US Bridges

Somonauk Road over W. Br. Big Rock Crk.

Fair

DeKalb County, Illinois · 1150N 1510E · Structure no. 019304600000000

Built
1993
32 years old
Condition
Fair
inspected March 2024
Type
Box Beam or Girders - Multiple
Prestressed Concrete
Length
46 ft
1 main span
Daily traffic
2,400
2021 count
Owner
County
County Highway Agency

About this bridge

Somonauk Road over W. Br. Big Rock Crk. is a prestressed concrete box beam or girders - multiple carrying Somonauk Road over W. Br. Big Rock Crk. in DeKalb County, Illinois. It was built in 1993, so it is 32 years old, younger 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 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 2,400 vehicles a day, roughly 11% of them trucks, projected to reach 2,688 by 2046. The structure is 46 ft (14.1 m) long and 30 ft wide. If it were closed, the detour would be 1.9 mi (3 km).

Location

Open in Google Maps
CarriesSomonauk Road
CrossesW. Br. Big Rock Crk.
Location1150N 1510E
RouteCounty Highway 0
CountyDeKalb County
StateIllinois
Coordinates41.79885, -88.65899
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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating48.6 US tons
Inventory rating35.7 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialPrestressed Concrete
DeckConcrete, precast panels
Main spans1
Design loadHS 20
Structure length46 ft (14.1 m)
Longest span44 ft (13.3 m)
Deck width30 ft (9.1 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,400 (2021)
Projected traffic2,688 by 2046
Trucks11%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.9 mi (3 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 Somonauk Road over W. Br. Big Rock Crk. built?

It was built in 1993, making it 32 years old in 2025.

What condition is Somonauk Road over W. Br. Big Rock Crk. 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 2024.

How much traffic does Somonauk Road over W. Br. Big Rock Crk. carry?

About 2,400 vehicles per day (2021 count), of which roughly 11% are trucks.

How long is Somonauk Road over W. Br. Big Rock Crk.?

The structure is 46 ft (14.1 m) long with a longest span of 44 ft (13.3 m) and a deck 30 ft wide.

Who owns Somonauk Road over W. Br. Big Rock Crk.?

It is owned by the County Highway Agency.