US Bridges

Mo 21 S over Knob CR

Fair

Iron County, Missouri · S 30 T 34 N R 4 E · Structure no. 1090

Built
1967
58 years old
Condition
Fair
inspected October 2023
Type
Culvert
Concrete Continuous
Length
60 ft
3 main spans
Daily traffic
6,248
2024 count
Owner
State
State Highway Agency

About this bridge

Mo 21 S over Knob CR is a concrete continuous culvert carrying Mo 21 S over Knob CR in Iron County, Missouri. It was built in 1967, so it is 58 years old, older than the Missouri average of 45.1 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 6,248 vehicles a day, roughly 18% of them trucks, projected to reach 9,372 by 2044. The structure is 60 ft (18.4 m) long. If it were closed, the detour would be 14.3 mi (23 km).

Location

Open in Google Maps
CarriesMo 21 S
CrossesKnob CR
LocationS 30 T 34 N R 4 E
RouteState Highway 21
CountyIron County
StateMissouri
Coordinates37.61783, -90.64203
Functional classRural Minor Arterial

Condition and inspection

Fair

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

ComponentRatingMeaning
Channel and channel protection7 GoodSome minor problems.
Culvert5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionOctober 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating95.2 US tons
Inventory rating57.5 US tons

Structure

Structure typeCulvert
MaterialConcrete Continuous
DeckNot applicable
Main spans3
Design loadH 20
Structure length60 ft (18.4 m)
Longest span11 ft (3.4 m)
Deck width0 ft (0 m)
Roadway width0 ft (0 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,248 (2024)
Projected traffic9,372 by 2044
Trucks18%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed14.3 mi (23 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState 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 Mo 21 S over Knob CR built?

It was built in 1967, making it 58 years old in 2025.

What condition is Mo 21 S over Knob CR 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 October 2023.

How much traffic does Mo 21 S over Knob CR carry?

About 6,248 vehicles per day (2024 count), of which roughly 18% are trucks.

How long is Mo 21 S over Knob CR?

The structure is 60 ft (18.4 m) long with a longest span of 11 ft (3.4 m).

Who owns Mo 21 S over Knob CR?

It is owned by the State Highway Agency.