Traffic deaths surged about 8% in the first nine months of last year, continuing an upward spiral that began in late 2014, according to National Highway Traffic Safety Administration estimates released Friday.
The sharp increase comes at the same time Americans are putting more miles on the road than ever, the government said. But the rise in deaths is outpacing the increase in travel. Vehicle miles traveled in the first nine months of 2016 rose about 3%.
Experts believe the increased travel is mostly a result of an improved economy and low gas prices. But NHTSA's data experts said increased travel and an improved economy alone can't explain the rise in deaths.
There were 27,875 deaths in the first three quarters of last year, compared with 25,808 deaths in the same period in 2015.
"We still have to figure out what is underlying those lives lost," NHTSA Administrator Mark Rosekind said. "If it was simple, we would already know that."
NHTSA found significant regional differences in the fatality increases. In the six-state New England region, for example, fatalities increased an estimated 20% in the first nine months of 2016. But in the six-state region that includes North Dakota, South Dakota, Wyoming, Colorado, Utah and Nevada the increase was only 1%.
There are also pockets of the country that have had success with efforts to reduce fatalities. New York City, for example, has seen a 23% drop in fatalities in recent years.
The increase in deaths is especially concerning because it happened at time when automakers are beginning to equip more cars with sophisticated safety technology like adaptive cruise control, automatic emergency braking and blind-spot monitoring. Nearly all new cars now have electronic stability control and rear-view cameras.
But there are also trends that are difficult to measure, such as increased use of cellphones and other mobile devices behind the wheel.
Weather is also a factor, NHTSA officials said. Research shows that traffic fatalities go up in warmer weather months, when daylight hours are longer and people do more driving.