Loaded Van Behind a Spraying Truck at -28°C
You are driving a loaded van from Ulaanbaatar to Darkhan on a paved highway. The posted limit is 80 km/h. It is -28°C with light snow; the road has wheel-track ice, and blowing snow cuts visibility to about 150 m. You are following a truck and trailer whose rear lights are dim and partly covered in snow; it throws up spray. Your GPS shows the next fuel station is 90 km away. Three passengers are asleep. The truck brakes suddenly for a pothole. You are 60 m behind it. Your speedometer reads 78 km/h. The van's tyres are all-season, with about 4 mm of tread. You have winter clothes and a full tank. There is no mobile signal for the last 20 km.
1. What speed and following distance should you be using now? Show the reasoning with numbers.
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At 78 km/h you are covering about 21.7 m/s. On ice, a sensible minimum gap is eight seconds, not the dry-road three or four seconds. Eight seconds at 21.7 m/s is roughly 174 m, far more than the 60 m you currently have. You also need to stop within the distance you can see. From 80 km/h on ice, braking distance can be around 126 m with poor grip, plus about 22 m of reaction distance, which is close to or beyond your 150 m visibility.
Reduce speed to about 40-50 km/h. At 50 km/h you cover 13.9 m/s; an eight-second gap is about 111 m, and stopping distance is much shorter. Keep low-beam headlights on; high beam reflects off snow and spray and makes things worse.
2. The truck brakes suddenly. What is your immediate sequence of actions?
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Brake gently and progressively, not sharply. A sharp brake on ice can trigger a skid or force the ABS to work harder, and it gives the vehicle behind less warning. Keep the steering straight and avoid swerving onto the shoulder, where snow may hide a ditch or a frozen rut.
Ease off the accelerator and increase the gap immediately. If you must stop, brake early and smoothly, then switch on hazard lights once stopped. Check your mirrors for the vehicle behind you. Do not try to overtake the truck while it is braking or immediately afterwards; the spray and ice make that worse, not better.
3. Should you overtake the truck in this visibility? Explain your decision.
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No. Visibility is about 150 m, the truck is throwing spray, its rear lights are dim, and the road has wheel-track ice. An overtake needs a clear view and enough space to complete the manoeuvre without exceeding the limit or forcing anyone to brake. At 78 km/h you would need several hundred metres of clear road, and the spray would blind you as you pulled out.
Wait behind at a safe gap, or stop for fuel and rest. Do not use high beam to pressure the truck driver. The lack of mobile signal also means that if something goes wrong, help will be slow to arrive, which is another reason to reduce risk rather than take it.