It is a challenging task to develop an efficient routing solution for a reliable data delivery in urban vehicular environments. Indeed, it is difficult to find a shortest end-To-end connected path especially in urban city given the mobility pattern of the vehicles and the various obstructions to a clear transmission such as buildings. To overcome these difficulties, we investigate how unmanned aerial vehicles (UAVs) can assist vehicles on the ground in relaying in urban areas. In this paper, we propose UVAR (UAV-Assisted VANET Routing Protocol), a new routing technique for Vehicular Ad hoc Networks (VANets). This protocol is based on the use of the traffic density and the knowledge of vehicular connectivity in the streets. With this approach UAVs collect information about the traffic density on the ground and the state of vehicles connectivity, and exchange them with vehicles through Hello messages. These information allow UAV to place themselves so as to allow relaying data when connectivity between sole vehicles on the ground is not possible. Through vehicle-To-UAV (V2U) communication, the overall connectivity between vehicles is improved and therefore the routing process is efficiently improved. The performance of the proposed protocol is evaluated and the results to different scenarios are discussed.