The Ontario government has rolled out details on a huge expansion of GO rail service, a $13.5-billion investment that leaves little money for other transit projects around the region and falls short of earlier promises.

More frequent service with electricity-powered trains across much of the Toronto-area rail network was a Liberal campaign pledge last year, and will be funded in part by the sale of a stake in the utility Hydro One.

"We're going to make massive improvements across the GO system," Premier Kathleen Wynne said on Friday at a Barrie rail station, where she and Transportation Minister Steven Del Duca started to spell out what this will mean.

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GO Transit service will start ramping up this year. At the end of five years, nearly 700 more trains will be running each week, an increase of about 40 per cent in capacity on weekdays, most at off-peak times. Weekend service will jump by more than 140 per cent.

Among the other details revealed on Friday was that it will take seven or eight years to electrify the GO corridors Toronto Mayor John Tory needs for his SmartTrack transit plan. During the municipal campaign last year he promised it would be running within seven years.

"We're absolutely confident in the timeline," Mr. Tory's spokeswoman Amanda Galbraith said. "The mayor has always talked about a seven-year timeline … and where there's a will there's a way."

According to Mr. Del Duca's spokesman, the money the province will spend electrifying the GO corridors Mr. Tory wants to use for his plan constitutes its contribution to the proposal. The mayor will still need to get billions from Ottawa, and hopes to raise the city's share of his $8-billion plan through transit-related development.

The price of $13.5-billion for GO expansion is higher than the figure put forward last summer by senior executives with Metrolinx, the regional transit agency that runs GO. At the time, Metrolinx chair Rob Prichard said it could be up to $12-billion and could drop.

With about $16-billion in total earmarked for transit investment across the Toronto region and Hamilton, the government's big bet on suburban rail will leave only a few billion for other priorities.

Among the projects with an uncertain future is the downtown relief subway line proposed for Toronto.

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Long described as the top priority by TTC head Andy Byford, the line is on the so-called "next wave" of projects proposed by Metrolinx. But its estimated $7.4-billion cost means an Ontario contribution for one-third would soak up all the remaining provincial transit money.

Asked where Friday's spending announcement left that plan and the other next wave projects, Mr. Del Duca promised more details are to come.

"Over the next days, we will be in a position to say more about how we plan to deal with implementing those projects that are closer in terms of readiness and also advancing those that require additional work," he said.

The province has been promising regional express rail (RER) – the shorthand for changing GO from a largely commuter service into frequent, two-way electrified service – for more than a year. Ms. Wynne promised in a speech to the Toronto Region Board of Trade last April to "phase in electric train service every 15 minutes on all GO lines that we own."

In fact, the improvements over the next 10 years will vary from line to line. Busier routes will have 15-minute service all day, while trains will be less frequent on some lines and at some times of day.

Mr. Del Duca said the government spent months analyzing the business cases for expanding service on the routes before making the decisions announced on Friday.