US Bridges

Colby Road over Flat River

Fair

Montcalm County, Michigan · 0.80 Mile West of M-91 · Structure no. 000000000007515

Built
1980
45 years old
Condition
Fair
inspected April 2023
Type
Box Beam or Girders - Multiple
Prestressed Concrete
Length
75 ft
1 main span
Daily traffic
723
2003 count
Owner
County
County Highway Agency

About this bridge

Colby Road over Flat River is a prestressed concrete box beam or girders - multiple carrying Colby Road over Flat River in Montcalm County, Michigan. It was built in 1980, so it is 45 years old, younger than the Michigan average of 48.3 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 723 vehicles a day, projected to reach 1,004 by 2023. The structure is 75 ft (22.8 m) long and 34 ft wide. If it were closed, the detour would be 6.2 mi (10 km).

Location

Open in Google Maps
CarriesColby Road
CrossesFlat River
Location0.80 Mile West of M-91
RouteCounty Highway 0
CountyMontcalm County
StateMichigan
Coordinates43.26459, -85.26891
Functional classRural Local

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.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure8 Very GoodNo problems noted.
Channel and channel protection7 GoodSome minor problems.
Last inspectionApril 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 adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating83.7 US tons
Inventory rating50.2 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialPrestressed Concrete
DeckConcrete, precast panels
Main spans1
Design loadHS 20 + Mod
Structure length75 ft (22.8 m)
Longest span71 ft (21.6 m)
Deck width34 ft (10.4 m)
Roadway width33 ft (10.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic723 (2003)
Projected traffic1,004 by 2023
Trucks0%
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 proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was Colby Road over Flat River built?

It was built in 1980, making it 45 years old in 2025.

What condition is Colby Road over Flat 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 April 2023.

How much traffic does Colby Road over Flat River carry?

About 723 vehicles per day (2003 count).

How long is Colby Road over Flat River?

The structure is 75 ft (22.8 m) long with a longest span of 71 ft (21.6 m) and a deck 34 ft wide.

Who owns Colby Road over Flat River?

It is owned by the County Highway Agency.