What is the primary reason trains must stop at highway crossings during an ABS failure?

The primary reason trains must stop at highway crossings during an ABS (Automatic Brake System) failure is to prevent accidents at grade crossings. In the event of an ABS failure, the train may not be able to stop effectively or as quickly as required when approaching a highway crossing. By stopping before the crossing, the crew can ensure that no vehicles or pedestrians are present on the tracks, thereby significantly reducing the risk of collisions. This safety measure is crucial because grade crossings are points of potential hazard where trains and roadway vehicles interact, and a malfunctioning braking system could lead to catastrophic outcomes if the train were to proceed without verifying the area is clear. The protocol to stop is a critical aspect of maintaining safety protocols in railway operations.