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On the west side of Toronto, the West Extension of Eglinton Line 5 has reached a major milestone. The segment of the tunnel immediately west of Mount Dennis station is now fully mined, and work on the elevated guideway is also advancing. As part of the 9.2-kilometre extension of the recently opened Eglinton Line 5 LRT, this project will bring the Light Rail Transit line across the entire western width of the city — through York and Etobicoke — before terminating at Mississauga's eastern limits.
In a recently released presentation to the Metrolinx Board of Directors, the provincial transit agency announced that the 500m segment of the extension's tunnel from the current Line 5 terminus at Mount Dennis station to Pearen Park has been entirely mined. The short tunnel will allow light rail vehicles to navigate the dramatic change in grade where Eglinton Avenue intersects with Weston Road before surfacing onto an elevated guideway over the Eglinton Flats. With mining now complete, the multi-step process to complete the tunnel structure can get underway in advance of installing the track bed and signalling infrastructure necessary to facilitate modern rapid-transit operations.
Work to the west of this initial tunnel has also advanced dramatically since UrbanToronto's last update earlier this year. Set to bridge 1.5 kilometres along the north side of Eglinton Avenue where it traverses the Humber Valley, an elevated guideway will carry Line 5 service over the Eglinton Flats, a broad lowland area divided into parkland and golf courses. With the majority of the support columns now erected, the piece-by-piece construction of the guideway's deck has made major progress. Though it will eventually cede the longest-elevated guideway in Toronto title to the northwest portion of the under-construction Ontario Line 3, this section of the Eglinton Crosstown West Extension marks the first segment of new elevated rapid transit built in Toronto in decades.
In the run-up to construction for this segment of the line, the guideway plan (as opposed to tunnelling under the valley) faced opposition from some locals who expressed concerns regarding the temporary loss of tree canopy in the Eglinton Flats, and the disruption of private events held within the public parkland. However, the elevated alignment was ultimately selected because the area is one of the most hydrologically complex in the City of Toronto.
As the name suggests, the Eglinton Flats are a series of lowlands stretching east of the Humber River near its intersection with Eglinton Avenue West. This already waterlogged locality is bounded on three sides by the geographic ridges where the neighbourhoods of Mount Dennis and Rockcliffe-Smythe sit. As a result, the area is infamously prone to flooding—the most damaging example being caused by Hurricane Hazel in 1954. In the years before the Toronto and Region Conservation Authority (TRCA) banned development in floodplains, homes and businesses extended from the historic centre of Mount Dennis down toward the Humber River. This settlement pattern abruptly ended with the devastating floods brought by Hurricane Hazel, which wiped away nearly all buildings within the Eglinton Flats and cost many people their lives.
The need to avoid another disastrous flood, this time affecting a multi-billion-dollar transit line carrying thousands of people, left Metrolinx with two choices. The first option was to bore a tunnel at an incredible depth beneath the Humber River, drilling through the solid sediments found dozens of metres below the loamy surface-level floodplain. This approach would have driven up project costs by hundreds of millions of dollars and necessitated extensive waterproofing that required constant upkeep and remained prone to leaking. The alternative option was to elevate Line 5, wholly separating it from the waterlogged ground below while delivering immense savings due to the lower costs and shorter timelines associated with elevated construction.
This technique is far from new to Toronto; the TTC implemented the exact same design almost directly south of the Eglinton Flats when constructing Old Mill station on Bloor Line 2 in the 1960s. In the decades since opening, Old Mill station has not only remained free from the near-annual floods below it, but has also gained a reputation for the stunning views riders enjoy while crossing the Humber River valley—a perk future riders of Line 5 will share when traversing the Eglinton Flats.
UrbanToronto will continue to follow progress on the Eglinton Crosstown West Extension, but in the meantime, you can learn more about it from our Database file, linked below. If you'd like, you can join in on the conversation in the associated Project Forum thread or leave a comment in the space provided on this page.
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