A tall, heavy bus is especially vulnerable in slippery conditions, fog, strong crosswind and rain. Here is the complete driving technique: adapted speed and distance, soft control, fog lamp rules, crosswind's grip on a high bus side, aquaplaning and driving with reduced visibility.
Introduction
The braking distance article shows how road grip (µ) controls braking distance, and the manoeuvring article covers geometry and blind spots. This article brings together what happens when the weather works against you: ice and snow, fog, strong side wind, rain and darkness. A bus is high, heavy and has a large side surface — precisely the properties that make it especially vulnerable under difficult conditions. Defensive driving and adaptation to road and weather conditions are part of the basic qualification's subject area on rational, safe driving.
The basic rule: match speed and distance
Regardless of what weather phenomenon you encounter, the two most important handles are the same: reduce speed and increase distance. In wet or slippery conditions braking distance drops significantly (see the µ table in the stopping distance article), so your stopping distance increases — and in a heavy bus it is already long. Therefore at least double the distance to the vehicle ahead in wet conditions, and make it even greater in snow and on ice. Drive so you can always stop within the distance you can see.
Slippery conditions — ice and snow
On snow and ice the road grip is a fraction of the dry and a heavy bus with many standing passengers can neither brake steer nor accelerate hard without losing grip. Everything must be done gently: gentle accelerator gentle brake gentle steering movements. Brake in good time and preferably with engine brake/retarder rather than just service brake so you avoid locking the wheels (ABS helps but does not remove the physics). Be particularly careful on bridges in shade and at stops where snow is packed into ice.
- 01All soft — speedo, brake and steering; avoid sudden inputs.
- 02Brake early, preferably with engine brake/retarder to save the linings.
- 03Extra distance — the braking distance is multiplied many times on ice.
- 04Watch out for bridges, shadows and stops where ice forms first.
- 05Standing passengers tip easily under hard braking — another reason to drive softly.
Fog and reduced visibility
In fog the problem is that you can neither see nor be seen. Reduce speed so you can stop within the distance you can actually see, and use dipped headlights — full beam reflects back in the fog and blinds you. Fog lights may be used with reduced visibility. The rear fog light is powerful and may only be used when visibility is severely reduced (the traffic regulations specify a limit — turn it off when visibility improves, so you don't blind following drivers). Keep good distance, and avoid overtaking when you cannot see the road ahead.
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