So here’s the 2.0 version of my previous map. Rather than branching – which as Gweed pointed out may require trains of different lengths – the Scarb section is simply an extension of the Crosstown. Malvern to Mount Dennis, completely grade-separated.
The current setup for the Crosstown’s east portal is for the line to enter Eglinton in the centre of the roadway, just east of Brentcliffe. I’d like this to be aligned to the south side, so that east of the CPR corridor it can arc south and become an elevated section above the valley. This viaduct would enter a portal into the valley’s west wall (alongside the Don Line). Doing so keeps the Crosstown grade-separated all the way to Don Mills (very important IMO), while omitting a Leslie surface stop (no biggie).
Below Don Mills/Eglinton, the Don and Crosstown can have paralleling platforms. As both travel north, the Don will rise in elevation while the Crosstown will lower - with the Crosstown passing under the Don and running alongside the CPR corridor where it surfaces via a portal. Or whatever seems logical. Perhaps a stacked configuration with the Crosstown overtop(?).
Everything north of Eglinton is mostly an amalgam of cheapest-where-possible alternatives and alignments – all grade-separated. Elevated, surface, trenched, cut/cover...possibly in-median for open stretches. Ellesmere has a solid a 6 lanes of through traffic + grassy boulevard, which is ample enough to handle a combination of elevated along the industrial section, and at/below-grade for the residential section. To join the current SRT just east of Kennedy, the line will be below-grade – as the SRT currently is while passing under the Stouffville line.
Don Mills I foresee as being mostly tunnelled (i.e - $$$). However, from just south of York Mills to the 401 there are opportunities for a lengthy elevated section.
Just as it was with the original SRT and pre-1996 open air subway extensions; greenspaces, vacant lots and industrial areas should be used to our advantage when connecting nodes/stations. Obviously using the right-of-way of an active rail corridor is a complex issue, but I don’t think it should be written-off completely when certain sections offer important connections. In my opinion this Crosstown/SRT would be a much better use of funds than either the SELRT or in-median portion of the Crosstown. Perhaps it could be built with the funds from both of them?