  Platooning of vehicles is a promising approach for reducing fuel consumption,
increasing vehicle safety, and using road space more efficiently. We consider
the important but difficult problem of assigning optimal routes and departure
schedules to a collection of vehicles. We propose an iterative
route-then-schedule heuristic for centralized planning that quickly converges
to high-quality solutions. We also propose and analyze a collection of valid
inequalities for the individual problems of assigning vehicles to routes and
scheduling the times that vehicles traverse their routes. These inequalities
are shown to reduce the computational time or optimality gap of solving the
routing and scheduling problem instances. Our approach uses the valid
inequalities in both the routing and scheduling portions of each iteration;
numerical experiments highlight the speed of the approach for routing vehicles
on a real-world road network.
