MONTREAL — The Crown corporation overseeing a planned high-speed rail line between Toronto and Quebec City says tunnels will be needed in Montreal and possibly Toronto.

In an update on its website, Alto says it plans to burrow from just north of the Prairies River, which borders Montreal’s north side, to downtown in a corridor that would exceed 10 kilometres.

It also says it is considering tunnels and elevated tracks to access Toronto’s downtown, terminating at either Union Station or a nearby location.

Rail tunnel construction has proven a pricey undertaking in recent years, ballooning the budgets of Toronto’s Eglinton Crosstown light-rail line and Ontario Line subway plans as well as Ottawa’s Trillium Line.

In the update, Alto further reveals it is weighing two possible corridors between Peterborough, Ont., and Ottawa. One is a more direct line between the two cities and the other curves south, closer to Lake Ontario.

Construction of the first phase of the 1,000-kilometre corridor is set to kick off in 2029 or 2030, linking Montreal and Ottawa in an effective test case for an infrastructure project estimated at $60 billion to $90 billion.

(C) The Canadian Press