One of the most challenging research issues in vehicular ad hoc networks (VANETs) is how to efficiently relay messages between vehicles. We propose a heuristic that uses the physical dimensions of vehicles to help determine whether or not a vehicle is an appropriate next hop. We base the heuristic on the intuition that taller vehicles have an advantage over shorter ones because the former are less susceptible to shadowing from other vehicles. We implement a model that evaluates the efficacy of the proposed heuristic and we perform the experiments to validate the model. Based on both the experimental measurements and the simulations performed using the model, it is shown that tall vehicles consistently and significantly increase both the effective communication range and the message reachability. The effective communication range increased by more than 50%: from 290 meters when short vehicles are communicating to 450 meters in the case of tall vehicles. The results suggest that, when available, tall vehicles are significantly more likely to better relays than short vehicles. The proposed heuristic is not dependent on any specific routing technique and can be used to improve the performance of different classes of routing protocols.
