By the advancement in technology on one side, and governmental as well as social demands for lowest rate of driving accidents and reliable communication among vehicles on the other side, particularly in highways, vehicular ad-hoc networks (VANETs) are of special interest as a reliable approach to this aim. VANET is typically defined as the communication network for wireless communicating between vehicles in a region. One of the most important challenges in such networks is reliable routing of data packages among the vehicle users. Several VANET routing topologies are published in the literature; however, there is still a lack of reliable scheme. This is due to the nature of users behaviour in such networks, in which the network may change its topology frequently and break the communication links. Up to now, there are few research efforts for proposing a reliable protocol for VANETs in highways. This paper introduces a novel approach for routing in VANETs, particularly for highways, based on the opposition based ant colony optimization (OACO) algorithm. In this approach, we model the network topology to a graph model and then solve it optimally based on our criteria for reliable routing in VANETs based on the OACO. Some simulations have been conducted to evaluate performance of the OACO. The results demonstrate that the proposed scheme significantly outperforms similar protocols in the literature.