NMA E-Newsletter #225: On Speedometers, Faulty Thinking and Shameful Consequences

Car buffs appreciate the subtle visual evolution of automotive features over time—from rooflines, to side view mirrors or taillights, every successive design tweak is studied and critiqued.

A great example of this ongoing refinement comes from the humble speedometer. This website charts the evolution of Chevrolet speedometer designs from 1941 through 2011. A quick review will bring back memories for many readers—some pleasant and some not so pleasant.  With its maximum 85 mph speed limit, the speedometer from the 1985 Chevrolet Silverado falls squarely into the latter category.

For years most speedometers topped out at 120 mph. But in 1980, the National Highway Traffic Safety Administration (NHTSA) mandated that speedometers could only go up to 85 mph, even though vehicles could travel faster. The idea was the brainchild of then NHTSA Administrator Joan Claybrook, who thought that lower speedometer numbers would discourage drivers from pushing their cars to the limits. And while the mandate only lasted for two years, Claybrook hasn’t given up

Thirty years later, she continues to rail against auto manufacturers for putting higher and higher limits on speedometers. In this recent article she blames the manufacturers for using the allure of speed to sell more cars: “‘They think that speed sells,’ she said of automakers. ‘People buy these cars because they want to go fast.’ ” The article continues: “Claybrook concedes there’s no data to show the 85 mph limit saved lives, but she believes it did. She called the ever-higher speedometer numbers immoral.”

Claybrook is right about one thing: Auto manufacturers have been inflating speedometer numbers to make their vehicles appear more powerful. Top speedometer readings for current family cruisers can be as high as 140 mph or 160 mph. Even the tiny Toyota Yaris shows a top limit of 140 mph.

This bit of marketing sizzle may help sell a few more cars, but does it create more speed demons on our roads? When was the last time you saw a Ford Fusion screaming down the interstate at 100 mph? Or any other car for that matter?

If Claybrook truly believes responsible drivers will put themselves in harm’s way because their speedometers tell them it’s OK, she understands nothing about driver behavior. The same holds true for those who believe that raising speed limits will encourage drivers to just drive that much faster.

The truth is that posted speeds have little impact on actual travel speeds; motorists tend to drive at a speed they believe is safe and reasonable. This turns out to be the safest speed to travel and forms the basis for the 85th percentile speed limit. Put another way, responsible motorists know what a safe speed is without having to be told. (Learn more about the 85th percentile here.)

Yet, “safety advocates,” such as the Insurance Institute for Highway Safety (IIHS) refuse to acknowledge the safety benefits of the 85th percentile formula. In a recent news story covering a proposal to raise interstate speed limits in Illinois, IIHS spokesperson Russ Rader discounted 70 years of traffic engineering practice:

Rader called the 85th percentile approach “a moving target” and disputed the National Motorists Association’s claims that motorists’ speed remains relatively static when limits are raised.

As speed limits rise, studies show that drivers tend to exceed that limit by 5 to 10 mph, he said.

“People drive the speed at which they don’t think they’re likely to be stopped and ticketed,” Rader said.

Note the sophistry in that last statement. To perpetuate the myth that speed limit signs or numbers on a dial compel drivers to behave recklessly—making them care more about getting caught than their own safety—represents, at best, faulty thinking, and, at worst, a cynical attempt to push an agenda.

In either case the result is the same: the chronic under posting of speed limits leading to more accidents and higher costs for drivers. Shameful.



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