As the underdog in the race for city hall, Projet Montréal needed a proposal that could grab the public's attention and swing votes its way. 

The party's proposed Pink line expansion to the Metro system, announced earlier this week, grabbed everyone's attention, all right. Whether it can accomplish the second goal will depend on how realistic Montrealers believe the project to be.

Denis Coderre, who is seeking a second term as mayor, abruptly dismissed the idea of building a new Metro line that would cut diagonally across the city and consist of 29 stations.

"You have to be realistic. The Just for Laughs Festival is over," he told reporters Wednesday in Pierrefonds. "We know it won't work, so why entertain false hopes?"

​​However, engineering and public policy experts consulted by CBC News offer a more nuanced analysis of the proposal to build a 29-kilometre Metro line from Montreal North to Lachine.

On the one hand, they acknowledge the line meets a need, and financing is available. On the other hand, they believe Projet's estimated price-tag of $6 billion and its six-year timeline might be overly optimistic.

The route

Projet Montréal has made appealing to the "sardine class" — its way of referring to cramped Metro commuters — a priority of its campaign. And the Pink line, it says, will alleviate some of the demand on the city's other subway lines.

Aging Infrastructure No Quick Fix

A tunnel-boring machine is assembled below New York's Second Avenue in 2010. Projet Montréal hopes similar technology will allow it to build a new Metro line in Montreal. (Mary Altaffer/Associated Press)

"We clearly, right now, still have a deficit in public transportation in Montreal," said Gérard Mounier, a strategic advisor specializing in infrastructure and project financing for the law firm Lavery. "Everyone is agreed that the Orange line is saturated."

The Pink line, as it's currently sketched out, is designed to travel through some of the densest neighbourhoods in the city, giving them more rapid access to the downtown core.

Normally that would give rise to concerns about disruption to businesses and residents during construction. But Projet's proposal banks on new engineering technology — a tunnel-boring machine — that digs pathways deep underground.

TBMs, as they're known in the industry, have allowed a number of cities in Europe and North America to undertake complicated infrastructure projects without getting bogged down in costly expropriations, rewiring electrical grids and digging up sewer systems. 

"Tunnel-boring machines are potentially more efficient and can minimize disruption in some ways, but they're not a magic bullet solution," said Matti Siemiatycki, a geography and planning professor at the University of Toronto. 

Because the machines operate deep underground and are difficult to access, technical problems can mean costly and lengthy delays, said Siemiatycki, who recently wrote a paper on cost overruns in public infrastructure projects. 

The financing

That raises the question of Projet's proposed $6 billion budget.

When the party announced the Pink line earlier this week, it mentioned three potential sources of funding: the new federal infrastructure bank, the federal public transit infrastructure fund and a provincial infrastructure fund. 

Valérie Plante

Valérie Plante's Projet Montréal is committing to build a new 29-station Metro line from Montreal North to Lachine, to serve some of Montreal's most economically disadvantaged neighbourhoods. (CBC)

These funds reflect the willingness of both Quebec and Ottawa to fork out cash for big infrastructure projects, and that should hearten the project's supporters. 

"There is a  a massive amount of capital available in Canada to finance any large-scale transportation project," said Mounier.

But although Projet has stated its preference for the Pink line to be entirely publicly funded, it may not have the choice if the infrastructure bank is involved.

Ottawa envisions the bank, which is not yet fully operational, being used to leverage private investment in public projects. Private investors are likely to want to recoup their investments through real estate developments along the Metro line.

"I really think that Projet Montréal ... is going to have to be candid about the fact that there is going to need to be development on these stations, and beside these stations, in a way that generates ... commercial income for the private partners," said Brian Kelcey, founder the urban affairs think-tank, State of the City.   

Budget and timeline

It is, arguably, the ability to bring a large infrastructure project in on time and on budget that has Montrealers most skeptical. 

The five-kilometre extension of the Metro's Orange line to Laval ended up costing $745 million, hundreds of millions more than initial estimates. 

That project, however, didn't make use of TBM technology, which has dramatically altered the infrastructure calculus. 

Madrid and Barcelona have used TBMs to complete projects in less time and for less money than Projet has budgeted for the Pink line, said Kelcey, a former adviser to Ontario's Ministry of Transportation.

But using European models ignores the different culture and context of infrastructure construction in Canada.  

"In North America ... and Canada in particular, we're lousy at containing costs for subway and transit construction. We're lousy at building quickly," he said. 

Projet's costing, moreover, may be on the ambitious side. In Europe and North America, the price range for subway projects is between $300 million and $500 million per kilometre.

If the Pink line comes in at the low end of that range, that means the 21-kilometre underground stretch alone would cost $6.3 billion. The plan also calls for an eight-kilometre overland corridor between downtown and Lachine, though that section will likely be cheaper to build. 

"Six billion dollars is a lot of money, don't get me wrong," said Jean Habimana, who heads the tunneling group in the Montreal office of Hatch, an engineering consulting firm. 

"But in the grand scheme of things, if you're talking about 30 kilometres, it may not be enough."

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With files from Ainslie Maclellan and Steve Rukavina