More than a decade after the city of Toronto and the Toronto Transit Commission first started developing plans to replace the Scarborough RT with something more reliable, the more than 35,000 Scarborough transit riders who use the aging transit route on an average weekday continue to wait.

What exactly they're waiting for, however, remains a bit of a mystery. The current plan to replace the RT with a subway extension is rife with unknowns, and the number of unknowns has only grown over the last few months as Premier Doug Ford has become involved in the process.

The number of stations along the proposed Scarborough subway route? Unknown. The cost? Unknown. A firm opening date? Unknown. The primary funding source — the share covered by the provincial or municipal government, and also whether the private sector will be expected to contribute? You guessed it — unknown.

Only two things about the plan are for certain: first, there is a strong political desire —supported by Ford, Mayor John Tory and previous compositions of Toronto city council — to build an extension of the Line 2 subway line into the middle of Scarborough, though there's renewed disagreement about the number of stops, and who's going to pay the mysterious bill.

The second thing we know for sure: Scarborough transit riders have been waiting for transit improvements for a very, very long time. And all the finagling over a subway plan has left them waiting for far longer than they would have otherwise.

Original transit plan would have been completed years ago

Flashback time. Scarborough transit planning wasn't the political hot potato it is today. In 2010, the city of Toronto and the TTC completed an environmental assessment of the Scarborough LRT. It would have modified the existing 6.5-kilometre Scarborough RT line to run light rail transit vehicles — maintaining the five current stops — while also extending the route 3.4-kilometres to Sheppard Avenue, adding two new stops.

Had that plan been executed without delay or interference, the transit line would not only be open by now, it would be old news, having opened almost four years ago in 2015. Planners wanted to get a new Scarborough LRT open before the 2015 Pan Am Games to ferry attendees to the new Pan Am Sports Centre near the University of Toronto's Scarborough campus.

Former Toronto mayor Rob Ford threw a wrench into Scarborough transit planning when he came out in favour of a subway extension instead of a light rail line to replace the RT. (Mark Blinch/Reuters)

The original date slipped due to delays at Queen's Park. Delays were further compounded by the election of Mayor Rob Ford, who decided he wanted a Scarborough subway. But things seemed to recover in 2012, when council voted to support the LRT plan. A CBC News story from that year reported that provincial transit agency Metrolinx expected four LRT lines — including the Scarborough LRT — to be "up and running" by 2020.

But that plan didn't last either, as politicians at Queen's Park and Toronto city hall again resurrected the subway idea.

Today, the best guess for the opening date of the Scarborough subway is 2026, though that's an estimate developed based on very early design, and one that doesn't take into account a plan from Queen's Park to add stations to the route and potentially introduce a private-sector funding plan.

The wait continues.

Aging RT trundles along — with a lot of help

An Aug. 30, 2006 report to the TTC warned that the Scarborough RT trains were "nearing the end of [their] useful service life" and that "it is expected that the aging vehicles will result in progressively-deteriorating service reliability over the coming years.

That was more than 12 years ago.

Since then, the Scarborough RT has been kept running through a combination of heroic efforts and money. In 2015, the TTC unveiled a program that saw the aging trains wrapped in vinyl "as an alternative to paint and body work."

Commuters hopping off a Scarborough RT vehicle. To combat the wear and tear threatening RT rail cars that were well past their use-by date, the TTC encased them in vinyl. (Lauren Pelley/CBC News)

In 2017, the agency spent $6.8 million on urgent repairs after finding a corrosion issue was creating holes — physical holes! — in the vehicles.

The TTC's capital budget for 2019-2028 includes $132 million for projected costs related to keeping the RT rolling as the subway debate continues. When you're debating transit for years, talk isn't cheap.

Would a subway actually help Scarborough transit riders?

Meanwhile, there's reason to question whether the subway will do much to help the people riding transit in Scarborough. A report by Toronto's planning department presented in 2016 reported that 48 per cent of Scarborough transit trips are to destinations within Scarborough. Just 23 per cent are bound for downtown.

A subway extension, whether it's built with one or three stations, will offer fewer stops than a planned LRT. It will do little to address that segment of the transit market.

This conclusion is further backed up by mobility analysis published in 2015 by academics Andre Sorensen and Paul Hess, who concluded that Scarborough transit riders would be best served by a network of LRT routes with multiple points of connectivity — not a subway extension.

This kind of mobility analysis has been largely overshadowed as the debate over Scarborough transit has dragged on. It's conspicuous by its absence, and points to a tough question: why build Scarborough transit infrastructure if not to best serve Scarborough transit riders?