A 24-year-old Surrey man is dead and three others are seriously injured following a head-on collision on the Coquihalla Highway near Merritt, B.C., with police investigating speed and suspected impaired driving as possible factors.BC Highway Patrol said officers received multiple reports around 8:30 a.m. on October 17 of a vehicle travelling southbound in the northbound lanes of Highway 5.Officers were responding to the complaints when they learned a head-on collision had occurred just south of the Helmer exit near Merritt.When police arrived, they discovered a black Toyota Tacoma pickup truck and a white Toyota RAV4, both with extensive damage.A 24-year-old Surrey man travelling as a passenger in the RAV4 was pronounced dead at the scene.Three other Surrey men, ranging in age from 24 to 38, were also in the SUV. All three were transported to hospital with serious injuries.The driver and lone occupant of the black Toyota Tacoma, a 22-year-old man from Coldwater, suffered what appeared to be minor injuries.Police detained the driver on suspicion of impaired driving.Investigators are now trying to establish the pickup driver's movements before the collision, including where he entered the highway and what he was doing before getting behind the wheel.Some witnesses reported seeing the black Toyota Tacoma enter Highway 5 near Lac Le Jeune.."We need more video and witnesses who can tell us what the driver of the black Toyota Tacoma was doing before he started driving," said BC Highway Patrol Sgt. Michael McLaughlin."Some witnesses say the black Toyota Tacoma entered Highway #5 near Lac Le Jeune. If you saw what the driver was doing before he started driving, we need to talk to you."Police believe speed and impairment may have contributed to the fatal crash, but the exact sequence of events remains under investigation.Investigators are appealing to motorists who travelled through the area that morning and may have witnessed the pickup driving in the wrong direction.They are particularly interested in dashcam footage showing the black Toyota Tacoma before the collision or any information about the driver's activities before entering the highway.Anyone with information or video is asked to contact BC Highway Patrol in Kamloops at 250-828-3111, quoting file number (2100) 2026-2997.