US Bridges

Duncan Road over California Aqueduct

Fair

San Bernardino County, California · 1.25 MI W Baldy Mesa RD · Structure no. 54C0496

Built
1971
54 years old
Condition
Fair
inspected February 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
134 ft
2 main spans
Daily traffic
236
2014 count
Owner
Local
Other Local Agency

About this bridge

Duncan Road over California Aqueduct is a prestressed concrete stringer/multi-beam or girder carrying Duncan Road over California Aqueduct in San Bernardino County, California. It was built in 1971, so it is 54 years old, younger than the California average of 54.8 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 5 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 236 vehicles a day, roughly 1% of them trucks, projected to reach 318 by 2042. The structure is 134 ft (40.8 m) long and 32 ft wide. If it were closed, the detour would be 6.2 mi (10 km).

Location

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CarriesDuncan Road
CrossesCalifornia Aqueduct
Location1.25 MI W Baldy Mesa RD
RouteCounty Highway 0
CountySan Bernardino County
StateCalifornia
Coordinates34.46987, -117.47249
Functional classRural Major Collector

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection9 ExcellentNo problems noted.
Last inspectionFebruary 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry6: Equal to present minimum criteria
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating60 US tons
Inventory rating36 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length134 ft (40.8 m)
Longest span66 ft (20.1 m)
Deck width32 ft (9.9 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic236 (2014)
Projected traffic318 by 2042
Trucks1%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed6.2 mi (10 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerOther Local Agency
Maintained byCounty Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Duncan Road over California Aqueduct built?

It was built in 1971, making it 54 years old in 2025.

What condition is Duncan Road over California Aqueduct in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in February 2024.

How much traffic does Duncan Road over California Aqueduct carry?

About 236 vehicles per day (2014 count), of which roughly 1% are trucks.

How long is Duncan Road over California Aqueduct?

The structure is 134 ft (40.8 m) long with a longest span of 66 ft (20.1 m) and a deck 32 ft wide.

Who owns Duncan Road over California Aqueduct?

It is owned by the Other Local Agency and maintained by the County Highway Agency.