In recent years, the Intelligent Transportation System (ITS) is gaining popularity for better road operations and convenience. One of the major application of ITS is integrating communication, control, computational, and sensing technologies deployed to improve road safety and efficiency, enhance mobility and reduce congestion. Vehicular communication technologies enable a decentralized network composed of moving vehicles which are equipped with wireless processing devices and Road Side Units (RSUs). Such networks allow vehicles for real-time exchange of traffic information with or without any support from fixed infrastructure. In vehicular ad hoc networks (VANETs), one major task is the distribution of safety alert messages generated by several interrelated applications. Safety applications are commonly linked to the hazardous circumstances that are accidents, traffic jams and pile ups. Thus, these applications require smaller data dissemination delay, vast coverage and unfailing delivery to all intended vehicles inside the vicinity. By considering the high speed of vehicles, VANETs present several unique challenges likely unbounded network size and topology, continual density variations, broadcast oriented communication, partitioned networks and intermittent connections among vehicles. This thesis emphasizes on the design and development of a data dissemination protocol to address the aforementioned challenges satisfying the provision of both highway and urban scenarios under varying traffic conditions. At first, this thesis provided a comprehensive comparative study of numerous multihop data dissemination protocols for VANETs. To achieve this objective, a large set of top quality references are considered which has been published during the preceding decade. Herein, a new scenario-driven taxonomy of data dissemination protocols is presented which assists the readers to review the interest of research community, advancement and innovation in the relevant technologies. After that an efficient and reliable data dissemination protocol is developed to improve the existing data ABSTRACT IX dissemination problems in VANETs working evenly in highway and urban scenarios under varying traffic densities. In this context, a store-carry-forward mechanism is employed to deal with disconnected sparse networks and a timer based broadcast suppression mechanism to mitigate the broadcast storm in dense networks. In addition, the proposed data dissemination solution is modified further to deal with scalability issues of vehicular networks. Thus, a Next Forwarding Vehicle (NFV) selection algorithm is used to select best vehicles as next forwarders of data packet inside vicinity. Afterward, this research addressed the challenging issue of data dissemination across network partitions. To overcome this issue, vehicles outside the Concerned Area (CA) are used for successful data delivery to all intended vehicles across the network partitions in urban scenarios. Finally, a mathematical model is developed for optimum NFV selection during data dissemination process. In this regard, Analytical Network Process (ANP) method is used to calculate the forwarding priorities of vehicles and selects the optimal NFV(s). To this end, criteria based on direction, position, and distance information of vehicles (with respect to the source vehicle) is set to compute the corresponding priorities of vehicles. The performance comparison was carried by simulation, using VEINS framework integrating the network simulator OMNET++ and mobility simulator SUMO. The simulation results revealed that the proposed work has improved the performance of data dissemination in VANETs against existing well-known data dissemination protocols. It performed better in terms of coverage by achieving approx. 100% delivery ratio in highway scenario. Even in partitioned urban scenario, it outperformed other evaluated protocols by 30 % more coverage. In addition, among the group of protocols that provide highest coverage, it showed reduced overhead by approximately 55%. In conclusion, the proposed protocol has significantly improved the data dissemination performance in terms of data packet delivery with acceptable minimum delay, reduced packet collisions and low overhead.