The number of traffic fatalities in the United States unexpectedly soared during the first three months of 2012, according to recently released data.

Approximately 7,630 people were killed in motor vehicle crashes in the first quarter, a 13.5 percent jump over the same period in 2011, according to the National Highway Traffic Safety Administration.

The increase represents the second-highest quarterly spike since the organization began keeping records in 1975, and also is a stark contrast to a recent downward trend. It is the first time in five quarters the rate has not decreased, and is only the third quarterly increase among the past 24 quarters.

Transportation officials were at a loss to explain the sudden increase. In a written release, NHTSA officials said it was "too soon to speculate on the contributing factors," although a few paragraphs later, they did just that.

It notes that weather in many parts of the country was unseasonably warm this past winter, which could have put more people on the roads at a time they were usually unable to log miles. Others said that the improving economy has put more motorists on the road. Indeed, the Federal Highway Administration says that vehicle miles traveled increased by about 9.7 billion miles, or 1.4 percent, over the 2011 figures.

"While it is likely not the only factor involved AAA agrees that warmer-than-average winter weather may have contributed to higher vehicle miles traveled, and ultimately more fatal crashes," Jacob Nelson, director of traffic safety advocacy and research with the Automobile Association of America tells CNN.

The number of first-quarter traffic fatalities has fallen steadily since 2006, when there were 9,558. In 2007, they dipped to 9,354, in 2008 reached 8,459, 7,552 in 2990 and 6,729 in 2010. In 2011, the number decreased by nine to 6,720 before jumping this year.

Overall, traffic fatalities reached their highest levels in 1972, when 54,589 people were killed, according to Department of Transportation figures. That annual number has also steadily fallen, reaching 32,310 last year.