When you say the word “subway,” the first images that come to mind are of long, dark tunnels with trains running beneath the ground.

After all, London’s original subway system gave us the iconic “underground” branding, and generations have grown up with images of urban voyages far below city streets. In fact, only about 45 per cent of that system is underground in tunnels, with much of the network on the surface.

So what are the upsides to looking up for sections of the future Ontario Line?

Is it just to reduce costs?

These questions were top of mind for many of the community members who came out to the recent round of open houses for the Ontario Line, with many comparing the project to former plans for a shorter line that was entirely underground.

While some may believe that certain sections are above ground simply to control costs, the most important motivations are making better connections and bringing more relief to more people.

When Metrolinx experts put together the Ontario Line proposal – with both below- and above-ground sections – factors like customer convenience, geography, the length of the route, and minimizing the impacts of construction on neighbourhoods were all part of the decision making.

A big advantage of the Ontario Line is that it will run for nearly 16 kilometres from the Ontario Science Centre to Exhibition Station at only a marginally higher cost than the previous Relief Line South proposal, which was just under half as long.

While that line would have ended at Danforth Avenue, the Ontario Line will go farther. It will emerge from the southern embankment of the Don Valley, west of the Leaside Bridge, on an elevated structure that will connect it to Thorncliffe Park and Flemingdon Park, ultimately terminating at the Ontario Science Centre. There, it will connect to the new station being built for the Eglinton Crosstown LRT.

This connection will divert more TTC riders away from busy Line 1, as people will take the Eglinton Crosstown LRT to connect with the Ontario Line. This will help reduce crowding at Bloor-Yonge station by 17 per cent and at Eglinton Station by 15 per cent.

Running along Overlea Boulevard and Don Mills Road, this elevated section of tracks will take advantage of a street layout that reduces the need for digging.

“In Thorncliffe Park and Flemingdon Park, the tracks will be elevated and this doesn’t have a significant impact on existing properties because there is such a wide street right of way,” said Daniel Cicero, Sponsor for the Ontario Line.

Above-ground tracks in this area also reflect the unique challenges of building a line that spans the Don Valley by the Leaside Bridge, and an offshoot of the valley that wraps around the eastern and northern edges of Thorncliffe Park. A tunnel that would be deep enough to go under both would require digging the deepest station in Toronto’s transit network, making for very long connections to buses at street level. This would also mean longer construction timelines. As well, stations further south would have to be dug deeper, before the line reaches the valley.

Elevated guideways are nothing new — they’ve been built for centuries. But advances, particularly in using concrete that can support thinner structures than in past decades, have enabled more attractive designs.

“They can be super thin to reduce the size when compared to structures like the Gardiner Expressway, which is very heavy,” said Becca Nagorsky, Metrolinx director of project planning.

Stations will also benefit from shorter construction times and updated design approaches.

“At-grade stations are generally less expensive and quicker to construct because you don’t need to spend as much time to excavate the soil,” said Michael Tham, deputy technical director for the Ontario Line. “You get to start building the structure of the station sooner, see visual progress sooner and complete the major works sooner.”

In many cities across Europe, modern urban design principles have led to the construction of new elevated rail stations and lines that are pleasing to look at.

Here in Canada, Vancouver’s TransLink network offers many great examples of elevated stations that fit nicely into surrounding neighbourhoods.

In Leslieville and the Don Lands, the line will run at-grade alongside the existing GO rail corridor, helping to reduce construction impacts.

Importantly, this approach eliminates the need for excavations along Carlaw Avenue that would have taken place under the previous Relief Line South proposal. This is because it aligns construction of the Ontario Line with the corridor improvements that were already planned to support the expansion of GO rail services.

Through the GO Expansion program, tracks will be upgraded to make it possible for Metrolinx to deliver more frequent, two-way, all-day service on quieter, emission-free, electric trains that run on the Lakeshore East line through Leslieville.

Proceeding with both the Ontario Line and GO expansion work at the same time – and along the same corridor – will help contain construction and ensure the neighbourhood is not inconvenienced twice.

Once up and running, the light, electric-powered Ontario Line trains will also operate more quietly and generate less vibration than the heavier diesel-fueled trains that run through the corridor today.

Teams are also studying measures that can be put in place along the actual rail infrastructure to ensure noise and vibration are kept to a minimum. Experts are looking at whole host of options to ensure Ontario Line operations are respectful of communities—from noise walls, to rail dampers, to enhanced maintenance standards.

One of the biggest benefits of the Ontario Line is how it will make it easier to transfer from the subway to other transit options throughout the network.

Simpler transfers will be important for commuters that will use East Harbour, a new station that will be built just east of the Don River and north of Lakeshore Boulevard. The station will accommodate both GO train and subway service in a corner of the city that is poised for growth.

To reach East Harbour, the Ontario Line will travel at ground level through the existing GO corridor, enabling travellers to move more easily between their connections.

“We are trying to build the Union Station of the East,” said Mathieu Goetzke, Metrolinx’s vice president for planning.

The plan is for the Ontario Line to connect to Lakeshore East and Stouffville GO trains and TTC surface routes at the station, where future transit demand is expected to be high. Having the Ontario Line above ground at this station will allow for more direct connections.

In many cases, people transferring from a GO train to a subway train will be able to walk straight from one to the other without having to go up or down a level.

“When you are at grade, or street level, it can make it easier to transfer to trains, buses and streetcars,” explained Devin Horne, Metrolinx manager of project planning.

The earlier Relief Line South proposal featured very deep tunnels — 38 metres below ground — in order to get under the Don River to the vicinity of East Harbour, adding four and a half minutes of escalator time to each transfer. That’s more than enough time to miss your connection. Studies have projected this would have reduced ridership by 15 per cent.

The unusually deep tunnel would reflect the challenging geography of the Don River. It is an environmentally sensitive area, in a floodplain, with changing soil conditions.

Bedrock forms a giant “V” that extends the valley under the water’s surface. Soft soils can be found in the bottom of the V, under the water.

There are significant engineering risks in building tunnels that go from firm bedrock to soft soil, forcing tunnels to go deeper underground.

As well, that Relief Line South plan would have essentially created two adjacent stations – one for the subway and another for surface vehicles – while the Ontario Line puts all the connections in one place.

The Ontario Line will also give commuters an easy connection from GO Trains to the subway at Exhibition station, where the line will also be above ground.

Taken together, these new transfer points will help reduce crowding at Union Station by 13 per cent – relief that would not have been realized under the previous proposal.

TTC subway riders have long enjoyed sunshine on sections that go above ground through stations like Rosedale, Keele and Yorkdale, and while crossing the Don Valley travelling across the Prince Edward Viaduct. The Ontario Line will offer up a similar experience.

Whether at-grade or elevated, Metrolinx will use the newest design techniques to deliver infrastructure that fits Toronto’s urban fabric and is well suited for the light of day.

For a story on how Ontario Line will benefit low-income neighbourhoods, just click here.

And keep checking back to Metrolinx News as we prepare more features on the new route.

Want to see other transit related progress Metrolinx is spearheading? Then check out this special page.