As a school bus driver, I can chime in on a few things.
One unresolved issue concerns the red stop-lights and signs. On the buses that I have driven, the lights are operated by two switches. The master switch arms the system and is either set on or off. The “Start” switch sets the whole thing in motion. So, on a route, the driver sets the master switch to on when leaving the school. At 250 feet (IIRC) before the stop, he/she hits the start button. This sets the amber lights flashing. When the door is opened, the red lights flash and the stop sign and crossing arm are deployed. When the door is closed, the arms and sign retract and the lights turn off. The system is reset.
However, if the master switch is on, the red lights will turn on and the sign and arm deploy even if the start switch was never pressed. This is true even if the ignition is turned off (on some buses). So, when the driver arrives at an RR crossing and opens the door, the lights et al may activate, even when they are not actually required. IMO, this is poor technique on the part of the driver. The red lights, etc. are a traffic control device. They require other drivers to do something specific (stop). They are not required to do this, however, at railroad crossings. I make sure that my master switch is off when arriving at railroad crossings.
As to opening the door, I don’t always do it. State law and my district do not require it. I think that opening the door helps drivers pay attention to the crossing. It’s just a physical reminder that they need to look and listen down the tracks. Sometimes the windows fog up when it is cold outside, so opening the door can help the driver see. I have even done that when arriving at regular street intersections.
Buses must stop at non-exempt railroad crossings. If the crossing is marked with a sign saying “Exempt”, they may proceed without stopping. This is what happens with those oddball crossings where the track has been abandoned or if the crossing is a spur into a mill or something.
Why stop at RR crossings? IMHO, it is because buses are exposed to the oncoming train for a longer period of time than private passenger cars. That, coupled with the larger number of lives at stake, more than justifies the stopping requirement. Yes, the stopping then causes the bus to move more slowly across the track. However, I will not proceed across a track if there is a train anywhere in sight. So, even though I’ve increased the danger time, I have virtually eliminated the chance of being hit. In a bus with manual transmission, it is also illegal to change gears while crossing. Therefore, the bus is always in first gear. If the bus becomes disabled while on the track, it is evacuated immediately, regardless of whether a train is coming or if the bus might be revived.