Abstract Manager

Parsons has been commissioned by Québec’s Ministère des Transports et de la Mobilité durable to replace an existing overpass and temporarily reconfigure the Autoroute 31/Autoroute 40 interchange. Parsons is responsible for preparing construction drawings, developing technical specifications, and providing technical support during construction. The interim configuration will enable motorists to travel in both northbound and southbound directions on Autoroute 31 via the replacement overpass for several years, until a future comprehensive redevelopment of the interchange is undertaken.

This future redevelopment, which extends beyond Parsons’ current mandate, will feature the replacement overpass designed by Parsons carrying northbound traffic, as well as a second future overpass designed by others to accommodate southbound traffic. The replacement overpass will be constructed adjacent to the existing one, situated approximately 200m north of a signalized intersection at the terminus of Autoroute 31 and roughly 200m south of another overpass crossing a local road. Both elements must remain in place until the permanent interchange is realized, serving as fixed tie-in points for the temporary configuration.

The project faced numerous safety and design challenges, particularly in establishing appropriate design speeds. North of the replacement overpass, Autoroute 31 remains a 4-lane divided highway with high speeds. The temporary configuration requires a transition to a 3-lane undivided roadway, necessitating a speed reduction. The design ensures a safe speed transition and guarantees safety in terms of horizontal and vertical alignments, superelevation, and sight distance. Given that the tie-in points are located no more than 400m apart, several geometric standards could not be fully respected. Consequently, critical user safety criteria dictated much of the design.

Furthermore, it was essential to maintain access for both motorists and agricultural vehicles from a local road onto Autoroute 31. To prevent substandard weaving conditions, several options were considered: creating a temporary agricultural access and entrance ramp further upstream, keeping the local road’s existing entrance ramp in service, or implementing a detour.

Another challenge was the need for lightweight embankments for the replacement overpass and its approaches. The temporary geometry and its new embankments, which will be in service for several years, will impact the unconsolidated clay soils in the area, necessitating an adequate pavement structure with lightweight fill to minimize consolidation activity.

In conclusion, this project exemplifies the adaptation of standards to complex existing conditions, the exploration of innovative solutions, and the prioritization of user safety in engineering design, offering valuable insights for TAC members.