Shortest path problems with time constraints

Abstract

We study a new version of the shortest path problem. Let G=(V, E) be a directed graph. Each arc e ∈ E has two numbers attached to it: a transit time b(e, u) and a cost c(e, u), which are functions of the departure time u at the beginning vertex of the arc. Moreover, postponement of departure (i.e., waiting) at a vertex may be allowed. The problem is to find the shortest path, i.e., the path with the least possible cost, subject to the constraint that the total traverse time is at most some number T. Three variants of the problem are examined. In the first one we assume arbitrary waiting times, where it is allowed to wait at a vertex without any restriction. In the second variant we assume zero waiting times, namely, waiting at any vertex is strictly prohibited. Finally, we consider the general case where there is a vertex-dependent upper bound on the waiting time at each vertex. Several algorithms with pseudopolynomial time complexity are proposed to solve the problems. First we assume that all transit times b(e, u) are positive integers. In the last section, we show how to include zero transit times.

On leave from IBM T. J. Watson Research Center, P.O.Box 218, Yorktown Heights, NY 10598, U.S.A.