US Bridges

County Road 99 over Willow Slough

Fair

Yolo County, California · 1 MI N C.R. #29 · Structure no. 22C0038

Built
1975
50 years old
Condition
Fair
inspected November 2021
Type
Slab
Concrete Continuous
Length
144 ft
5 main spans
Daily traffic
2,830
2009 count
Owner
County
County Highway Agency

About this bridge

County Road 99 over Willow Slough is a concrete continuous slab carrying County Road 99 over Willow Slough in Yolo County, California. It was built in 1975, so it is 50 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 2,830 vehicles a day, roughly 10% of them trucks, projected to reach 3,715 by 2043. The structure is 144 ft (43.9 m) long and 33 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesCounty Road 99
CrossesWillow Slough
Location1 MI N C.R. #29
RouteCounty Highway 0
CountyYolo County
StateCalifornia
Coordinates38.60468, -121.78534
Functional classRural Minor Collector

Condition and inspection

Fair

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

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionNovember 2021
Inspection intervalevery 48 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating101.1 US tons
Inventory rating60.7 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans5
Design loadHS 20
Structure length144 ft (43.9 m)
Longest span32 ft (9.8 m)
Deck width33 ft (10.2 m)
Roadway width32 ft (9.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,830 (2009)
Projected traffic3,715 by 2043
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
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 proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was County Road 99 over Willow Slough built?

It was built in 1975, making it 50 years old in 2025.

What condition is County Road 99 over Willow 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 November 2021.

How much traffic does County Road 99 over Willow Slough carry?

About 2,830 vehicles per day (2009 count), of which roughly 10% are trucks.

How long is County Road 99 over Willow Slough?

The structure is 144 ft (43.9 m) long with a longest span of 32 ft (9.8 m) and a deck 33 ft wide.

Who owns County Road 99 over Willow Slough?

It is owned by the County Highway Agency.