This report describes the transportation planning process and discusses where and how environmental factors can be addressed effectively at the state and metropolitan levels. This report should be especially useful to federal, state department of transportation (DOT), metropolitan planning organization (MPO), and local transportation planners, as well as other practitioners concerned with addressing environmental factors within transportation systems planning, priority programming, and project development planning leading to implementation. The research focused on environmental issues within the long-range transportation planning processes of state DOTs and MPOs and included the following: (1) a comprehensive review of recent literature; (2) a survey of approaches employed by state DOTs, MPOs, and environmental regulatory agencies; (3) a review of federal regulations and guidance on environmental factors; and (4) case studies to synthesize current practice in environmental planning.