Vehicular Ad hoc NETworks (VANETs) are classified as an application of Mobile Ad hoc NETwork (MANET). VANET applications make travel both safer and fun. Vehicles can be turned into a network by incorporating the wireless communication and data sharing capabilities. So VANET provides promising approach for Intelligent Transport System (ITS). The design and survey of routing protocols in VANETs is important and necessary issue for the support of smart ITS. This paper discusses the classification of routing protocols based on the transmission strategies i.e. unicast, multicast and broadcast protocols.