Paris' disconnect with its suburbs, its lack of suburban transportation in particular, became all too apparent with the Paris agglomeration's growth. Paul Delouvrier promised to resolve the Paris-suburbs mésentente when he became head of the Paris region in 1961: two of his most ambitious projects for the Region were the construction of five suburban villes nouvelles ("new cities") and the RER commuter train network. Many other suburban residential districts (grands ensembles) were built between the 1960s and 1970s to provide a low-cost solution for a rapidly expanding population: these districts were socially mixed at first, but few residents actually owned their homes (the growing economy made these accessible to the middle classes only from the 1970s). Their poor construction quality and their haphazard insertion into existing urban growth contributed to their desertion by those able to move elsewhere and their repopulation by those with more limited possibilities.