Descending a 7% Grade with a Loaded Bus
You are operating a 38-passenger bus with air brakes, loaded with 34 passengers and luggage, descending a 6-mile 7% mountain grade. The posted truck speed is 35 mph. Your service brakes are warm from a previous stop, and you notice the pedal feels slightly lower than at the top of the grade. The speedometer shows 48 mph and climbing. A passenger asks why you are 'riding the brakes.'
1. What is happening and what is the correct braking technique on this grade?
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Continuous service-brake application on a long grade generates heat faster than the drums can shed it, which leads to brake fade - the pedal feels lower or softer and stopping power drops. The correct technique is to select a lower gear before or at the top of the grade so engine braking holds the speed down, then use the service brakes in controlled applications to bring speed back to the target rather than holding them on continuously. Target the posted 35 mph, not 48. If speed is already climbing and the pedal is changing, you are behind the curve: slow down now, get into a lower gear, and use short firm applications with time off between them to let the brakes cool.
2. The pedal is lower than at the top of the grade. What does that tell you, and what do you do if the speed will not come down?
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A lower or spongy pedal with warm brakes is a warning of fade or, worse, a developing air or fluid problem. Treat it as a brake emergency in progress. Immediately reduce speed using the transmission and the brakes you have, and identify an escape route - a runaway truck ramp, a wide shoulder, or a pullout. If speed continues to climb and brakes are ineffective, use the escape ramp rather than ride it out; a controlled stop in a ramp is survivable, a runaway bus on a 7% grade is not. Do not announce a brake problem to the cabin in a way that causes panic, but do tell passengers to remain seated and belted.
3. How do you answer the passenger's question, and what does that have to do with your responsibility?
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Answer briefly and factually: the bus is heavy, the grade is long, and the correct method is a low gear plus controlled brake applications so the brakes do not overheat. The passenger's question is also a cue that your driving is being observed - abrupt or repeated hard braking with standees or unrestrained passengers is a fall risk. Your responsibility is to manage the vehicle so that the ride stays smooth and controlled, and to communicate enough that passengers trust the operation without being alarmed.