US Bridges

FM 646 over Gum Bayou

Fair

Galveston County, Texas · 0.90 MI W of FM 3436 · Structure no. 120850304901006

Built
1984
41 years old
Condition
Fair
inspected August 2024
Type
Stringer/Multi-beam or Girder
Concrete
Length
120 ft
3 main spans
Daily traffic
11,441
2020 count
Owner
State
State Highway Agency

About this bridge

FM 646 over Gum Bayou is a concrete stringer/multi-beam or girder carrying FM 646 over Gum Bayou in Galveston County, Texas. It was built in 1984, so it is 41 years old, younger than the Texas average of 44.4 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 11,441 vehicles a day, roughly 6% of them trucks, projected to reach 11,100 by 2033. The structure is 120 ft (36.6 m) long and 46 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesFM 646
CrossesGum Bayou
Location0.90 MI W of FM 3436
RouteState Highway 646
CountyGalveston County
StateTexas
Coordinates29.49263, -95.02167
Functional classUrban Other Principal 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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionAugust 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour evaluation has not been made
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating75 US tons
Inventory rating45 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialConcrete
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length120 ft (36.6 m)
Longest span40 ft (12.2 m)
Deck width46 ft (14.1 m)
Roadway width43 ft (13.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic11,441 (2020)
Projected traffic11,100 by 2033
Trucks6%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 km)
TollOn a free road
National Highway SystemYes

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—
NavigationNo navigation control on waterway

Frequently asked questions

When was FM 646 over Gum Bayou built?

It was built in 1984, making it 41 years old in 2025.

What condition is FM 646 over Gum Bayou 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 August 2024.

How much traffic does FM 646 over Gum Bayou carry?

About 11,441 vehicles per day (2020 count), of which roughly 6% are trucks.

How long is FM 646 over Gum Bayou?

The structure is 120 ft (36.6 m) long with a longest span of 40 ft (12.2 m) and a deck 46 ft wide.

Who owns FM 646 over Gum Bayou?

It is owned by the State Highway Agency.