Emissions Analysis Techniques for TCMs
Overview - The Congestion Mitigation/Air Quality (CM/AQ) Evaluation Model is a software program designed to calculate the emissions benefits of candidate CMAQ projects and to rate projects based on various effectiveness criteria.
Strategies Addressed - Improved transit; HOV lanes; park and ride; carpooling and vanpooling promotion; bicycle and pedestrian facilities; traveler information; telecommuting/work hours; pricing/subsidies; parking management; traffic flow improvements; intermodal freight; traffic calming; idle control; cold start; alternative fuel vehicles (total of 59 individual strategies).
Methodology - The model is a menu-driven custom application designed within the Paradox database software. The methodologies to estimate travel changes are similar to those employed in the TCM Tools model. For some strategies, travel changes are estimated based on elasticities; for others, program participation must be estimated by the user. Emission reductions are estimated based on changes in travel characteristics (VMT, trips, and speed) and user-entered emission factors. The model also estimates cost-effectiveness and provides an overall ranking of projects, based on user-defined weighting factors.
Data Requirements - User inputs include baseline travel characteristics (e.g., number of person-trips, percent of trips in peak period) and behavioral assumptions (elasticities or participation) for the strategy being analyzed. Local emission factors from the MOBILE and PART5 models are also required. Default values are provided for many of the parameters, although local data are preferred.
Outputs - Changes in trips, VMT, speed, and idling time for peak and off-peak periods.
Level of Effort - The model is relatively easy to use, but requires a basic knowledge of Paradox and also requires local data such as MOBILE emission factors and baseline travel characteristics.
Advantages - The CM/AQ Evaluation Model covers a wide range of potential CMAQ strategies. The cost-effectiveness and criteria weighting modules provide capabilities beyond most CMAQ and TCM evaluation packages, allowing users to rank projects based on various effectiveness criteria. The model accounts for the impacts of reduced idling and cold-start and hot-start trips as well as reduced VMT.
Limitations - The model is limited in its ability to forecast the travel impacts of TDM strategies. Many strategies require the user to estimate participation rates (e.g., telecommuting participants, number of new walkers/bicyclists), as well as to make other assumptions that affect the magnitude of travel impacts.
Source/Availability - The model was originally developed for the Denver Regional Council of Governments by JHK Associates, and was adopted in 1995 by the Texas Transportation Institute for use by metropolitan areas in Texas. The CM/AQ Evaluation Model and User's Guide are available from the Texas Transportation Institute (979-845-4853, http://tti.tamu.edu/).
Reference: TTI CM/AQ Evaluation Model User's Guide and Workshop Training Materials. Research Report 1358-1, Texas Transportation Institute, College Station, TX (August 1995).