US Bridges

Mariposa ST over Caltrain & UP RR

Poor

San Francisco County, California · At SR 280 · Structure no. 34C0005

Built
1968
57 years old
Condition
Poor
inspected December 2024
Type
Box Beam or Girders - Multiple
Concrete Continuous
Length
100 ft
2 main spans
Daily traffic
20,000
2017 count
Owner
County
County Highway Agency

About this bridge

Mariposa ST over Caltrain & UP RR is a concrete continuous box beam or girders - multiple carrying Mariposa ST over Caltrain & UP RR in San Francisco 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 poor condition with a lowest component rating of 4 out of 9. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

It carries about 20,000 vehicles a day, roughly 10% of them trucks, projected to reach 26,809 by 2042. The structure is 100 ft (30.5 m) long and 71 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesMariposa ST
CrossesCaltrain & UP RR
LocationAt SR 280
RouteCity Street 0
CountySan Francisco County
StateCalifornia
Coordinates37.76401, -122.39328
Functional classUrban Minor Arterial

Condition and inspection

Poor

The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

ComponentRatingMeaning
Deck4 PoorAdvanced section loss, deterioration, spalling or scour.
Superstructure8 Very GoodNo problems noted.
Substructure7 GoodSome minor problems.
Last inspectionDecember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation7: Better than present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Approach roadway alignment6: Equal to present minimum criteria
Operating rating100.3 US tons
Inventory rating60 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length100 ft (30.5 m)
Longest span51 ft (15.4 m)
Deck width71 ft (21.6 m)
Roadway width55 ft (16.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic20,000 (2017)
Projected traffic26,809 by 2042
Trucks10%
Lanes on structure5
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesRailroad
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedRehabilitation because of general structure deterioration or inadequate strength
Estimated improvement cost$1.1 million (2017 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was Mariposa ST over Caltrain & UP RR built?

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

What condition is Mariposa ST over Caltrain & UP RR in?

The National Bridge Inventory rates it in poor condition. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. The last reported inspection was in December 2024.

How much traffic does Mariposa ST over Caltrain & UP RR carry?

About 20,000 vehicles per day (2017 count), of which roughly 10% are trucks.

How long is Mariposa ST over Caltrain & UP RR?

The structure is 100 ft (30.5 m) long with a longest span of 51 ft (15.4 m) and a deck 71 ft wide.

Who owns Mariposa ST over Caltrain & UP RR?

It is owned by the County Highway Agency.