Photo courtesy of IIHS.

Photo courtesy of IIHS.

Since Utah raised its speed limit from 75 mph to 80 mph on stretches of rural interstate highways, passenger vehicles are over 120% more likely to travel more than 80 mph in those zones, according to a recent study from the Insurance Institute for Highway Safety.

The study “adds to the abundant evidence that raising speed limits results in higher travel speeds and more vehicles exceeding the new limit,” IIHS said in a report on the study. “It also undercuts the claim that raising limits reduces speed differences among vehicles on the same road.”

The study focused on the effects of 2010 and 2013 speed limit increases. Wen Hu, an IIHS senior research transportation engineer, collected speed data for passenger vehicles and large trucks on several sections of Interstate 15 before and after the speed limit changed from 75 mph to 80 mph.

Hu found that average passenger vehicle speeds within the 80 mph zones were about 3 mph higher after the speed limit increase. This jump from 75 mph to 78 mph would raise the rate of fatal crashes by 17%, he estimated.

“Six states now have maximum speed limits of 80 mph, and Texas allows speeds as high as 85 mph, said Chuck Farmer, IIHS vice president for research and statistical services. “These extreme speeds shave off a few minutes of travel time at the expense of people’s lives.”