Do Roadway Guidance Tools Encourage Speeding?

The January-February TR News has an interesting piece about research which suggests some of the most common devices used to lower crash rates may actually accomplish the opposite. Alison Smiley, a Canadian human factors specialist, compiled several studies on improving roadway visibility and guidance and found that these measures often lead to increased speeds and crashes.

Smiley attributed the findings to the phenomenon of “driver adaptation” -- if driving tasks are made easier, the driver will change their behavior. While post-mounted delineators and raised pavement markers improve the level of information available to drivers at night, that information also gives them the confidence to drive faster and leads to more crashes, she said.

Guidance improvements that aren’t visible do not embolden drivers to speed and were therefore suggested as more effective. Rumble strips, which give an audible warning and rattle the vehicle, were mentioned as an effective means to help distracted or fatigued drivers. Statistics show rumble strips placed on the road shoulder reduce run-off-road crashes by 21 percent, and those along the centerline reduce frontal-impact crashes by 25 percent.

According to Smiley, the Dutch believe setting up less guidance on busy neighborhood streets is best because it makes drivers uncertain about the proper right-of-way delineations, causing them to slow down. A similar school of thought involves the roundabout, which entails a heavier workload for drivers. The intimidation factor of navigating roundabouts encourages drivers to slow down and observe all of their surroundings, according to Smiley. When roundabouts replace signalized intersections, she said crashes have been shown to drop by one-third.