Traffic in the Snake River Canyon was blocked on and off through most of the day yesterday after a tractor-trailer carrying Coke products veered off the road and plunged over the guardrail near Lunch Counter, between mileposts 123 and 124. According to Lieutenant Matt Brackin of the Wyoming Highway Patrol, the unidentified local driver apparently fell asleep at the wheel at about 5:00 am as he was headed southbound toward Alpine. The driver sustained only minor injuries in the mishap, but the truck required most of the day to remove it. The effort, which required several tow trucks caused the highway to be closed for about three hours in the middle of the afternoon. The scene was finally cleared at about 6:00 pm.