LAVAL - Laval Mayor Gilles Vaillancourt has a plan to boost urban density in the rapidly-growing city north of Montreal, and it involves pouring more than $1 billion into an extension of Laval's recently-built metro line.

One key part of the EvoluCite proposal is an expansion of public transit throughout Laval.

Four years after the orange line extended to Laval with a trio of stations, Vaillancourt is now presenting a plan to get more Laval residents out of their cars.

He is asking for the region's public transit agencies to build an additional five metro stations that would loop the orange line further west in Laval and back to the Cote-Vertu station in St-Laurent, but the cost for the plan is up in the air.

When pressed, Vaillancourt estimated it would cost $150 million per kilometre of track, plus the cost of building each station and a tunnel under Riviere des Prairies.

He says that works out to a ballpark figure of at least $1.2 billion.

"It's going to be less cars, less traffic, less pollution," he said. "It's a good idea."

Vaillancourt said he sees no problem with extending the orange line while the Metropolitan Transit Agency also extends the blue line east to Anjou, and the yellow line in Longueuil.

"Once the studies have been conducted it's very easy to have three big job sites," said the mayor.

Marvin Rotrand, vice-chair of the STM, says his priority is extending the blue line first.

"There's 350,000 people who live on the east side in St-Michel, Anjou, St-Leonard, Montreal North and parts of RDP," Rotrand said. "Those people don't have a subway. Their population is larger than the entire city of Laval, and they need a subway."

Rotrand adds that even if there were enough money available to pay for the extension of all three lines at once getting enough subway cars to run on them would pose a problem, both financially and in terms of time because each order takes years to complete.

Regardless of the cost, Vaillancourt said planning around increased urban density, and creating environments where people are not dependent on their cars, would save much more in the long run.

"The cost for society is a lot more when we're building roads to put people further and further away than when we try to bring them closer to public services," Vaillancourt said.

He expects that as fewer people drive cars air pollution would decrease, improving air quality and people's health.

Parts of the EvoluCite design philosophy are already being implemented at the Concorde and Cartier metro stations, which are zoned for industrial development, but the first real project under the plan is the Urbania project near the Montmorency metro and bus terminal.

Construction on any metro line extensions would not begin before 2013, which is the deadline for the province to decide on its overall plan for the metro network's expansion.