The Sound of Safety.

In Arizona, centerline crossover crashes result in a significant percentage of serious injuries and fatalities on the state's rural, high-speed, two-lane roads. To enhance safety, in 2002 the Arizona Department of Transportation (ADOT) began pilot installations of centerline rumble strips (CLRSs) on 14 stretches of low-volume, high-speed, two-lane, rural State highways. The roadways included principal arterials, minor arterials, and minor collectors. The rumble strip pattern used was based on the standard pattern in use at that time for milled edge-line rumble strips. Crash data from 3 years before (2000-2002) and 3 years after (2003-2005) the installations was evaluated to determine the effectiveness of CLRSs in mitigating centerline crossover crashes. Results showed that the number of fatal and serious injury crashes decreased by 61% after CLRSs were installed. Centerline crossover crashes accounted for 36% of the total fatal and serious injury crashes occurring in 2000-2002 and 22% in 2003-2005. CLRSs helped reduce the number of serious injury and fatal head-on and opposite direction sideswipe crashes from 18 in the "before" period to 7 in the "after" period. The ADOT study found that serious injury and fatal centerline crossover crashes involving fatigued, inattentive, and impaired drivers may be independent of roadway alignment. CLRSs have the potential to reduce these crashes. ADOT found no degradation of pavement that could be attributable to the milled CLRSs and no negative impact of CLRSs on snow and ice removal. ADOT's pattern for milled rumble strips generates about 70 decibels of sound at 152 meters (500 feet), which limits installations near roadside residences. Based on these findings and those of other studies, ADOT believes that milled CLRSs have the potential to prevent and reduce opposite direction crashes on undivided highways. ADOT currently is finalizing a CLRS policy, developing installation guidelines, creating CLRS groove pattern standard details, and defining the elements of an implementation program.