WASHINGTON — Roll back the clock to 1961: John F. Kennedy was inaugurated president. The Peace Corps was founded. The Dow Jones industrials hit 734. Gasoline reached 31 cents a gallon.

And the number of people killed in U.S. traffic accidents that year topped 36,200.

This year, gasoline climbed to more than $4 a gallon, and the traffic death toll — according to one study — appears headed to the lowest levels since Kennedy moved into the White House.

The number is being pulled down by a change in Americans' driving habits, which is fueled largely by record high gasoline prices, according to the Transportation Research Institute at the University of Michigan.

The institute's study — which covers 12 months ending in April — found that as gas prices rose, driving and fatalities declined. The surprise, said professor Michael Sivak, author of the study, was the huge decline in fatalities in March and April as gasoline prices surged above $3.20 a gallon.

Over the previous 10 months, monthly fatalities declined an average of 4.2 percent compared to the previous year. Then, Sivak's data show, fatalities dropped 22.1 percent in March and 17.9 percent in April of this year — numbers that did not show up in a recent federal report that tracked a drop in traffic deaths through the end of 2007.

The declines found by Sivak suggest that motorists reached what he calls a "tipping point" and have begun significantly changing their behavior — altering not only how much they drive, but where, when and how they drive. Sivak said early data for May and June show similar trends.

"There is something more than just the reduction in driving that has to be brought in as an explanation for the huge drop in fatalities," Sivak said.

If the pattern continues for the rest of this year, it would lead to "an unheard of improvement" in motor vehicle fatalities, said Sivak, who used data from the National Safety Council, National Center for Health Statistics and the National Highway Traffic Safety Administration.

Sivak predicts that highway deaths this year will drop below 37,000 for the first time since 1961 if the March and April trends continue. The government motor vehicle death count for 1961 totaled 36,285. The number of highway deaths peaked in 1972 at 55,600, then generally declined over the next two decades. For the past several years, the number has hovered above 42,000 a year.

NHTSA reported last week that motor vehicle deaths in the United States totaled 41,059 last year, the lowest level in more than a decade. And the Federal Highway Administration said Americans drove 12.2 billion fewer miles in June than a year earlier, the biggest monthly decrease in a downward trend that began in November.

Experts who have studied motor vehicle fatality trends said one reason for the dramatic decline is that people are reducing their nonessential driving first, which is often leisure driving at night or on weekends. That also happens to be riskier than daylight commuting on congested highways at lower speeds.

Teenage and elderly drivers — who also have higher accident rates — are more likely to feel the pinch of higher gas prices, and thus may be cutting back more than other drivers. Federal data also show that driving declines have been more dramatic on rural roads, which have higher accident rates than urban highways.

And some drivers are simply trying to save on gas by slowing down, which also decreases risk. "It could be that the safety benefits of driving slower are proportionately greater than the fuel economy benefits," Sivak said.

The steepness of the fatality decline underscores a point several experts have made recently — that raising the price of gas is more effective than almost any other means of reducing fatalities.

"It's really very interesting that with all these efforts that have gone into building safer highways, safer cars, better enforcement ... this really dramatic change we're seeing is due to economics, to the price of gasoline," said Paul Fischbeck, director of Center for the Study and Improvement of Regulation at Carnegie Mellon University.