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Driving safety guide · Michigan City Ford · Michigan City, IN
Low Clearance Signs Explained
A low bridge or overpass is a real risk for anyone driving a tall vehicle, towing a camper or carrying a roof load. Here is what the federal Manual on Uniform Traffic Control Devices (MUTCD) says about the signs that warn of low vertical clearance.
14 ft 6 inthe W12-2 threshold, or 12 in over the statutory maximum vehicle height if greater
1 inchthe posted clearance should be shown to the nearest inch, never above the actual
Up to 3 inthe reduction that should be used where frost action changes clearance
W12-2a / W12-2boverhead signs that may be mounted on the structure
The short answer
A low clearance sign warns that a structure ahead has limited vertical clearance. The MUTCD says the Low Clearance Advance (W12-2) sign shall be used for clearances less than 14 feet 6 inches, or less than 12 inches above the statutory maximum vehicle height, whichever is greater. The posted figure should be the actual clearance to the nearest inch without exceeding it, reduced by up to 3 inches where frost action occurs. Overhead W12-2a or W12-2b signs may be mounted on the structure itself.
When a low clearance sign is used
The rule: the Low Clearance Advance (W12-2) sign shall be used to warn road users of vertical clearances less than 14 feet 6 inches, or vertical clearances less than 12 inches above the statutory maximum vehicle height, whichever is greater.
Who should pay attention: the sign matters most if you drive a tall vehicle or carry something on the roof or on a trailer. Know the total height of your vehicle and load before you head out, and compare it with the posted clearance.
From the Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition with Revision 1, Section 2C.25, read November 4, 2026.
How the posted height is set
Rounded down: the actual clearance should be displayed on the sign to the nearest 1 inch, not exceeding the actual clearance.
Frost action: in areas that experience changes in temperature causing frost action, a reduction not exceeding 3 inches should be used for this condition.
Rechecked over time: clearances should be evaluated periodically to decide whether more low clearance signing is needed, particularly after resurfacing, on routes onto which over-height vehicles are normally directed under the permit process, and at structures susceptible to catastrophic failure when struck by over-height vehicles.
From the Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition with Revision 1, Section 2C.25, read November 4, 2026.
The three low clearance signs
The MUTCD describes three low clearance signs:
| Sign | What the MUTCD says |
|---|---|
| Low Clearance Advance (W12-2) | The required advance warning sign. A diamond-shaped warning sign, listed at 36 x 36 inches on conventional roads. |
| Low Clearance Overhead (W12-2a) | May be installed on the structure to supplement the advance warning sign. Listed at 84 x 24 inches. |
| Low Clearance - Lane Overhead (W12-2b) | If used, shall be placed over a lane or shoulder to indicate the portion of the structure with low clearance if the posted clearance does not apply to the entire structure. Listed at 102 x 24 inches. |
From the Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition with Revision 1, Section 2C.25 and Table 2C-1, read November 4, 2026. Under an arch or another structure where the clearance varies greatly, two or more overhead signs should be installed to show the clearances over the low portions of the roadway, and the advance sign should match the overhead sign or, with several W12-2b signs, the lowest clearance.
Detour points and intersecting roads
A place to turn: the W12-2 sign with a supplemental distance plaque should also be placed at the nearest intersecting road or wide point in the road at which a vehicle can detour or turn around.
On side roads and exits: where there is a need to warn of a low clearance on an intersecting road or off a freeway or expressway exit, a rectangular warning sign with an appropriate word legend should be used rather than a W12-2 sign.
Tight structures: where a structure is too narrow for the overhead signs to fit, a W12-2 sign may be installed overhead on the structure or post-mounted in front of it, in addition to the required W12-2 sign at the advance location.
From the Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition with Revision 1, Section 2C.25, read November 4, 2026.
Keep your truck or SUV ready for the road
The Works® at Michigan City Ford includes a synthetic blend oil change, tire rotation and pressure check, brake inspection, Multi-Point Inspection, fluid top-off, battery test, and a filter, belts and hoses check.
Schedule service online and see our service specials first. Michigan City Ford is at 3930 Franklin St. in Michigan City. Get directions.
Michigan City Ford service hours
| Days | Hours |
|---|---|
| Mon-Fri | 7:30 a.m.-5:30 p.m. |
| Sat | 8 a.m.-3 p.m. |
| Sun | closed |
From Michigan City Ford's website, November 4, 2026. Holiday hours can differ.
Low clearance sign FAQ
What does a low clearance sign mean?
It warns that an overhead structure ahead has a low vertical clearance. The sign shows the clearance, and drivers of tall vehicles need to know whether their vehicle, including any load or roof equipment, will fit under it.
When is a Low Clearance sign required?
The MUTCD says the Low Clearance Advance (W12-2) sign shall be used to warn of vertical clearances less than 14 feet 6 inches, or less than 12 inches above the statutory maximum vehicle height, whichever is greater.
Is the posted clearance exact?
The MUTCD says the sign should show the actual clearance to the nearest 1 inch, not exceeding the actual clearance. In areas where temperature changes cause frost action, a reduction of up to 3 inches should be used.
What is the difference between W12-2, W12-2a and W12-2b?
The W12-2 is the advance warning sign. The Low Clearance Overhead signs, W12-2a and W12-2b, may be installed on the structure itself to supplement it. If used, the W12-2b shall be placed over a lane or shoulder to show the part of the structure with low clearance when the posted clearance does not apply to the entire structure.
What if a tall vehicle cannot fit?
The MUTCD says the W12-2 sign with a supplemental distance plaque should also be placed at the nearest intersecting road or wide point where a vehicle can detour or turn around, so watch for that sign and plan another route.
Why can the clearance change over time?
The MUTCD says clearances should be evaluated periodically, particularly when resurfacing operations have occurred, on routes where over-height vehicles are normally directed under the permit process, and at structures susceptible to catastrophic failure when struck by over-height vehicles.
What does The Works at Michigan City Ford include?
The Works® at Michigan City Ford includes a synthetic blend oil change, tire rotation and pressure check, brake inspection, Multi-Point Inspection, fluid top-off, battery test, and a filter, belts and hoses check.
Book a routine checkup
Book The Works, which includes a brake inspection, tire rotation and pressure check, and battery test, at Michigan City Ford.
Sources
Sign descriptions are from the Federal Highway Administration's Manual on Uniform Traffic Control Devices, 11th Edition with Revision 1 (Revision 1 dated December 2025), read November 4, 2026. This page is a plain-language summary of national standards, not legal advice; state law sets the rules of the road where you drive. Service details, address and hours are from Michigan City Ford's own website, checked the same day. Photo is illustrative.
- Manual on Uniform Traffic Control Devices (MUTCD), 11th Edition with Revision 1 (Sections 1D.05, 2C.01, 2C.02, 2C.25 and Table 2C-1), Federal Highway Administration, Revision 1 dated December 2025 (PDF updated February 12, 2026), read November 4, 2026
- General service: The Works, Michigan City Ford, November 4, 2026
- Address and service hours (structured data), Michigan City Ford, November 4, 2026