Maclay Bridge/South Avenue Bridge

The Montana Department of Transportation is planning to construct a new bridge over the Bitterroot River on South Avenue, west of Missoula. Construction is tentatively planned for 2026. As a result, the Maclay Bridge will no longer be used for vehicular traffic. Missoula County will not retain ownership of the bridge. Listed in the National Register of Historic Places, the bridge is available for adoption by public or private entities under MDT’s Historic Bridge Adoption program. Adopters must maintain the bridge as a historic structure for 10 years and submit required materials by Dec. 16, 2024. Further details can be found on MDT’s website.

Missoula County reopened the Maclay Bridge west of Missoula on June 11.

Missoula County Public Works completed the necessary repairs to allow traffic back on the bridge, and engineering firm HDR has inspected the repairs. Crews started resurfacing the bridge with asphalt this morning, and it will reopen to traffic, bikes and pedestrians later this afternoon.

The weight limit for the bridge remains at 11 tons for now. The Montana Department of Transportation plans to complete an inspection to evaluate that limit.

Though the repairs allowed the County to reopen the one-lane bridge, placed at its current location in 1953, these repairs are not intended as a long-term fix. Construction on a new bridge upstream that would connect South Avenue to River Pines Road is tentatively slated to begin in 2026. More information on the South Avenue Bridge is  online. 

We know the bridge closure has been a major disruption, and we appreciate your patience as staff worked to reopen it.

Missoula County is pushing back the reopening date for Maclay Bridge following an inspection by engineering firm HDR on Wednesday morning that determined the County is required to do additional repairs to the bridge deck to safely reopen it. Missoula County Public Works had hoped the bridge could be reopened by May 9 or 10, but the additional repairs, coupled with the need to have additional materials delivered, will delay this.

Once all required structural repairs are complete, crews will install the driving surface, which includes pouring concrete that requires a seven-day cure time before the final asphalt surfacing can be placed. The County may need another inspection and a weight-limit review before opening. Based on this, Public Works officials are now aiming for the bridge to reopen by the second week of June.

The bridge will remain closed to all traffic, including bicycles and pedestrians, until after repairs are complete. County officials urge members of the public to abide by this closure.

We appreciate your continued patience as our staff work to reopen the bridge. More information on the new bridge that will be constructed upstream is on this page.

Missoula County Public Works continues to work on the repairs to Maclay Bridge, with crews now focusing on the required structural repairs to the pony truss, which are expected to be complete by Wednesday, May 1.

Once all required structural repairs are complete, crews will install the driving surface, which includes pouring concrete that requires a seven-day cure time before the final asphalt surfacing can be placed. The County may need another inspection and a weight-limit review before opening, which could extend the closure. Given the progress to this point, though, staff expect to reopen the bridge on May 9 or 10.

The bridge will remain closed to all traffic, including bicycles and pedestrians, until after repairs are complete. County officials urge members of the public to abide by this closure.

We appreciate your patience as our staff work to reopen the bridge. More information on the new bridge to be constructed upstream is online.

Crews are planning to begin repairs the week of March 18 by removing the deck surfacing and portions of the corrugated steel deck pans, which will then need to be replaced after new stringers are installed. The materials for the deck replacement are expected to be delivered in the next three to five weeks, which will dictate the repair schedule. The County tentatively plans to have the bridge reopened around the end of April, though this timeline is heavily dependent on weather conditions and other factors.

Repair work on the bridge can move ahead following receipt of the required environmental documentation from the Montana Department of Transportation. Chief Public Works Officer Shane Stack also confirmed delivery of the new steel stringers needed to replace the deteriorating structural components beneath the bridge deck.

The bridge will remain closed to all traffic, including bicycles and pedestrians, until after repairs are complete. County officials urge members of the public to abide by this closure.

Missoula County has completed a funding agreement with the Montana Department of Transportation, and MDT will fund the cost of the repairs up to $70,000. The state funding provided through Senate Bill 536 requires completion of a Montana Environmental Policy Act (MEPA) document prior to spending any funding. Engineering firm HDR plans to complete an Environmental Checklist and share that with MDT early in the week of March 4. MDT will then have to complete the MEPA document based on the checklist before the SB 536 funding can be spent. MDT’s turnaround time for the MEPA document is estimated to be one week, but this will depend on the checklist submittal being error-free.

Missoula County Public Works ordered materials for the repair, and delivery is estimated to be two to three weeks.

Once MEPA is complete and the materials are delivered, repairs would begin. It’s estimated the repairs will take four weeks to complete. This is heavily dependent on weather conditions. Public Works staff will complete the repair work. Other tasks around the county could pull staff away from repair work, which could impact the repair schedule.

