After a decade-long shift in emphasis in regional transportation planning, steadily impacted by politics and planning commissions, environmental impact studies, and national, state and local legislation, the authors interpret and explain the meaning of the transportation planning process in the United States today. The book focuses on the interrelations between federal legislation, the judicial process and transportation planning, particularly in light of two important landmark federal acts - The Clean Air Act of 1990 and the Intermodal Surface Transportation Efficiency Act of 1991. The repercussions of these Acts have caused planners throughout the US to be much more circumspect about commitments they include in transportation plans and travel forecasting.