Vehicle ad hoc networks(VANETs) which depend on special application scenarios are different from mobile ad hoc networks(MANETs).The existing routing protocols of MANETs cannot be applied to VANETs effectively.Many new routing protocols are presented for VANETs.Firstly

we describe the characteristic features of VANETs

then introduce the conceptions of unicast routing

broadcast routing and geocast routing.Moreover

we classify and characterize the existing representative routing protocols for VANETs

and also discuss their advantages and disadvantages.We give a qualitative comparison of these routing protocols with respect to application scenarios

classification methodology

characteristic features and assumptions involved.Finally

the important features that ideal routing protocols possess are summarized

and open research issues and possible directions of future research related to VANETs routing are proposed.