The study scope and physical restraints of the area are outlined for the Puget Sound Regional Transportation Study (PSRTS). The program objective was to formulate a transportation plan as part of a general development plan of the region. PSRTS studied the following transportation systems: streets and highways, mass transit, ferry boats, bridges, and parking facilities. The system development is outlined for the transportation system made up of streets and highways. The traffic assignment procedure begins with the assignment of current origin and destination traffic to a base year network. In Seattle, the basic building block for all study systems was the existing base year network of 1961. Use of selected link and screenline analyses is discussed. The following principles were used in this activity: (1) initial network evaluations were viewed as part of normal study procedures to develop staff analyst comprehension of system operating characteristics, (2) continued system evaluations were keyed to a demand-type analysis until system balances are resolved as contrasted to performance analysis where individual link operational analysis is emphasized, and (3) network performance analysis then refines or performs detailed evaluations of the recommended systems and/or their alternatives for implementation purposes. The Seattle study developed a population distribution model based on a statistical evaluation of the factors that determined the growth that occurred in the region between 1950 and 1960. Five factors were isolated as attracting and influencing the locations of population growth. An employment distribution model was developed. The importance of land-use patterns are discussed as they influence and permit flexibility in transportation planning.
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