US Bridges

Nelson RD (cr 20) over Boulder Feeder Ditch

Fair

Boulder County, Colorado · 1.0 MI W of CO RD 39 · Structure no. BC-20-3.3-ID

Built
1950
75 years old, rebuilt 1981
Condition
Fair
inspected February 2025
Type
Tee Beam
Prestressed Concrete
Length
32 ft
1 main span
Daily traffic
2,692
2023 count
Owner
County
County Highway Agency

About this bridge

Nelson RD (cr 20) over Boulder Feeder Ditch is a prestressed concrete tee beam carrying Nelson RD (cr 20) over Boulder Feeder Ditch in Boulder County, Colorado. It was built in 1950 and reconstructed in 1981, so it is 75 years old, older than the Colorado average of 42.2 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 2,692 vehicles a day, roughly 16% of them trucks, projected to reach 3,230 by 2043. The structure is 32 ft (9.8 m) long and 29 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

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CarriesNelson RD (cr 20)
CrossesBoulder Feeder Ditch
Location1.0 MI W of CO RD 39
RouteCounty Highway 0
CountyBoulder County
StateColorado
Coordinates40.1523, -105.22515
Functional classRural Major 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.
Substructure8 Very GoodNo problems noted.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionFebruary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating40 US tons
Inventory rating36 US tons

Structure

Structure typeTee Beam
MaterialPrestressed Concrete
DeckOther
Main spans1
Design loadHS 20
Structure length32 ft (9.8 m)
Longest span30 ft (9 m)
Deck width29 ft (8.8 m)
Roadway width25 ft (7.6 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,692 (2023)
Projected traffic3,230 by 2043
Trucks16%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 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 proposedWidening with deck rehabilitation or replacement
Estimated improvement cost$186,000 (2019 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was Nelson RD (cr 20) over Boulder Feeder Ditch built?

It was built in 1950, making it 75 years old in 2025. It was reconstructed in 1981.

What condition is Nelson RD (cr 20) over Boulder Feeder Ditch 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 February 2025.

How much traffic does Nelson RD (cr 20) over Boulder Feeder Ditch carry?

About 2,692 vehicles per day (2023 count), of which roughly 16% are trucks.

How long is Nelson RD (cr 20) over Boulder Feeder Ditch?

The structure is 32 ft (9.8 m) long with a longest span of 30 ft (9 m) and a deck 29 ft wide.

Who owns Nelson RD (cr 20) over Boulder Feeder Ditch?

It is owned by the County Highway Agency.