Vehicular networks have attracted a lot of attention in recent years.Many projects have been initiated by govment,industry,and academia to improve driving safety,provide travel assistance,improve traffic flow,and decrease fuel consumption.These projects exploit vehicular communications and networking technologies,generally referred to as vehicular ad-hoc networks (VANETs) or more generally,vehicular networks.VANET includes vehicle -to-infrastructure and vehicle-to-vehicle communications and can be based on short-range and medium-range communication as well as cellular systems.The development and deployment of vehicular networks is also considered one of the critical foundations of the intelligent transportation system industry.