Rich Muth is exactly right. Even with a exempt sign, a bus driver should not assume anything. What if a track machine or track car got lose and rolled down the mountain? It does not have to be a train or a car that could cause a collision. Where is the common sense questioning that bus stop? About equal to the Fire truck driver in Detroit that parked the ladder rig on the main line and made one million dollars damage for the city, and injured some fireman when Amtrak came along on schedule.
How would any bus driver, even if he worked for the railroad, know what the dispatcher might have in mind or what track was out of use?