Something tells me the agenda is: present the overpass as the cheaper option to rule out the underpass, but it’s so visually obtrusive that they’ll just say “we’ll keep it at-grade”
The report makes it pretty clear that one of these options will be needed.
Traffic Analysis
Ellerslie Road is currently a four lane divided arterial road, with future plans to widen it to six lanes. As part of the IIS00553 Capital Line South Extension Project Update and Budget Approval report, an initial traffic analysis conducted in 2021 using forecasted peak 2050 traffic volumes indicated that
grade separation of LRT across Ellerslie Road performed better than an at grade option.
As part of the 2024 feasibility study, a subsequent traffic analysis was conducted to assess the potential impacts of Ellerslie Road going over or under the LRT, using the same forecasted peak traffic volumes in 2050. The analysis indicated that
having no grade separation would increase traffic delays on Ellerslie Road, particularly for eastbound traffic. Additional traffic delays at the intersection, during peak hours, were projected to range from 20 to 30 seconds with the existing four lane configuration and from 10 to 25 seconds with the proposed six lane configuration.
These delays are less than the anticipated delays at the 127 Street and 135 Street intersections with the proposed six lane Ellerslie Road configuration.
The introduction of grade separation, either with an overpass or underpass, is expected to mitigate these delays by eliminating direct interactions between road traffic and the LRT.
The overpass option would facilitate smooth traffic flow over the LRT, reducing the likelihood of traffic congestion. However, it is worth noting there would be temporary traffic disruptions during overpass construction. The underpass option would similarly eliminate traffic-LRT interactions, but construction would cause more traffic disruption than the overpass due to deep excavation and advanced drainage systems.
Cost Analysis
The feasibility study included preliminary cost estimates for the grade separation options in 2023 dollars at approximately -30/+50 per cent confidence level. These cost estimates are early stage approximations and would continue to be refined through design development. The overpass option is estimated at $64 million for a six lane crossing. This cost includes earthworks, utility relocation, overpass construction and traffic management. The overpass design, with its relatively straightforward engineering and reduced need for extensive groundwater management, presents a more predictable cost.
In contrast, the underpass option is estimated at $99 million for a six lane crossing. This higher
cost reflects the additional expense related to deep excavation, complex structural requirements such as retaining walls and the implementation of permanent water mitigation solutions. Greater exposure to unforeseen ground conditions contributes to increased risks associated with the underpass option.
Both grade separation options are feasible and viable. However, the overpass is assessed to be less expensive and less complex.