Loaded Bus on a 7% Grade
You are driving a 6-speed manual Type C school bus loaded with 44 students on a rural North Dakota state highway. The route descends a 7% grade for 2.5 miles. The pavement is wet, the temperature is 38°F, and the speed limit is 50 mph. At the top of the grade you are in 6th gear at 35 mph. The bus is near its gross vehicle weight rating. A sign warns 'Steep Grade - Trucks Use Lower Gear.' You have a clear view of the first quarter mile, but a curve at the bottom limits sight distance. The engine temperature is normal, and the air pressure gauge reads 105 psi. You smell only normal diesel exhaust. Your job is to set up the descent before the bus gains speed, not to discover a problem halfway down.
1. What gear and speed plan should you set before the grade, and why?
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Slow to about 25-30 mph before the grade, select the gear you would need to climb the grade - likely 3rd or 4th in a loaded 6-speed - not 6th. Use engine braking to hold speed; do not coast in neutral or with the clutch in. Keep RPM below the governor and above the lugging point. Test the brakes at low speed before committing. A loaded bus on 7% wet pavement can gain speed quickly, and the curve at the bottom removes recovery room.
2. Halfway down, you smell hot brakes and the pedal feels low. What do you do?
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Treat it as brake fade. Downshift immediately to the next lower gear to increase engine braking, apply firm steady brake pressure, and look for a pullout or wide shoulder. If you have anti-lock brakes, do not pump the pedal rapidly; apply firm pressure. If you can stop safely off the travel lane, do so, set the parking brake, let the brakes cool, and inspect before moving. Call dispatch. If no safe pullout exists, continue in the lowest safe gear and use a runaway truck ramp if one is available. Do not continue at normal speed.
3. Why is waiting until you are already speeding to downshift a poor choice?
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At higher speed, the transmission may refuse to engage a lower gear or you may over-rev the engine; forcing it can damage the driveline or cause a loss of control. The safe time to select a lower gear is before the descent, when speed is low and the engine can hold the bus back. If you must downshift mid-grade, slow first, match engine speed, and do it deliberately.