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Updated 11:15 AM August 29, 2008




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Major drop in traffic deaths: It's more than high gas prices

Rising fuel prices, resulting in less driving, may very well be a reason for the decline in traffic deaths, as recent reports have suggested. But a new report shows that something more may be at play — a major shift in driving behavior.

Changes in gasoline sales and miles driven cannot fully explain the reduction in motor vehicle fatalities, says Michael Sivak, research professor and head of the Human Factors Division at the U-M Transportation Research Institute.

While the decline in traffic deaths has outpaced the drop in gas sales and number of miles driven since at least last year, the change especially has been noticeable since this spring.

Motor vehicle deaths plummeted 22 percent in March and 18 percent in April, while gas sales decreased about 3 percent and 1 percent and estimated miles driven fell roughly 4 percent and 2 percent for each of those months. The data are based on year-to-year percentage changes and are not yet available for May and June.

"Should the March and April trends continue, the 2008 annual fatalities would drop to under 40,000 for the first time since 1961," Sivak says.

There are several possible explanations, he says.

First, the reduction in distance driven, albeit smaller than the drop in traffic deaths, might have been disproportionately greater for more risky driving conditions. For example, the reduction in miles driven on rural roads — the more risky roads — for March and April was greater than the reduction on urban roads (-4 percent vs. -2.6 percent).

Second, since the increasing cost of gas might have significantly decreased the amount of driving for people with less income, such as teenagers and the elderly, this high-crash rate group is experiencing fewer accidents.

Third, motorists may be driving slower to save gas. It could be that the safety benefits of driving slower are proportionally greater than the fuel-economy benefits, Sivak says. The reduction of driving on rural roads — where speeds are generally faster than on urban roads — also tends to decrease the overall speed profile, he adds.

"It appears that the increased cost of gasoline has finally begun to influence driver behavior both in terms of the amount and type of driving," Sivak says. "Consequently, one of the indirect benefits of the increased cost of gasoline — in addition to, for example, a reduction in emitted CO2 — is likely to be a decrease in motor vehicle fatalities."

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