US Bridges

Marshall RD (cr 51 over South Boulder Creek

Fair

Boulder County, Colorado · 0.5 MI N of ST HWY 170 · Structure no. BC-51-11.0-SB1

Built
1988
37 years old
Condition
Fair
inspected February 2025
Type
Slab
Wood or Timber
Length
38 ft
1 main span
Daily traffic
318
2022 count
Owner
County
County Highway Agency

About this bridge

Marshall RD (cr 51 over South Boulder Creek is a wood or timber slab carrying Marshall RD (cr 51 over South Boulder Creek in Boulder County, Colorado. It was built in 1988, so it is 37 years old, younger 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 318 vehicles a day, roughly 4% of them trucks, projected to reach 382 by 2042. The structure is 38 ft (11.6 m) long and 30 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesMarshall RD (cr 51
CrossesSouth Boulder Creek
Location0.5 MI N of ST HWY 170
RouteCounty Highway 0
CountyBoulder County
StateColorado
Coordinates39.96002, -105.23228
Functional classUrban Local

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.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionFebruary 2025
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating60.4 US tons
Inventory rating43.3 US tons

Structure

Structure typeSlab
MaterialWood or Timber
DeckWood or timber
Main spans1
Design loadHS 20
Structure length38 ft (11.6 m)
Longest span36 ft (11 m)
Deck width30 ft (9.2 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic318 (2022)
Projected traffic382 by 2042
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.9 mi (3 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 Marshall RD (cr 51 over South Boulder Creek built?

It was built in 1988, making it 37 years old in 2025.

What condition is Marshall RD (cr 51 over South Boulder Creek 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 Marshall RD (cr 51 over South Boulder Creek carry?

About 318 vehicles per day (2022 count), of which roughly 4% are trucks.

How long is Marshall RD (cr 51 over South Boulder Creek?

The structure is 38 ft (11.6 m) long with a longest span of 36 ft (11 m) and a deck 30 ft wide.

Who owns Marshall RD (cr 51 over South Boulder Creek?

It is owned by the County Highway Agency.