Yellowhead Trail Freeway Conversion Reaches a Major Milestone

The Yellowhead Trail – St. Albert Trail to 97 Street project is the largest and most complex segment of the citywide Yellowhead Trail Freeway Conversion Program and has recently surpassed the halfway point of construction. The project is progressing on schedule toward its estimated total investment of approximately $635 million.

As prime consultant, ISL Engineering and Land Services Ltd. (ISL) has been with this project from concept through construction, and this milestone is a good moment to look at the engineering behind converting one of Edmonton’s busiest corridors into a modern freeway, all while traffic keeps flowing and the surrounding communities stay connected. From complex interchange structures constructed around live traffic to major drainage infrastructure deep below the corridor, much of the engineering behind the freeway conversion is not immediately visible to drivers.

Across the wider Yellowhead Trail corridor, traffic today ranges from 63,000 to 81,000 vehicles a day, a number the City projects could climb as high as 155,000 by 2047. To handle that growth, the Yellowhead Trail will carry three lanes of free-flowing traffic in each direction at a design speed of 80 km/h. Getting there means removing every signalized intersection and direct access point along this stretch of Yellowhead Trail and replacing them with grade-separated crossings and new roadway connections, including major interchange structures at 127 Street and 121 Street. In practical terms, that means reducing overall emissions by eliminating stop-go traffic, fewer conflict points between vehicles and a safer, more predictable commute for the tens of thousands of drivers who rely on this corridor every day.

The benefits reach beyond the road itself. Alongside the freeway, ISL’s Landscape Architecture team has designed a new linear greenway along the corridor’s south edge, running through the communities of Dovercourt, Sherbrooke and Prince Charles. Shaped by public and community input, the design includes more than 34,000 new trees and over 45,000 shrubs, ornamental grasses and forbs, although the planting scope will be a phased execution that may go beyond the construction completion date. The planting design goes beyond aesthetics: over 3.8 hectares of naturalized plantings will boost biodiversity along the corridor, while a diverse mix of drought- and disease-resistant species, planted in enhanced soil, are designed to thrive over the long term.

The City of Edmonton’s Yellowhead Trail Strategic Plan first identified the corridor as a future freeway, and the City retained ISL to develop a functional plan for the segment between St. Albert Trail and 97 Street. That planning phase, which ran from 2019 to 2021, had to solve a difficult puzzle: this segment carries the highest traffic volumes and has the narrowest protected right-of-way of anywhere along the Yellowhead corridor, boxed in by rail lines, a cemetery, a future LRT extension and long-established neighbourhoods. ISL’s answer was to shift the freeway’s alignment to protect existing communities and recommend an interchange configuration at 121 Street that could support a future 109 Street connection, all without compromising how the freeway will perform decades from now.

Public engagement has been part of this project at every stage, from the concept plan through to design and now construction. Over the years, ISL and the City have used a variety of engagement formats to share project details and gather feedback at key milestones. Much of the design-phase engagement took place during the COVID-19 pandemic, when in-person events weren’t possible, so ISL got creative, producing a fly-through video walking through the project’s key features and hosting interactive virtual open houses, giving residents a way to see the plans and ask questions directly.

Design and construction followed, running from 2021 through to an expected completion in 2027, delivered using a Construction Manager at Risk (CMAR) model with PCL as main contractor. ISL has continued as prime consultant through design, tender preparation and construction administration.

ISL’s structural design approach was driven by the distinct constraints at each interchange. At 127 Street, maintaining traffic through a constrained brownfield site required a solution that could be constructed in stages within the existing corridor. ISL developed a top-down construction approach using tiered tangent pile retaining walls to support staged excavation and accommodate the new roadway and pedestrian bridges while keeping Yellowhead Trail operational.

At 121 Street, the ability to construct the interchange largely offline reduced traffic staging constraints but introduced a different challenge: poor foundation soils beneath the elevated approaches. ISL’s design combined a single-span bridge with MSE wall-supported approaches and incorporated ground improvement measures, including rigid inclusions and wick drains, to improve stability and manage settlement. The contrasting solutions demonstrate how ISL tailored the structural and geotechnical design to the specific site conditions rather than applying a single approach across the corridor.

Beyond the two interchanges, the project’s structural scope also includes retaining walls, a 1,400-metre-long noise attenuation wall extending from St. Albert Trail to 124 Street, and new overhead sign structures supporting freeway operations throughout the corridor.

Beneath the surface, a new drainage system is tackling one of the corridor’s most persistent problems: flooding. Underpasses along Yellowhead Trail have long been vulnerable to flooding during major storms, closing roads and disrupting traffic for hours at a time.

Servicing the corridor from St. Albert Trail to the CN Bridge, a new 2.5 metre diameter storm tunnel running about 1.4 kilometres and sitting 13 to 15 metres below the surface, paired with an upgraded roadway drainage network, is designed to protect the new underpasses even during a 1-in-100-year storm, the kind of event that would otherwise shut the corridor down.

The east portion of the project including the new 121 Street underpass drains a portion of the Yellowhead Trail roadway to a stormwater pond being built next door as part of the Blatchford redevelopment. Work as part of this project includes the construction of Phase 1 of the Blatchford Storm Pond as well as a 2.4 metre diameter storm pipe connecting the two.

Progress on the ground shows just how much has moved since the concept plan was first approved. Building demolition is complete, with 20 buildings removed to clear the corridor, and earthworks are 75 per cent complete with around 340,000m3 of material excavated to date. Roadworks are underway across the corridor, and the new 121 Street/107 Street intersection is nearly finished, with traffic set to shift onto the new road in September 2026. Traffic will flow on the 127 Street bridge in Fall 2026, with 121 Street to follow in the summer.

The Blatchford stormwater pond that’s helping manage runoff from the eastern part of the corridor is now 90 per cent complete, with only landscaping left to finish this summer, another example of drainage work moving faster than what’s visible at street level.

Below ground, franchise utility relocation is complete, and drainage tunnelling that will protect the corridor from flooding is 95 per cent complete, with only shaft and manhole work remaining. Storm/sanitary drainage is past the halfway mark, with almost 10,000 metres of sewer mains, sewer services, catch basin leads and subdrains installed to date.

The scale and complexity of the Yellowhead Trail project set it apart from most projects ISL has delivered. Reaching the halfway point in construction expenditure marks a significant milestone and reflects the substantial multidisciplinary effort required to bring the project this far. To date, 189 ISL employees from 22 service units across eight offices have contributed to the Yellowhead Trail project between September 2021 and July 2026. Few projects call on this much of the company at once, spanning transportation, buildings, bridges, drainage, landscape architecture, geotechnical and public engagement expertise, and more, all working together on the same corridor for years at a time – an average of 271 workers and subcontractors were on site daily in July 2026.

As construction progresses toward completion, the transformation of Yellowhead Trail is becoming increasingly visible. Behind that transformation is an integrated engineering effort, spanning transportation, structures, geotechnical, drainage, utilities and landscape architecture, to deliver a free-flow freeway through one of Edmonton’s most constrained and heavily travelled urban corridors.