Highway 91 at 72nd Avenue Interchange Project Design
Goals of the Design
Improve Traffic Flow
Today, highway 91 and 72 Avenue is currently a three-legged intersection controlled by a partial traffic signal. Currently:
- Southbound traffic is free-flow with no traffic signal
- Northbound traffic is required to stop at the signal to accommodate southbound traffic turning left onto 72 Avenue
- Traffic stopped at this signal often extends over 2.5km to the existing truck pullout out of the 64 Avenue interchange
The proposed new design will allow for free-flow in both directions on Highway 91, with a left turn signal for southbound traffic on an elevated interchange off an exit ramp on the west side of the highway. It increases the safety and efficiency of the corridor by replacing the existing traffic signal with an interchange.
Protect Burns Bog
We are committed to minimizing the impacts of the project on Burns Bog.
Burns Bog is the largest and last remaining raised peat bog in the Northern Hemisphere, located on the delta of the Fraser River. The bog's ecosystem sustains a wide variety of flora and fauna, including 24 species of mammal and 150 bird species. The bog provides habitat to numerous species at risk (including the Sandhill Crane and Pacific Water Shrew) and it is a key rearing ground for Fraser River salmon.
Burns Bog is located on the west side of Highway 91. The proximity of the bog to Highway 91 required designers to develop a compact interchange design that avoids impacts to the bog. A tight half diamond interchange was selected as the preferred interchange configuration because it avoided impacts to the bog while providing a grade separated solution for Highway 91 and 72nd Avenue. The overall footprint on the interchange is entirely within the Ministry of Transportation and Infrastructure right-of-way with no encroachment into the Bog.
Designing the Interchange
Learning from Experts
Throughout the design process, the ministry worked with the Burns Bog Conservation Society Scientific Advisory Panel in order to fully understand the complexities of Burns Bog, and find workable solutions to the limitations the bog presents.
Project designers worked with environmental coordinators from the ministry, urban designers, engineers, climate action and environmental experts, natural resource managers, environmental consultants and water model consultants in order to create an optimal design for this interchange. Together, these experts provided invaluable information which led to the unique half-diamond shaped intersection.
Protecting the Bog
The interchange was designed in a unique half-diamond shape to minimize impacts on Burns Bog.
In consultation with the Scientific Advisory, the following factors were considered during the design process:
- Maintaining existing drainage patterns to minimize disturbance to the bog, as recommended by the Scientific Advisory Panel
- Replacing drainage culverts across Highway 91 that are in poor condition
- Using overflow drainage measures - such as ditches and swales - instead of enclosed drainage systems (i.e. storm pipes and manholes) to provide primary treatment before surface runoff goes into the ground near the bog
- Ensuring the existing ditch on the west side of Highway 91 adjacent to the bog remains undisturbed
- Ensuring future contractors remove all temporary gravel working pads and that the work site is restored back to its existing condition
- Minimizing the amount of mineral waters moving westward into the bog when designing the southbound on and off ramps
Geotechnical investigations were done for this project during the design phase. Given the location of the project, the interchange was designed to balance area traffic demands with the environmental sensitivity of the adjacent bog.
The general subsurface conditions at the site consist of compact sand, hog fuel fill and soft fibrous peat with a ground water table 2 m below the existing highway. Because of the existing ground condition and given the close proximity to Burns Bog, the design of the interchange needed to use timber pile rafts along the Hwy 91 southbound on and off ramps to ensure the design is environmentally friendly for the bog.
For the Highway 91 southbound on and off ramps – the mechanically stabilized earth (MSE) approach embankments are supported by a 300 mm-thick reinforced concrete raft with 12.0 m-long, 300 mm-diameter, untreated timber piles embedded in the compact sand.
In consultation with the Scientific Advisory Panel, the current was deemed the most suitable for the bog given the environmental factors for this project.