Traffic density estimation in vehicular ad hoc networks: A review

Nowadays, vehicular Ad hoc Networks (VANETs) are gaining enormous research interest. Even though the leading reason for developing VANETs is traffic safety, many applications such as traffic status monitoring, road traffic management, routing and distribution of data, have been considered. Road traffic density estimation provides important information for such applications. Various infrastructure-based mechanisms were proposed to estimate traffic density relying on vehicle detection devices that require pre-deployment. However, as utilizing wireless communication capabilities in vehicles is developing rapidly, more accurate and real-time infrastructure-free density estimation methods are emerging day-to-day. Some of the infrastructure-free methods depend mainly on statistical estimations, while others are based on VANET communications and traffic flow information. In addition, clustering and group members counting are the main characteristic of a third type of infrastructure-free methods. This review paper explored different techniques and algorithms used in both infrastructure-based and infrastructure-free density estimation methods. Furthermore, the main features, limitations and critical issues for each density estimation method are depicted.