Road traffic accidents can be reduced by providing early warning to drivers through wireless ad hoc networks. When a vehicle\r\ndetects an event that may lead to an imminent accident, the vehicle disseminates emergency messages to alert other vehicles that\r\nmay be endangered by the accident. In many existing broadcast-based dissemination schemes, emergency messages may be sent to\r\na large number of vehicles in the area and can be propagated to only one direction. This paper presents a more efficient contextaware\r\nmulticast protocol that disseminates messages only to endangered vehicles that may be affected by the emergency event. The\r\nendangered vehicles can be identified by calculating the interaction among vehicles based on their motion properties. To ensure\r\nfast delivery, the dissemination follows a routing path obtained by computing a minimum delay tree. The multicast protocol uses\r\na generalized approach that can support any arbitrary road topology. The performance of the multicast protocol is compared\r\nwith existing broadcast protocols by simulating chain collision accidents on a typical highway. Simulation results show that the\r\nmulticast protocol outperforms the other protocols in terms of reliability, efficiency, and latency.
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