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Prospect Ave-us 12 over Int Capitol-i 15

Lewis and Clark County, Montana · rated Fair in the 2025 National Bridge Inventory

United States Bridge Conditions2025 National Bridge Inventory, FHWACompiled August 20, 2026

Prospect Ave-us 12 over Int Capitol-i 15 in Lewis and Clark County, Montana, is rated in fair condition in the 2025 National Bridge Inventory (as of August 20, 2026).
Its lowest-rated component is the deck, rated 6 (satisfactory condition) on the 0-9 scale.
It was built in 1961, making it 64 years old at the 2025 inventory.
It carries about 12,054 vehicles a day (traffic count year 2023).
Its listed owner is the state highway agency.
It is one of 75 of the 204 inventoried bridges in Lewis and Clark County rated fair (36.8%); 11 (5.4%) are rated poor.
A fair rating means the lowest-rated major component scores 5 or 6 on FHWA's 0-9 scale: some deterioration or minor section loss, but the structure is sound. It is the middle class, not a warning.

Component ratings


Structure	Steel stringer or multi-beam girder
Length	about 260 ft
Location	Helena-prospect Ave
NBI structure number	P00008046+12211
Condition class	Fair

Source: FHWA National Bridge Inventory, 2025 data as reported by the Montana department of transportation.

Bridge	Built	Vehicles/day	Condition
Lyndale Ave-us 12 over Great Northern Area	2003	20,397	Good
US 12 over RR	1978	19,327	Good
N Last Chance Gulc over RR	2003	18,569	Good
E Custer Ave over Int Custer Ave-i 15	2012	16,988	Good
US 12 over Prickly Pear Creek	1978	15,333	Good
I 15 over Sep Boulder Ave-rr	2016	14,810	Fair