WASHINGTON â€"  Highway deaths declined again last year, reaching their lowest rate when compared to miles driven since such record-keeping began in 1921, according preliminary government data released Monday.

The National Highway Traffic Safety Administration's early estimate of 2011 traffic fatalities released Monday said there were 32,310 deaths in motor vehicle crashes last year, a drop of 1.7 percent from the previous year. That's the lowest number of deaths in more than 60 years.

Safety experts have attributed the historic decline to a variety of factors, including less driving due to a weak economy, more people wearing seat belts, better safety equipment in cars and efforts to curb drunken driving.

Jackie Gillan, president of Advocates for Highway and Auto Safety, said she welcomed the trend, but cautioned against complacency.

"You are still losing 32,000 people a year," Gillan said. "And we still don't know whether when the economy comes back and is really robust, what that is going to do."

In the past, when "the economy bounces back and people are doing more discretionary driving and things like that," highway deaths have gone back up, she said.

The number of miles driven on America's roadways declined last year by 35.7 billion miles, or 1.2 percent, the safety administration said. There were 1.09 deaths per 100 million miles traveled, down slightly from 1.11 deaths in 2010. That's the lowest rate on record, NHTSA says.

Overall, traffic fatalities have plummeted 26 percent since 2005.

There were significant regional differences in the fatality reductions last year, with the sharpest drop - 7.2 percent - in the six New England states. NHTSA divides states into 10 regions. Highway deaths in the five-state Region 7 - Nebraska, Kansas, Iowa, Missouri and Arkansas - also registered a significant decline of 5.3 percent. But the three-state Region 9 - California, Arizona and Hawaii - experienced a 3.3 percent increase in fatalities, and deaths in the five-state Region 6 - Texas, New Mexico, Oklahoma, Louisiana and Mississippi remained essentially flat.