The increasing demand for wireless devices and wireless communication tends to research on self-organizing, self-healing networks without the interference of any pre-established or centralized infrastructure/authority . The networks with the absence of any pre-established or centralized authority are known as Ad hoc networks . Ad hoc Networks are the kind of wireless networks that uses multi-hop radio relay.There are many comparative studies and surveys that compare various ad hoc routing in VANET environment. The simulations performed in these comparative studies are very basic do not incorporate with a large number of nodes in real Vehicular Ad hoc Network environment. The main aim of our dissertation work is to firstly investigate the reactive and proactive routeing protocols than examine the performance of selected reactive routing protocols i.e. Destination Sequence Distance Vector Routing (DSDV), Ad hoc On-Demand Distance Vector (AODV), Optimized Link State Routing (OLSR) and Dynamic Source Routing (DSR)by taking three performance metrics like network load, throughput and end-to-end delay with varying number of mobile nodes or vehicle node densityOPNET: Optimized Network Engineering Tool (OPNET) is a commercial network simulator environment used for simulations of both wired and wireless networks . Several different OPNET versions have been released over the last few years; the latest version of OPNET is the OPNET 16.0. At present OPNET is licensed under Riverbed technologies. It allows the user to design and study the network communication devices, protocols, individual applications and also simulate the performance of routing protocol. It supports many wireless technologies and standards such as, IEEE 802.11, IEEE 802.15.1, IEEE 802.16, IEEE 802.20 and satellite networks. OPNET IT Guru Academic Edition is available for free to the academic research and teaching community.