More than half of those killed in District traffic accidents and 20 percent who died in Maryland were pedestrians, according to a 2010 federal study released Monday.

The District and its highly urbanized neighbor joined other densely populated parts of the country where the number of pedestrian deaths in car accidents far exceeded the national average of 13 percent. Virginia was below that average, at 9.9 percent.

The report on 2010 fatalities by the National Highway Traffic Safety Administration found that for the first time in five years, the number of pedestrians who died in traffic increased, even as the overall number of traffic fatalities continued to decline.

“We don’t know why they’re up,” said Jonathan Adkins of the Governors Highway Safety Association, which also has collected data on pedestrian deaths. “We think distraction plays a role, but we need more research on that.”

The nation’s leading crusader against distracted driving, U.S. Transportation Secretary Ray LaHood, said the uptick in pedestrian deaths underscored that “ it’s important to share the roads and stay alert.”

The NHTSA report said that three-quarters of pedestrian fatalities happened in urban areas.

Kansas, which ranks 40th in population density in the United States, had the lowest percentage of pedestrians killed in car accidents, 3.4 percent.

The District, where 13 of the 24 people killed in 2010 traffic accidents were on foot, ranked highest by percentage. Among states, New York, New Jersey, Hawaii and California topped the list.

In Maryland, 101 of 493 traffic fatalities were pedestrians. In Virginia, 73 of the 740 who died were on foot.

Only 21 percent of pedestrians killed in traffic died at intersections, and the overwhelming majority — 68 percent — died after dark, the report said.

Several pedestrians have been struck and killed by vehicles in the Washington region this summer, most of them dying in the hours between dusk and dawn.

Prince George’s County police said a woman was killed just before 5:30 a.m. on June 27 when a vehicle struck her in the 6100 block of Baltimore Avenue in the Riverdale Park neighborhood.

A man who walked into an Arlington intersection where street lights had been darkened by a storm on July 1 was killed by a driver who did not heed police advice to treat intersections where traffic lights were out as four-way stop signs.

A 62-year-old visitor from Boston died about 5:30 a.m. near the Pentagon on July 9, apparently after his vehicle broke down near the Interstate 395 exit ramp at Route 110.

A Takoma Park woman was killed when she was struck by two vehicles — a tow truck and a Toyota — in Langley Park on July 14 at 8:40 p.m. Police said Irma Glover, 76, had stepped into the eastbound lanes of University Boulevard when she was hit by a tow truck leaving the lot of a Pep Boys auto parts shop.

Prince William County police said a man was killed by a car at 5:49 a.m. on July 29 as he crossed Lee Highway near the intersection with Old Carolina Road.