This Chapter studied the required amount of radio spectral resource enough to support timely and reliable vehicular communication via vehicular ad-hoc networks (VANETs). The study focussed on both DSRC/WAVE and the European standard ITS-G5 that are based on recently approved IEEE 802.11p specification, which uses a simplified version of CSMA/CA as MAC protocol, and an STDMA MAC recently proposed by European Telecommunications Standards Institute (ETSI). The Chapter further carried out a feasibility analysis of radio spectrum requirement for timely and reliable vehicle-to-vehicle (V2V) communication. In the feasibility analysis, synchronized STDMA MAC is compared with the CSMA/CA MAC protocol, which 802.11p is based on. Message Reception Failure (MRF) probability is used as a performance metric to investigate and ascertain the minimum spectrum requirement for efficient, timely, and reliable V2V communication. Simulation results show that even at the same allocation of 10 MHz channel bandwidth, STDMA MAC outperforms the CSMA/CA based MACs due to the fact that STDMA based MACs provide a structured shared medium access and prevent negative impact of unhealthy contention for shared channel access. The results further show that up to 40 MHz channel bandwidth over 5.9GHz band would be required to guarantee optimal reliability of safety packets exchange in vehicular networks as opposed to 10 MHz allocated in US.