## 1 Introduction  
In the growing world economy, the number of vehicles is increasing day by day, thus making driving more risky and unsafe. The Global Status Report on Road Safety of the World Health Organization (WHO) summarized the statistics on road safety around the world. The report mentions 182 countries covering 99% population of the world. According to the report, the total number of road traffic deaths worldwide due to various traffic accidents on road is 1.24 million per year. The UN General Assembly declared the report as the basis for all the actions that would be taken for road safety during the entire decade 2011-2020 [1]. Further, the Delhi government's 12 th five year development plan for transport department is based on a survey conducted by a group comprising RITES Ltd, MVA Asia and LDT in October, 2010. This survey demonstrates that the _per capita_ trip rate has increased from 0.72 in 1981 to 0.87 in 2001 and it has been projected to increase to 1.2 by 2021. It further specified that Delhi Intra-City Motorized Person's trips are likely to rise from 11.7 million in 2007 to 17.4 million in 2021. An upsurge in Inter-City trip from 3.34 million per day in 2007 to 7.96 million per day has been predicted in 2021. This group has recommended the use of intelligent signaling system with Global Positioning System (GPS)- and Geographic Information System (GIS)-based applications to cope up with high degree of traffic population growth. The story of traffic population growth is similar for other capital cities of the world as well [2]. The aforementioned studies show that controlling both traffic congestion and vehicle accidents throughout the world is highly desirable. In order to achieve these goals, expensive sensors, radars, cameras and other state-of-the-art technologies have been currently incorporated into vehicles to improve safety and comfort during traveling [3]. Recently, Vehicle to Vehicle (V2V) and Vehicle to  
Figure 1: Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication. Infrastructure (V2I) applications have attracted more attention from industries and governments around the world because of their matchless potential to address safety and traffic congestion challenges at lower operational cost [4, 5, 6]. Both these applications (V2V and V2I) can also be used for commercial and vehicular infotainment [7, 8]. In Figure 1, an example of V2V and V2I communication in Vehicular _ad hoc_ Networks (VANETs) has been illustrated for the advancement of traffic control system and ease of travel in urban traffic environment. VANETs have become a promising area of the research due to their potential to provide solutions for most of the traffic problems. VANETs are a contemporary concept, evolving as a new research area that incorporates three earlier communication research areas, namely _ad hoc_ networks, wireless LAN, and cellular telephony [9]. VANETs are distinct from other kinds of _ad hoc_ networks due to their hybrid network architectures, high speed vehicle movement, battery usage, self-organizing nature, distributed communication networks and wide range of new comfort applications [10]. VANETs employ a variety of advanced wireless technologies such as Dedicated Short Range Communications (DSRC) [11], which is an enhanced version of the Wi-Fi technology suitable for the VANET environment [12]. DSRC was developed to support data transfer in a rapidly changing communication environment, where time critical response and high data rates are desired. IEEE 802.11p is a wireless communication protocol especially designed for VANETs [13, 14]. To incorporate Delay Tolerant Network capabilities in VANETs, a new network architecture has evolved. It is known as Vehicular Delay Tolerant Network (VDTN). The major characteristics of VDTNs, which are different from VANETs, are listed below. They are based on a store-and-carry-forward technique. They facilitate communication without end-to-end connectivity.