Some Issues Relating to the Optimal Design of Bus Routes

The following is mostly a discussion of some issues relating to the design of minimum cost bus routes serving a multiple origin-multiple destination trip distribution. The main difficulty in determining any “optimal” routing originates from the fact that the objective function (total cost) is a nonconvex function of the assignment; the higher the demand for trips on a route, the better is the service that one can provide. One consequence of this is that a square grid of straight line bus routes is not likely to be an optimal geometry even under highly idealized conditions. “Good” geometries are more likely to focus routes onto a single street and past a common junction.