I knew all what you have found, just how close is the station stop to the terminal, accross the street or in the treminal? The tube map shows that they are also building to terminal 5. By the way the northern or black line as it is reffered to is the oldest line of all the tubes. In 1977 I rode just behind the driver and watched the speedometer needle peg at 90 mph with a full cup of coffee sitting on top of the console not spilling a drop.