RALEIGH — A bill opening the door to 75-mph speed limits on some highways in North Carolina was sent back to a House committee last week after lawmakers put off a vote over safety concerns.

The House debated the measure at length but decided to return it to the Transportation Committee. The Senate already passed the bill, which would allow the Department of Transportation to raise the speed limit from 70 to 75 on highways and interstates if studies proved the change was safe.

An amendment bumping up the threshold for more serious speeding violations to 85 mph from 80 mph to reflect the bill’s changes failed after some lawmakers argued it would allow people to drive faster without facing penalties. The amendment would have applied uniformly, not just to roads where the speed was raised.

Supporters of the bill say it improves efficiency and allows DOT to change speeds only after careful consideration. Rep. Tom Murry, R-Wake, said the safest speed is the one at which most drivers are already traveling. “Our freeways are wide open. They are safe roads,” he said. “I think we should let the engineers at DOT do their job, and I’d ask that you support this bill.”

Most lawmakers who debated the bill questioned its usefulness and said they fear it would lead to more deaths. “This bill came as a result of a politician who wanted to go faster on the highway,” said Edgar Starnes, R-Caldwell.

Rep. Nelson Dollar, R-Wake, said raising the speed limit will make the effective rate that people drive without fear of getting a violation that much higher.

Ann McCartt, a senior vice president at the Insurance Institute for Highway Safety, said concerns that the average speed would edge upward are backed by research.

Fifteen states, mostly clustered in the West, have maximum speed limits of 75 mph, according to the Insurance Institute for Highway Safety. Maine is the only East Coast state with a 75-mph limit, and it applies only to a remote interstate approaching the Canadian border. State DOT hasn’t publicly given an opinion on the bill.

Rep. Frank Iler, R-Brunswick and the House lawmaker shepherding the bill, said he thinks the bill could return to the floor after changes are made in committee, though he didn’t point to any specific amendments that would make the measure more palatable to some members.