A Greyhound bus driven by a replacement driver crashed Thursday, injuring eight passengers, authorities said. The driver told investigators a tractor-trailer forced him off the road, but at least three witnesses indicated he may have fallen asleep at the wheel, said patrolman Steve Kelso of the highway patrol. Investigators from the National Transportation and Safety Board went to the scene. Greyhound has reported at least 30 incidents of violence against the company, including shootings of buses, since its drivers began a nationwide strike March 2. Kelso said the Greyhound bus carrying 46 passengers went off Interstate 80 just east of Wamsutter early Thursday when it failed to make a curve. The bus crossed the median and went into a drainage ditch. All 46 passengers were taken to Carbon County Memorial Hospital in Rawlins, and eight were being held for overnight observation and treatment, Hospital Administrator Dick Mills said. All eight were in stable condition, said Mills, who did not know the extent of their injuries. The driver, 50-year-old Bobby Williamson of Chicago, was not hurt. Kelso said Williamson told him a large truck had played ``highway tag,'' repeatedly passing the bus, then slowing to make the bus pass until the bus was finally forced off the road. However, the patrolman said, there were reports from at least three witnesses who were awake either during or immediately before the accident that Williamson had been drowsy and was crossing lanes. Greyhound spokesman Bill Kula said the driver had fulfilled the rest quota prescribed by the Department of Transportation before getting behind the wheel in Cheyenne. ``The driver had had a 13-hour rest and break period which more than met DOT requirements,'' Kula said. ``He had all the rest he needed. It would not have impaired his driving ability in the least.'' George Gravely, another Greyhound spokesman, said the company was investigating whether the bus was forced off the road. ``I don't want this to sound like we've lost confidence in the driver or support everything he said. But typically, we will review everything he says.'' Williamson is a replacement driver who began driving for Greyhound when members of the Amalgamated Transit Union went on strike, Gravely said.