AASHTO Journal - Montana DOT to Build State's Very First DDI in 2027

The Montana Department of Transportation recently awarded a contract to construct the next segment of the Billings Bypass project, which will transform the Johnson Lane Interchange in the City of Lockwood into the state’s first diverging diamond interchange or DDI.

[Above image by Montana DOT]

The agency explained that, unlike a traditional interchange, DDIs briefly shift traffic to the left side of the roadway – allowing motorists to access interstate ramps more efficiently and with fewer conflict points. Although the traffic pattern may be unfamiliar at first, directional signs, traffic signals, and pavement markings will help guide drivers through the interchange.

Montana DOT added that minor construction activities, such as the relocation of select underground utilities, are already underway, with construction of the DDI anticipated to begin in spring 2027.

“We’re excited to bring this new interchange to Montana because of its many operational and safety benefits,” said Mike Taylor, administrator for the Montana DOT’s Billings District, in a statement. “The Johnson Lane DDI will help improve current traffic operations while accommodating future demand and supporting continued growth in the greater Billings area.”

Due to the size and complexity of the Johnson Lane Interchange improvements, building the DDI is expected to be completed over three construction seasons, the agency said.

The first two seasons will focus on reconstructing the I-90 bridges over Johnson Lane to accommodate the additional roadway width required for the DDI as well as completing the roadway improvements needed to construct the new interchange. Improvements south of I-90 are anticipated to be completed first, followed by work north of the interstate during the second season. Then the third and final season will include final pavement treatments throughout the project, Montana DOT noted.

[Editor’s note: Montana DOT often conducts roadway safety tests to ensure new interchanges function properly. The video below provides a look at some of the roadway safety testing Montana DOT conducted two years ago with commercial trucks before starting work on the Gore Hill Interchange project.]

In addition to reconfiguring the Johnson Lane Interchange into a DDI, this segment of the Billings Bypass project includes other key improvements:

Sidewalk and Americans with Disabilities Act-compliant upgrades along adjacent streets that tie into the DDI sidewalk facilities.
Roadway improvements on North Frontage Road, Old Hardin Road, Cole Street, and Becraft Lane.
New traffic signals and upgrades to existing signals throughout the project area, including new signals at the Cole Street/Old Hardin Road and Johnson Lane/North Frontage Road intersections.
A shared-use path through the DDI for pedestrians and bicyclists.