Here is a fantasy map I made to explore the option of building the DRL with mainline rail technology (single-deck high-platform EMUs using Metrolinx's 2x25kv 60hz AC overhead system). It really ended up blurring the lines between commuter rail and metro. The system's centerpiece is a quad-track express/local mainline rail tunnel across the city centre.
(Higher resolution
here)
The primary objectives were:
1. To divert passenger loads from Bloor-Yonge station (hence Line 3 going to STC, not Line 2)
2. To divert rail traffic away from the Union Station Rail Corridor
3. To divert passenger loads from the southern Yonge Line
4. To divert passenger loads from the Bloor line between Yonge and Kennedy
In order to have efficient passenger distribution between the services, this design would require a common fare system for TTC and GO. It could potentially have a small premium ($1 or so) for GO services on the basis that they are faster, more comfortable and more attractive for commuters.
An experiment here is that I nominally separated Line 1 - Yonge from Line 5 - University. This helps simplify wayfinding signage and announcements. At Union Station, it would eliminate the confusion currently faced by visitors as to which platform they want. It would help distinguish the two functionally independent halves, especially for the stop announcements on east-west lines. I don't think it's an issue that two "lines" are in fact the same service, given that no one seems to be bothered by this situation existing on Lakeshore West and Lakeshore East lines currently.
Although I started with the normal TTC style map, I ended up moving toward the London Underground style, partly because the London Overground is an real-life example of mainline rail being used as part of a metro system and partly because the map was getting really cluttered.
I kept the lines as simple as possible while still mostly maintaining geographic relativity. For example, Lawrence West, Lawrence, York Heights, and Lawrence East are aligned along Lawrence, and Port Credit, Cooksville and Bramton Central are aligned along Hurontario.
Some details:
Only relatively short-distance and frequent services use the new central tunnel. Longer distance services such as the Kitchener, Barrie and Niagara falls services continue to use Union Station, as do peak-only commuter services such as the Richmond Hill line.
GO Regional services are limited-express services which connect city centres in Southwestern Ontario. They would generally operate at 1-2 trains per hour, all day.
GO Express services are sectional-express services serving commuter demand to the financial district. They are the equivalent to current GO Train service. They would generally operate at 2-4 tph in the peak direction.
Line 3 Eglinton is still LRT, though I envision it having more grade-separation in the east end than currently planned, in order to allow interoperation with the Scarborough LRT.
I have omitted the Finch West and Sheppard East LRTs from the map on the basis that they are not sufficiently rapid.