Tuesday March 31, 2009

Is Faster Safer?

Ohio's plan to raise the speed limit for trucks will lead to more fatalities on state highways, says a University of Dayton researcher.

The increased speed limit for trucks on Ohio highways awaiting a vote in the General Assembly will likely increase the number of truck-crash fatalities in the state, according to research by a University of Dayton professor.

"The research is clear. With trucks or cars — it doesn't matter — if you raise speed limits, you're going to see an increase in fatalities," said University of Dayton political science professor Grant Neeley.

Neeley and University of Missouri public affairs professor Lilliard Richardson published research that studied the effect of speed-limit regulations on truck-crash fatalities in the March 2009 issue of the American Journal of Public Health.

The study used state-level data from 1991 to 2005 with a model that controlled for several policy measures and considered variables such as traffic volume and weather conditions. Hawaii was the only state excluded from the study.

The Ohio state transportation budget approved by a House-Senate conference committee late Monday, March 30, will raise the speed limit for trucks on Interstate highways from 55 to 65 miles per hour, the current speed limit for smaller vehicles.

Ohio currently is one of 11 states that sets different speed limits for cars and trucks.

Advocates of the change say roads will actually be safer if all vehicles are going the same speed, as differential speed limits have the potential to create two streams of traffic on the same road.But Neeley's research found otherwise.

"Overall, higher speed limits for all vehicles appeared to be a major factor in the truck-crash fatality rate, and a speed limit difference between cars and trucks was not a significant issue," he said.

While some studies have found that a greater speed difference is associated with significantly more fatalities, other research has shown that differences in actual speeds are often smaller than differences in posted speeds.

"The bottom line is that higher speeds for either trucks or cars create more fatalities," Neeley said. "It doesn't really matter if one kind of vehicle is regulated at one speed limit."

The results of Neeley's national study suggest that states can reduce traffic fatalities from crashes involving large trucks by lowering speed limits for all drivers.

Neeley and Richardson developed a model that predicted changes in the fatality rate if states adopted uniform speed limits of 55 mph and uniform speed limits of 75 mph. The model suggested that if all states had changed their actual 2005 speed limits to a 75 mph limit, 362 more fatalities would have occurred. If all states had dropped their 2005 speed limits to 55 mph, 561 fewer fatalities would have occurred. The difference of 923 fatalities represents almost 18 percent of the actual 5,200 truck-crash fatalities nationwide in 2005.

On a local level, Ohio experienced 177 truck-crash fatalities in 2005. If a uniform speed limit of 55 mph were adopted, Neeley's model estimated the total number of fatalities would be reduced by 9. If a uniform speed limit of 75 mph were adopted, the number of fatalities would increase by 26.

For more information, contact Meagan Pant, assistant director of news and communications, at 937-229-3256 or mpant1@udayton.edu.