US Bridges

State Route 12 over Mokelumne River

Fair

San Joaquin County, California · 10-SJ-012-0.01 · Structure no. 29 0043

Built
1942
83 years old, rebuilt 1978
Condition
Fair
inspected April 2023
Type
Movable - Swing
Steel
Length
1,436 ft
2 main spans
Daily traffic
15,000
2009 count
Owner
State
State Highway Agency

About this bridge

State Route 12 over Mokelumne River is a steel movable - swing carrying State Route 12 over Mokelumne River in San Joaquin County, California. It was built in 1942 and reconstructed in 1978, so it is 83 years old, older 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 15,000 vehicles a day, roughly 14% of them trucks, projected to reach 62,444 by 2043. The structure is 1,436 ft (437.7 m) long and 36 ft wide. If it were closed, the detour would be 34.8 mi (56 km).

Location

Open in Google Maps
CarriesState Route 12
CrossesMokelumne River
Location10-SJ-012-0.01
RouteState Highway 12
CountySan Joaquin County
StateCalifornia
Coordinates38.12689, -121.58239
Functional classRural Principal Arterial - Other

Condition and inspection

Fair

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

ComponentRatingMeaning
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionApril 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation7: Better than present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment3: Basically intolerable, requiring high priority of corrective action
Operating rating69.3 US tons
Inventory rating41.4 US tons

Structure

Structure typeMovable - Swing
MaterialSteel
DeckConcrete, cast-in-place
Main spans2 (+26 approach)
Design loadHS 15
Structure length1,436 ft (437.7 m)
Longest span144 ft (43.8 m)
Deck width36 ft (11 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deck15 ft (4.7 m)

Traffic and service

Average daily traffic15,000 (2009)
Projected traffic62,444 by 2043
Trucks14%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesHighway and waterway
Detour if closed34.8 mi (56 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusEligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was State Route 12 over Mokelumne River built?

It was built in 1942, making it 83 years old in 2025. It was reconstructed in 1978.

What condition is State Route 12 over Mokelumne River 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 April 2023.

How much traffic does State Route 12 over Mokelumne River carry?

About 15,000 vehicles per day (2009 count), of which roughly 14% are trucks.

How long is State Route 12 over Mokelumne River?

The structure is 1,436 ft (437.7 m) long with a longest span of 144 ft (43.8 m) and a deck 36 ft wide.

Who owns State Route 12 over Mokelumne River?

It is owned by the State Highway Agency.