US Bridges

Suydam RD over Somonauk Creek

Fair

DeKalb County, Illinois · 145N 1565E · Structure no. 019301700000000

Built
1955
70 years old, rebuilt 2009
Condition
Fair
inspected March 2023
Type
Slab
Concrete Continuous
Length
104 ft
3 main spans
Daily traffic
1,950
2021 count
Owner
County
County Highway Agency

About this bridge

Suydam RD over Somonauk Creek is a concrete continuous slab carrying Suydam RD over Somonauk Creek in DeKalb County, Illinois. It was built in 1955 and reconstructed in 2009, so it is 70 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 1,950 vehicles a day, roughly 10% of them trucks, projected to reach 2,184 by 2046. The structure is 104 ft (31.7 m) long and 32 ft wide. If it were closed, the detour would be 6.2 mi (10 km).

Location

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CarriesSuydam RD
CrossesSomonauk Creek
Location145N 1565E
CountyDeKalb County
StateIllinois
Coordinates41.65262, -88.64972
Functional classUrban 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.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure8 Very GoodNo problems noted.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 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 typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length104 ft (31.7 m)
Longest span38 ft (11.7 m)
Deck width32 ft (9.9 m)
Roadway width32 ft (9.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,950 (2021)
Projected traffic2,184 by 2046
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed6.2 mi (10 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 proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$540,000
NavigationNo navigation control on waterway

Frequently asked questions

When was Suydam RD over Somonauk Creek built?

It was built in 1955, making it 70 years old in 2025. It was reconstructed in 2009.

What condition is Suydam 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 March 2023.

How much traffic does Suydam RD over Somonauk Creek carry?

About 1,950 vehicles per day (2021 count), of which roughly 10% are trucks.

How long is Suydam RD over Somonauk Creek?

The structure is 104 ft (31.7 m) long with a longest span of 38 ft (11.7 m) and a deck 32 ft wide.

Who owns Suydam RD over Somonauk Creek?

It is owned by the County Highway Agency.