Highway fatalities on U.S. roads hit a 55-year low last year as 3,228 fewer people -- more than  were killed on 9/11 -- died in traffic crashes than in 2008.

The death toll of 33,963, an 8.9 percent decrease  from the previous year, was the lowest total since 1954. And while  a recession-related drop in the amount of total miles driven contributed to the decline, economic factors alone do not account for the dramatic drop.

The agency reported that the traffic fatality rate on the basis of vehicle miles traveled (VMT) fell from 1.25 million per 100 million miles  in 2008 to  a record low of 1.16 million in 2009.

In addition to economic factors, NHTSA attributed the drop to multiple factors, including high-visibility campaigns against drunk and distracted driving, increased seat belt use, better-engineered roads and safer vehicles.