Idaho Bridge Infrastructure: A Complete Analysis

Idaho is home to 4,646 bridges spanning 44 counties, making it one of the most significant bridge inventories in the country. These bridges carry a combined 15,389,127 vehicle crossings every day. Here is a comprehensive look at the state of Idaho's bridge infrastructure based on the latest National Bridge Inventory data.

Idaho earns an overall infrastructure grade of B based on the percentage of its bridges in poor condition. Currently, 250 bridges (5.4%) are rated poor, compared to the national average of 6.7%. The average bridge in Idaho is 46 years old, younger than the national average of 48 years.

Of the state's 4,646 bridges, 1,468 are in good condition, 2,928 are fair, and 250 are poor. View the full breakdown on the [Idaho report card](/reports/idaho).

These are the bridges carrying the highest daily traffic volumes across Idaho. High-traffic bridges are critical infrastructure -- their condition directly affects the commutes of tens of thousands of drivers.

The following bridges have the lowest sufficiency ratings in Idaho. These structures are the most likely candidates for federal repair or replacement funding under the Bipartisan Infrastructure Law.

Idaho's oldest bridges tell the story of the state's transportation history. Some of these structures have been in continuous service for over a century.

Idaho's bridge infrastructure grade of B reflects both the current condition of the state's bridges and the scale of the challenge ahead. With an average bridge age of 46 years, many of these structures are approaching or past the 50-75 year design life typical of most bridges. The state's ability to maintain and replace aging bridges will determine whether conditions improve or deteriorate in the coming decade.

For county-by-county breakdowns, historical trends, and individual bridge profiles, visit the [Idaho state page](/bridges/idaho) or the [Idaho report card](/reports/idaho). You can also explore how Idaho compares to other states in our [state rankings](/blog/best-bridge-infrastructure-by-state-2025).