Over the last four decades, the numbers of injuries and fatalities per traveled mile have decreased significantly. However, over the last two decades these numbers have leveled off, indicating that new approaches will be needed in order to achieve additional reductions. Thus automotive suppliers have begun developing active safety products, whose goal is to prevent or mitigate crashes, as opposed to passive safety products, e.g. seat belts and air bags that provide protection only in a crash. An active safety system senses aspects of the vehicle, driver, traffic and/or roadway to identify and assess impending crash events, then attempts to avoid the crash either by warning the driver or by taking appropriate control actions such as braking. Active safety products in development include adaptive cruise control, collision warning, lane-departure warning, and lane-keeping systems.