Myrtone wrote: Consider the amount of floor space, not just seating capacity, in case of low floor vehicles, wheel-box intrusions do eat into the floor space. Even on part high floor vehicles, this can be seen where the articulations are. The issue is the capacity relative to length, not absolute capacity. While the S70s may have the same number of seats as the high floor LA fleet, is the latter slightly shorter than 81 ft. This is one of the unavoidable trade-offs with low floor vehicles. Reduced capacity relative to train length is one. Some have part high floor, while most other have reduced bogie movement. Building high platforms, if they are possible in all locations, avoids the trade-offs in designing each new generation of rolling stock.There's almost as many low floor intercity, commuter, and light rail railcars in America as high floor trains. There is no trade off, there's advantages and disadvantages to both. America isn't the only country in the world that uses low floor trains and low platforms. Every transit agency, sometimes different for different lines, makes a choice which type platform they want.
The only real advantage I've read for trains having higher floors (and therefore stations with higher platforms) is a higher maximum speed. There are TGV double deck trains with low floor heights and maximum speeds of these trains is still 186 mph. Light rail vehicles, in dedicated lanes or not, in dedicated right-of-way or not, do not travel fast enough (186+ mph) for floor heights to matter.