Convert an existing-culvert field assessment into a transparent FHWA recommendation for maintenance, repair, rehabilitation, replacement, or Level 2 investigation. The workflow follows FHWA-CFL/TD-10-005 and the Culvert Assessment module in the FHWA Hydraulic Toolbox.
Condition decision support - not a capacity calculation
Assessment results
Enter the field ratings and performance observations, then select Assess Culvert.
How the FHWA decision process works
- Rate each applicable barrel and appurtenance element as Good, Fair, Poor, Critical, Unknown, or Not Applicable. The lowest elemental rating governs.
- Identify performance problems. Debris, localized sediment, buoyancy damage, alignment, overtopping, and local scour can trigger Level 1 maintenance or repair independently of the condition rating.
- Stop for a Level 2 investigation when indicators such as embankment piping, channel degradation, a migrating headcut, aggradation, exposed footing, rapid deterioration, or inadequate access are present.
- For Poor or Critical barrels, apply the all-material screen and then the material-specific repair logic. Size, cover, access, deterioration extent, overtopping, and embankment damage determine whether lining, localized man-entry repair, or replacement is carried forward.
- If replacement is reached, use excavation needs, workspace, traffic closure constraints, and nearby trenchless work to screen open-trench versus trenchless construction.
Scope and safety limits
The source procedure covers roadway culverts with spans less than 20 feet. It is a rapid project-level screen, not structural certification, load rating, confined-space guidance, or hydraulic design.
A Critical rating or observed collapse risk demands immediate owner/emergency response. Never enter a culvert without the training, permits, atmospheric testing, equipment, and site controls required by the owner and applicable safety regulations.
FHWA rating meanings
| Rating | General meaning |
|---|---|
| Good | Like new, structurally sound, and functionally adequate. |
| Fair | Some deterioration, but structurally sound and functionally adequate. |
| Poor | Significant deterioration or functional inadequacy requiring repair action. |
| Critical | Possible imminent failure threatening public safety; immediate action is required. |
| Unknown | The element is inaccessible or a defensible rating cannot be assigned. |
Frequently asked questions
Does this calculator determine culvert capacity or headwater?
No. It reproduces the FHWA Level 1 condition and performance decision workflow for an existing culvert. Capacity, headwater, overtopping frequency, and replacement size require a separate hydrologic and hydraulic analysis, typically with FHWA HY-8 or another accepted model.
How is the overall condition rating selected?
FHWA assigns Good, Fair, Poor, Critical, Unknown, or Not Applicable to the relevant elements. The lowest elemental rating governs the culvert rating. Unknown means an adequate rating could not be assigned; it is not the same as Good.
What is the difference between Level 1 and Level 2?
Level 1 is a rapid visual field assessment and routine action screen. Level 2 requires specialists in hydraulics, geotechnical engineering, structures, or materials, and may require special access equipment or further testing.
When does FHWA favor replacing a small culvert?
The default flowchart screens a Poor or Critical culvert at 36 inches of rise or less. A small culvert with 4 feet of cover or less and no headwalls generally proceeds to replacement; a small culvert without access for lining also proceeds to replacement. Project conditions and agency criteria still require engineering judgment.
Can this tool replace a qualified culvert inspection?
No. Ratings must come from a safe field assessment by appropriately trained personnel. Do not enter a culvert or approach a potentially unstable roadway or embankment solely to complete this screening tool.
Standards and related tools
FHWA-CFL/TD-10-005
Culvert Assessment and Decision-Making Procedures Manual - governing source.
FHWA HY-8
Separate FHWA software for culvert capacity, headwater, and hydraulic design.
Culvert Outlet Control
Evaluate an outlet-control headwater case after condition screening.
Outlet Protection
Design HEC-14 riprap protection when local outlet scour needs correction.
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Last verified: August 2026