Vehicle ad hoc networks (VANETs) are the most interesting area of research in smart transport systems as they provide convenience and safety information to drivers. However, VANET's unique features make security, privacy and trust management promising issues in the design of VANET's. It is a challenging problem to provide an effective anonymous authentication system in ad hoc vehicle networks (VANETs) with low computational cost. Blockchain technology in VANET provides a decentralized, secure, and reliable database, which is maintained by the network node. Earlier, vehicle authentication is performed whenever the vehicle enters the RSU range. In this paper, authentication will be done if a vehicle fails to travel certain distance. This decreased number of authentications and time required for it leads to increase in efficiency of the system.