A DE-GAS MECHANIC WAS OPERATING A DIESEL JEEP WHILE ACTING AS AN ESCORT FOR A CREW FROM A CONTRACTOR WHEN THE JEEP WENT OFF THE TRACK DUE TO THE TRACK BEING OUT OF GAUGE. HE WAS JOSTLED IN THE JEEP & STRAINED HIS LOWER BACK. HE FINISHED THE SHIFT & DID NOT SEEK MEDICAL ATTN. UNTIL AFTER HIS SHIFT, 09/26/05. ON 09/28/05 HE WAS TAKEN OFF WORK.