I put this in the Arbutus Corridor thread, but I think it also belongs here.
I've been thinking about how this could work for some time and I developed some concepts. I think it's pretty clear how the middle of the corridor will look, however, both the northern and southern ends present different options. I decided to map out these possibilities.
This map shows the corridor with the different options extending north, to Marine Drive and to the River District.
This map shows the options at the northern end. At first, I think the terminus will be at Arbutus - Broadway because that would provide connectivity with the Millennium Line extension and the fact that the corridor gets narrower and more complicated north of Broadway.
The Main St. extension is technically the easiest and would run largely on the Olympic Streetcar route. This would connect several Skytrain stations and provide access to Granville Island.
The Downtown Extension is much more complex, but I think might be necessary in the future to deal with congestion on the Canada Line section between Broadway-City Hall and Downtown. Without this extension all the people coming from the western and southern parts of Vancouver as well as Richmond will be using this section. Once the Millennium Line is extended to UBC, this could end up being a
bottle neck.
I envision the Downtown Extension going underground at Arbutus-Broadway, east along Broadway to Granville and emerging at surface level just south of the Granville Bridge. There would be a station on the Granville Bridge and the line would continue on the surface on Granville all the way to Waterfront. This line would allow people from the west to get Downtown faster and provide an easy connection from Downtown to Granville Island. (If you think a station on the Granville Bridge is crazy, it is mentioned in Granville Island's future plans)
Now for the southern options! I see two possibilities extending to Marine Drive Station, along 70th St. and along the rail corridor.
I prefer the 70th St. option as it is shorter, would get better ridership and could integrate better with Marine Drive station. You would probably still need a spur on the rail corridor south to an OMC. 70th would become a 2-way street with light rail down the middle.
The problems I see with the rail option is that the connection with Marine Drive station is a bit awkward and the area it serves is less built up. I also think the portion east of the bridge is still being used.
Both of the previous options could lead to extensions to the River District. For the 70th St. option, the best way to do this that I see is continuing it down Marine Drive and then joining the rail corridor at Fraser St. The Rail Option would require a separate line that would connect the River District with Marine Drive Station and would run along the rail corridor. Again, I prefer the 70th St. Option as it could be a seamless line and serves existing areas better.