  Multi-vehicle routing has become increasingly important with the rapid
development of autonomous vehicle technology. Dial-a-ride problem, a variant of
vehicle routing problem (VRP), deals with the allocation of customer requests
to vehicles, scheduling the pick-up and drop-off times and the sequence of
serving those requests by ensuring high customer satisfaction with minimized
travel cost. In this paper, we propose an improved tabu search (ITS) heuristic
for static dial-a-ride problem (DARP) with the objective of obtaining
high-quality solutions in short time. Two new techniques, initialization
heuristic, and time window adjustment are proposed to achieve faster
convergence to the global optimum. Various numerical experiments are conducted
for the proposed solution methodology using DARP test instances from the
literature and the convergence speed up is validated.
