Bridge conditions in Boulder County, Colorado
321 inventoried bridges · 7 rated poor · 2025 National Bridge Inventory
United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled
The federal inventory lists 321 bridges in Boulder County: 103 rated good, 211 fair, and 7 poor.
- 7 of the 321 bridges in Boulder County, Colorado, are rated in poor condition (2.2%) in the 2025 National Bridge Inventory, as of .
- 103 bridges (32.1%) are rated good and 211 (65.7%) fair.
- The median Boulder County bridge was built in 1990.
- The busiest poor-rated bridge is US 36 Ml Wbnd over Boulder Creek (built 1952), carrying about 18,000 vehicles a day.
Good 32.1% · Fair 65.7% · Poor 2.2% of 321 bridges
Bridges rated poor
Every bridge in the county with a poor rating, busiest first. Poor means a major component is rated 4 or lower on FHWA's 0-9 scale; it is a repair flag, not a closure notice.
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| US 36 Ml Wbnd over Boulder Creek | 1952 | 18,000 | Poor |
| SH 7 Ml Wbnd over Boulder Creek | 1938 | 15,000 | Poor |
| 3rd Ave WB over Gw RR | 1974 | 9,116 | Poor |
| Rock Creek Pkwy over Community Ditch | 2000 | 7,760 | Poor |
| South Bowen Street over Left Hand Creek | 1965 | 1,835 | Poor |
| No. 30th Street over Four Mile Creek | 1973 | 1,424 | Poor |
| US 36 Fr Rd over Boulder Creek SR | 1952 | 1,264 | Poor |
Busiest bridges in the county
| Bridge | Built | Vehicles/day | Condition |
|---|---|---|---|
| US 36 Ml over South Boulder Creek | 1951 | 77,000 | Good |
| US 36 Ml over Davidson Ditch | 2015 | 77,000 | Good |
| US 36 Ml over Coal Creek | 2015 | 66,000 | Good |
| US 36 Ml over Canyon Creek | 1951 | 45,000 | Fair |
| Table Mesa Drive over US 36 Ml | 1951 | 44,000 | Fair |
| SH 157 Ramp over US 36 Ml | 1971 | 44,000 | Fair |
| SH 157 Ml over Skunk Creek | 1978 | 43,000 | Fair |
| SH 157 Ml over Pearl Street | 1985 | 43,000 | Fair |
| SH 157 Ml over BNSF RR | 1981 | 43,000 | Fair |
| SH 157 Ml over Boulder Creek | 1981 | 43,000 | Fair |
Source: FHWA National Bridge Inventory, 2025. Counts cover inventoried highway bridges over 20 feet; ratings are reported by the state DOT.
All of Colorado: Colorado bridge conditions by county · every download on the data page.
Background: how bridge ratings work · what "poor" and "structurally deficient" actually mean · how often bridges are inspected.