Soft pedal on a snow-covered mountain descent
At the top of a 6 km descent with an average gradient of 8%, a 40 t articulated combination is travelling at 60 km/h. The road is snow-covered, the temperature is -4 °C, and visibility is good. The lorry has a manual gearbox, an engine brake and a retarder. The driver selects 7th gear, switches the retarder to setting 2, and uses the footbrake continuously to hold 60 km/h. After 2 km the pedal feels soft, there is a burning smell, and the speed rises to 75 km/h even with the brake pressed hard. Air pressure is 8.5 bar. The next escape lane is 800 m ahead. The driver's load is 24 t of paper rolls, and the combination has a valid winter tyre setup with 6 mm tread on the drive axle.
1. What is happening, and what should the driver do in the next few seconds?
Read the worked answer
The continuous service brake use has overheated the brakes and produced brake fade: the friction material is too hot to generate the expected retardation, which is why the pedal feels soft, there is a burning smell and the speed is rising despite hard braking. The driver should release the footbrake, keep the retarder at maximum and use the engine brake, and downshift immediately to a much lower gear to increase engine braking. Hazard lights should be switched on. The driver should not use the parking brake at speed, should not coast in neutral, and should not make a sudden steering input. If the speed cannot be brought under control before the escape lane, the escape lane must be used deliberately and early rather than waiting until the speed is too high. With 24 t of paper rolls, a rollover or run-off would be far worse than a controlled stop in the escape lane.
2. How should the descent have been planned and driven from the top?
Read the worked answer
The driver should have stopped before the descent, checked the brakes and air pressure, and selected a low gear that would hold a safe speed without continuous service braking. The retarder and engine brake should have been used together, with the retarder set high enough to do most of the work. A safe speed on an 8% snow-covered descent with 40 t is much lower than 60 km/h; the driver should have been able to stop within the visible distance and should have used short, controlled brake applications only if needed. On snow, the retarder must be used smoothly because it acts on the drive wheels and can cause a skid if it is too aggressive. The driver should also have allowed for the load pushing the combination and for the longer stopping distance on the gradient.
3. After stopping safely, what checks and decisions are required before continuing?
Read the worked answer
The driver should let the brakes cool, keep the vehicle secured, and check for air leaks, damaged brake chambers, overheating and any warning messages. A brake test should be carried out at low speed in a safe area before rejoining the descent. The load and straps must be checked because heavy braking can move paper rolls. The driver should contact the operator, report the brake fade and not continue if the pedal is still soft, the brakes pull to one side or the air pressure behaviour is abnormal. If there is any doubt, recovery is the correct decision. Continuing down a further descent with overheated brakes would turn a warning into a serious incident.