US Bridges

US 21 over I-20

Fair

Richland County, South Carolina · 5 MI NE of Columbia · Structure no. 000000000004881

Built
1966
59 years old
Condition
Fair
inspected January 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
275 ft
4 main spans
Daily traffic
6,700
2023 count
Owner
State
State Highway Agency

About this bridge

US 21 over I-20 is a prestressed concrete stringer/multi-beam or girder carrying US 21 over I-20 in Richland County, South Carolina. It was built in 1966, so it is 59 years old, older than the South Carolina average of 48 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 6,700 vehicles a day, roughly 3% of them trucks, projected to reach 8,777 by 2043. The structure is 275 ft (83.8 m) long and 67 ft wide.

Location

Open in Google Maps
CarriesUS 21
CrossesI-20
Location5 MI NE of Columbia
RouteU.S. Route 21
CountyRichland County
StateSouth Carolina
Coordinates34.07369, -81.99953
Functional classUrban 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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJanuary 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
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
Approach roadway alignment8: Equal to present desirable criteria
Operating rating73.2 US tons
Inventory rating32.2 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20 + Mod
Structure length275 ft (83.8 m)
Longest span70 ft (21.3 m)
Deck width67 ft (20.3 m)
Roadway width56 ft (17.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,700 (2023)
Projected traffic8,777 by 2043
Trucks3%
Lanes on structure4
Traffic directionTwo-way traffic
CarriesOverpass structure at an interchange
CrossesHighway
Detour if closed—
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 proposedWidening with deck rehabilitation or replacement
Estimated improvement cost$101,000 (2024 estimate)
NavigationNot applicable (no waterway)

Frequently asked questions

When was US 21 over I-20 built?

It was built in 1966, making it 59 years old in 2025.

What condition is US 21 over I-20 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 January 2024.

How much traffic does US 21 over I-20 carry?

About 6,700 vehicles per day (2023 count), of which roughly 3% are trucks.

How long is US 21 over I-20?

The structure is 275 ft (83.8 m) long with a longest span of 70 ft (21.3 m) and a deck 67 ft wide.

Who owns US 21 over I-20?

It is owned by the State Highway Agency.