Bridge Clearance Maps for Trucks: Free Sources Compared (2026)

Search for a “bridge clearance map” and you get a mix of federal data, state DOT spreadsheets, truck GPS apps and permit tools. They are not the same thing. Some are raw inventories, some are lists a state keeps for permit loads, and some are warnings layered onto a route.

For an over-height load the question is never just “how low is that bridge?” It is “which structures are on the route I’m cleared for, how was each one measured, and how fresh is the number?” This guide compares the free sources by those three questions, using only what each agency publishes.

MI 01

Quick comparison

• Federal bridge data (National Bridge Inventory). Nationwide and free, but FHWA itself says not to use it for route clearance.
• State DOT clearance lists and maps. The best published numbers for that state’s roads. Format, coverage and update dates vary by state.
• Posted low clearance signs. What you must obey at the structure. Posting rules differ, and signs can change after resurfacing.
• Truck GPS and routing apps. Convenient warnings for a vehicle profile. Ask each vendor where its clearance data comes from and how it handles loads over legal height.
• Permit tools and permit flags. Useful for checking structures near the route a state already issued. A flag is a prompt to look, not a clearance.
• The issued permit. The authorized route and any height conditions or survey requirements. It wins over every map.

MI 02

Federal bridge data: nationwide, but not for route clearance

The National Bridge Inventory (NBI) is the federal database of highway bridges. You can download it from FHWA’s National Bridge Inventory download page or look bridges up through FHWA’s LTBP InfoBridge data tool. The NBI record format includes fields such as Item 10, “Inventory Rte, Min Vert Clearance,” and Item 54, “Minimum Vertical Underclearance.”

The catch is spelled out on FHWA’s own download page: “NBI data should not be used for route clearance purposes. In general, bridges are inspected every 24 months, so clearance data displayed may not be current.” The same page notes that 2025 was the last year data was submitted in the old ASCII format, as states move to the newer SNBI specifications.

Two more limits matter for haulers. The NBI covers bridges, so it does not list every overhead sign structure, utility line or traffic signal. And a map built on NBI clearances inherits its age. Treat any map that cites NBI as a starting point for questions, not an answer.

MI 03

State DOT clearance lists: the best published numbers

Many states publish their own low clearance lists, often aimed at permit loads. A few examples, all checked October 29, 2026:

• Iowa. The Iowa DOT motor carrier maps page links a vertical clearance log (PDF and spreadsheet), a separate log for overhead signs and mast arms, clearance diagrams, and vertical clearance maps for Interstates and primary roads.
• California. The Caltrans height and low clearances page lists state-route clearances of 14 feet 0 inches or less by route, county, postmile and direction. It says the numbers are measured from the edge of the traveled way, that clearance at the shoulder may be lower, and that the list does not include local roads running under state routes.
• Texas. TxDMV’s low vertical clearance page lists low clearance structures for each of TxDOT’s 25 districts and points to a statewide map with a “Vertical Clearance” overlay. Its disclaimer says a structure’s status may change before the website is updated.
• Wyoming. The WYDOT limited vertical clearances table can be filtered by height, route and county, and shows a measurement date for each structure, including sign structures, tunnels and interchanges.
• North Dakota. The NDDOT bridge vertical clearance page lists the bridge permittable vertical clearance, which it describes as the maximum height the ND Highway Patrol will permit when you buy an over-height permit. It warns that construction and weather can change conditions.

Read the notes on any state list before you trust a number: where it was measured (lane, edge of traveled way, shoulder), what it covers (state routes only, or local roads too), and when it was last updated. Then match each structure to the roads actually written on your permit. On a Multi-State Oversize Permits: Reading Each State's Permit trip, each state’s list only covers that state.

MI 04

Posted signs: what you obey, and why numbers differ

The federal sign manual sets the baseline. The MUTCD 11th Edition, Section 2C.25 (PDF) says the Low Clearance Advance sign shall be used for clearances under 14 feet 6 inches, or under 12 inches above the statutory maximum vehicle height, whichever is greater. It says the sign should show the actual clearance to the nearest inch without exceeding it, with a reduction of up to 3 inches where frost action changes the road surface.

States add their own practice on top. TxDOT’s sign manual section on vertical clearance says the signed clearance should be three inches less than the measured clearance, as a buffer for future overlays, and that clearances must be re-measured after construction or maintenance that could affect them.

So the sign, the state list and a map can all show different numbers for the same bridge, and none of them is necessarily wrong. The sign at the structure is the one you must obey. If your load is close to any of the numbers, stop and confirm with the permit office before you roll, not at the overpass.

MI 05

Truck GPS and routing apps: ask where the numbers come from

Routing and navigation apps can warn about low clearances for a truck profile, which is helpful for legal-size freight. For a permit load, ask any vendor the same questions before relying on its map:

• Where does the clearance data come from (state lists, NBI, field reports, its own surveys), and how often is it refreshed?
• Does it include overhead sign structures, signals and wires, or bridges only?
• What is the maximum vehicle height its profile accepts?
• Can it follow the exact road sequence on an issued permit without recalculating around it?

Our guides to Oversize Load Routing Software: What It Plans vs Your Permit and After Routing Software Plans the Move: Reading the Issued Permit cover why a planned route and a permitted route can differ.

MI 06

The permit and permit flags: check what is on your route

When a state issues a routed oversize permit, the roads written on it are the authorized route. Some permits also carry height conditions, such as a required route survey or instructions for specific structures. Read those first. Our guide on How to Read an Oversize Load Permit shows where they usually sit.

JaloPermit is a reading aid for issued permit PDFs. After it lays out the route on one card, it flags rated low-bridge clearances near that route and checks them against the load height. There is also a JaloPermit Bridges page in the app. Use those flags as a list of structures to double-check against the state’s own list and the posted signs. A missing flag does not prove clearance, and a flag does not replace any survey the permit requires.

For the rest of pre-trip planning, see Plan an Oversize Load Route That Matches Your Permit and Check Oversize Permit Curfews & Travel Restrictions Fast.

MI 07

A five-minute clearance check for an over-height load

1. Measure the loaded height yourself and compare it with the height on the permit.
2. List every road on the permitted route, in order.
3. Pull the state DOT clearance list or map for each state on the trip, and note anything within a few inches of your height.
4. Read the list’s notes: where it measured, what it covers, and when it was updated.
5. Read the permit’s height conditions and any survey requirement.
6. Obey posted signs at every structure. If anything is close or conflicting, call the issuing permit office before you move.

JaloPermit, which publishes this guide, is a reading aid for issued permit PDFs. It is not a permit-filing service and it does not plan routes or provide navigation. The issued permit always wins.

MI 08

FAQs