Project Overview

Missoula County has identified the need to relocate a crossing structure over the Bitterroot River west of Missoula. The purpose of the project is to enhance the operational characteristics and increase safety for the traveling public over the foreseeable future by constructing a facility that meets current design standards as well as meeting the current and future traffic demands for the area. The South Avenue Bridge Project will involve construction of a new 2-lane bridge over the Bitterroot River and the removal of the single-lane Maclay Bridge on North Avenue.

The existing Maclay Bridge has been the subject of several previous technical and planning analyses, and was analyzed in detail during development of the 1994 Maclay Bridge Site Selection Environmental Assessment. The Maclay Bridge is a composite structure of varying ages. Based on recent Bridge Inspection Reports the bridge is categorized as functionally obsolete based on the single-lane width of the bridge being sub-standard for the current traffic volumes, and the sub-standard curves on both approaches to the bridge. The Maclay Bridge is "fracture critical," meaning if one part of the truss should fail, the entire bridge span may fail. Although no immediate concern has been identified due to its fracture critical status, special fracture critical inspections are required to reduce chance of failure.

Missoula County, in cooperation with the Montana Department of Transportation (MDT) and the Federal Highway Administration (FHWA), completed the Maclay Bridge Planning Study in 2013, which identified a preferred new bridge alignment. The Maclay Bridge Planning Study was a pre-National Environmental Policy Act (NEPA)/Montana Environmental Policy Act (MEPA) planning study that allowed for coordination with community members, stakeholders, environmental resource agencies, and other interested parties. The study examined known resource issues and included a robust alternatives screening analysis, the results of which are intended to streamline environmental review during design phase. The Maclay Bridge Planning Study is intended to benefit future project development through streamlining approvals and ultimately reducing costs.

HDR is the local engineering firm that has been retained by Missoula County to provide the following services:

  1. Preparation of final design documents including plans, specifications, and estimates for the crossing structure and associated approach roadways.
  2. Conduction of a public participation process prior to any design to ensure that interested citizens and/or organized citizen groups can be involved on functional elements and the aesthetics to be incorporated into the project.
  3. Preparation of plans for the removal of the existing crossing structure and remediation of that site.
  4. Preparation of the required environmental documentation.
  5. Securing all applicable permits.

Tetra Tech is providing geotechnical investigation and reporting; roadway geotechnical recommendations; and structures geotechnical recommendations.

HRA is providing cultural resource investigating and reporting.

DJ&A is providing topographical ground survey; cadastral survey; and river bed cross-section and bathymetric (where required) surveying.