Mark Schoonmaker of Ocala, sitting in the bed of a Chevrolet pickup, had just witnessed one wreck: A woman was thrown into the left lane of I-75north Friday afternoon in Sumter County after she swerved trying to avoid a semitrailer truck. A line of about five vehicles, including the pickup Schoonmaker was riding in, had stopped to try to help her. Then a refrigerated semitrailer truck slammed into the stopped vehicles. The woman, Michelle Damron Hulinek, 30, of Bushnell was taken to Tampa General Hospital, where she was in intensive care late Friday. No one else was seriously injured. The wrecks backed up traffic south of State Road 50 for four hours. Troopers cited trucker Timothy J. Pierson of Richland, Miss., with careless driving in the second wreck. Among the smashed cars, a couple in a Cadillac who had to be cut out of their car, and another driver said he considered himself lucky to be alive: "I'm going straight to church on Sunday," said Michael Allen.