VANCOUVER — Liberal leader Justin Trudeau on Thursday became the first of the major party leaders to pledge to invest billions of dollars in transportation improvements.

Using a private rooftop garden at Vancouver City Hall's engineering services as a backdrop for his announcement, Trudeau said his party would quadruple the Conservatives' infrastructure investment program and put nearly $20 billion in "new dollars" into transit infrastructure over the next decade.

But he would leave it to local governments to decide which projects get funded, saying it's not the federal government's role to pick and choose.

He cited the proposed Broadway rapid transit line, Surrey's light rail and increased SeaBus service as examples that could be funded under the plan.

He said a Liberal government would work with local leaders who know which projects are most important to their communities.

"Here in the Lower Mainland and in communities all across Canada, local leaders know what needs to be done," he said. "Things like increasing SeaBus service to every 10 minutes during the morning and afternoon rushes. Or extending rapid transit service along Broadway to Arbutus ... currently the busiest bus transit corridor in North America."

Trudeau said the funding would include $1.7 billion in spending in each of the first two years.

Any money left unspent in those years would be put into the gas tax transfer program for municipalities.

When asked for details of how projects would be funded, Trudeau said his government's job would be to work with local officials.

"It is not federal government's role to pick which rapid transit project is most suitable for Vancouver or other cities across the country. It is up to the federal government to work with the province and the municipality to respond to what their priorities are," he said.

"So I trust Mayor (Gregor) Robertson and I trust the premier and her team to ensure the decisions made around what Vancouver needs are the right ones for the future of this city and the region."

The Liberals' choice of City Hall property for the announcement raised some eyebrows, especially since Robertson's director of communications and policy, Braeden Caley, is the president of the Liberal Party of Canada in B.C.

Robertson, a former NDP MLA, whose civic Vision Vancouver party largely appeals to liberal and left-leaning members, has been critical of the Harper government on issues around housing, transit and transportation, and climate change.

City manager Penny Ballem said Caley wasn't involved in the decision to allow the Liberals to use the rooftop garden, which is privately accessed through the engineering services department. Caley said in an email he wasn't involved in the discussions but said it was made by the city manager's office "and other appropriate staff."

Ballem said Trudeau's advance team contacted her for a suitable space that would provide a backdrop to the city. Given that Vancouver has made transportation a priority and Robertson is the chairman of the Big City Mayors' Caucus, which is lobbying Ottawa for infrastructure improvements, she didn't think it was inappropriate to allow them to use the private-access rooftop or the engineering offices for staging.