A Department of Public Works chipper trailer broke loose from the truck towing it and hit a school bus, occupied by the driver who was sweeping. The 29-year-old Milwaukee woman fell and was taken to the hospital. The bus was parked on E. Capitol Drive east of N. Morris Blvd. about 7:40 a.m. April 6. The trailer hitch was found to be defective. The safety chains had become disconnected from the truck, which the driver, a 45-year-old Shorewood man, said happens sometimes due to going over bumps.