Montana Department of Transportation

Malcolm “Mack” Long, Director


View the Governor’s Coronavirus Task Force site for more information.

Public Involvement

South of Boulder South project logo

South of Boulder South

Project Overview

The Montana Department of Transportation (MDT) is rebuilding two segments of Whitetail Road (S-399) south of Boulder in Jefferson County. The new design will bring the road up to current standards, improve motorist safety, and lower the maintenance costs for Jefferson County. Construction is anticipated to begin in April 2020 and be completed in fall 2020.

Improvements include:

  • Raising and rebuilding the gravel road.
  • Improving ditch drainage and installing new culverts.
  • Repaving currently paved surfaces.
  • Replacing two culverts at Little Boulder River with a larger culvert.
  • Reducing some sharp curves and minor realigning the road (see Rocky Canyon Creek map below).

See Project Benefits page for more information about the improvements.

south of boulder south new road image

Project Location

The project is divided into two segments. The first segment of the project starts near Antelope Lane and extends north on the gravel surface ending approximately a half mile beyond the Deerlodge National Forest boundary. Improvements include raising and rebuilding the gravel road, improving ditch drainage, installing culverts, and reducing sharp curves.

The second segment of the project starts at the intersection of Whitetail and Hot Springs roads and continues north to the Jefferson County Fairgrounds. Improvements include repaving the roadway and installing a large culvert at the Little Boulder River crossing.

South of Boulder south Project map


Construction activities will begin in the spring of 2020 and are expected to be completed in the fall of 2020.

What to expect during construction:

  • Traffic will be reduced to one lane and controlled with pilot cars, traffic signals or flaggers through work zones.
  • Motorists should expect 15-minute delays during the day.
  • Short-term closures up to 60 minutes may be necessary for rock removal.
  • Speed limits will be reduced; slow down and use caution.

Stay Updated

Communication with local residents and the traveling public is a priority. MDT is committed to notifying the public about anticipated construction scheduling and impacts to motorists. Sign up for construction email updates by texting the word BOULDER to 42828. Questions and comments can be directed to Brandon Coates or by phone at 406-465-3350.

UPN 6097000