Project Overview
The Montana Department of Transportation (MDT) is developing improvements to the Interstate 15 (I-15) Gore Hill Interchange (Exit 277) in Great Falls. The Gore Hill Interchange provides access to the Great Falls International Airport as well as the surrounding residential, commercial, and industrial developments. The project will reduce delays, improve traffic flow, and enhance safety features on I-15 between 10th Avenue South and the Gore Hill Interchange.
Gore Hill Interchange project map
Project Background
In 2015, MDT developed the I-15 Gore Hill to Emerson Junction Corridor Planning Study in partnership with the Federal Highway Administration (FHWA) and the Great Falls Metropolitan Planning Organization. The study identified safety and operational concerns, and recommended improvement options to address the transportation needs within the corridor through 2035. Among these improvement options were the addition of a southbound auxiliary lane between the Gore Hill and 10th Avenue South interchanges, and intersection improvements at the Gore Hill Interchange.
The Great Falls Long Range Transportation Plan (LRTP) 2018 Update also included recommendations to make improvements to the Gore Hill Interchange as outlined in the Corridor Planning Study.
The 2015 I-15 Gore Hill to Emerson Junction Corridor Planning Study and 2018 Great Falls Long Range Transportation Plan identified several safety and operational concerns at the Gore Hill Interchange. Transportation issues and concerns included:
- Congestion and safety concerns due to high traffic volumes, especially during peak hours, and close intersection spacing.
- Limitations in current intersection designs to handle increasing airport, truck stop and other commercial truck traffic volumes.
- Merging conflicts with truck traffic on I-15 due to the short distance between the 10th Avenue South Interchange and the Gore Hill Interchange.
Proposed Improvements
New Interchange Design
- The I-15 Gore Hill Interchange overpass bridge will be replaced. The new structure will be built to the east of the current overpass to keep the interchange open during construction. The new bridge will be wider and include shoulders and a sidewalk.
- Two single-lane roundabouts will be added on 31st Street Southwest at the I-15 southbound off-ramp and northbound on- and off-ramps. A sidewalk will be added between the roundabout intersections.
- An additional southbound lane will be added to I-15 between the 10th Avenue South and Gore Hill interchanges. The lane will exit on to the southbound Gore Hill Interchange off-ramp.
- The Tri Hill Frontage Road and 31st Street Southwest intersection will be relocated to the south.
The new bridge design and roundabouts will accommodate over-sized trucks through the intersections.
Why is MDT considering roundabouts at the intersections?
Several improvement options for the intersections including traffic signals were evaluated. MDT is considering roundabouts at the intersections because they have proven to be the safest way to efficiently control traffic based on initial traffic projections. Roundabouts have been shown to improve efficiency and provide a smoother traffic flow including an 89% reduction in delays and 56% reduction in stops.
Roundabouts have several other safety benefits including:
- Enhanced safety due to a reduction of conflict points and a reduced speed throughout the intersection.
- A 90% reduction in fatal collisions when compared to stoplights or stop signs.
- A 40% reduction in pedestrian collisions.
View More Information about Roundabouts
Roundabout Design Testing
MDT and Robert Peccia and Associations (RPA) conducted roundabout testing with several types of large trucks in October 2024. This testing allowed MDT and RPA to identify where problems could potentially arise in a real scenario with trucks entering and exiting the proposed roundabouts designed for the Gore Hill Interchange.
Testing took half a day to complete with each truck making several passes at different angles through the roundabout. MDT laid out a replica of the same sized roundabout planned for the Gore Hill Interchange at a gravel pit near Helena. Several drivers from trucking companies volunteered their time to test the design of the roundabout.
The longest truck was an oversized load with a low-boy trailer and total length of 113 feet. Additionally, a double tanker fuel truck, a 110-foot long “hay train”, a double side-dump trailer, and an MDT snowplow with a trailing tow plow, tested the roundabout layout. During testing, turning tolerances and angles were measured to see if the trucks could make it through the roundabout without hitting curbs or going beyond the truck apron. All trucks were able to navigate the roundabout design successfully.
The test data and the feedback gathered from the drivers about how these trucks navigate the roundabout, are being used to help minimize potential issues for trucks in the design.
Project Process and Tentative Schedule
| I-15 Gore Hill to Emerson Junction Corridor Planning Study identified issues and concerns | 2015 |
| Great Falls Long Range Transportation Plan recommends improvement options to evaluate | 2018 |
| Potential alternatives evaluated and improvements developed | 2018-2019 |
| Recommended improvements presented to the public | 2019 |
| Detailed plans for new interchange design developed | 2020 |
| Preferred alternative presented to the public | 2020 |
| Design plans developed | 2020–2026 |
| Construction anticipated to begin | 2027* |
*Depending on the availability of funding
UPN 9345000