DES MOINES — Gov. Tom Vilsack on Tuesday signed a law raising the speed limit on the state’s rural interstate highways to 70 mph from 65 mph, also doubling fines for motorists who exceed the new speed limit.

The governor, who has opposed higher speed limits in the past, said he would direct the Iowa State Patrol to strictly enforce the 70 mph limit, which takes effect July 1.

“With strict enforcement, we shouldn’t see increased accidents,” Vilsack said.

The higher fines will raise more than $7 million, which will help pay for the state’s court system. The governor vetoed a portion of the measure which would have set aside up to $800,000 a year for new cars for the Iowa State Patrol.

“We’re not going to link fines with funding for the Department of Public Safety,” the governor said. He asked lawmakers to come up with that money from the general state budget.

Vilsack said the bill was sent to his desk late Monday and he studied it into the early morning hours.

He signed the measure into law within minutes of announcing his decision.

“I’m pleased,” said House Speaker Chris Rants, R-Sioux City, a longtime backer of boosting the speed limit. “I think it’s a long overdue change.”

Critics of the higher speed limit said they were disappointed, but said the additional money contained in the measure left Vilsack with little choice.

“It had money,” said Rep. Pam Jochum, D-Dubuque. “Those who supported increasing the speed limit knew that packaging all of that together would make it very difficult for him to veto. I think it’s still a safety issue.”

The higher speed limit got strong support in sparsely populated western Iowa, but was less favored in eastern Iowa, where traffic is heavier.

Vilsack conceded that more troopers are need to enforce traffic laws, but said his directive on enforcement is clear.

“If there’s someone who says, ‘Great, the speed limit has gone up to 70, so now I can go 75’ — that would be a mistake,” the governor said.

Officials have said motorists largely ignore the state’s current 65 mph speed limit. Vilsack said he was told the average speed is 69.8 mph.

That won’t be the case with the new speed limit, he said.

Having laws that aren’t enforced only undermines respect for the law.

“There are troopers on the road today checking traffic, I want them to make sure that they understand that as long as I’m governor I want them to enforce the law as it’s posted,” Vilsack said.

The bill also allows state highway officials to exclude sections of interstate where a higher speed limit could be dangerous.

Those areas tend to be in cities, but the governor said he will direct state transportation officials to study anew which sections should be excluded.

Rants said he disagreed with Vilsack on using money from the higher fines to pay for more cars for state troopers, but said lawmakers would adjust.

“We’ll find the money for the cars,” Rants said.