The current front-runner in Ottawa's mayoral race says city council needs to exercise caution before pushing ahead with a proposed light-rail transit plan that he says could cost the city as much as $1.4 billion.

Former mayor Jim Watson said he had concerns over the city's plans to move the LRT project forward despite receiving less money than anticipated from federal and provincial partners.

On Tuesday federal Transport and Infrastructure Minister John Baird, who is also the Conservative MP for Ottawa West-Nepean, committed about $600 million for the $2.1 billion project, matching a similar commitment from the provincial government in December.

So far, the city has also committed $600 million, meaning there is now $1.8 billion in government funds available for the project. However, the city treasurer has confirmed the plan remains affordable for Ottawa. So far, the city has also committed $600 million.

But Watson expressed concern that the city might be taking on more than it can handle, and said if the city considers the $500 million in contingency costs, the total bill for the city could rise to $1.4 billion. "The plan, by city staff's own estimates is $2.1 billion and it could go up by $500 million, so we could be short $800 million before a shovel gets in the ground," said Watson.

Coun. Alex Cullen, who is chair of the city's transit committee and a rival candidate in the upcoming mayoral race, criticized Watson for failing to consider the city manager's own assessment of Ottawa's finances.

"The City Treasurer, in her October 2009 affordability memo, indicated that the City had the capacity to contribute to these costs without raising taxes, through the use of development charges ($450 million), federal and gas tax rebate revenues ($375 million), and existing transit capital funding ($75 million)," wrote Cullen in a letter to media. "In short, the City can afford its share of this project."

Mayor Larry O'Brien also dismissed the criticism, calling Watson a "scaredy-cat" in an interview on CFRA Radio. "You know [when] you want to build something... there's going to be barriers," said O'Brien. It's like listening to a little old lady who's afraid of taking any chances."

The 12.5-kilometre rail line would run from Tunney's Pasture, just west of downtown, to Blair station in the east, and includes a 3.2-kilometre tunnel under downtown Ottawa.

Watson said rail projects with tunnels are notorious for cost-overruns.

"Let's get the facts and figures and the finances right before we rush off and have a photo op for the tunnel," he said.