Try to keep up Who are you to advise nonsense to me when there are clearly no mention of track sharing in any of UITP USDT or APTA s references Please read the references if you haven t done so In fact you have clearly not kept up with the sources that were posted a long time ago and just to name a few Again this is gong nowhere without a single source verifying anything here Like you say a source trumps everything so you better stop inventing nonsense claims like Seoul Subway Lines 1 9 that is non existent in the very reference you quote