US Bridges

N1-S280 Connector over Southgate Avenue

Fair

San Mateo County, California · 04-SM-001-R47.62-DLC · Structure no. 35 0238G

Built
1968
57 years old
Condition
Fair
inspected October 2024
Type
Box Beam or Girders - Multiple
Concrete Continuous
Length
156 ft
3 main spans
Daily traffic
3,850
1998 count
Owner
State
State Highway Agency

About this bridge

N1-S280 Connector over Southgate Avenue is a concrete continuous box beam or girders - multiple carrying N1-S280 Connector over Southgate Avenue in San Mateo County, California. It was built in 1968, so it is 57 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 3,850 vehicles a day, roughly 2% of them trucks, projected to reach 5,100 by 2042. The structure is 156 ft (47.4 m) long and 26 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesN1-S280 Connector
CrossesSouthgate Avenue
Location04-SM-001-R47.62-DLC
RouteState Highway 1
CountySan Mateo County
StateCalifornia
Coordinates37.67566, -122.47244
Functional classUrban Principal Arterial - Other Freeway or Expressway

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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionOctober 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating47.5 US tons
Inventory rating36.8 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length156 ft (47.4 m)
Longest span88 ft (26.8 m)
Deck width26 ft (7.9 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,850 (1998)
Projected traffic5,100 by 2042
Trucks2%
Lanes on structure1
Traffic directionOne-way traffic
CarriesHighway
CrossesHighway
Detour if closed1.9 mi (3 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNot applicable (no waterway)

Frequently asked questions

When was N1-S280 Connector over Southgate Avenue built?

It was built in 1968, making it 57 years old in 2025.

What condition is N1-S280 Connector over Southgate Avenue 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 October 2024.

How much traffic does N1-S280 Connector over Southgate Avenue carry?

About 3,850 vehicles per day (1998 count), of which roughly 2% are trucks.

How long is N1-S280 Connector over Southgate Avenue?

The structure is 156 ft (47.4 m) long with a longest span of 88 ft (26.8 m) and a deck 26 ft wide.

Who owns N1-S280 Connector over Southgate Avenue?

It is owned by the State Highway Agency.