Goldilocks and the Little Dude in the Back of Your Brain

While the following article isn't exactly related to linguistics, I have previously posted about the semantics of slower traffic and the article does an excellent job of explaining why driving too slow can be dangerous.

Here is the article as it appeared in this month's Hour Detroit magazine:



If you think driving slowly is the safe way to travel, think again. Dawdling can be a hazard. And stepping on the gas might be the prudent thing to do, or so say studies supporting efforts to raise speed limits.

The key is to find the Goldilocks speed — not too fast, not to slow, but just right, a pace to keep you in the flow of traffic.

“At 65 mph, on the vast majority of our freeways, you are one of the slowest vehicles on the road,” says Lt. Gary Megge, a traffic crash reconstruction expert for the Michigan State Police. “Everybody is going to pass you if you go 60 or 65. Those slower vehicles are outside the pace, the speed of the normal drive. That slowest driver causes everyone on the road to react to him. You either have to slow down, hit the brakes, or change lanes to pass him. The slow driver forces everyone else on the road to do something different.”




Chalk up the lieutenant as Michigan’s expert in reasonable speed limits — on freeways, highways, and local roads alike. He’s done hundreds of speed studies, and so far, has had a hand in raising some 200 speed limits across the state.

In deciding limits, traffic engineers calculate the “85th percentile speed,” the number signals that 85 percent of the drivers along a stretch of pavement are traveling at that speed or slower.

Motorists themselves set the 85th percentile speed — often by blissfully ignoring those unnecessarily low speed limits. For example, the speed limit on I-69 near Flint used to be a pokey 55 mph, but drivers still zoomed along at 74 mph (the 85th percentile speed). Authorities raised the speed limit to 70 and the percentile speed dropped by 1 mph to 73, or about the same as before.

Of the I-69 change, Megge says, “Fewer faster drivers, fewer slower drivers; it’s one example of how a correction made a road much more user-friendly. It increased the capacity; it reduced the spread [between high and low speeds]. It was a beautiful thing.”

Make no mistake; the lieutenant distinguishes between appropriate speed and excessive speed, such as going 100 mph on a freeway or 50 mph in a subdivision. “When we talk about speed kills, it’s just not true,” he says. “Excessive speed kills, absolutely.

“But the vast majority of our roads are under-posted, meaning the speed limit is too slow and nearly everyone violates it.”

Insurance companies aren’t crazy about higher speed limits. “The problem is that drivers tend to travel at a speed at which they don’t think they’ll get a ticket,” says Russ Rader, spokesman for the Insurance Institute for Highway Safety in Arlington, Va. “In most places, that’s five or 10 miles over the posted speed limit. The 85th percentile becomes a moving target. When you raise the speed limit, you shift the people who were going 10 miles over the speed limit before into a higher bracket. The 85th percentile keeps moving.”

Speeding contributes significantly to fatal accidents, says the institute, a nonprofit research organization sponsored by insurance companies. Clearly, insurers and 85th percentilers interpret data differently.

Megge says accident-speed statistics can be misleading. For example, a car traveling 20 mph on an icy freeway slides and crashes. Police chalk it up as speed related, traveling too fast for conditions. But the accident has nothing to do with exceeding the posted speed limit.

“The big three causes of crashes are fatigue, alcohol, and distractions, whether that’s a cell phone, a cheeseburger, a cup of coffee, a baby in the back seat, the radio, putting your makeup on, working on your laptop, tying your tie, brushing your teeth — I’ve seen people do all of these things,” Megge says. “That’s why people crash.”

Robert Hoepfner, county highway engineer for the Road Commission of Macomb County, says speed limits are an emotional issue for many people. “[They think] if you travel faster, it has to be more dangerous. That’s not true. We’re very concerned about people who travel too fast and travel too slow. They cause accidents. But people that drive at that uniform rate of speed drive the safest.

“No one can deny that at higher rate of speed, if something happens, a more severe accident could occur. But when we’re talking speed versus safety on any particular roadway, what’s more important is that the traffic is moving at a uniform rate without a lot of radical changes occurring at any particular time.”

Macomb County, using the 85th-percentile rule, raised the speed limit on a stretch of Mound Road from 45 to 50 mph. As predicted by Megge, actual speeds didn’t increase, and even dropped 1 mph.

“I call it the little dude in the back of our brain that tells us how fast we can go without crashing,” Megge says. “We just take in the whole driving environment — everything that affects the way we drive — road conditions, weather, traffic, all those things bounce around in our brain, and we pick a safe and comfortable speed.”

“Seventy-five miles an hour on I-696 is not going to kill anybody,” he says. “But drunk driving at 50 miles an hour, that’s going to kill somebody.

“We need to get off this speeding thing. It’s just not the major traffic safety issue people make it out to be.”