3 Speed Management
3.1.5 Target Crash Population
The downhill speed advisory systems highlighted above target the population of crashes that involve trucks on downgrades and sags.
According to a FARS query,(2) 868 rural fatal crashes occurred in 1998 involving trucks [single unit trucks, truck/trailers, truck tractors (bobtails), tractor semitrailers and other medium/heavy trucks] on grades and sags. It was not possible to separate downgrades from upgrades.
Severe downgrades are a localized problem, and these systems hold the maximum amount of potential payoff for steep downgrades with high crash frequencies and/or frequent use of runaway truck ramps.