By designating East-West Gateway as the metropolitan planning organization (MPO) for the St. Louis region, the federal government and the states have vested legal authority and responsibility in East-West Gateway for the development and adoption of long- and short-range regional transportation plans. Any transportation project within the boundaries of the eight member counties that will be wholly or partially funded with federal dollars must be contained in one of East-West Gateway's approved plans. Transportation planning is not simply an exercise in design and engineering. It requires understanding and addressing the complex relationship between mobility and the region's economy, community, and ecology and its final product is an evolving federal, state, and local transportation investment strategy to serve the region's broad quality of life goals. For that reason, the tools of planning include population and employment estimates, land use and transportation facility inventories and maps, environmental quality assessments, computer models of existing and future travel patterns, and activities to engage interest groups and community residents in setting priorities.

Transportation Redefined is the term that describes the more customer-focused approach to transportation planning that was adopted by East-West Gateway with the 1995 long-range transportation plan and its 1999 update that go by that same name. Because all other transportation planning functions are derived from the goals and processes set out in the long-range plan, a wide range of short-range plans and corridor studies are also included under this section. They support the decision-making process under which more than 18 billion federal and local dollars will be invested in regional transportation infrastructure and operations over the next 20 years.