Between 1999 and 2000, the National Transportation Safety Board investigated nine rear-end collisions in which 20 people died and 181 were injured. Common to all nine accidents was the rear following vehicle driver's degraded perception of traffic conditions ahead. As the Safety Board reported in 1995 and further discussed at its 1999 public hearing, existing technology in the form of Intelligent Transportation Systems can prevent rear-end collisions. In the nine accidents investigated by the Safety Board, one (and sometimes more) of the available technologies would have helped alert the drivers to the vehicles ahead, so that they could slow their vehicles, and would have prevented or mitigated the circumstances of the collisions.