Four pedestrians were struck and killed while walking on D.C.-area roadways within a 36-hour period over the weekend, police said, adding to a troubling pattern of rising pedestrian fatalities.

In each case, the pedestrian was crossing or walking along a major thoroughfare — with multiple travel lanes, few to no facilities for pedestrians and higher travel speeds. The victims — two women and two men — were traveling in the dark or low light and were outside of crosswalks, authorities said.

Three of the incidents occurred in the span of 12 hours.

Maryland State Police are investigating an early Monday incident in which a man was hit and killed while walking in the middle of a three-lane stretch of Branch Avenue in the Clinton area of Prince George’s County.

Police said Jordan C. Baber, 26, of Upper Marlboro was struck shortly after 4:30 a.m. after he got out of a vehicle in which he was a passenger. He was seen walking in the middle lane of Branch Avenue, north of Woodyard Road, when he was hit by a car traveling in the southbound direction. The car’s driver remained at the scene.

A few hours earlier, at 2 a.m., a 36-year-old woman was struck while crossing Arlington Boulevard in the Falls Church area of Fairfax County. Police said the woman was walking outside the marked crosswalk, near Graham Road, when she was struck by a westbound vehicle.

Authorities said that neither speed nor alcohol appeared to be factors in that case and that the driver was cooperating with investigators.

On Sunday night, a man walking along Route 1 in Jessup, Md., was struck and killed by a sedan. Howard County police said the Hyundai Elantra was traveling in the southbound lanes about 9 p.m., near Hicks Road, when it hit the man, who was walking in a travel lane.

The victim died at the scene, police said. Police said the driver of the Hyundai remained at the scene.

Another fatality, the fourth this weekend, was reported early Sunday in the Greenbelt area of Prince George’s County. Police said Paulinette F. Pearl Bedran, 29, of Silver Spring was walking on the left shoulder of the southbound ramp of Kenilworth Avenue, heading onto Route 193, when she walked into the travel lane and was struck by two vehicles. The incident occurred about 4:20 a.m. Both drivers remained at the scene, Greenbelt police spokesman George Mathews said.

The deaths this holiday weekend come as the region appears to be experiencing a surge in pedestrian fatalities.

Public safety and transportation officials said they are troubled by the deaths, which mirror a national upward trend, and come as jurisdictions make commitments to lower the number of traffic fatalities. In Montgomery County, for example, there have been at least 11 pedestrian fatalities this year, according to reports — and four occurred in a two-week period last month.

Officials have urged pedestrians to cross in designated crosswalks and be more aware — even when they have a right of way.

In several incidents, including at least three this weekend, the victims were not in crosswalks or were crossing roads illegally.

Pedestrian deaths, and traffic fatalities in general, tend to be higher during long holiday weekends, when more people are on the road.

“Seasonally, there is an uptick in pedestrian deaths that manifests itself in late summer, a tragic pattern that continues throughout the balance of the year,” AAA Mid-Atlantic spokesman John Townsend said. “On average, Labor Day weekend is one of the deadliest times for traffic fatalities.”

The National Safety Council estimated 420 traffic deaths nationwide this Labor Day holiday weekend.

A recent report by the Governors Highway Safety Association estimates the number of pedestrian deaths nationwide last year was nearly 6,000, a 33-year high. The report highlights a number of factors for the continued increase, including distracted drivers using mobile devices and a larger number of cars on the road due to an improved economy. Studies also point to distractions among pedestrians, including texting while walking.