A 70-year-old crossing guard is in critical condition after being struck by a pickup truck Thursday morning near the Merrick Long Island Rail Road station, according to Nassau County police.

Authorities say the incident occurred at approximately 8 a.m. in Merrick, leaving residents shaken and prompting the arrest of a 30-year-old driver who police say was under the influence of drugs.

Police identified the driver as Joshua Alvarado, 30, who has been charged with driving while ability-impaired by drugs and vehicular assault. He is scheduled to face a judge on those charges Friday.

Nassau County Police Commissioner Patrick Ryder said Alvarado failed a field sobriety test at the scene. He was taken to police headquarters, where a blood sample was drawn to determine what substance he had allegedly used.

Officials said the driver fell asleep at a red light, moments before the crash. When traffic began moving again, he allegedly misjudged his turn and drove onto the sidewalk, striking the crossing guard.

The victim, whose name has not been released, underwent emergency surgery and remains in critical condition.

A shovel was seen near the crash site, and witnesses said the crossing guard may have been attempting to clear snow from the sidewalk at the time he was hit.

Residents described the victim as a familiar and reassuring presence in the neighborhood.

“He’s here usually around school time in the morning and the afternoon, and he stops traffic to make sure the kids cross,” said Merrick resident Michael Shapiro. “I didn’t see what happened this morning, but it was terrible.”

Nassau County Executive Bruce Blakeman noted the crossing guard’s dedication to protecting children on their way to and from school.

“He was somebody who went out each and every day with the thought of protecting our young people,” Blakeman said.

Police said Alvarado has a prior drug-related arrest and has previously been cited for speeding.