WESTON, Mass. (AP) — A Massachusetts State Police trooper seriously injured when his cruiser was struck from behind by a tractor-trailer on Interstate 95 in Weston has been released from the hospital, authorities said Wednesday.

The trooper, working a construction zone detail, was inside the stationary cruiser when it was struck at about 11:45 p.m. Tuesday, according to state police. The cruiser was unmarked but had it’s emergency lights on and sustained heavy damage.

The truck driver, a 27-year-old man from Montreal, fell asleep at the wheel and veered into the breakdown lane, police said. He awoke at the last second and applied his brakes, but it was too late to avoid impact.

The truck continued past the police vehicle and jack-knifed across the highway, shutting down all southbound lanes until just after 1 a.m., police said.

The 33-year-old trooper was pinned in the vehicle and sustained serious injuries but was alert and radioed in the crash himself. He was taken to a Boston hospital and has been discharged. He is on injured leave.

The truck driver was cited for negligent operation, failure to move over, and marked lanes violation, police said. No names were released.