As he was being sworn in last week, Toronto's new mayor renewed his central campaign pledge: to push through a controversial $8-billion public-transit plan that he says will make it faster and easier to get around Canada's biggest city.

Critics call John Tory's SmartTrack proposal ill-conceived, dubbing it a grandiose scheme unlikely to get off the ground. But much the same was once said of Crossrail, the £15-billion ($27-billion) expansion of London's rail network, which crews have nearly finished tunnelling. It is to open in 2018.

One of Europe's leading engineering projects, Crossrail promises to provide the city's biggest increase in transit capacity in 70 years. There will be an added 21 kilometres of twin-bore tunnels, allowing trains to run through the city core every 2½ minutes at peak times, carrying 200,000 people an hour. Outside the city, the central tunnels will link up with existing surface track to create a 118-kilometre transit spine connecting London and its suburbs.

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The need for more transit has long been clear, says Isabel Dedring, London's deputy mayor for transport. "There's nobody really in London who's arguing that there should be more car traffic in the centre of the city, or indeed even the same amount," she says.

A congestion charge for central London introduced in 2003 prompted a 10-per-cent drop in traffic levels in the core. But the population is climbing and "the size of the roads is not growing," she notes. London is home to about eight million people, and is projected to add a million more by 2030. The city is expected to grow by another one or two million in the 20 years after that.

Despite the looming demand, Crossrail languished on the drawing board for a generation. Even after its approval in 2008, it was by no means certain to go ahead.

Now, five years after work began, it enjoys broad support. What happened? The ways it is being financed, justified and promoted all offer lessons that could prove valuable not only to Toronto but to other Canadian cities, including Vancouver as it pushes for the Broadway SkyTrain extension.

Have business chip in

Almost one-third of Crossrail's cost will be covered by London businesses, without whose contribution the project likely would not have gone ahead. London First, a lobby group representing the city's biggest corporations, played a key role.

David Leam, the group's infrastructure director, says London First was born in 1992 when business was concerned about the city's lack of long-term planning. It seized upon Crossrail, recognizing it was "clearly a good project, which would bring economic benefits." Mr. Leam says that business realized that, if a private-sector contribution was necessary, "that was a price worth paying."

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A 2-per-cent levy added to the tax rate on non-domestic London properties worth more than £55,000 is expected to raise £4.1-billion.

Think bigger than transit

A vital part of Crossrail's pitch is that the project is about economic regeneration, not just moving people, says Ms. Dedring. And key to that is how it taps into East London, traditionally a less developed part of the city.

"London is historically going through this really fundamental structural reshifting, rebalancing between east and west, and Crossrail fits that narrative obviously very well," says Michael Hebbert, a professor of town planning at University College London, who chaired the review process for Crossrail's design. "Part of this is to enable London to grow its capacity without growing physically."

The new line will make East London a much-needed "dormitory" for the rest of the city, says George Iacobescu, the Romanian-born engineer who went to England more than 25 years ago to help Canada's Olympia & York build its renowned redevelopment of Canary Wharf.

Today, as chief executive officer of the Canary Wharf Group, he sees the need for "a place where the nurses and the teachers and the policemen and the firefighters can live very close to the city." As he said in an interview for the book Londoners, "if they all have to travel two or three hours to get to work, how productive are they and how tired are they by the time they get home?"

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Sell the sizzle

Below Soho Square, southwest of where Oxford Street meets Tottenham Court Road, there's a tunnel that could fit a three-storey house. The huge space for the platform area of a key new Crossrail station began with a pass of a tunnel-boring machine (TBM) before being dug out to its current size.

The scale gives the site a sense of grandeur, even drama. Down here, the bustle of London – whose narrow streets and historic buildings posed the sort of logistical headaches that Andy Alder, project manager of western tunnels for Crossrail, cites as the biggest challenge to construction work – feels far away.

And it was here that one of the most attention-grabbing parts of the project took place. The 7.2-metre-wide TBM had to "thread the needle," clawing its way through the clay within 80 centimetres of an existing subway line, and just 35 centimetres from an adjacent escalator. The 1,000-tonne boring machine made it through without a hitch, not stopping service on the other line. The engineering feat was great for project PR, attracting a lot of attention, and featuring prominently in a three-hour BBC program on Crossrail, anchoring a segment dubbed "Urban heart surgery."

Be specific about benefits …

Walk past a Crossrail site, and the hoarding will make a very granular pitch for how the project will help Londoners.

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Among the touted benefits: bringing 1.5 million people within 45 minutes of "all the best of London." There will be 57,000 new homes thanks to neighbourhood regeneration around stations. The project is pushing ahead by 100 metres every week and, when done, passengers will be able to get across the city in 12 minutes.

Prof. Hebbert said that people behind major infrastructure projects have gotten better in the last generation at identifying the sorts of effects that resonate with the public. "I think it's part of the new-style project management," he says. "Big civil-engineering projects in town have always involved public relations … but that aspect is being taken much more seriously nowadays."

Other selling points: cutting nearly in half the trip into the city from Heathrow Airport, reducing crowding at stations and carrying 200 million passengers a year. The new line is promising to increase capacity by 10 per cent, which would be the greatest single increase since the the Second World War.

… but manage expectations

London's Commissioner of Transport, Sir Peter Hendy, raised eyebrows last year when he said that Crossrail would be full immediately upon opening. He was exaggerating a bit, but the comment makes simple sense: New transportation options quickly attract new passengers. And it also made clear the fact that the project is no silver bullet.

"It's carrying 200,000 an hour in the peak. Now, that's a huge number, but because the city's growing, it'll fill in pretty quickly," Ms. Dedring says. "That's not going to solve the problem of capacity in the peaks in London for the next 100 years. So it's not transformational in that sense. But that isn't what Crossrail is trying to do, alone. That is part of its objective."

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According to an oft-quoted statistic, every week one subway train's worth of people moves into London. The city's plan seeks to restrict urban sprawl by emphasizing growth within existing boundaries. Like other major cities, London is seeing increased downtown densification. Transportation strains will continue to arise. And future projects will seek to manage them, not solve them.

There are already plans to follow Crossrail with a new north-south line to be dubbed, yes, Crossrail 2.