Emissions Analysis Techniques for TCMs
Overview - The TCM/Commuter Choice Model is a spreadsheet-based software program developed for the EPA. It is designed specifically to analyze the travel and emission impacts of employer-based voluntary travel demand management strategies.
Strategies Addressed - Improved transit; HOV lanes; carpooling and vanpooling promotion; bicycle and pedestrian programs; telecommute and work hour strategies; pricing and subsidies.
Methodology - The data and methodologies used to estimate travel impacts are similar to those in the TDM Evaluation Model. Strategies that affect the time and/or cost of travel are evaluated using a "pivot-point" mode choice model. Other strategies, such as employer-based support programs and work hour shifts, are evaluated using lookup tables based on empirical evidence. Emission changes are based on changes in trips, VMT, and speed, using lookup tables derived from MOBILE5a.
Data Requirements - Total persons affected, baseline mode shares, and average trip lengths by mode for an individual site or area; impacts of the strategy on changes in travel time and cost by mode; and description of other (non-time/cost-based) TDM programs. The user has the option to change default parameters.
Outputs - Changes in modal share, vehicle-trips, VMT, and emissions.
Level of Effort - The TCM/Commuter Choice Model is easy-to-use, off-the-shelf software. Some effort may be required to identify reasonable assumptions on baseline mode shares, trip lengths, and affected employment for the analysis area.
Advantages - The logit-based pivot point mode choice approach is theoretically sound, consistent with common practice in travel demand forecasting, and capable of analyzing the joint impacts of multiple strategies. The empirical lookup tables allow for differences in impacts by size and type of employer.
Limitations - Some of the default data on strategy effectiveness date from around 1990 or earlier. The model is not directly capable of analyzing multiple "market segments." The ability of the software to manage scenarios is limited.
Source/Availability - The EPA TCM/Commuter Choice Model was developed in 1998. It can be downloaded at no charge from the EPA's Office of Transportation and Air Quality web site (http://www.epa.gov/oms/transp.htm).