US Bridges

S-21-66 over Big Swamp

Fair

Florence County, South Carolina · 3.0 MI NW Salem · Structure no. 000000000007454

Built
1981
44 years old
Condition
Fair
inspected March 2023
Type
Channel Beam
Prestressed Concrete
Length
120 ft
4 main spans
Daily traffic
200
2023 count
Owner
State
State Highway Agency

About this bridge

S-21-66 over Big Swamp is a prestressed concrete channel beam carrying S-21-66 over Big Swamp in Florence County, South Carolina. It was built in 1981, so it is 44 years old, younger 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 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 200 vehicles a day, roughly 7% of them trucks, projected to reach 256 by 2043. The structure is 120 ft (36.6 m) long and 33 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesS-21-66
CrossesBig Swamp
Location3.0 MI NW Salem
RouteState Highway 66
CountyFlorence County
StateSouth Carolina
Coordinates33.90981, -79.5386
Functional classRural 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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 2023
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 geometry7: Better than present minimum criteria
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating82.9 US tons
Inventory rating43.5 US tons

Structure

Structure typeChannel Beam
MaterialPrestressed Concrete
DeckConcrete, precast panels
Main spans4
Design loadH 15
Structure length120 ft (36.6 m)
Longest span30 ft (9.1 m)
Deck width33 ft (10.2 m)
Roadway width32 ft (9.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic200 (2023)
Projected traffic256 by 2043
Trucks7%
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

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—
NavigationNo navigation control on waterway

Frequently asked questions

When was S-21-66 over Big Swamp built?

It was built in 1981, making it 44 years old in 2025.

What condition is S-21-66 over Big Swamp 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 March 2023.

How much traffic does S-21-66 over Big Swamp carry?

About 200 vehicles per day (2023 count), of which roughly 7% are trucks.

How long is S-21-66 over Big Swamp?

The structure is 120 ft (36.6 m) long with a longest span of 30 ft (9.1 m) and a deck 33 ft wide.

Who owns S-21-66 over Big Swamp?

It is owned by the State Highway Agency.