orbitmic

To me the main difference between the Heathrow Express (which I never use) and the Paris project is the competition available. HEX is competing with the Piccadilly line which has my personal preference but still means 45-55 minutes to central London against 15 for the HEX. Of course, with Crossrail there will be much better competition to fight (which this time could work for me). By contrast, the RER competition in Paris is pretty good. Yes ok, it's 'dirty' as you say but I can't imagine people paying a big premium for cleanliness. When you get the fast RER, it takes 25-35 minutes to some key interchange stations: Gare du Nord, Chatelet Les Halles and St Michel Notre Dame, all of which are better connected than Gare de l'Est, but mostly the time to get there is pretty short overhaul. I can't imagine many people paying a big premium to cut 5 or 7 minutes off journey time unless they specifically need to go to Gare de l'Est. In short, IMHO, any venture which condition of competitiveness would require you to make existing current services worse than they are (i.e removing the fast version of the RER B service) can't be a good venture.