US Bridges

State Route 1 over Millerton Gulch

Fair

Marin County, California · 04-MRN-001-33.40 · Structure no. 27 0114

Built
1997
28 years old
Condition
Fair
inspected May 2024
Type
Culvert
Concrete Continuous
Length
31 ft
2 main spans
Daily traffic
2,300
2020 count
Owner
State
State Highway Agency

About this bridge

State Route 1 over Millerton Gulch is a concrete continuous culvert carrying State Route 1 over Millerton Gulch in Marin County, California. It was built in 1997, so it is 28 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 6 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 2,300 vehicles a day, roughly 3% of them trucks, projected to reach 8,981 by 2045. The structure is 31 ft (9.3 m) long and 35 ft wide. If it were closed, the detour would be 21.7 mi (35 km).

Location

Open in Google Maps
CarriesState Route 1
CrossesMillerton Gulch
Location04-MRN-001-33.40
RouteState Highway 1
CountyMarin County
StateCalifornia
Coordinates38.10927, -122.83971
Functional classRural 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
Channel and channel protection3 SeriousLoss of section, deterioration, spalling or scour have seriously affected primary structural components.
Culvert6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionMay 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment4: Meets minimum tolerable limits to be left in place as is
Operating rating59.6 US tons
Inventory rating35.7 US tons

Structure

Structure typeCulvert
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20 + Mod
Structure length31 ft (9.3 m)
Longest span14 ft (4.3 m)
Deck width35 ft (10.8 m)
Roadway width32 ft (9.7 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,300 (2020)
Projected traffic8,981 by 2045
Trucks3%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed21.7 mi (35 km)
TollOn a free road
National Highway SystemNo

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 State Route 1 over Millerton Gulch built?

It was built in 1997, making it 28 years old in 2025.

What condition is State Route 1 over Millerton Gulch 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 2024.

How much traffic does State Route 1 over Millerton Gulch carry?

About 2,300 vehicles per day (2020 count), of which roughly 3% are trucks.

How long is State Route 1 over Millerton Gulch?

The structure is 31 ft (9.3 m) long with a longest span of 14 ft (4.3 m) and a deck 35 ft wide.

Who owns State Route 1 over Millerton Gulch?

It is owned by the State Highway Agency.