US Bridges

Prospect Ave-Us 12 over Int Capitol-I 15

Fair

Lewis and Clark County, Montana · Helena-Prospect Ave · Structure no. P00008046+12212

Built
1961
64 years old
Condition
Fair
inspected August 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
260 ft
4 main spans
Daily traffic
12,054
2023 count
Owner
State
State Highway Agency

About this bridge

Prospect Ave-Us 12 over Int Capitol-I 15 is a steel stringer/multi-beam or girder carrying Prospect Ave-Us 12 over Int Capitol-I 15 in Lewis and Clark County, Montana. It was built in 1961, so it is 64 years old, older than the Montana average of 47 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 12,054 vehicles a day, roughly 1% of them trucks, projected to reach 12,656 by 2043. The structure is 260 ft (79.4 m) long and 32 ft wide.

Location

Open in Google Maps
CarriesProspect Ave-Us 12
CrossesInt Capitol-I 15
LocationHelena-Prospect Ave
RouteU.S. Route 12
CountyLewis and Clark County
StateMontana
Coordinates46.59128, -111.99861
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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionAugust 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation6: Equal to present minimum criteria
Deck geometry3: Basically intolerable, requiring high priority of corrective action
Approach roadway alignment7: Better than present minimum criteria
Operating rating44 US tons
Inventory rating34 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length260 ft (79.4 m)
Longest span76 ft (23.2 m)
Deck width32 ft (9.7 m)
Roadway width28 ft (8.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic12,054 (2023)
Projected traffic12,656 by 2043
Trucks1%
Lanes on structure2
Traffic directionOne-way traffic
CarriesOverpass structure at an interchange
CrossesHighway
Detour if closed—
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 proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$650,000
NavigationNot applicable (no waterway)

Frequently asked questions

When was Prospect Ave-Us 12 over Int Capitol-I 15 built?

It was built in 1961, making it 64 years old in 2025.

What condition is Prospect Ave-Us 12 over Int Capitol-I 15 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 2023.

How much traffic does Prospect Ave-Us 12 over Int Capitol-I 15 carry?

About 12,054 vehicles per day (2023 count), of which roughly 1% are trucks.

How long is Prospect Ave-Us 12 over Int Capitol-I 15?

The structure is 260 ft (79.4 m) long with a longest span of 76 ft (23.2 m) and a deck 32 ft wide.

Who owns Prospect Ave-Us 12 over Int Capitol-I 15?

It is owned by the State Highway Agency.