system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do school buses open thier doors at train tracks?
gpt
Not all crossing are controlled by signals and gates, so without stopping to check a train could run into the bus. Also controlled crossing are not immune to failure, it's​ safer to stop, look and listen for a train than risk the lives of 40+ people.  

More to speaking of opening the door, it's easier for the driver to hear a train approaching the crossing. Trains must honk or ring their bell or both at level crossings. If there was an obstruction that prevents the driver from seeing the train, opening the door aids in hearing the train.