TRUST is a program to analyze and evaluate a given set of bus transit routes and associated frequencies, in terms of several descriptors, including measures of user costs, service quality, and operator resources. The procedure assigns a known demand matrix to the transit network according to a path choice logic that explicitly considers transfers. As such, it calculates the percentages of the total demand trips that are able to reach their destination with no transfer, via one transfer, via two transfers, or simply cannot be satisified (with two or fewer transfers). Also computed are several node-level and route-level descriptors for use in the route network planning and design process. After the assignment is executed, the program determines the service frequency necessary on each route to maintain the passenger load factor below a specified maximum. The procedure can be used iteratively until the calculated frequencies are consistent with the input frequencies. TRUST is written in the LISP language because the latter's" list" data structure representation is particularly well suited to support the path search and enumeration activities inherent in the assignment logic and path choice rules appropriate in a transit network. The application of the program to the transit network of the Austin, Tex., urban area (with some simplifying assumptions) is presented, illustrating the program's capabilities and computational performance.

The purpose of this paper is to describe TRUST (Transit Routes Analyst), a LISP program developed to analyze a set of bus transit routes and associated service frequencies. It can be used either separately in a design-support function, or in the context of a formal solution procedure for the transit network design problem (TNDP). Such problems have been studied by several authors in the past (1-8). In the TNDP, one seeks to determine a configuration, consisting of a set of transit routes and associated frequencies, that achieves some desired objective, subject to the constraints of the problem. Mathematical formulations of the TNDP have been concerned primarily with the minimization of an overall cost measure, generally a combination of user costs and operator costs. The former is often captured by the total travel time incurred by users in the network, while a proxy for operator costs is the total number of buses required for a particular configuration. Feasibility constraints may include, but are not limited to:(1) minimum operating frequencies on all or selected routes (policy headways, where applicable);(2) a maximum load factor on any bus route; and (3) a maximum allowable bus fleet size.