Traffic fatalities on the nation’s roads have spiked dramatically this year, ending six years of steady decline that had seemed to herald success after decades of effort to make vehicles and roadways less risky.

The 7.1 percent increase in the first nine months of the year was the biggest jump during the January-through-September span since 1975, the year that federal officials began compiling traffic-death data.

In releasing the preliminary statistics, federal officials pointed out that the year-to-year comparison was made against 2011, when highway deaths reached their lowest point in more than 60 years. Even with the increase this year, they said the total was 26 percent below the number killed during the first nine months of 2005.

The projections were made by the National Highway Traffic Safety Administration based on data collected from state officials. They showed that fatalities increased this year by 1,696, to 25,580. The increase far outpaced the 0.6 percent increase in total miles driven this year.

“There is a relationship between the economy, gas prices, driving and fatalities,” said Jonathan Adkins, deputy executive director of the Governors Highway Safety Association. “However, the increase can’t be explained solely because of an improving economy and more discretionary driving. Vehicle miles of travel likely didn’t increase that much in 2012. Other factors may be at play. For example, 2012 had one of the warmest winters on record. That may have resulted in a longer motorcycle riding season and more pedestrian activity and hence, more fatalities.”

The preliminary data do not break down the deaths by state or the type of vehicle involved.

The downward national trend had been attributed to several factors, including increased use of air bags, seat belts and other safety features, improved roadway designs, and increasing awareness of the perils of driving drunk.

“Despite the increase, the country has been tremendously successful in reducing motor vehicle deaths and injuries,” Adkins said. “These successes have been achieved through the improvements in driver behavior, safer roadways and safer vehicles, and the interaction of all three.”

In 2011, highway deaths dropped to 32,367, almost 2 percent lower than they were in 2010. Maryland outpaced the nation with a 2.2 percent decrease, but deaths rose by 3.2 percent in Virginia and 13 percent in the District. Maryland had 11 fewer deaths than the 496 it recorded in 2010. In Virginia, 764 people died in 2011, compared with 740 in 2010, and deaths in the District increased by three, to 27.

The big increase this year was driven by a 13 percent jump in the first three months of the year. The total for April, May and June was 4.7 percent higher than in 2011. The two summer months and September saw a 4.9 percent increase.