Haukelifjell in February: snowplough, slush and 4 mm tyres
It is 14:20 on a Friday in February. You are driving a fully loaded estate car westbound over a mountain pass. You have three passengers, a roof box, and Nordic friction winter tyres with 4 mm tread left. The temperature has risen from –8 °C to +1 °C in the last hour, wet snow is falling, and the wind gusts from the side. You are in a queue behind a snowplough doing 35–40 km/h with amber flashing lights. The road behind the plough is bare; you cannot see the surface ahead of it at all. Behind you a van is sitting about 8 metres off your bumper. An overhead sign at the last junction warned that the pass can close at short notice, and your fuel gauge shows a quarter tank with 40 km to the next station. The next lay-by is 3 km ahead.
1. Should you overtake the snowplough? Give your reasoning, not just a yes or no.
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No. Three things make this the wrong overtake even though the queue is frustrating you:
- You cannot see the road you would be driving into. The plough is clearing the surface ahead of it; everything in front of the blade is uncompacted snow and possibly drifting. Overtaking means committing to an unknown surface at speed with a loaded car.
- The plough's path is unpredictable. It may move towards the centre to clear the crown, throw snow sideways, or turn off without much warning. Drivers who overtake ploughs regularly end up in the ditch on the far side of the pass.
- Your car is not in a state to bail you out. A roof box raises the centre of gravity and catches the crosswind, and 4 mm friction tyres with a full load on wet slush are already at the limit of what you want.
Add the context: at +1 °C the slush is the most slippery thing on the road, the pass can close behind you, and you have a quarter tank. The correct decision is to sit 4–5 seconds back, accept 40 km/h, and use the lay-by 3 km ahead to let the van past if it is still glued to your bumper.
2. Assess the tyre and vehicle situation. Is 4 mm acceptable, and what specifically should you change?
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4 mm is legal but not comfortable. The Norwegian minimum tread depth for a passenger car is 1.6 mm, so you are not breaking a rule. But that figure is a legal floor, not a winter standard: friction (Nordic) winter tyres lose a large part of their grip on snow and slush once they drop below roughly 4–5 mm, because the lamellas and the soft compound that do the work are worn down. On wet slush at +1 °C the dominant risk is slushplaning - the tyre rides up on the film instead of clearing it - and shallow tread makes that happen at lower speed.
Concretely:
- Cut your speed now rather than when you feel the car move. Slushplaning gives almost no warning.
- Check the pressures when you next stop; they drop roughly 0.1 bar per 10 °C of falling temperature, and under-inflation makes aquaplaning worse.
- Turn off cruise control. On a variable surface you want your foot on the pedal.
- Plan for new winter tyres before next season, and treat the roof box as a reason to drive slower, not a reason to drive faster.
- Fuel: at a quarter tank in a closed-pass scenario you have no margin for a long detour or hours of idling in a queue.
3. The van behind stays 8 metres from your bumper. What do you do, and what do you not do?
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What you do: open up your own gap to the plough to 4–5 seconds. This sounds backwards, but it is what breaks the chain: a bigger gap in front lets you brake gently and progressively over a long distance, which gives the tailgating van time to react. If you keep a short gap and the plough slows suddenly, you brake hard and the van hits you.
Also: indicate early, use the lay-by 3 km ahead and wave the van past. Getting a tailgater in front of you is a win - the risk is then his problem and no longer yours, and you are not the one who gets shunted if the plough stops.
What you do not do:
- Do not brake-check. On slush that is how you cause the collision you are trying to avoid.
- Do not switch on the rear fog light to «teach him a lesson». In Norway the rear fog light may only be used when visibility genuinely requires it, and at 8 metres you will blind him and make his distance judgement worse.
- Do not speed up to escape him. On this surface, speed is your only remaining safety margin, and you would be spending it on someone else's mistake.