If you're running the same trains on the red, blue and green lines to save money by sharing garages, then you need some way that trains can drive between the lines to get to the garages. That's the connection that is required. It doesn't matter how much land CT does or doesn't have next to Metis Trail, they would either need to build a connection that connects red/blue above grade and green below grade track in the absolute middle of the downtown, or build some out-of-downtown connection, and at a minimum that **will** cost a billion dollars, whether there's one track or two.
Here's a question for you. Let's say I own a Toyota Prius sedan, a Toyota Highlander Hybrid SUV, and a gas-powered Volkswagen Jetta sedan. Do I take the Highlander to a garage for the SUV technology and the other two to the same sedan-technology mechanic? If not, why not?
There are a hundred technical systems inside a rail car; the height of the floor is only one of them. Actually, it's none of them; it's the result of a design that combines motors, brakes, bogies, controls, panels, etc.
There is a grain of truth in that there is an efficiency in operating a fleet of identical vehicles rather than a mix.That efficiency only goes so far; if we had two trains of one type and one of another and two of a third, there would be a benefit to ensuring we have five trains of the same model instead. But Calgary operates fleets of 50 to 80 vehicles of a given model; that's plenty large enough to get that increase in efficiency.