You're looking at this with a very closed-minded approach. While I could argue that TYSSE could've easily been built in a much cheaper fashion, to say that a full capacity subway to Vaughan wasn't justified isn't exactly correct. People here seem to not understand that one of the things that hurt rapid transit projects is when there is a need to do pointless transfers and mode changes. One of the worst examples of this was the Sheppard East LRT, where if you were travelling from Scarborough to North York, you would have to make a transfer onto the Sheppard Line, just because you wanted to spend a lot less money on an extension. If you needed to get to the Yonge Line, you would have to transfer twice for seemingly no reason. The same logic can be applied to TYSSE. Sure you could've found a much cheaper technology to build the extension, but all that means is if you want to get to someplace in Toronto (not necessarily just downtown), you'd have to ride the viva orange to VMC, then take this TYSSE line down to Sheppard West, and from there ride the University line to wherever. This is what kills rider enthusiasm. When you have to constantly leave the train to make connections, you're further discouraging the use of rapid transit, and are pushing people to take the car places. So what if the immediate density of TYSSE doesn't justify a full heavy rail subway? Not only will the subway help push new developments (which is happening tenfold since unlike the Sheppard Line, Vaughan is really pushing for a large amount of densification around the subway extension), but if it can be used to funnel riders directly into Toronto through Viva Rapidway connections as well as park and riders from Highway 407, in that sense its entirely justified. The same exact thing could be said about SSE. Why should the residents of Scarborough have to deal with a pointless (and rather long) transfer at Kennedy, instead of having a train service that runs directly through Kennedy? By offering more direct services to destinations, you're increasing transit accessibility tenfold. The less you have to leave the train to get to another, the better. A good example of proper design can be found in Paris where when designing the metro, they set a rule to have every destination be accessible from anywhere with 2 or fewer transfers.Having random transfers to different modes hurts this philosophy.