Warning signs
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.
- Diamond
- Yellow
- MUTCD W12-2
Shape and background first
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.
What the MUTCD specifies
Designation: W12-2
MUTCD Section 2C.25
Conventional road size: 36 x 36 in
Standard: Use an advance low clearance sign below 14 ft 6 in of clearance or within 12 in above the legal maximum vehicle height, whichever threshold is greater.
Source: Federal Highway Administration, MUTCD 11th Edition (December 2023), Part 2, Table 2C-1; Section 2C.25, verified 2026-09-26.
How states handle it
The exact clearance height on the plate is measured and posted locally by whichever agency owns the structure, so the number varies bridge to bridge even though the warning sign itself is federally standardized.
What the test wants you to know
The mistake people make
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.
