Ottawa city council has taken the next step towards building a $2.1 billion light rail system, which will include a transit tunnel under the city's core.

Council voted 19 to 4 in favour of the design plan for the project's first phase, which includes a 12.5-kilometre light rail line from Tunney's Pasture to Blair Station, and a 3.2-kilometre tunnel through the downtown.

Now that the plan is approved, the environmental assessment phase can begin.

It wasn't quite unanimous. Coun. Gord Hunter was among only four members of council to vote against the underground option.

"It's time that we see the light, and end the tunnel. Thank you very much Mr. Mayor," Hunter said.

But the tunnel won the day, with an overwhelming majority -- 19 councillors -- in favour.

The vote comes just a day after mayoral candidate MPP Jim Watson expressed concern over the project's $2.1-billion price tag, and said he'd re-think the downtown tunnel, and even consider a "BRT," or bus-only plan.

Transit committee chair Alex Cullen, who's also running for mayor, had this to say:

"[It's] time to get on the train. The BRT option we've looked at. We took it very, very seriously. But you have to choose; we made a choice; it's electric light rail using a transitway system, and it's going through a tunnel, so the BRT days are gone."

The vote was a victory for Mayor Larry O'Brien.

"Yeah, I think it sends a very, very clear message to those that would be second-guessing the entire plan. It's a bold plan, it's a bold plan, it's a plan for the future, and one that I could stand behind in any kind of campaign should I be in one," O'Brien said.

There are still two vital pieces of the plan missing -- confirmation of federal funding for the project, and permission from the National Capital Commission to use the Ottawa River Parkway. The project's backers promise both are on the way.