The Dominion Creek Tunnel and Trestle are located on an abandoned section of the Milwaukee Railroad near the top of Lookout Pass along the border of Montana and Idaho. The intent of this project was to rehabilitate the 650’ long bridge and the adjacent 450’ long tunnel in order to provide public pedestrian access to approximately 8 miles of the old railroad grade. All rehabilitation work had to retain historical accuracy, and preserve as much of the existing elements as possible.

Based on the preliminary investigation, it was determined that the 100 year old steel bridge girders could remain in place on the trestle but it was necessary to remove the concrete ballast boxes as they had deteriorated extensively. Additionally, handrails needed to be installed over the entire length of the structure and repairs needed to be conducted on the concrete abutments on both ends of the trestle.

The tunnel rehabilitation involved patching two sections of the existing concrete lining and removing the ballast material to increase the drainage of the walls and floor of the tunnel. The trail itself was also improved by filling in low areas and sinkholes, and removing rock and debris from localized slides near the trail.

Key Services

  • Conducted site visit and investigation
  • Inspected tunnel, trestle, and major culverts
  • Provided a summary of existing condition of trestle, tunnel and specified drainage structures
  • Documented alternatives for repairing the trestle and tunnel and associated costs
  • Recommended preferred alternative for repairs
  • Designed tunnel and trestle repairs
  • Designed trail surfacing , slump repair, drainage structure repairs or replacements

Value Added

In 2013, the Dominion Creek Trestle project was awarded the Carl Anderson Conservation Engineering Award of Excellence. This project was also selected as a “case study” for the new Sustainable Infrastructure Rating System (envision™).