OPTIMIZATION OF GROUP LINE-HAUL OPERATIONS FOR MOTOR CARRIERS USING TWIN TRAILERS.

Group line-haul operation involves the daily movement of trailers between a central breakbulk terminal and a set of end-of-line satellite terminals. When each tractor can pull two trailers, there are many possibilities for creating tractor tours that accomplish the required pickup, delivery, and empty-balancing operations. The challenge is to create optimal tours that minimize transportation costs. An optimization procedure is described that is based on a branch-and-bound framework. It involves Lagrangian relaxation for lower bounds and two upper-bound heuristics for solving this problem.