Low Clearance sign
A bridge, overpass or tunnel ahead has limited vertical height. Drivers of trucks, buses and other tall vehicles must check the posted clearance before continuing.
Federal designation W12-2 in the MUTCD, the national standard every state signs to. Mounted at railroad underpasses, older bridges and parking structure entrances where the structure itself, not a rule, sets a hard physical limit.
How to recognise it
This sign is a diamond stood on its point in yellow, the warning colour. Yellow diamonds telling you what the road is about to do. They are advisory rather than mandatory, but ignoring them is how people end up in ditches and how examiners end up failing you.
What the test wants you to know
The number that matters is the lowest point measured under the structure, not the average, so a beam or pipe crossing lower than the rest of the span sets the real limit. This sign is aimed at commercial and oversize vehicles rather than ordinary cars, which is the fact most exam questions are actually checking.
Practise it
Reading about a sign is not the same as recognising it in half a second with an examiner watching. Every state road signs test on this site shows the sign and asks you to name it, then shows four faces and asks you to pick the right one.
Right Curve
Left Curve
Cross Road
Side Road
Merge
Lane Ends