<p>Vehicular Ad-hoc NETworks (VANETs) enable vehicles to exchange safety-based information via broadcasts to get updates on the vehicle’s speed, direction and road conditions. Highly dynamic topology, high mobility, and varying traffic density lead to network performance degradation in VANETs. Media Access Control (MAC) protocols are responsible for reliable and delay-tolerant delivery of safety messages. As vehicular density increases, MAC adapts to the changing data traffic patterns by multi-channel access mechanism, thereby guaranteeing delay-tolerant transmission and increased throughput for various VANET applications. Several MAC protocols have been proposed to reduce the delay and packet loss, allowing the vehicles to send safety messages without collision. Though, providing safety services without compromising the delay and throughput is still a challenge. This paper proposes an Adaptive Contention Window (ACW) for high vehicular density to mitigate the above issues. The approach is based on the optimization of CW to provide reliable and efficient data dissemination. Packet collision increases as vehicular density increases. Therefore, the collision probability is computed based on the number of contending vehicles, compared with a threshold value to adapt the CW for delay-tolerant channel access. A numerical analysis-based result shows the collision probability, channel throughput, delay and channel busy probability of channel occupancy using the Poisson distribution. The analytical study is then compared with the traditional 802.11p MAC protocol of VANET. The result of the analysis aid in selecting a CW value for different vehicular densities and analyzing the collision probability. The performance evaluation demonstrates that the optimal CW value reduces the packet collision rate by 50% and access delay by 56%, and maximizes the network throughput by 45%.</p>