Partly because of a tendency among carriers to drive slower to save fuel, the number of US highway fatalities involving heavy trucks decreased again last year, according to the National Highway Traffic Safety Administration (NHTSA).

The number of traffic fatalities involving large trucks decreased 4.4% in 2007 when compared to 2006. At 4,808 fatalities, it's the lowest level since 1992.

Truck occupant fatalities decreased 0.4 percent and fatalities among occupants of other vehicles involved in a crash with a large truck dropped 5.2%. Truck-related fatalities involving people not in a vehicle (such as pedestrians) decreased 4.7 percent.

The American Trucking Associations (ATA) credits other factors for the improvement, including new safety technologies such as collision avoidance systems, lane departure warning systems, stability systems and brake stroke monitoring systems. The ATA also noted the recent improvements occurred under the current hours-of-service regime.

The fatality decline took place in all vehicle groups in addition to trucks. Thanks in part to safer vehicles and aggressive law enforcement, the number of people overall who died on the nation's roads reached historically low levels, the U.S. Department of Transportation says.

The overall number of traffic fatalities in 2007 fell to 41,059, the lowest number since 1994. In addition, the fatality rate per 100 million vehicle miles traveled was 1.37, the lowest fatality rate on record.

In addition, 2.49 million people were injured in highway crashes last year, the lowest since the National Highway Traffic Safety Administration began collecting injury data in 1988.