Dalton Bridge replacement formalized as MDT Project

Bridge Replacement

The Dalton Mountain Bridge replacement is moving ahead under the Montana Department of Transportation, but construction of the new bridge is probably still about two years off.

Lewis and Clark County signed a two-party agreement with the State of Montana Tuesday, June 2 that formalizes the project as an MDT project.

The agreement provides MDT with the $600,000 in Treasure State Endowment Program funding awarded to the county by the 2019 Legislature.The TSEP grant covered about half the cost of the bridge replacement project.

Lewis and Clark County engineer Dan Karlin explained at the June 5 Government Day listening session that the remainder of the project will be funded through the Federal Highways Administration's off system bridge program. He said aside from the $15,000 spent to create the Professional Engineering Report and the hours of staff time to facilitate that, the bridge replacement will be fully funded by the state and federal government, rather than the county. Karlin said that frees up county funds for use in other priority road and bridge projects, including repairs to bridges in the Augusta area damaged in the floods of 2018 and 2019.

At the May 19 meeting of the the Upper Blackfoot Community Council, Lewis and Clark County Commission Chairperson Susan Good Geise, said the bridge replacement has been pushed out beyond 2021. A project schedule was being developed in April to determine when the new bridge can be built. Zach Muse, president of the Council and Lincoln's Fire Chief, has taken part in discussions about the bridge and said the new bridge will likely be built in 2022.

The Dalton Mountain Bridge provides critical access to the Willow Creek and Dalton Mountain areas for both residents and emergency response personnel. Muse has noted in the past that the amount of insect killed trees in the area of Upper Willow Creek and Dalton Mountain present a notable wildfire danger.

"Everyone knows how critical it is to us," Muse said during the meeting.

As a result the current bridge, which is now open to only one lane of traffic, is inspected regularly. The county plans to maintain the structure and improvements to county roads that access area.

MDT earlier in the year selected Great West Engineering as the project's engineering consultant.

Those Big X's

For people wondering about the large white X's that appeared in various locations in a wide area surrounding the Dalton Mountain Bridge, Karlin explained they are part of a photogrammetry survey completed by MDT earlier this month. The Light Detection and Ranging, or LIDAR, survey uses lasers to build a detailed topographic map of the area and will be used primarily for hydraulic modeling.

"They survey those using terrestrial means to calibrate the photogrammetry to the ground," Karlin said in an e-mail to the BVD. "They generally like to do a wide area to avoid something called 'plane tilt' (not the airplane, but the computer generated surface they use to design from)."

He explained the X's also cover a wide area to help ensure they don't have to pay for multiple flights over the same area, which in the end allows for a faster processing of the photogrammetry and saves costs.

Karlin said a separate ground survey will be used to design the improvements to the road and bridge.