I. Introduction
Although traffic deaths have declined in recent history due to passive safety technologies such as seat belts and airbags, vehicle-related deaths and injuries continue to be a major health isse. Vehicle safety can be improved via active safety technologies using vehicle safety communications (VSC). VSC includes ad hoc vehicle-to-vehicle communications without support from an infrastructure. That is, vehicles communicate when they are within the same radio range, or when multiple-hop relay via other vehicles is possible. A number of automotive manufacturers have incorporated technologies such as Global Positioning System (GPS) and IEEE 802.11 wireless radios in their future vehicle designs which can be leveraged to support VSC applications.