Researcher: Speed limiter proposal 'a problem of perception'

By Greg Grisolano, Land Line associate editor | Wednesday, January 18, 2017

The speed limiter problem is a problem of perception, according to Dr. Steven Johnson.

“I think it’s the perception of many motorists that slower trucks are a safer situation. The problem is they’re not looking at the number of interactions between vehicles. From my standpoint, it’s that number of interactions between vehicles that causes the risk, not the speed itself.”

Johnson, one of the foremost experts on the subject of speed differentials on rural interstates in America, is a retired professor of industrial engineering at the University of Arkansas and the former head of the Mack-Blackwell Transportation Center. He spoke with Land Line and Land Line Now last week. A portion of his interview will air during Wednesday’s broadcast of Land Line Now on Sirius XM’s Road Dog channel.

The Owner-Operator Independent Drivers Association opposes any mandate from federal regulators to limit the speed of commercial trucks, advocating instead for uniform speeds for all highway vehicles. In December 2016, the Association filed comments against a proposed mandate from the Federal Motor Carrier Safety Administration and the National Highway Traffic Safety Administration. It would impose speed limiters on all vehicles in excess of 26,000 pounds, and would set the speeds at either 60, 65 or 68 mph for those vehicles.

Johnson’s research supports OOIDA’s contention that cars and trucks going the same speed on the roadways not only improves safety, but also has a positive impact on fuel economy, emissions and even road wear.

When it comes to speeding trucks rear-ending passenger cars, Johnson says if you remove crashes that occurred during inclement weather, when a driver was going too fast for conditions, “very rarely does the data show rear-end collisions by big trucks on rural interstates.”

“I’ve been all the way from California to Connecticut. I’ve seen all the speed configurations,” he said. “Smooth, even flow at the same speed (is the best). It has the best fuel economy and the lowest emissions. And that makes sense.”

Johnson said he became interested in the issue of differential speeds more than a dozen years ago, when he noticed a sign on an Arkansas highway had one speed for cars and another for trucks posted.

“What you find is the actual posted speed limit has very little to do with the average traffic speed, he said. “(Officials) post what they will, but the people who are enforcing it are moving things along in general.”

Johnson said the enforcement personnel he’s spoken to generally want traffic moving safely in as fast and efficient manner as possible. But mandating speed limiters will take the variability of enforcement out of the equation, increasing the differential between cars and trucks.

While acknowledging that plenty of motorists can feel uncomfortable riding next to a large truck, he said that the maneuvering they engage in to get around a large truck takes a toll on the fuel efficiency of their vehicles, something that will only be exacerbated by mandating speed limiters. Those repeated accelerations and decelerations have a much greater impact on road wear.

If a speed limiter mandate is pushed through the regulatory process, Johnson says its consequences will be felt by motorists as well as truckers.

“It won’t be a safety issue. It’ll be a congestion issue,” he said. “There’s no way it’s going to stay down (at 60 mph or 65 mph) without the public having a serious problem.”

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