Use Data

Default Local Default Explanatory Notes

Vehicle Fleet VMT Mix Percentages of total VMT by vehicle type

LDGV - Light-Duty Gas Vehicles

LDGT1 - Light-Duty Gas Trucks 1 To 6,000 lbs GVW (gross vehicle weight)

LDGT2 - Light-Duty Gas Trucks 2 From 6,001 to 8,500 lbs GVW

HDGV - Heavy-Duty Gas Vehicles Over 8,500 lbs GVW

LDDV - Light-Duty Diesel Vehicles

LDDT - Light-Duty Diesel Trucks To 8,500 lbs GVW

HDDV - Heavy-Duty Diesel Trucks Over 8,500 lbs GVW

MC - Motorcycles

TOTAL (must add to 100%) 0.0%

Affected Vehicle Speed (mph) Average speed (mph) of TCM-affected trips

Peak Period Average Speed 34.6

Off-Peak Period Average Speed 39.7

Cold Start Percentages Percent of trips that start "cold"

Baseline - Peak Period 48.0% Peak period trips that start cold

Baseline - Off-Peak Period 40.0% Off-peak period trips that start cold

Eliminated Trips - Peak 48.0% TCM-eliminated peak trips that start cold

Eliminated Trips - Off-Peak 40.0% TCM-eliminated off-peak trips that start cold

Vehicle Fleet VMT Mix

MOBILE5b generates emission factors for each of the eight different vehicle classes listed. Fleet "composite" emission factors

are then calculated by weighting these emission factors by the percentage of travel (i.e., VMT) in each vehicle class. The 

default VMT mixes provided by this program are MOBILE5b national default values. These defaults are calendar year and 

season specific. This input is required only when you are using the pre-loaded emission factors. If user-supplied factors are

used, the VMT mix is obtained automatically from the MOBILE5b runs and these input cells are ignored.

Affected Vehicle Speed

Vehicle emissions vary with speed. The values entered here should represent regional network average speeds during the 

peak and off-peak periods. Default values supplied are based upon HPMS (Highway Perfermance Monitoring System) 

averages compiled by urban area size. This input must always be entered whether using either pre-loaded or user-supplied 

emission factors.

Cold Start Percentages

Emission factor models address the fact that vehicles have higher emission rates when started "cold" before the catalyst and 

engine are fully warmed up. In MOBILE5b, trips are defined as either cold starts or hot starts, depending on the time the 

engine was off (referred to as "soak time") prior to the previous trip. A cold start is defined as any start with a soak time of at 

least 4 hours for non-catalyst vehicles and at least 1 hour for catalyst vehicles. In MOBILE5b, all other starts are hot starts. 

For example, if the cold start percentage is 80%, the hot start percentage is 20% (100-80). The user must enter the cold start

trip percentage of trips for both the baseline trips and for the trips that would be eliminated by TCMs. Note that separate cold 

start percentages must be entered for both peak and off-peak periods. This input must always be entered whether using 

either pre-loaded or user-supplied emission factors.

NOTE TO MOBILE5b USERS: The cold start percentage inputs used by this program should not be confused with the 

operating mode fraction inputs required by MOBILE5. Those fractions include specification of the amount of stabilized (Bag 2) 

operation. In this program, the amount of stabilized operation is internally calculated from the start percentage inputs and the 

average trip length.

Figure 14

Other Emissions-Related Data Input Screen
* In most cases, the MPO for a given region is responsible for both transportation planning and emissions

analysis. The MPO maintains local data related to travel demand, speed, and emissions inventories for

regional planning purposes. These data are typically available to member agencies (counties, cities, transit

operators) and businesses. Metropolitan-level emissions inventory data sets generally provide local data on

travel speeds by peak and off-peak periods that are generated from the travel demand modeling process and

used in regional air quality conformity analysis.

** MOBILE5b users should not confuse the cold start percentage inputs used by this program with the

operating mode fraction inputs required by MOBILE5b. Those fractions include specifying the amount of

stabilized (Bag 2) operation. In COMMUTER, the amount of stabilized operation is calculated internally

from the start percentage inputs and the average trip length.

-53-

You will need these values for both peak and off-peak periods.* Peak period travel speed

should be the average of travel speeds in the AM and PM peak periods, if these values differ. 

CAUTION: Do not specify travel speeds at a geographic area

smaller than the county level. Even if you are performing a sitespecific analysis, the speed inputs should reflect average regional

network travel speeds that employees at the site experience driving

to and from work.

You may also choose to use default travel speeds, shown in Table 2, if local data from the

regional MPO are not available. These default values have been estimated from national

highway data. Travel speeds will vary depending on metropolitan area size, since larger areas

tend to be more congested.

Table 2

Default Speeds (mph) by Area Size

Metropolitan Area Size Peak Period Off-Peak

1 - greater than 2 million 31.8 37.1

2 - 750,000 to 2 million 34.6 39.7

3 - less than 750,000 34.8 39.7

Cold Start Percentages - This refers to the percentage of the vehicles trips that are made

from a “cold” start.** Vehicles have higher emission rates when started “cold” before the

catalyst and engine are fully warmed up. Therefore, emission factor models, including
-54-

MOBILE5b, require that trips be defined as either “cold starts” or “hot starts,” depending on

how long the engine has been turned off (referred to as “soak time”) since the previous trip.

A cold start is defined as any start with a soak time of at least four hours for non-catalyst

vehicles (in other words, it has been at least four hours since the vehicle was turned off after

the previous trip); for vehicles equipped with a catalyst, it refers to any start after a soak time

of at least one hour. In MOBILE5b, all other starts are hot starts. For example, if the

baseline peak period cold start percentage is 80%, the hot start percentage is 20% (100-80). 

You must supply the percentage of all trips under baseline travel conditions (before

implementation of the TCMs) that are estimated to start cold, estimating this separately for

both the peak and off-peak periods. (These periods were defined earlier in Section 3.2.) 

Many metropolitan areas that have had to prepare detailed emission inventories have

developed estimates of these percentages. You should contact the local air quality or

transportation planning agencies for this information

You must also enter the cold-start percentage for the number of trips that would be

eliminated by the TCMs being evaluated, again in both the peak and off-peak periods. For

example, if 100 trips were being eliminated during the peak period and 90 of those were from

a cold start, the cold start percentage would be 90. Because “eliminated trip” cold start

percentages are usually not readily available, you may wish to use the default values, as

explained below. If you do not want to use defaults for this input, you should consider the

types of TCM programs being evaluated and the specific trips that these programs would

eliminate. For example, door-to-door carpool/vanpool programs are focused on eliminating

morning-evening commute trips, which are almost always (close to 100%) cold start trips. 

If local data are not available, you can use the default values supplied by COMMUTER,

which are based upon instrumented vehicle measurements collected by EPA. To use the

default values, simply check the boxes in the “Use Defaults” column.

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1. J. R. Kuzmyak, et. al., "Procedures Manual for Estimating Emission Reductions

from Voluntary Measure and Commuter Choice Incentive Programs", prepared for

the U.S. Environmental Protection Agency," Draft Final Report, September 19,

1999.

2. Federal Register, Vol. 55, pg. 23658, June 11, 1990.

6. REFERENCES

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