Since the Utah Department of Transportation increased the posted speed limit from 75 mph to 80 mph on two stretches of I-15 in southern Utah, drivers have actually slowed down.

With an 80 mph posted speed limit, people are driving 81 mph to 85 mph, said Carlos Braceras, UDOT deputy director. With a 75 mph posted speed limit, people were driving 83 mph to 85 mph.

The speeds don't reflect an average driver, however, but the behavior of 85 percent of the drivers north of Scipio in Millard County to south of Fillmore.

Utah is the only state besides Texas with 80 mph postings. In Texas, the 80 mph sections are rural, too.

The Utah Legislature passed a law in 2008 that permits speeds over 75 mph in low-population areas if UDOT studies traffic engineering and safety and reports its analyses to the Transportation Interim Committee.

On Wednesday, Braceras was doing that, reporting to the committee that drivers were, on the whole, speeding less and that accidents have not increased. UDOT engineers did not expect an increase in accidents, however, based on studies of the two stretches, which both lack extreme curves and mountainous terrain.

Braceras told the committee it was important to continue studying the area over time to get trend data.

Although accidents and illegal speeding haven't increased, "speed differentials" have increased. Speed differentials are the difference between the fastest and slowest vehicles. Almost all drivers have come up on a slow-moving vehicle or have been tailgated by a speeder. That can be unsafe, Braceras said.

"We'd like to keep speeds consistent as much as possible because that consistency does create, we believe, a safer condition," he said.

Most of the legislators said they enjoyed being able to drive faster.

"When you ran this bill a couple of years ago, I was hesitant to vote for it," said Rep. Lynn Hemingway, D-Salt Lake City. "But I drive to St. George all the time. Thank you very much."

Committee members laughed at Hemingway's comments and at Mike Morley's.

Morley, R-Spanish Fork, asked Braceras whether drivers were speeding on I-15 between the two 80 mph stretches. Braceras said that hadn't been studied.

"I got a warning between there," Morley said. "So maybe speeds have increased a little bit. I don't know."

Janice Fisher, D-West Valley City, was more somber, saying speed kills.

"Is it true that we're more likely to get killed in a crash the faster we're going?" she asked Braceras.

"It's simple physics," Braceras said. "Yes."