The city of Laurel, situated near the majestic Yellowstone River in Montana, is a quaint, diverse community with historic ties to industry and agriculture. Lately the city has experienced unprecedented levels of building and development growth, prompting transportation planners to seek out mobility solutions that enhance connections for local and area travelers.
One critical access point is the West Laurel Interchange, an Interstate 90 junction where average daily traffic counts are anticipated to swell from 14,150 in 2017 to 23,180 by 2037 – a 63 percent increase. Currently, the Montana Department of Transportation (MDT) is reconstructing the outdated interchange to meet current bridge and roadway design standards, improve connections to the local road network, and boost safety for motorists.
The overall project scope includes the installation of new eastbound and westbound interstate bridges over the Montana Rail Link (MRL) rail lines and West Railroad Street. Construction crews will also build a new compressed diamond interchange containing on and off ramps in both directions that will permit easier access to 19th Avenue West.
“This project will benefit citizens and businesses in the community by opening up the west end of Laurel, which is limited in access,” says MDT Project Manager James Stevenson. “On the main street access there’s an underpass beneath the railroad tracks, and there’s not a good exit on the west end.” Additionally, project plans include the reconstruction of a roadway section that is notorious for serious vehicular crashes.
This project is being completed in two phases, with Phase 1 commencing construction just west of Laurel in October 2017. With an estimated price tag of $24 million, this phase consists of rebuilding 1.2 miles of I-90 and also realigning and replacing the two bridges with modern, steel structures. Project officials expect Phase 1 to achieve substantial completion next summer.
Phase 2 is a future undertaking estimated to cost about $8 million and scheduled to be advertised later this year. Planned improvements include constructing four ramps at the new interchange and rebuilding 19th Avenue West over the interstate, as well as other street improvements. The new road will have two lanes, wide shoulders and a center turn lane. The intersection of 19th Avenue West/Golf Course Road and Old U.S. Highway 10 will also be rebuilt and shifted approximately 70 feet west to better align with Golf Course Road and avoid irrigation ditches and utilities. According to MDT officials, Phase 2 construction should take about a year to complete.
Stevenson adds, “Once Phase 2 is completed, there will be on and off access to both eastbound and westbound commuters. With the [CHS] refinery in place, it should alleviate some of the main street traffic.” The CHS refinery, known as Cenex before it merged with Harvest States in 1998, dominates the southern half of the city of Laurel and is a major distributor of crude oil products throughout the northern United States.
Time for an Overhaul
According to Stevenson, the original West Laurel Interchange was constructed sometime in the 1960s. Under this old design, drivers could only access the westbound lanes of I-90 from Old U.S. Highway 10. From the interstate, eastbound travelers had to exit I-90 immediately west of Laurel while westbound motorists were forced to use a different interchange.
MDT began discussing options to upgrade the West Laurel Interchange well over a decade ago. Several design and construction firms with roots in Montana have been key to making these improvements possible. Morrison-Maierle – a Helena-based company providing engineering, surveying, planning and scientific services – has provided design consulting expertise since the project’s inception. Missoula-based Riverside Contracting is serving as the prime contractor and Sletten Construction, headquartered in Great Falls, is handling bridge construction work. SK Geotechnical, located in Billings, has provided geotechnical engineering, drilling and materials testing support. MDT also partnered with KLJ, an engineering firm headquartered in Bismark, North Dakota, to handle public outreach for the project.
Stevenson notes, “It’s been a team effort between MDT, the contractor, the design firms, the local government and others. It’s a project that’s been going a long time, so there’s been a lot of involvement over the years.”
The project team had to devise solutions that addressed multiple deficiencies in the existing interchange system, which has contributed to a higher-than-average rate of vehicular crashes. The main problem is the configuration of the partial interchange, which is closely spaced with two functionally obsolete bridges that skew over active rail lines on sharp, superelevated curves. Also, the bridges – as well as the section of I-90 connecting to them – have narrow shoulders that offer little room for correction when vehicles deviate from the main lanes.
Other engineering challenges affecting the project’s design include highly compressible soils, environmentally sensitive areas and the two-acre Figgins Pond located within the project work zone. After a thorough Value Analysis review, the final alignment plans approved by MDT offered potential savings estimated at $17.3 million – and also eased the construction process by reducing conflicts with utilities, requiring fewer right-of-way acquisitions, avoiding building through Figgins Pond, and requiring fewer project materials and less construction time.
Ingenuity Spotlight on Drainage Solutions
The project will improve drainage by adding new pipes and culverts around the interchange to ensure drainage flows off the roadway. A large 800-foot-long culvert is being replaced to avoid exacerbating flood hazards downstream in the city of Laurel. New detention ponds are being built to slow down the speed of water and avoid runoff entering into Figgins Pond or the nearby Italian Irrigation Ditch.
