Which road surface may cause anti-lock brakes to be less effective?

Explanation: If the road surface is loose, it's possible for the loose surfaces to slide over each other. A vehicle's tyres may grip the surface layer but this may slide across a lower layer. An anti-lock braking system would be less effective in this situation.

Category: Band 2 traffic signs and signals

References: The official DVSA guide to driving: section 5, Highway code: rule 120