Here's how Toronto is building a subway on top of a bridge on top of a highway
Toronto's transit network is undergoing a generational transformation, with the forthcoming Ontario Line subway set to become the crown jewel of the city's rapid transit system when it opens in the 2030s.
The 15.6-kilometre, 15-station subway route between Exhibition Place and the shuttered Ontario Science Centre at Don Mills and Eglinton will introduce a pair of impressive new bridges spanning the Don River — both well under construction at different points along the line.
Motorists on Toronto's Don Valley Parkway (DVP) have undoubtedly noticed construction on both of these bridges as work ramps up. The Lower Don Bridge may be the smaller of these two crossings, but it is without a doubt the flashier of the pair, thanks to its arch-supported design that will eventually span the Don River and DVP.
First announced in 2021, construction on the 120-metre-long bridge kicked off in 2024 before things really ramped up at the start of this year. Sections of the new subway bridge were installed at the end of January, giving the public a first glimpse at the future landmark.
Now, Metrolinx is sharing a closer look at what it describes as a "huge engineering feat" with a behind-the-scenes backgrounder with the bridge's project manager.
The Lower Don Bridge is being constructed using a temporary trestle technique, which allows crews to build the bridge structure overtop of active highway lanes. The bridge's project manager described the process as similar to putting LEGO blocks together.
Constructing over the DVP was the biggest hurdle faced by the project team, requiring the assembly of bridge sections adjacent to the highway to minimize disruption, before the pre-assembled sections were slid into place via hydraulics on an "elaborate rail system" during a weekend DVP closure.
Meanwhile, Metrolinx crews continue to work away at the second half of the bridge structure, running double shifts six days a week to get the project across the finish line as fast as possible.
Metrolinx
