"Despite the substantial social and technological changes that have occurred since the original speed synthesis was published [1982], vehicle speed remains an important public policy, engineering, and traffic safety issue. Speed is cited as the related factor in 30 percent of fatal crashes and 12 percent of all crashes ... Excessive vehicle speed reduces a driver's ability to negotiate curves or maneuver around obstacles in the roadway, extends the distance necessary for a vehicle to stop, and increases the distance a vehicle travels while the driver reacts to a hazard."