The McGuinty Liberals and the city are set to announce a massive $12.4-billion plan to extend the Sheppard subway line and build a new light rail line, sources tell CTV.

The provincially-funded $8.2-billion light rail line will run underneath Eglinton Avenue from Black Creek Drive in the west to the existing Scarborough Rapid Transit line at Kennedy Station. From there, the route will travel above ground on the Scarborough RT line.

The 20-kilometre route will be faster and more convenient for riders travelling across the city, sources say.

Meanwhile, the city is taking on the $4.2-billion cost to extend the Sheppard subway line in both directions - west to Downsview Station and east to Scarborough Town Centre. The subway extension calls for a public-private cost-sharing partnership that would be one of the largest in the world.

Construction of both projects should be completed by 2020. Shovels will hit the ground later this year.

Mayor Rob Ford and Premier Dalton McGuinty are holding a press conference Thursday morning to formally announce the plan.

Senior officials within the McGuinty government are said to be "very pleased" with the deal because it maintains the cross-city routes that serve some of the neediest neighbourhoods in the city.

The revamped transit plan comes after Ford nixed former mayor David Miller's Transit City initiative shortly after he was elected to the mayor's chair last fall. The province's contribution to the new plan was previously committed to Transit City.

With a report from CTV's Paul Bliss and Alicia Markson.