An effort to reduce the speed gap between cars and trucks is
headed to Michigan Gov. Jennifer Granholm.
Backed by advocates who say it will make roads safer by
improving traffic flow and more closely resembling “85th percentile” speeds,
the Senate approved the bill 25-11 Tuesday, Jan. 31. House lawmakers gave their
final endorsement Wednesday, Feb. 1, clearing the way for the bill to move to
the governor’s desk.
Sponsored by Rep. Bruce Caswell, R-Hillsdale, the bill –
HB5104 – would increase the 55 mph speed limit for trucks to 60 mph on highways
where the maximum limit is 70 mph.
The higher limit would apply to vehicles with a gross weight
of 10,000 pounds or more and truck-tractors with trailers.
Other motorists would continue to drive at the current 70
In testimony on the bill last fall, 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 said. “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
Michigan is one of 11 states that post different speed
limits for cars and trucks on rural interstates.
For the sake of safety, Caswell 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,” Caswell told Land Line.
“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.”
Todd Spencer, executive vice president for OOIDA, said he is
encouraged to see legislation to address safety problems resulting from a large
speed gap move forward.
“While we think a uniform speed limit clearly makes the most
safety sense for speed limits, the measure now headed to the governor’s office
moves us a little closer to that,” Spencer said.
Walker said any concerns 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.
If Granholm signs the bill, it would take effect in nine
– By Keith Goble, state legislative editor