US Bridges

Il 78 over Rock River

Fair

Whiteside County, Illinois · N Edge Prophetstown · Structure no. 098010000000000

Built
1994
31 years old
Condition
Fair
inspected June 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
806 ft
5 main spans
Daily traffic
2,950
2023 count
Owner
State
State Highway Agency

About this bridge

Il 78 over Rock River is a steel stringer/multi-beam or girder carrying Il 78 over Rock River in Whiteside County, Illinois. It was built in 1994, so it is 31 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 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 2,950 vehicles a day, roughly 15% of them trucks, projected to reach 3,232 by 2046. The structure is 806 ft (245.6 m) long and 43 ft wide. If it were closed, the detour would be 29.2 mi (47 km).

Location

Open in Google Maps
CarriesIl 78
CrossesRock River
LocationN Edge Prophetstown
RouteState Highway 78
CountyWhiteside County
StateIllinois
Coordinates41.68779, -89.93792
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJune 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 geometry6: Equal to present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating68.9 US tons
Inventory rating41.1 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans5
Design loadHS 20
Structure length806 ft (245.6 m)
Longest span195 ft (59.4 m)
Deck width43 ft (13.2 m)
Roadway width40 ft (12.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,950 (2023)
Projected traffic3,232 by 2046
Trucks15%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed29.2 mi (47 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—
NavigationNavigation control on waterway (bridge permit required)

Frequently asked questions

When was Il 78 over Rock River built?

It was built in 1994, making it 31 years old in 2025.

What condition is Il 78 over Rock River 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 June 2023.

How much traffic does Il 78 over Rock River carry?

About 2,950 vehicles per day (2023 count), of which roughly 15% are trucks.

How long is Il 78 over Rock River?

The structure is 806 ft (245.6 m) long with a longest span of 195 ft (59.4 m) and a deck 43 ft wide.

Who owns Il 78 over Rock River?

It is owned by the State Highway Agency.