Transportation demand management (tdm) is increasingly popular as a response to traffic congestion, air pollution, and related problems. Innovative institutional arrangements have been conceived to implement tdm in a more efficient and effective manner. Careful evaluation is necessary to determine whether tdm has been successful, however. Tdm evaluation efforts have tended to lag behind tdm implementation efforts. Results of few tdm evaluation studies have been published. Tdm evaluation may be based on direct observation, revealed preference, stated preference, or organizational survey sampling methods of data collection. Tdm programs generally are complex policy instruments with modest goals and objectives, providing marginal impactson travel behavior that are difficult to discern. This description suggests that tdm evaluation methods should be complex in order to be accurate. Yet, effects of tdm programs may not be sufficient to justify costly tdm evaluation efforts. The challenge to the tdm evaluator is to develop tools appropriate to the task in terms of both cost and accuracy. This challenge could be accomplished by integrating tdm evaluation into the general framework of transportation system performance monitoring at the regional level. The urban transportation planning system is in use in most urban areas where tdm is likely to be implemented. Additional data are needed to assess tdm impacts in such areas. The art of tdm evaluation has a long way to go beforeit reaches maturity as a practical transportation planning and evlauation tool. The time for greater action on tdm evaluation, as in tdm implementation, is now. This paper appears in transportation research record no. 1321, Rideshare programs: evaluation of effectiveness, trip reduction programs, demand management, and commuter attitudes1991.
Abstract