I can't see it happening, Milton trains diverting onto the Lakeshore West that is. Not for at least a decade but more likely two (see bottom).
The move makes sense from an operational irregularity standpoint(line shutdowns) but not a complete diversion. Its also very wise to buy CPs Obico yard for use as a TTC subway yard and/or GO yard. But most importantly, there is really no need to divert Milton trains onto the Lakeshore West line. The area east of the jct. between the Canpa sub & the Galt sub(Kipling and points further east) is not where the Milton line has capacity constraints(with the exception of the Humber bridge), the main problem area is through Mississauga.
There are numerous problems such a proposal would face. For one the jct. to the Canpa sub is westward facing. There's an industrial facility in the way of making an Eastward connection but a more relevant physical obstacle is that Canpa is the western entrance to Willowbrook yard. A Eastern wye would interfere with the western yard lead and vice versa;
western yard lead in red/hypothetical eastern Canpa wye in yellow
As we can see the tracks would have to cross. This interface would normally require a diamond interlocking, the kind they've spent hundreds of millions eliminating over the last few years re: West Toronto/Hagerman/Snider. But one may not even be physically possible at that kind of narrow angle. Nor would it be preferably from a safety/maintenance/operation point of view to have a mainline track and a yard track cross each others path and so close to the yard itself to boot.
A controlled location with switches is a much more viable alternative. However the problem with that is that there may not be sufficient space for it. Yard movements frequently travel up to the Kipling overpass. A controlled location would extend eastward beyond that. I cant possibly see them allowing yard trains to occupy the maintrack in order to make their moves considering how busy the line is (plus it would require extensive qualification upgrading for the yard operators which would come with significant pay increases). I don't know if the yard could be reconfigured, however if so that would reduce its capacity and therefore isn't something that could be done at least until the East Maintenance facility is completed in 2017, if this kind of reduction has even been taken into consideration.
A fly-over option is another possibility but it would be extremely expensive compared to the other options and again may not even be physically possible, depending on the grade and other obstacles; Horner, Kipling Ave. It would also require extensive land acquisition from VIA if the ramp were to be built on the south side. Which would still be preferable to building it on the north side. In addition to reducing available yard space it would be operationally problematic since Milton trains would have to cross over to the south side of the corridor at a later point so as to not occupy the tracks used by westbound Lakeshore trains servicing stops at Mimico & Exhibition on the north side of the corridor.
Track space/time on the Oakville sub would be an even bigger problem going east to Union with local/express/equipment Lakeshore West trains and revenue/equipment VIA trains. The corridor already sees over 200 train movements per day (break down of train movements;
http://urbantoronto.ca/forum/showth...n-Express-(Metrolinx-U-C)?p=766327#post766327).
An additional 16 trips may seem insignificant but the problem is the timing of those trips. Between 7:52 am at 8:20, 6 eastbound and 5 westbound GO trains pass by Mimico on the Lakeshore West line. You can tell there already is congestion on this segment as the 7:58 eastbound express out of Oakville takes 5 more minutes (27 mins) to reach Union than the 7:43 eastbound express (22 mins). Extended to 7:42-8:30 you add 2 westbound VIAs, 2 eastbound VIAs and one more westbound GO to the mix. Meanwhile in the same time period you have 3-4 Milton trains making their way to Union (the 7:40, 7:50, 8:00 & 8:15 out of Kipling). Holy congestion batman! I think we can all see why this might be a very bad idea...
The 5th track will be needed for any increases in service. But that's not going to happen until the city commits to rebuilding the Dunn, Jameson & Dowling Ave overpasses (not to mention the widening of 6 other bridges along the corridor). Maybe you can make it happen after that, but then the Milton trains would eat up most of the new found track time. Which brings me back to the question of WHY? Why use up that new found track space on a service for another line that already has enough capacity in its own corridor save for one pinch point.
Now once they implement cab signalling or some other advanced form of train control, such diversions may present an interesting option for differing routes. However GO continues to purchase Bombardier bi-level coaches and MPI locomotives, both of which are currently incompatible with such technology. I suppose a complete overall is possible, but would likely be prohibitively expensive. Most likely the next generation of equipment will be fully compliant with such technology i.e. after electrification, which as we know outside of the UPX is realistically 1-2 decades out from completion for the Lakeshore West, East & Kitchener corridors. Don't think so? Well, it will have
only taken about
14 years from conception to implementation for the ARL/UPX to come to fruition. And the electrification of those corridors is a far larger project... only time will time I guess.