What do bells hanging across the road warn drivers of?

Explanation: If your vehicle touches bells suspended over the road, they'll obviously ring. This will warn you that your vehicle exceeds the safe travelling height beneath electrified overhead cables ahead. You must stop immediately and either find another route or take advice.

Category: Vehicle Weights and Dimensions

References: The Official DVSA Guide to Driving Buses and Coaches: Section 3, The Official DVSA Guide to Driving Goods Vehicles: Section 2, Know Your Traffic Signs: Page 26