“Laurel has a history of flooding problems, most of which are related to stormwater runoff and inadequate conveyance in existing drainage facilities. The large increase in developed surface area and associated runoff needed to be mitigated on the project and improve existing stormwater runoff and flooding conveyance when feasible,” says Matt Pool, PE, a Project Engineer at Morrison-Maierle.
Stormwater runoff and attenuation was designed using Natural Resources Conservation Service (NRCS) TR-20 methodology. Engineers often use this evaluation tool to assess flooding problems, flood control alternatives (such as reservoirs, channel modification and diversion), and impacts of changing land use on the hydrologic response of watersheds.
Construction workers are also building settlement basins to remove contaminants from drainage water before it is released into Figgins Pond or the Italian Irrigation Ditch.
“Two smaller detention/water quality basins were designed to reduce sediment loading to the stormwater ponds and to prevent nutrient loading from occurring at receiving water bodies due to normal irrigation wastewater discharge,” Pool adds.
Phase 1 Reaches Halfway Point
Crews have already constructed the new I-90 eastbound bridge and approaches. Embankments for the new bridges were built outside of the existing traveled way and surcharged to allow for settlements in the poor soils.
Workers also built the median crossovers used to detour all I-90 traffic onto the existing eastbound bridge. Once traffic was shifted, the team constructed the new westbound lanes on a flatter curve alignment to the west of the bridges. Next, I-90 traffic was switched onto the existing westbound bridge so crews could finish constructing the eastbound road connections. These detour routes permitted only single-lane travel in each direction.
Work has been temporarily halted since mid-November 2018 because MDT requires four lanes of I-90 to be open to travelers during winter months. Eastbound drivers are currently using two lanes on the new bridge while westbound drivers traverse both lanes of the existing bridge.
Project activities are scheduled to resume this spring with workers constructing the westbound surcharge and erecting the new I-90 westbound bridge.
Surcharge timelines and railroad sequencing are two of the biggest obstacles on this interchange overhaul. “The surcharge has been the biggest challenge out there,” Stevenson says. “Construction crews have already constructed the surcharge for Phase 2 during Phase 1, so when Phase 2 does get let, the contractor will be able to come in and remove the surcharge and use that material to build portions of Phase 2.”
Contractors are relying on leading brands such as Caterpillar, Komatsu and Ingersoll Rand for their heavy equipment needs. Dozers equipped with GPS blade control systems are also being used to enhance the construction process.
Staying Ahead of the Curve with Safety
This project’s emphasis on boosting drivers’ safety is part of MDT’s “Vision Zero” campaign, which aims to eliminate highway-related deaths and injuries in Montana. Vision Zero strives to meet this goal through various initiatives, including pushing roadway engineers to design infrastructure that augments safety in meaningful ways. In a state where more than 21,000 roadway crashes occurred between 2008 and 2017, such change is definitely needed.
Drivers traversing the West Laurel Interchange often collide with fixed objects such as concrete barriers, guardrails, bridge railing, other moving vehicles or wild animals. Most accidents have occurred during winter months because the curving roadway is particularly tough to negotiate during Montana’s icy, snowy winters. Further analysis of crash data statistics between 2012 and 2017 reveals that 78 percent of accidents happened on the eastbound lanes.
The replacement bridges on the West Laurel Interchange project will play a key role in preserving life and property. Under current National Bridge Inspection Standards (NBIS), bridge inspectors gave both of the existing structures a sufficiency rating of 77. A low appraisal rating of “3” under NBIS’ “underclearances” category is what resulted in the functionally obsolete classification.
MDT selected a welded steel-plate girder design featuring wider shoulders, 12-foot passing and driving lanes, and gentler curves to help motorists more easily navigate these elevated crossings. The new 556-foot-long eastbound structure contains three lanes to accommodate the future eastbound on-ramp. The 470-foot-long westbound structure being built will have two travel lanes with 10-foot shoulders to accommodate traffic. The 8 percent superelevation of both bridges will provide additional lateral acceleration when vehicles navigate turns, but isn’t too steep for when the roadway becomes icy.
The West Laurel Interchange project certainly demonstrates the state’s strong commitment to preserving travelers’ safety. And in Yellowstone County – a region boasting 15 percent of the state’s population – such engineering ingenuity is sure to make a difference in countless lives for multiple generations.
Highlights of West Laurel Interchange Project
Snapshot of Project’s Estimated Material Quantities (2017-2020)
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