Abstract: The performance of routing protocols was studied in vehicular Ad hoc networks (VANETs) based on the Manhattan mobility model. Integrated with the AODV routing protocol, an analytical model was proposed, which was able to quantificationally measure the route breaking rate and routing overhead of VANETs. It is indicated by the analytical model that classic routing protocols in mobile Ad hoc networks can cause serious declination in the performance of VANETs; therefore, a direction based AODV routing protocol (DBAP) was proposed. The vehicle's moving direction was used in DBAP as its auxiliary parameter in routing discovery process, which remarkably improved the routing stability. Simulations show the validity of this model and prove DBAP's lower route breaking rate and routing overhead as well as its significantly improved performance in VENETs in comparison with AODV in urban vehicular environment.