Effects of Traffic Density on Communication Requirements for Cooperative Intersection Collision Avoidance Systems (CICAS)

Intersection collisions are difficult to mitigate or eliminate by use of ITS technologies for a variety of reasons. These include the complexity of the driving environment and of the driver decision making process at intersections, but also the difficulty of accurately detecting the movements of all potentially conflicting vehicles.  Prior research by Calspan-Veridian Engineering (now part of General Dynamics) (1) showed the near impossibility of detecting the relevant information using vehicle-mounted sensor systems.  Current research under the IDS program is revealing the challenges associated with detection using infrastructure-based sensor systems. As our understanding of intersection crashes and the performance needs of intersection collision avoidance systems have been improving, so has the interest in cooperative system implementations. In these Cooperative Intersection Collision Avoidance Systems (CICAS), information detected by both vehicle- based and infrastructure-based sensors can be combined to produce better real-time knowledge of the dynamic “state map” of an intersection. Wireless communications between the vehicles and the infrastructure and among the vehicles makes it possible for each entity (every vehicle, as well as the intersection’s traffic controller) to have complete intersection state map information, so that it can then use its own intelligence and threat assessment logic to determine whether to alert a driver to an impending hazardous condition. In this report, Section 2 identifies the contents of the intersection state map, Section 3 sketches out the general architecture for information sharing among vehicles and the intersection infrastructure, and Section 4 defines the “worst case” traffic scenarios in which this information needs to be exchanged. This information is important in specifying the capacity of the wireless communication system that supports the information exchange. Although most operations will take place under much less demanding conditions, it is still important to ensure that the communication system can support operations under “worst case” conditions, so that intersection safety is not compromised then.