US Bridges

Il 23 over Somonauk Creek

Fair

DeKalb County, Illinois · 1.4 MI N JCT US 30 · Structure no. 019200800000000

Built
1975
50 years old
Condition
Fair
inspected February 2023
Type
Culvert
Concrete
Length
37 ft
3 main spans
Daily traffic
3,150
2023 count
Owner
State
State Highway Agency

About this bridge

Il 23 over Somonauk Creek is a concrete culvert carrying Il 23 over Somonauk Creek in DeKalb County, Illinois. It was built in 1975, so it is 50 years old, older than the Illinois average of 45.3 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 3,150 vehicles a day, roughly 9% of them trucks, projected to reach 3,696 by 2046. The structure is 37 ft (11.3 m) long and 47 ft wide. If it were closed, the detour would be 39.8 mi (64 km).

Location

Open in Google Maps
CarriesIl 23
CrossesSomonauk Creek
Location1.4 MI N JCT US 30
RouteState Highway 23
CountyDeKalb County
StateIllinois
Coordinates41.78807, -88.75419
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 protection5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Culvert6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionFebruary 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating44.3 US tons
Inventory rating26.5 US tons

Structure

Structure typeCulvert
MaterialConcrete
DeckNot applicable
Main spans3
Design loadHS 20
Structure length37 ft (11.3 m)
Longest span13 ft (4.1 m)
Deck width47 ft (14.2 m)
Roadway width44 ft (13.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,150 (2023)
Projected traffic3,696 by 2046
Trucks9%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed39.8 mi (64 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 Il 23 over Somonauk Creek built?

It was built in 1975, making it 50 years old in 2025.

What condition is Il 23 over Somonauk Creek 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 February 2023.

How much traffic does Il 23 over Somonauk Creek carry?

About 3,150 vehicles per day (2023 count), of which roughly 9% are trucks.

How long is Il 23 over Somonauk Creek?

The structure is 37 ft (11.3 m) long with a longest span of 13 ft (4.1 m) and a deck 47 ft wide.

Who owns Il 23 over Somonauk Creek?

It is owned by the State Highway Agency.