Why do U.S. school buses stop at most railroad crossings even when no train is in sight?

Answer: The driver must stop to look and listen for approaching trains

The driver must stop to look and listen for approaching trains ✓ — The stop gives the driver a chance to look and listen for approaching trains before committing to the crossing. U.S. rules require this safety check for school buses at most crossings, though precise requirements and exceptions vary. A quiet or apparently empty track is not enough reason to skip it.

The driver must shift gears before driving onto the tracks — Changing gears is not the reason for the safety stop. Drivers should choose a suitable gear before crossing and avoid shifting on the tracks, where a stalled bus could be in a train's path.

Stopping triggers the crossing signals to clear a route — A school bus stopping does not make the railroad signals reserve a route for it. Signals warn road users about train movements; the driver's look-and-listen check is a separate safety step, including where there are no active warning lights.