The National Highway Traffic Safety Administration attributed the 2.4% drop partially to technology in newer vehicles that can prevent crashes. A total of 36,560 people died on the nation's roads in last year, the latest full-year statistics available.
The agency said the downward trend is continuing into 2019. First-half estimates show fatalities down 3.4%.
"This is encouraging news, but still far too many perished or were injured, and nearly all crashes are preventable, so much more work remains to be done to make America's roads safer for everyone," Transportation Secretary Elaine Chao, whose department oversees NHTSA, said in a statement.
The overall declines in 2017 and 2018 came after two years of large increases blamed on people driving more as the economy improved.
But pedestrian deaths rose 3.4%, and the number of people killed on bicycles and other pedaled vehicles went up 6.3%. People killed in large-truck crashes rose just under 1%.
The agency reported 6,283 pedestrian deaths, the highest total in 28 years, according to Consumer Reports, which said pedestrian fatalities have risen about 53% since 2009.
NHTSA said alcohol-impaired fatalities dropped 3.6% in 2018, while fatalities attributed to speeding fell 5.7%. Motorcycle deaths declined 4.7%, the agency said.
Most of the pedestrian deaths, 76%, and half the bicyclist deaths occurred after dark, and the some pedestrians and cyclists had some alcohol in their systems. Seventy-four percent of the pedestrian deaths occurred outside of intersections, the agency reported.
NHTSA also said it would look into the increase in SUVs as a factor in the increases. SUVs sit taller than cars, which can make it more difficult for drivers to see pedestrians and cyclists.
The agency said in a statement that it's also studying changes in its five-star crash assessment program and will consider including new technologies such as pedestrian detection systems. It's also working with the Federal Highway Administration to reduce bicycle and pedestrian deaths.
"This is an epidemic of preventable deaths," said Jake Fisher, senior director of auto testing for Consumer Reports. "We need to double down to figure out how to achieve better pedestrian detection and more widespread adoption."
The agency said that the number of deaths in crashes with distracted drivers hit 2,841 in 2018, or 7.8% of total traffic deaths. But the 2018 number is down 12.4% from 2017, according to the agency.
The Truck Safety Coalition, an advocacy group, said crashes involving at least one large truck killed 4,951 people last year. In a statement, the group said fatalities involving large trucks have increased 46.5% in the past decade, yet the administration of President Donald Trump has pushed for proposals that would make it easier for truck drivers to work 17-hour days, and to remove a 30-minute break requirement for truck drivers after eight hours of work.
At the same time, the Transportation Department hasn't done anything to advance safety rules that would require automatic emergency braking or electronic speed limiters for big rigs, the statement said.
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