Humpback bridge

A humpback bridge rises sharply and falls away just as sharply, usually over a canal or a railway. The warning sign is a red triangle showing the arch. What makes it a hazard is simple geometry: at the top you cannot see the road on the far side, and neither can anyone coming the other way.

So treat the crown as blind. Slow down on the approach, keep to the left, and do not overtake — there may be an oncoming vehicle, a cyclist or a pedestrian immediately beyond. Many of these bridges are also narrow enough that two vehicles cannot pass on them at all, so be ready to give way.

For long or low vehicles there is a second problem: a long wheelbase can ground on the crown as the vehicle pivots over it, and a low one can scrape. Where that risk exists the bridge carries additional signs, and they are worth reading rather than assuming your vehicle will clear.