Even as Toronto is embroiled in the debate over the eastern section of the Gardiner Expressway, the future of rapid transit in Scarborough remains a hot topic for discussion. Following on the heels of a report that draws into question the sustainability and worth of a new subway line based on density and projected ridership, an alternative option is starting to get a little traction.

Dubbed SmartSpur, the proposal modifies John Tory's SmartTrack plan by using the existing GO rail corridor that runs partially alongside the SRT to service Scarborough Town Centre and possibly beyond. This proposal would cost way less than both the current subway plan or the previously proposed LRT and provide direct rapid transit to Union Station.

"Costs of the connection to STC from the SmartTrack line, using the east-west part of the current SRT corridor, were calculated at $425-million in 2010 dollars, with the full route to Malvern via Centennial College's Progress Campus for around $1.7-billion," writes transit blogger Stephen Wickens.

"That's about $2-billion less than preliminary estimates for the Eglinton-McCowan subway idea with a fourth station added."

The proposal isn't without complications. Right of way conflicts would need to be managed on the tracks for one, but there's also the question of what kind of service frequency can be attained using the GO corridor here. That said, it's a simple idea that's worth some more thought.

Check out a high resolution version of the above map here.