At what air pressure level will the emergency braking system stop the bus?

The emergency braking system is designed to activate when the air pressure in the system falls below a critical threshold, specifically between 20 and 45 psi. This feature ensures that the bus can still be brought to a stop in the event of a significant loss of air pressure, which is vital for the safety of the bus, its passengers, and other roadway users.

At pressures below this range, the system recognizes that normal braking capabilities may be compromised, prompting the emergency brakes to engage. This mechanism is a safety precaution to prevent situations where a bus may struggle to stop due to insufficient air pressure.

In contrast, the other options either indicate thresholds that are not applicable for emergency braking activation or describe conditions that do not lead to an immediate safety response. For instance, a drop below 60 psi indicates a reduced performance of the braking system but does not trigger the emergency brakes as effectively as the specified range.