A vehicular ad hoc network (VANET) is a relatively new term for an old technology – a network that does not rely on pre-existing infrastructure. When integrated into the intelligent transportation systems (ITS), it can provide direct vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications, thereby can greatly improve the safety and efficiency of road traffic. The emerging and promising VANET technology is distinguished from mobile ad hoc networks (MANET) and wireless sensor networks (WSN) by large-scale deployed autonomous nodes with abundant exterior assisted information, high mobility with an organized but constrained pattern, frequently changed network topology leading to frequent network fragmentation, and varying drivers behavior factors. Without the presence of centralized entities such as base stations, mobile hosts also need to operate as routers in order to maintain network connectivity. Therefore, various ad hoc routing protocols have been proposed, but there have previously been few studies on how the specific mobility patterns of vehicles may influence the protocols performance and applicability. In this paper, we compare and evaluate the performance of following routing protocols: AODV, DSDV, and DSR. A variety of highway scenarios, characterized by the mobility, load, and size of the network were simulated. Our results indicate that those routing protocols dedicated for MANET is unsuitable for VANET scenarios in terms of packet delivery ratio, routing load, and end-to-end delay