Other Existing General Guidelines to Evaluating Strategies
The literature review revealed a substantial effort to uncover benefits brought about by TDM initiatives. There exist numerous practitioner oriented guidelines to TDM impact assessment based on formalized approaches to comprehensive evaluation[11-16]. Several studies have culled findings of program evaluations to compare the empirical evidence of a range of TDM alternatives[16, 17].
Some of the guidelines list relevant impact measures to evaluate TDM projects[11, 12, 18], and outline the major constraints to a comprehensive TDM evaluation. These research efforts all recognize that, generally, TDM projects result in relatively small impacts over a large number of individuals. They are more difficult to evaluate for the following reasons:
Impacts are different across users, whereas in project infrastructure evaluations users are assumed homogeneous (i.e., they receive the same benefits); and,
Different TDM strategies are simultaneously implemented calling for a comprehensive evaluation.
This leads to a trade-off between evaluation procedures that estimate all of the individual responses to TDM strategies and procedures that provide a more aggregate appraisal using a greater level of approximation. The approximation is an inevitable trade-off of the requirement of a standardized approach. These issues have been considered in the literature.
TDM measures are social plans and their benefits encompass a vast sphere of social life. For example, a congestion reduction program might benefit not only from reductions in VMT, but might also gain from air quality improvements, decreased fossil fuel consumption, and reduced parking demand. Price changes can have a variety of impacts on travel, affecting the number of trips people take, their destination, route, mode, travel time, type of vehicle (including size, fuel efficiency and fuel type), parking location and duration, and which type of transport services they choose. All these are essential indicators in evaluating a TDM project.
Approaches that are currently available to evaluate the cost effectiveness of TDM programs and strategies deal with assessing the impacts on a comparative basis. This
is usually carried out by assessing TDM impacts in terms of
measures date, the
measuring the effectiveness of TDM programs on a emission reduction is represented by the Transportation
comparative basis in terms of Research Board Special Report
264. This research effort summarized seminal work on the cost effectiveness of programs funded under the reduction.
conducted to date with a focus objective of pollution emission