The Detroit Metropolitan Area Traffic Study (1953–55) and the Chicago Area Transportation Study (1955–62) turned household travel surveys into a computable procedure: divide the region into zones, then generate trips from land use, distribute them between zones with a gravity model, split them between modes, and assign them to network links. Alan Voorhees's 1955 general theory of traffic movement supplied the gravity formulation. Run on early mainframes, the model produced forecast link volumes twenty years ahead, and those numbers justified motorway lanes, interchanges and parking standards. The 1962 US Federal-Aid Highway Act made such a continuing regional study a condition of federal funds.
This is the moment planning became quantitative and predictive at metropolitan scale — the technical machinery of regional transport plans, and of the road building they legitimised. Its assumption that land use is an input and traffic an output built the predict-and-provide loop that induced the demand it forecast, a critique that shaped later integrated land-use and transport models and accessibility planning. Practically every metropolitan transport plan since is a descendant or a deliberate rebuttal.
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