AN INTEGER L-SHAPED ALGORITHM FOR TIME-CONSTRAINED TRAVELING SALESMAN PROBLEM WITH STOCHASTIC TRAVEL AND SERVICE TIMES

The time-constrained traveling salesman problem (TCTSP) is a variant of the classical traveling salesman problem, where only a subset of the customers can be visited due to the time limit constraint. In this paper, we consider the TCTSP with stochastic travel and service times. Given the normal working hours T and a tolerance time ΔT, the total travel and service times of a route can exceed T as long as it is within T+ΔT, though a penalty proportional to the amount in excess of T will be imposed. The problem consists of optimally selecting and sequencing a subset of customers to visit in the presence of random travel and service times to maximize the expected profit while satisfying the time limit constraint. We formulate the problem as a two-stage stochastic program with recourse, and propose an integer L-shaped solution method for solving it. Computational results show that the algorithm can solve problems with moderate size to optimality within reasonable time.