It's roughly 13 miles from Union to Snider on the Barrie line, and then a further five miles across the York Sub to Doncaster for a total of 18 miles, versus 16 miles up the Don Valley. Doesn't sound like a lot further, but there would not be much in time savings given that trains would have to slow to navigate the connecting tracks at both points. And the trip up the Barrie line is not really that much faster than the Don Valley when one considers there may be stopping trains ahead that stop at some or all of Spadina, Liberty, Bloor, and Downsview Park.
As noted, CN would be far from eager. That's a congested area for CN. They too will be using the connecting track at Doncaster, again at lower speed ....so GO might encounter delays. It's common for both existing main tracks to be occupied at the same time. GO would have to build its own track.... and there would be the added challenge of GO having to cross from north to south, or vv, leaving CN without a through route for its trains whenever a GO is on line. That might actually force construction of a flyover similar to Silver or Snider or Davenport.
Could GO add enough track to make this workable? Possibly, with a pile of money. It would probably be cheaper to grade separate the Doncaster diamond so that GO doesn't tie up CN's line when it crosses.
I too am curious what you'd see as the benefits of this routing?.
- Paul