US Bridges

Chicago RD over Somonauk Creek

Fair

DeKalb County, Illinois · 550N 1405E · Structure no. 019301200000000

Built
1946
79 years old, rebuilt 1995
Condition
Fair
inspected January 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
120 ft
2 main spans
Daily traffic
1,550
2021 count
Owner
County
County Highway Agency

About this bridge

Chicago RD over Somonauk Creek is a steel continuous stringer/multi-beam or girder carrying Chicago RD over Somonauk Creek in DeKalb County, Illinois. It was built in 1946 and reconstructed in 1995, so it is 79 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 1,550 vehicles a day, roughly 12% of them trucks, projected to reach 1,736 by 2046. The structure is 120 ft (36.6 m) long and 30 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesChicago RD
CrossesSomonauk Creek
Location550N 1405E
RouteCounty Highway 0
CountyDeKalb County
StateIllinois
Coordinates41.70967, -88.68001
Functional classRural Major Collector

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.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJanuary 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating48.9 US tons
Inventory rating35.7 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans2
Design loadHS 20
Structure length120 ft (36.6 m)
Longest span56 ft (17.2 m)
Deck width30 ft (9.1 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,550 (2021)
Projected traffic1,736 by 2046
Trucks12%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty 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 Chicago RD over Somonauk Creek built?

It was built in 1946, making it 79 years old in 2025. It was reconstructed in 1995.

What condition is Chicago RD 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 January 2023.

How much traffic does Chicago RD over Somonauk Creek carry?

About 1,550 vehicles per day (2021 count), of which roughly 12% are trucks.

How long is Chicago RD over Somonauk Creek?

The structure is 120 ft (36.6 m) long with a longest span of 56 ft (17.2 m) and a deck 30 ft wide.

Who owns Chicago RD over Somonauk Creek?

It is owned by the County Highway Agency.