US Bridges

Mo 221 S over Knob Br

Fair

Iron County, Missouri · S 20 T 34 N R 4 E · Structure no. 7692

Built
1954
71 years old, rebuilt 1991
Condition
Fair
inspected October 2023
Type
Culvert
Concrete Continuous
Length
33 ft
2 main spans
Daily traffic
2,220
2024 count
Owner
State
State Highway Agency

About this bridge

Mo 221 S over Knob Br is a concrete continuous culvert carrying Mo 221 S over Knob Br in Iron County, Missouri. It was built in 1954 and reconstructed in 1991, so it is 71 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 2,220 vehicles a day, roughly 5% of them trucks, projected to reach 3,330 by 2044. The structure is 33 ft (10.1 m) long and 39 ft wide. If it were closed, the detour would be 14.3 mi (23 km).

Location

Open in Google Maps
CarriesMo 221 S
CrossesKnob Br
LocationS 20 T 34 N R 4 E
RouteState Highway 221
CountyIron County
StateMissouri
Coordinates37.62858, -90.61986
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 protection6 SatisfactoryStructural elements show some minor deterioration.
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 within limits of footing or piles
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating42.7 US tons
Inventory rating25.8 US tons

Structure

Structure typeCulvert
MaterialConcrete Continuous
DeckNot applicable
Main spans2
Design loadH 10
Structure length33 ft (10.1 m)
Longest span12 ft (3.7 m)
Deck width39 ft (11.9 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,220 (2024)
Projected traffic3,330 by 2044
Trucks5%
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 221 S over Knob Br built?

It was built in 1954, making it 71 years old in 2025. It was reconstructed in 1991.

What condition is Mo 221 S over Knob Br 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 221 S over Knob Br carry?

About 2,220 vehicles per day (2024 count), of which roughly 5% are trucks.

How long is Mo 221 S over Knob Br?

The structure is 33 ft (10.1 m) long with a longest span of 12 ft (3.7 m) and a deck 39 ft wide.

Who owns Mo 221 S over Knob Br?

It is owned by the State Highway Agency.