Accessibility has often been considered as a valuable evaluation criterion in attempt to analyze alternative transportation systems. The subject of this research is the development and application of a computerized accessibility model to aid in evaluating the distribution of transit services throughout an urban area. Included is an investigation of the various definitions of accessibility and a presentation of several past and present attempts to measure accessibility, both qualitatively and quantitatively.

In attempting to establish an exact criterion for evaluation employing accessibility measures, the scope of the problem becomes quite complex. It must be broad enough for use in all transportation evaluation applications; precise enough to insure the optimization of established goals; and, obviously, simple enough to be understood by decision makers as well as engineers and planners. The development of a Transit Accessibility model, TRANSAC, meeting these qualifications, is described herein.

The concept of accessibility employed within TANSAC is based primarily on the summation of opportunities accessible to small geographic zones via the transit system. The model is compatible with current UMTA Transportation Planning System (UTPS) programs, and incorporates travel time data computed by these programs as input data for accessibility calculations.