Why are so many real estate executives on the MTA board? Because transportation drives real estate development, and they want to control that. So did the French government, and the Paris municipal government, and the regional government of the Ile-de-France, in the 1960s. They had particular ideas about where they wanted people to live and work, and they set about making it easy for them to do that.
Of particular interest was the planning and construction of five new towns in the Paris suburbs, with the idea of concentrating and organizing the new population of the region: Cergy-Pontoise, Marne-la-Vallée, Sénart, Evry and Saint-Quentin-en-Yvelines. There were also the two airports in Orly and Roissy, the business district in La Défense, and the new peripheral and suburban campuses of the University of Paris.
Alon Levy's proposal for an RER-style system in New York ties together every single commuter rail line. However, if you look at the map of commuter rail lines in Paris (PDF), you will notice that even after forty years, only a small number (lettered A-E on the map) have been converted to RER service. The RER program is very precisely targeted to achieve specific development goals. The first four lines served all these centers, as follows:
Line A: Cergy-Pontoise, Marne-la-Vallée, La Défense, University campuses VIII, X and XII
Line B: Orly and CDG airports, University campuses XI and XIII
Line C: Saint-Quentin-en-Yvelines, Orly airport, University campuses IX and XII
Line D: Sénart, Evry, University campuses VIII, XII and XIII
Line A in particular included an entirely new branch to serve the new town at Marne-la-Vallée. It attracted so many passengers that within ten years it was transporting more than 55,000 passengers per hour in each direction at peak times. I have been told that during the late 1980s and early 1990s it was the most crowded line in the world.
The long-term value of the RER is potentially debatable: the poorer Paris suburbs are notorious for the extreme alienation of their residents, and we can speculate that the RER had some role in that. An anonymous Wikipedia author alleges that because residential development has been concentrated east of Paris and job development to the west, there is a commute imbalance resulting in overuse of the A line.
That said, it seems to have been fairly successful at accomplishing at least some of our goals. All RER lines except the Malesherbes branch of the D line have service at least half-hourly, and large sections of the suburbs are within walking distance of an RER station. According to the INSEE (PDF), car ownership in the Paris suburbs is 77%, compared with 45% for the city itself and 81% for the country as a whole. I'd like to get the comparable numbers for the New York region, as well as figures for pollution, energy usage and carnage, to make a full comparison, but these figures make a good impression.
As I wrote in my earlier post, I think we need to think out in more detail the reasons for any of these regional rail improvements. That thinking out can quantify some of the potential benefits more and lead to better prioritization of the steps involved in implementing such improvements, and hopefully to a better chance of selling them to politicians and the public.