Method for optimizing transit service coverage

Abstract

A method is presented for determining the optimal length of transit routes that extend radially from the central business district (CBD) into low-density suburbs. In addition to the route length, the route spacing, headway, and stop locations are also optimized. The equations for the route length, route spacing, headway, and stop spacing that minimize the sum of operator and user costs are derived analytically for many-to-one travel patterns with uniform passenger trip density. These equations provide considerable insight into the optimality conditions and interrelations among variables. The equations are also incorporated within an efficient algorithm that computes the optimal values of decision variables for a more realistic model with vehicle capacity constraints. The algorithm is applied to rectangular and wedge-shaped urban corridors with uniform and linearly decreasing passenger densities. The results show that in order to minimize the total cost, the operator cost, user access cost, and user wait cost should be equalized. At the optimum, the total cost function is rather shallow, thus facilitating the tailoring of design variables to the actual street network and particular operating schedule without substantial cost increases. The actual stop spacing pattern is determined for each corridor type. For a uniform passenger density, the stop spacing increases along the route in the direction of passenger accumulation toward the CBD. For a linearly decreasing passenger density, the stop spacing first decreases and then increases along the route toward the CBD. The sensitivity of design variables to some important exogenous factors is also presented.

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