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. Renewal of the rail infrastructure and rolling stock is necessary to cope with this situation. But renewal alone will not be enough. Major investments are planned to increase capacity by either building new lines, or by increasing capacity of existing lines. The Grand Paris Express is the best known of these projects. For the socio-economic appraisal, it is necessary to quantify all impacts of these investments. However, little is known about the value that passengers attach to these reduced congestion levels. The Syndicat des Transports en Île-de-France commissioned Significance in 2011 to conduct a new study focused on the perception of comfort inside public transport vehicles in general, and more particularly on the issue of crowding. This study covered all modes of public transport in Île-de-France.