In case you haven't been keeping track, the TTC 10-year capital requirements 'bubble' has now jumped from $3.8 billion to $4.5 billion.
TheStar.com - TTC outlines budget plan
Despite streetcar track rebuilding projects of recent years (Lakeshore West, King, Carleton, College etc.) there is still $270 million left to do. In fact, it never ends. Streetcar track is far more expensive to maintain that subway-track - or railway track on standard ballast. This is because it is set in the concrete. The rebuilding requires ripping up the concrete. The projects are not only expensive, but also very disruptive to people and businesses in those neighbourhoods effected.
Aside from keeping the ruinously expensive and ineffective streetcar system, the TTC's biggest problem has been the failure to set aside reserves. In the TTC's way of accounting, it only depreciates the net capital paid by the TTC itself. This is a very small amount - as 99% of the Commission's captital has been provided by the city and province. This approach has assumed that governments would show equal largesse in funding asset replacements as they did with the initital projects. In theory, the city could have (and should have) ensured the reserves existed. However, this has't been the history.
In comparison, Montreal's STM and Vancouver's Translink show debt, interest and sinking fund payments on their financial statements.