Lincoln Road – Montana Avenue to 1-15

The Montana Department of Transportation (MDT) initiated this project to improve the congested Lincoln Road Interchange six miles north of Helena, Montana on Interstate 15 (I-15). RPA provided holistic professional civil engineering and land surveying services spanning from preliminary traffic engineering analysis and concept development through final design and construction assistance.

Problem

The north valley outside of Helena has experienced rapid growth due to development activity and changes in land use. Construction of the Custer Interchange six miles to the south also resulted in unanticipated changes to traffic patterns and operations at the Lincoln Interchange. Traffic performance deteriorated as traffic volumes increased. This area has experienced vehicle congestion during the peak hours and is expected to experience increased growth in the coming years due to continued development. If remained unchanged, increasing vehicle delay and safety issues were likely to compound. A successful solution was needed to accommodate peak traffic while not unduly delaying motorists during less congested times of the day.

Solution

RPA completed a traffic engineering study to identify and evaluate potential options to improve safety and operations for the Lincoln Road corridor between North Montana Avenue and I-15. The alternatives were intended to be implementable in the short-term and did not include full reconstruction of the Lincoln Interchange or the Lincoln Road corridor. Potential barriers and constraints to project development were also identified to evaluate the feasibility of alternatives. The preferred alternative included single-lane roundabouts at the Lincoln Road intersections with Montana Avenue and the I-15 northbound off-ramp, an additional southbound on-ramp lane, and left-turn lane onto the southbound on-ramp.

Key Project Elements

  • Safety project with the replacement of two intersections with roundabouts and the addition of I-15 ramp lanes
  • Performed initial feasibility study and alternatives analysis with multiple geometric options
  • Implemented broad public relations campaign that overcame public resistance to the improvements
  • Designed PCCP single-lane and PMS tear-drop roundabouts
  • Coordinated with the irrigation district for siphon extension, structure replacement, and specialty safety cable system
  • Investigated future roundabout metering to extend roundabout life

Project Details​

Client

Montana Department of Transportation (MDT)

Location

Lewis & Clark County, Montana

Completed Montana Avenue roundabout
Completed NB ramp roundabout
Completed I-15 ramps, looking north
Completed SB on-ramp with additional lane

Rocker Interchange

Project Description

RPA was contracted to provide design services to implement a previous high-level planning study’s preferred configuration of roundabouts for the Rocker Interchange ramp terminals. Five- and six-legged roundabouts were developed to accommodate the interstate ramps, frontage roads, and business accesses in this tightly-constrained setting. Due to landowner opposition and political pressure, the south roundabout was converted to a standard intersection during design, implementing improved geometrics where feasible. The north roundabout includes outer truck aprons to accommodate the high volume of trucks, pedestrian amenities, and landscaping. Drainage is collected through the new storm drain system and retained on-site in a series of retention ponds. The plan sequence of operations allowed traffic to all roadways and businesses throughout construction.

Project Details​

Client

Montana Department of Transportation

Location

Rocker, Montana

US 2 – Poplar

Project Description

The US 2 – Poplar project began as a surfacing rehabilitation through the town of Poplar. A roundabout was added early in the design phase at Kirn Road to improve safety and slow speeds in a heavily used pedestrian area. MDT and the Tribes agreed upon the addition of a roundabout at 5th Ave. E to accommodate a new residential and commercial development. SK Geotechnical, RPA, and MDT District and MDT Surfacing cooperatively developed a constructible, cost-effective cement-treated pulverized base surfacing section for the rehabilitation efforts in town. The reconstruction portion of the project utilized cement-treated base course.  The project plans included new separated shared-use paths, ADA upgrades, pedestrian bulb-outs and RRFBs, landscaping, accommodations for oversized trucks, and construction detours and phasing that allows for each roundabout to be constructed in two phases. RPA’s school crossing study resulted in the addition of bulbouts, raised refuge islands and RRFBs for the Poplar Public Schools.

 

MDT and RPA  worked exhaustively to obtain and keep community and Tribal Executive Board acceptance with multiple visits and presentations to the Board, two community meetings, and several landowner meetings. Crucial to community acceptance was the culturally relevant landscaping designs and sculptures in the center of the roundabouts.

Project Details​

Client

Montana Department of Transportation

Location

Poplar, Montana