The western side of the Yonge-University subway line, south of Eglinton West, follows the Nordheimer Ravine and therefore curves southeast, but I don't see why the new DRL line can't run directly south from Eglinton West (ideally incorporating a continuation of the Allen Expressway underground within the same tunnel). If what we're seeking is a parallel north-south subway line west of the Yonge-University-Spadina Line, it will need to be tunneled. As mentioned in previous posts, it's much easier to tunnel under parkland and streets. This route for a DRL would tunnel under existing roads, such as Winnett and Arlington, and under parks that follow the alignment of buried Taddle Creek: Hillcrest Park, Christie Pits, and Trinity Bellwoods. That means you get stations at St. Clair and Arlington, Christie Station (overlap with the existing Bloor-Danforth station), Grace and College (or thereabouts), Dundas and Grace, and Gore Vale and Queen (Trinity Bellwoods). There are streetcar stops at each of these points where the DRL would intersect with east-west streetcar lines. The expressway entrances and exits could be very discrete. Simply have single-lane ramps funnel onto the right-hand lanes of existing streets. In terms of where the expressway/subway would go south of Queen, I would continue it eastbound and have it divide into two branches at Bathurst, so that eastbound expressway exits into downtown spill out onto Adelaide just east of Bathurst and on Adelaide just east of Spadina (and one or two more east of Yonge?). The westbound entry points onto the expressway would be just east of Bathurst on Richmond and just east of Spadina on Richmond (and east of Yonge). An expressway exit to the Gardner could travel south, maybe to a Front St. extension where it would travel westward. At the east end, the expressway would connect with the DVP at the existing Richmond interchange, making the elevated Gardiner redundant. I'm sure there are many ideas for where to locate the subway station stops in the core. I realize this is big, but again, if the tolls are pricey (on the Allen Expressway branch, not necessarily on the buried Gardiner portion) and you amortize this bad boy over a long enough period, you've basically covered the subway tunneling capital costs for the western half of your Downtown Relief Line. I think it's critical that we open up more of our best neighbourhoods to tourists and Torontonians. Areas like Corso Italia, Little Italy, Trinity Bellwoods (and by association West Queen West) should be very accessible. That's also why I'd suggest putting a SmartTrac station in the Distillery District. The track is already there. This isn't the 19th century. It's silly to expect tourists to hike everywhere with backpacks or get on clunky streetcars to get to attractions. I don't think we should see SmartTrac and DRL as either/or situations. They shouldn't compete with each other, as having both will provide better transit coverage across the city. SmartTrac is substantially cheaper, easier to build, and fully funded. I also don't think we should remove the Queen and King streetcar lines. They provide added transit options and streetcars along these streets are synonymous with the character of Toronto. I can't imagine Toronto without the Queen car, or the King car for that matter, especially in the St. Lawrence area by the gas lights. I realize subway tunneling will have to be funded for the eastern portion of the DRL. I also realize that some would like the western side of the DRL to branch north further west, but there's no reason why the portion of the line running east-west couldn't be extended over time and north-south extensions/spurs added as funding allows. You can call this type of plan too big, but really it's cost effective and allows us to meet a multitude of long-term goals incrementally. We can leave the elevated Gardiner in place until it's done. SmartTrac and existing infrastructure are left largely intact. We have a funding tool (road tolls) for some of the DRL construction.
Oh, and don't worry too much about the PATH or other obstacles. The London Underground has proven that if you dig deep enough, there's always an unobstructed route. There would likely only be a few stretches where trains would have to descend more than a few stories. We're not tunneling under skyscrapers.