A semi truck passes by a newly posted 80 mph speed limit sign on Interstate 90 near Brandon, S.D., on Wednesday. (Associated Press - Ap/The Minnesota Star Tribune)

The drive to Mount Rushmore can go a little faster now.

South Dakota became the latest state to raise the speed limit Wednesday, allowing interstate drivers to travel up to 80 miles per hour.

States across the country have been raising their speed limits as lawmakers argue that roads and cars are safer. Idaho, Wyoming and Utah have already raised their limits to 80 mph; on one toll road in Texas, it's 85. Minnesota, where interstate limits are 70 mph, has started raising speed limits to 60 mph on 340 miles of highways.

But auto safety experts warn that with increased speed, comes increased crashes and fatalities. Already nearly one-third of motor vehicle fatalities are speed related, a figure that has remained constant for the past decade or so.

South Dakota House Majority Leader Brian Gosch said South Dakota already has good roads, and "with improved car and safety technology … it seemed like a reasonable step."

Most stretches of Interstate 90, which takes travelers from Sioux Falls to the Black Hills, and I-29, which goes to Fargo, already allow drivers to go 75 miles per hour. "It seemed like if I was doing 75, I was getting passed quite a bit," said Gosch, a Republican from Rapid City who championed the amendment. The higher limit, which garnered little legislative discussion, was folded into a transportation bill signed last month by Gov. Dennis Daugaard that raises the gas tax and vehicle registration fees to pay for road and bridge repairs.

Federal traffic safety regulators run crash tests at between 30 and 35 mph.

"When you get to speeds of 80 miles an hour, vehicles and safety features aren't built to protect people," said Anne McCartt, senior vice president of research at the Insurance Institute for Highway Safety, which runs its own crash test program.

The organization estimates that higher speed limits across the country led to 12,545 additional deaths since the end of 1995, when Congress repealed the national 55 mph speed limit and states approved their own speed limit increases.

"People believe we've got safer highways, that people are wearing their seat belts and we have much safer vehicles than we used to so its safe to travel at these very high speeds, and that's just not true," McCartt said.

In South Dakota, interstate crashes and fatalities were rising leading up to 1996, when South Dakota bumped its speed limit from 65 to 75 mph — and they kept going up, for a time.

But more recent statistics show that crashes and traffic fatalities have been on the decline, echoing national trends. Speed-related car crashes in South Dakota have fallen 30 percent since 2010; fatal crashes dropped by half.

Still, South Dakota has issued an increasing number of speeding tickets, up 38 percent in the last three years. Unlike North Dakota, where speeding tickets run as low as $10, South Dakota's range from $100 to $220.

Lee Axdahl, director of South Dakota's Office of Highway Safety, cautioned that the new limit is just that — it doesn't mean everyone should go 80 mph all the time.

"Look, if your vehicle isn't built for 80, you need to throttle it back," Axdahl said. "If you don't feel safe at 80 because of the weather or other road conditions … then you should throttle it back."

He added: "All that we ask is that you make those judgments carefully and continue to process them as you're driving so that whatever speed you're at is a safe speed."

South Dakota's Highway Patrol said the law wouldn't change the number of state troopers it had on the road — 177.

"A 5 mile an hour increase in our speed limit, from my perspective, is not concerning," said Minnehaha County Sheriff Mike Milstead, whose territory includes the intersection of I-90 and I-29. "What concerns me most about it will be drivers who think that that is a safe speed during heavy rains or during freezing rain and snow."

South Dakota Highway Patrol Superintendent Col. Craig Price said that when the speed limit last increased, "it's not like everybody changed over and started driving 75 the very next day. People became more comfortable with their driving habits and I suspect as time passes on, people will start to travel a little faster."

Gosch, a father of six, regularly takes his Ford Expedition to see relatives in Minnesota and throughout the Midwest. The decline in speed limits as he heads east is "painful," he said, lengthening his time on the road.

"I would just ask Minnesota to take a look at it," Gosch said.

Maya Rao • 612-673-4210