Effect on vehicle safety of nonexistent or silenced basic safety messages

In future vehicular ad-hoc networks (VANETs), Basic Safety Messages (BSMs) would be transmitted by all vehicles every 100ms in order to help prevent inter-vehicle crashes. At first not all vehicles would contain the hardware and software necessary to transmit BSMs; there would be an interval when only a percentage of vehicles would transmit. Further, even after all vehicles install the equipment, some privacy researchers recommend silent periods, spans of time during which vehicles deliberately cease transmissions. This is because BSMs may expose vehicle locations to wireless surveillance, and silent periods could thwart eavesdroppers. Whether due to lack of equipment or due to privacy protocols, silent periods would defeat safety provided by BSMs. This paper quantifies this tradeoff, presenting the Safety-Silence Tradeoff Equation, and showing an inverse exponential relationship between the proportion of vehicles transmitting BSMs and the proportion of potential collisions between vehicles unprotected by BSMs.