All of these estimated timeframes are subject to change. We appreciate your patience as we work to repair the bridge and re-open it to traffic.

Engineering firm HDR has been investigating the stringers on the bridge and will inform the County when they have a recommendation on what repairs would be necessary to re-open it. The Montana Department of Transportation will then need to approve any repair plans before the County moves forward.

Once we have confirmed information, Missoula County is tentatively planning to hold a public meeting to update residents on next steps with the bridge. This meeting could be held late next week, but this is not set in stone and could be postponed until there is significant news to share. We will provide details about a meeting when confirmed.

We appreciate your patience as this process plays out. Make sure to follow the project at missoulacountyvoice.com for the latest updates.

The Missoula County commissioners host "The Agenda" podcast, which aims to help county residents better understand how local government works and how it affects their lives. In each episode, the commissioners sit down with fellow staff, elected officials and community partners to discuss public sector projects and trending topics.

Missoula County is grateful to have MCAT as partner in local government, as that partnership allows us to use their podcast recording equipment free of charge, and it allows us to produce a high-quality podcast without the County needing to purchase this necessary equipment.

The Agenda's foray into transportation issues continues this week with Shane Stack, director of Missoula County Public Works, and Erik Dickson, county engineer.

With the recent closure of Maclay Bridge in Target Range, residents have a lot of questions about how we got here. The commissioners, Shane and Erik tackle those questions and much more in this episode. Click here to listen online, or find it wherever you download your podcasts under the title "The Agenda with the Missoula County Commissioners."

This episode has a lot of acronyms and engineering terms, so be sure to follow along with this glossary.

This project has a lot of acronyms and engineering terms, so here's a glossary to help you:

• BIP: The Bridge Improvement Program, a funding opportunity administered by the Federal Highway Administration.
• Categorical exclusion, also called a CE or Cat Ex: A finding of a National Environmental Protection Act process that determines a project has no significant effect on the human environment. If a CE is granted, the project does not need an environmental assessment or environmental impact statement.
• Creosote: A material derived from tar that is used to preserve wood.
• EA: Environmental assessment. If a categorical exclusion does not apply to a project, then an environmental assessment must be developed before the project can move forward. This is a public document that provides sufficient evidence and analysis for determining whether the project meets the criteria for a Finding of No Significant Environmental Impact (FONSI) or if an Environmental Impact Statement (EIS) is needed.
• Environmental Impact Statement (EIS): Federal agencies prepare an Environmental Impact Statement if a project is determined to significantly affect the quality of the human environment. The regulatory requirements for an EIS are more detailed and rigorous than the requirements for an EA.
• FHWA: The Federal Highway Administration, a division of the federal Department of Transportation.
• FONSI document: Finding of No Significant Impact. A FONSI document is the decision document of an EA and is signed by the federal agency.
• HDR: An engineering firm employed by both Missoula County and MDT to assist with bridge planning.
• Load rating: The amount of weight a structure can safely carry. A load posted or load limited bridge is restricted by its load rating.
• Local option gas tax: A voter-approved 2-cent tax on gas sold within Missoula County. Revenue from this tax was specifically designated for road and bridge improvements. County residents approved this measure in 2020, but the state repealed in 2021.
• MDT: Montana Department of Transportation, the state's transportation agency
• NEPA: National Environmental Protection Act, passed in 1970 to promote and protect the environment.
• No-rise [certification]: A state law that requires bridges or any project within a floodplain must not raise the height of flood waters.
• Off-System Bridge Program: Bridges in Montana that are not maintained by MDT. One of the many federal aid programs at MDT, this one funds the repair and replacement of locally owned bridges.
• Pilings: The vertical posts in a body of water that support a bridge.
• RAISE: The Rebuilding American Infrastructure with Sustainability and Equity grant program, which the federal Department of Transportation administers.
• Right of way acquisition: The process of obtaining property or easements for the use of public infrastructure.
• Safe Streets for All: A federal grant program the Department of Transportation administers. Click here to learn more about the Third & Clements project.
• Scour critical: A bridge that has erosion or deterioration at the abutment (where the bridge attaches to land) or pier.
• Section 106: Part of the National Historic Preservation Act of 1966, Section 106 requires federal agencies to identify and assess the effects its actions may have on historic structures.
• Senate Bill 536: A law the state legislature passed in 2023 that designated $100 million toward the reconstruction and repair of local bridges and roads.
• Stringers: Steel beams that run lengthwise under the bridge to help support the part of a bridge that you drive over.
• Two-span bridge: A bridge that has two sections (spans).