Safety in Numbers

| May 29, 2007

After the 1995 repeal of the 55 mph national speed limit cap, 31 states had raised speed limits to 70 mph or higher by mid-2006. Yet highway fatality rates per 100 million vehicle miles fell from 1.73 in 1995 to 1.46 in 2005, a 16 percent decline, according to NHTSA data cited in a 2006 Wall Street Journal editorial.

Of those 31 states, “29 saw a decline in the death and injury rate and only two – the Dakotas – have seen fatalities increase,” wrote the Journal. “Two studies, by the National Motorists Association and by the Cato Institute, have compared crash data in states that raised their speed limits with those that didn’t and found no increase in deaths in the higher speed states.”

That 16 percent decline in fatalities, however, pales before the 50 percent decline in fatalities between 1974 and 1995, when the national speed limit was in effect, wrote Judith Stone, president of Advocates for Highway and Auto Safety, in response to the Journal editorial. “Fatalities have increased on roads with speed limits of 65 mph and higher, while fatalities on roads posted at 50 mph and lower have remained stable,” she wrote.

TRUCK-RELATED SPEED DATA
Only 0.2 percent of truck crashes occur at speeds above 70 mph.
- A 1991 National Highway Transportation Safety Administration report to Congress

In the 20 percent of truck-involved crashes where speed was a factor, it exceeded 68 mph.
- American Trucking Associations study of crash data

The problem with the first statistic, a favorite among governing opponents, is it’s based on a period when the nationwide speed limit was capped at 55 mph or, in the case of many rural Interstates, 65 mph. So one would expect wrecks at 70-plus mph to be somewhat rare, says Anne McCartt, senior vice president for research for IIHS. Blower of UMTRI offers a similar, updated analysis. From 1999 to 2003, when speed limits were similar to today’s, 6.7 percent of the trucks involved in fatal wrecks were traveling faster than 68 mph, he says.

As for the second statistic, though speed was not the sole factor, it still correlated with one in five truck crashes. And even when speeding is not cited as a contributing cause of an accident, speeds of 68-plus mph obviously contribute to the severity of an accident, McCartt says.

The 1991 NHTSA report was one of the most ambitious of any that have focused on heavy trucks at speeds above 65 mph. The study supported speed governors for fleets but found insufficient justification to mandate it.

The 2006 Large-Truck Crash Causation Study showed that among the crash causes attributed to trucks, the most common “were driver factors, such as legal drug use, traveling too fast for conditions, [and] unfamiliarity with the roadway.”

Because this and other studies still don’t present enough of the information needed to weigh all the issues involved with governing trucks, better data is needed – and on the way, says Dan Murray, American Transportation Research Institute vice president. ATRI’s survey of carrier speed and safety “will bring more clarification to what is safe speed,” Murray says.

Preliminary results showed 69 percent of respondents govern trucks, at an average governed speed of 69 mph. That’s encouraging, Murray says, because it’s so close to the 68 mph requested in the petitions – though he admits that correlation is primarily based on posted speed limits, not a proven optimal level for safety.

DIFFERENTIAL SPEEDS
“Vehicles traveling 10 to 15 mph slower than the mean speed of
traffic were much more likely to be involved in accidents than vehicles traveling slightly above the mean speed.”
- Testimony before a Senate committee in 2003 by Julie Cirillo, former head of the Federal Motor Carrier Safety Administration, citing a 1963 study by David Solomon

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