Structure 35 0126 · San Mateo County, CA

US 101 Mcdonnell over Millbrae Slough

Carries US 101 Mcdonnell over Millbrae Slough, 04-sm-101-18.09-mlbr.

Overall conditionFair

Set by its lowest-rated component: Culvert at 5 of 9.

How ratings work
Culvertsets the rating5/9 · Fair
Channelnot part of overall7/9 · Good
0 failed4 poor6 fair9 excellent

Elevation

Side view, colored by inspection rating
CAR · 15 FT34 FT ACROSS25 FT0ELEVATION · LENGTHS TO SCALE
Culvert 5/9

A culvert 34 ft across with 3 openings. Lengths and the car on the deck are drawn to the same scale. Each part is colored by its latest inspection rating. The inventory records lengths but not heights, so those are drawn as typical for a culvert.

Built1947rebuilt 1961
Length34.1 ft10.4 m
Daily traffic226,000counted 2009
Last inspectedApril 2023every 24 months

Location

StateCalifornia
CountySan Mateo
Location04-sm-101-18.09-mlbr
CarriesUS 101 Mcdonnell
CrossesMillbrae Slough
Coordinates37.60406, -122.38226

Physical Characteristics

MaterialConcrete Continuous
DesignCulvert
Total Length34.1 ft (10.4 m)
Max Span9.8 ft (3 m)
Deck Area266.2 sq m
Main Spans3
Year Built1947 (reconstructed 1961)

Traffic

Avg Daily Traffic226,000 (2009)
Truck Traffic4%
Lanes On Bridge17

Inspection & Ownership

Last InspectionApril 2023
Inspection FrequencyEvery 24 months
OwnerState Highway Agency
Historical SignificanceBridge is not eligible for the National Register
Scour Critical8 — Stable, low risk
Structure Number35 0126

How Bridge Ratings Work

Inspectors rate each major part of a bridge (the deck you drive on, the superstructure of beams that holds it up, and the substructure of piers and abutments beneath) on a 0–9 scale. A bridge's overall condition is its lowest of those ratings, so one deteriorated component makes the whole bridge "poor."

0Failed
1Imminent failure
2Critical
3Serious
4Poor
5Fair
6Satisfactory
7Good
8Very good
9Excellent
Good · lowest component 7–9
Fair · lowest component 5–6
Poor · lowest component 0–4

A poor rating is not a closure. It means the bridge is flagged for priority repair or replacement; bridges judged unsafe are closed or posted with weight limits. The waterway (channel) rating is reported, but it does not count toward the overall classification.

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