US Bridges

Csah 21 over Big Cobb River

Fair

Blue Earth County, Minnesota · 1.4 MI E of JCT Csah 52 · Structure no. 07530

Built
1972
53 years old
Condition
Fair
inspected November 2024
Type
Channel Beam
Prestressed Concrete
Length
93 ft
3 main spans
Daily traffic
176
2021 count
Owner
County
County Highway Agency

About this bridge

Csah 21 over Big Cobb River is a prestressed concrete channel beam carrying Csah 21 over Big Cobb River in Blue Earth County, Minnesota. It was built in 1972, so it is 53 years old, older than the Minnesota average of 38.5 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 5 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 176 vehicles a day, projected to reach 205 by 2041. The structure is 93 ft (28.4 m) long and 38 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesCsah 21
CrossesBig Cobb River
Location1.4 MI E of JCT Csah 52
RouteCounty Highway 21
CountyBlue Earth County
StateMinnesota
Coordinates43.93515, -93.86927
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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection7 GoodSome minor problems.
Last inspectionNovember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating59.7 US tons
Inventory rating35.6 US tons

Structure

Structure typeChannel Beam
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length93 ft (28.4 m)
Longest span31 ft (9.5 m)
Deck width38 ft (11.6 m)
Roadway width34 ft (10.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic176 (2021)
Projected traffic205 by 2041
Trucks—
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 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 Csah 21 over Big Cobb River built?

It was built in 1972, making it 53 years old in 2025.

What condition is Csah 21 over Big Cobb River 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 2024.

How much traffic does Csah 21 over Big Cobb River carry?

About 176 vehicles per day (2021 count).

How long is Csah 21 over Big Cobb River?

The structure is 93 ft (28.4 m) long with a longest span of 31 ft (9.5 m) and a deck 38 ft wide.

Who owns Csah 21 over Big Cobb River?

It is owned by the County Highway Agency.