In fact, Crossrail in London closer is to the $30 billion.
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With 850,000 passengers per day the RER B is the second busiest line in Paris.
Pictures by me
Gentilly station
The next train in this platform is express is don't make stop at this station
The express train
The next train is in three minutes
Two minutes after the depart of the first train a second train in the other platform.
My train.
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Laplace station
Picture by Metropolitan
http://www.skyscrapercity.com/showpo...&postcount=137
Rush hour in Chatelet les Halles station (busiest station in Paris with 800,000 passengers per day)