Five bicyclists were killed on Thursday morning when they were struck by a box truck on a highway outside Las Vegas, the authorities said.
The crash happened at 9:39 a.m. as a group of about 20 bicyclists were riding on the shoulder of U.S. 95 at mile marker 36 in Clark County, just north of Searchlight, Nev., according to the Nevada Highway Patrol.
The box truck left the roadway and hit the group from behind, and then struck a Subaru hatchback that was accompanying the cyclists and another group of cyclists that was in front of the Subaru, the Highway Patrol said.
In addition to the five cyclists killed, four people were injured, including one who was in critical condition, according to Trooper Jason Buratczuk, a Highway Patrol spokesman.
Trooper Travis Smaka, another Highway Patrol spokesman, said investigators did not know what had caused the driver to plow into the cyclists. The driver of the box truck stayed at the scene of the crash and was cooperating with the investigation, Trooper Smaka said.
Investigators do not believe that the driver was impaired by alcohol or drugs, he said, and no charges have been filed as the investigation continues.
The authorities have not released the names of those killed or the name of the driver. The speed limit on that portion of the highway is 75 m.p.h.
Clay Weeks, who works at Pro Cyclery, a bike shop in Las Vegas, said he knew some of the riders that were in the group, including a mechanic who works at the store who was unharmed but “very emotionally hurt.”
He said the group had been on a 155-mile ride that was to take them from the M Resort Spa Casino in Henderson, Nev., to Searchlight and back when they were struck by the truck.
He said the group had been celebrating the recent retirement of one of the riders from a police force in California.
“It’s a road that typically would be safe,” Mr. Weeks said. “The shoulder is plenty wide to ride out there. It’s not a narrow, sketchy road.”
He said news of the crash had traveled quickly through the close-knit cycling community.
“Everyone is just devastated,” he said. “Hopefully this opens eyes for people and will make them more vigilant of cyclists on the road because stuff like this happens way too often in the community.”
Bicycle rides account for only 1 percent of all trips in the United States, but cyclists face a higher risk of crash-related injuries and death than people in cars and trucks, according to the Centers for Disease Control and Prevention.
Last year, the National Highway Traffic Safety Administration reported that more pedestrians and cyclists had been killed in 2018 in the United States than in any year since 1990.
The number of pedestrians killed grew by 3.4 percent in 2018, to 6,283, and the number of cyclists killed rose by 6.3 percent, to 857, even as total traffic deaths decreased, the agency said. On average, about 17 pedestrians and two cyclists were killed each day in crashes.