WASHINGTON (Reuters) - Traffic deaths in the United States rose about 9 percent in the first nine months of 2015 compared to same period a year earlier, the U.S. Transportation Department said on Friday, as low gasoline prices increased road travel.

The department’s National Highway Traffic Safety Administration did not offer an explanation for the increase in traffic deaths to an estimated 26,000 in the first nine months of 2015, the highest level since the same period in 2008.

The northwestern United States reported a 20 percent increase in road deaths, higher than any other region.

The NHTSA said 94 percent of crashes result from human error, and that it is working to address driver behavior.

“We’re seeing red flags across the U.S. and we’re not waiting for the situation to develop further,” NHTSA Administrator Mark Rosekind said. “It’s time to drive behavioral changes in traffic safety, and that means taking on new initiatives and addressing persistent issues like drunk driving and failure to wear seat belts.”

The fatality rate for the first nine months of last year was 1.1 deaths per 100 million miles traveled, compared to 1.05 deaths per 100 million miles during the same period the previous year. That represented the highest fatality rate since 2012.

Russ Rader, a spokesman for the Insurance Institute for Highway Safety, a group funded by insurers, called the increase in traffic deaths troubling but not unexpected.

“There is a strong correlation between economic conditions and the number of traffic deaths,” Rader said.

More people drive more miles when the economy is improving.

“New vehicles are safer than the ones they’re replacing,” Rader added. “Beyond safer vehicles, we know what policies work to reduce road deaths - strong laws that are vigorously enforced to increase belt use and decrease impaired driving and speeding.”

U.S. traffic deaths had been falling, with a 22 percent decline from 2000 to 2014.

The rate of road deaths was greater than the growth in vehicle travel. The Transportation Department said last month U.S. drivers logged 2.88 trillion miles in the first 11 months of 2015, up 3.5 percent over the same period in 2014, and on pace for the highest yearly total on record.

A drop in gasoline prices and lower unemployment means more people are driving and they are logging longer distances, increasing the likelihood of accidents. Traffic was up 3.5 percent in first nine months of 2015, compared to the same period the year before, according to government figures.