US Bridges

Third Avenue over Seal Slough

Fair

San Mateo County, California · 0.4 MI W Mrnrs Island Bl · Structure no. 35C0152

Built
1985
40 years old
Condition
Fair
inspected May 2023
Type
Slab
Prestressed Concrete Continuous
Length
1,060 ft
16 main spans
Daily traffic
11,290
2015 count
Owner
City
City or Municipal Highway Agency

About this bridge

Third Avenue over Seal Slough is a prestressed concrete continuous slab carrying Third Avenue over Seal Slough in San Mateo County, California. It was built in 1985, so it is 40 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 11,290 vehicles a day, roughly 5% of them trucks, projected to reach 18,170 by 2040. The structure is 1,060 ft (323.1 m) long and 80 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesThird Avenue
CrossesSeal Slough
Location0.4 MI W Mrnrs Island Bl
RouteCity Street 0
CountySan Mateo County
StateCalifornia
Coordinates37.57048, -122.2947
Functional classUrban Minor Arterial

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.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionMay 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating80.4 US tons
Inventory rating35.7 US tons

Structure

Structure typeSlab
MaterialPrestressed Concrete Continuous
DeckConcrete, cast-in-place
Main spans16
Design loadHS 20 + Mod
Structure length1,060 ft (323.1 m)
Longest span70 ft (21.3 m)
Deck width80 ft (24.4 m)
Roadway width66 ft (20.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic11,290 (2015)
Projected traffic18,170 by 2040
Trucks5%
Lanes on structure4
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed3.7 mi (6 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal 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 Third Avenue over Seal Slough built?

It was built in 1985, making it 40 years old in 2025.

What condition is Third Avenue over Seal Slough 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 May 2023.

How much traffic does Third Avenue over Seal Slough carry?

About 11,290 vehicles per day (2015 count), of which roughly 5% are trucks.

How long is Third Avenue over Seal Slough?

The structure is 1,060 ft (323.1 m) long with a longest span of 70 ft (21.3 m) and a deck 80 ft wide.

Who owns Third Avenue over Seal Slough?

It is owned by the City or Municipal Highway Agency.