A measure that would reduce the speed gap between cars and trucks traveling Michigan highways is headed to the state’s House, backed by advocates who say it will make roads safer by improving traffic flow and more closely resembling “85th percentile” speeds.

The House Committee on Transportation voted 13-1 Tuesday, Sept. 20, to increase the 55 mph speed limit for vehicles with a gross weight of 10,000 pounds or more to travel at 60 mph on freeways in the state. It also would apply to all passenger vehicles and pickup trucks that pull trailers.

Other motorists would continue to drive at the current 70 mph limit.

In testimony on the bill earlier this month before the transportation panel, James C. Walker, an automotive consultant, spoke of the importance of setting speed limits based on the 85th percentile rule – the speed at or below which 85 percent of drivers operate their vehicles.

“Recent (Michigan) State Police data shows the 85th percentile speed for heavy trucks is 64 mph. A higher limit will merely be closer to reality,” Walker said.

Walker also told lawmakers the closer that speed limits are to 85th percentile speeds, the smoother and safer the traffic flow tends to be.

“Reducing differential speeds is one key to this smoother and safer traffic flow,” Walker added. “No safety benefit accrues to setting posted speed limits below the 85th percentile … and no safety benefit accrues from differential speed limits for trucks versus cars.”

State Police experts agree the wide speed disparity creates more hazards for all drivers than if the speeds were uniform.

“It’s not speed, but conflicts in speed that cause accidents,” State Police Lt. Thad Peterson, head of the traffic services section, told the Detroit Free Press. “When you have people driving different speeds, you have more lane changes, they speed up and slow down. A lot of decision-making occurs there.

“At similar speeds, it’s more possible to maintain a proper following distance between the car or truck in front of you. You make fewer lane changes.”

For the sake of safety, Rep. Bruce Caswell, the bill’s sponsor, agreed it’s imperative the existing speed gap between cars and trucks be minimized.

“What we’re seeing is that’s too large of a gap on divided highways. It’s creating some very unsafe situations,” said Caswell, R-Hillsdale.

“When trucks pull out to pass other trucks and can only go 55 we are seeing a huge backup in traffic. We’re seeing a lot of problems in that regard so what we are trying to do is narrow the top end and the bottom end. Get them closer together so traffic is moving more smoothly with a more uniform speed down the highway. It’s safer for everybody.”

Caswell said he would be open to reducing the speed gap even more, but it would be nearly impossible to pull off.

“Politically, I don’t think that’s doable,” he said. “I think 60 is the best we’re going to get. And that’s better than we got. So that’s what we’re going to go after.”

Todd Spencer, executive vice president for the Owner-Operator Independent Drivers Association, said that while he is encouraged to see that legislation to address safety problems resulting from a large speed gap move forward, lawmakers are missing a greater opportunity to do away with split speeds.

“One of the main reasons highway safety has improved even as states nationwide increase speed limits is because higher speed limits tend to eliminate or minimize speed variances that are often key contributors to accidents,” Spencer said. “It makes sense now for lawmakers to use this legislation as an opportunity to once and for all establish uniform speed limits.”

Walker said any concerns by lawmakers that higher speed limits for trucks would be more dangerous are not based on the scientific traffic safety engineering research from the past 60 years.

He asked lawmakers to keep in mind that the fatality rate on freeways is five times lower than on other roads.

In addition, Spencer said it is important that Michigan truck drivers communicate to their elected officials that uniform speeds are safer for all drivers.

Caswell echoed Spencer’s call to truckers.

“Any help truckers could give would certainly be appreciated,” Caswell said.

If approved by the state’s House, the bill – HB5104 – would still need to gain approval from senators. It would then head to Gov. Jennifer Granholm, who has yet to take a position on the bill.

– By Keith Goble, state legislative editor
keith_goble@landlinemag.com