Emissions Analysis Techniques for TCMs
Overview - The TDM Evaluation Model is a software program that analyzes the vehicle-trip reduction effects of a wide range of travel demand management strategies. The TDM model has been widely applied throughout the U.S. for the purpose of analyzing Transportation Control Measures or other TDM programs.
Strategies Addressed - Improved transit; HOV lanes; carpooling and vanpooling promotion; telecommute and work hour strategies; pricing and subsidies.
Methodology - Strategies that affect the time and/or cost of travel are evaluated using a "pivot-point" mode choice model. The pivot point model is a derivative of the logit mode choice model commonly used in four-step travel demand models. It requires information on baseline mode shares and changes in travel time or cost. Other strategies, such as employer-based support programs and work hour shifts, are evaluated using lookup tables based on empirical evidence.
Data Requirements - Baseline travel data requirements include zone-to-zone person and vehicle trip tables for the analysis area (these may be derived from the regional travel model or constructed from employee commute survey data), or total person and vehicle trips for an individual site/area. Other data requirements include impacts of strategies on travel time and cost by mode and descriptions of other (non-time/cost-based) TDM programs. The user has the option to change default parameters affecting strategy effectiveness.
Outputs - Changes in modal share, vehicle-trips, VMT, average vehicle occupancy and ridership.
Level of Effort - The TDM model is easy-to-use, off-the-shelf software. Some effort is required to develop inputs in the form of matrices showing the number of trips by mode and the distance between each pair of zones.
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 time and cost-based strategies. The empirical lookup tables allow for differences in impacts by size and type of employer. Trip-table inputs allow "market segmentation" by origin/destination, and impacts vary for each "market" depending upon trip lengths and starting mode shares.
Limitations - The TDM model does not estimate emissions benefits directly. The user must apply VMT and/or trip-based emission factors. The default coefficients and data on strategy effectiveness in the TDM model date from around 1990 or earlier.
Source/Availability - The TDM Evaluation Model is a DOS-based software program. It is distributed by McTrans (352-392-0378, firstname.lastname@example.org) at a cost of $250.