I've no doubt that better performance can be wrung out of the double decks
but the fact is that no high capacity mass transit railway in the world
uses them for good reason. Even the much discussed RER Line A in Paris
struggles to throughput more than 25 trains and hour and that's with
automated driving, the attendant concentrating on the doors/dwells and
three doors per side per car. The Sydney double decks also won't fill
properly because of their lack of doors and unwillingness of people to move
away from the doors because they don't want to get trapped inside when they
want to get out. Human nature defies theory!

Tony P