Since the mid 90’s, public transport patronage in Île-de-France (the Paris region) has increased substantially: over the last decade alone a 20% growth was observed. This growth, even though it was an aim of the Sustainable Urban Mobility plan adopted in 2000, was not completely anticipated. Consequently, the capacity is no longer sufficient to meet the demand during the peak hours, particularly on several parts of the network in the dense central area of the region. This results in over-crowded vehicles and long waiting times for passengers at rail platforms and bus stops. The lack of maintenance and modernisation of the transport system causes additional operational difficulties.