Fleet switching would be impossible without a huge renovation since there isn't a standardization of door location or vehicle length with low floor vehicles. Sure they can ask for customization but articulation points and bogie locations would interfere with door location. On high floor vehicles, these aren't issues so the can design a new vehicle to match the door location of an existing fleet. They would be stuck with Flexity's for life if they put in PSDs.
Well, it can help with crowded platforms. Trains don't charge in cause they fear someone could have slip when they are pack to the platform edge. Track fire is not an issue with overhead rails.Nope it wasn't designed to have them because they make no sense on a low floor light rail line.