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What effect does an oncoming heavy vehicle have? What effect does an oncoming heavy vehicle have?

  • A. Nothing - the frontal area of a bike is small compared to a car

  • B. The wind will initially push you away, then suck you towards the vehicle

  • C. The wind will initially suck you towards the vehicle, then push you away

    The correct answer is B
    Correct. The pressure front at the front of the vehicle will push you away, but the slipstream behind it will suck you towards it.

Pressure waves from oncoming trucks

This video shows how a truck affects the air around it with different aerodynamic aids. You can get the idea of the truck pushing a wave of air in front of it - this is pressurised air that will push you away. Behind it there is rarefied air which is low pressure and will suck you towards it. At the sides of the truck it is dragging low-pressure air along.

The other dangers with an approaching truck are that the size of the truck can obscure vehicles travelling behind it, and obscure you from them. Adjust your road position to the left to be more visible to vehicles following the truck, and to give you more of a buffer. If the road is narrow, this is even more important.

In wet weather the effect of an oncoming truck might also be to throw up spray which can temporarily blind you. This spray will also be affecting any vehicle following the truck.