The public transit system in the Outaouais has confirmed it will build a light rail line of its own in Gatineau, Que., casting aside the idea it could serve its expanding ridership with buses alone.

The Société de transport de l'Outaouais (STO) announced Thursday that it is now considering three possible transit scenarios between Aylmer in the west and downtown: an "all-tram" option and two that rely on a hybrid system of trams and buses.

Two other bus-only scenarios have been shelved after studies suggested they wouldn't be able to meet an anticipated boost in ridership, including over the Portage Bridge to Ottawa.

"Over the next 15 years, the number of public transit users crossing the [bridge] in the direction of Ottawa during the morning peak period will increase from 3,500 to around 7,500 riders per hour," a press release from the STO noted.

"In order to respond to that increase, the total number of buses required would saturate the reserved lane, even with articulated or bi-articulated buses."

The STO added that upping the number of buses along the proposed routes would only compound traffic problems in the area.

One of the suggested rapid lines would be built along chemin d'Aylmer, while the other would start further north and serve the city's Plateau sector.

One or both will be served by light rail trains — if only one is, the other would be served by express buses.

All three plans see trains crossing the Portage Bridge.

One of the three scenarios studied by the STO involves a tram-only option that serves two routes before connecting with Ottawa's downtown LRT system. If it goes with a hybrid system, the buses would roughly follow the proposal for the rail line. (Provided by STO)

Ottawa connection points unknown

The STO's board of directors approved the use of $16 million from the Quebec government to fast-track further analysis of the project, as the City of Ottawa had requested.

$730,000 of those funds will be used to explore how to connect Gatineau's proposed tramway to Ottawa's light rail line.

Its buses currently stop near Lyon station, but not right outside.

"At this stage … We would try to get a sense of how many stations we need, try to depict [the] distance between them," said STO president Myriam Nadeau.

STO President Myriam Nadeau said the hybrid scenarios would include one lane with buses and a separate lane for trams.

But working out how to incorporate a new tramway into downtown Ottawa's existing LRT infrastructure could be challenging.

"It's dense, there are lots of heritage buildings, security concerns [and] it's also the Parliamentary precinct," Nadeau explained.

After a detailed analysis is complete, the STO will appear before Ottawa's transportation committee in the spring to present the preliminary options.

A recommendation for the new system will be made following a period of public consultation, with a final plan expected by the end of this year.

The province has said it will pay for 60 per cent of the cost, with Infrastructure Minister and Ottawa Centre MP Catherine McKenna saying the federal government will help pay for the project without giving specifics.