Enlarging perspectives on the Grand Paris Express: Modelling speed and accessibility increases within the public transportation network of the Paris region (1995-2050)

This paper studies the transformations of the Paris region public transportation network that will be induced by the new infrastructures of the Grand Paris Express (GPE) (2024-2030). We constructed a multi-modal database, that covers the perimeter of the functional area of Paris over a relatively long term period (1995-2050), taking into account transportation speed (especially along the RER and Transilien express lines) and connection times. Results show that the GPE does not radically change the dimension parameters of the network in terms of total number of stations, total network length, average speed at the regional scale (that continually decreases from 1995 to 2050). However, the impacts of the GPE are very clear when analysed at the municipality scale. The gains in maximal speed appear clearly at a scale wider than that of the Grand Paris region. Inside a radius of around 30 km, the network is thus considerably densified not only by the GPE but also by new trams and buses, which appear in the interstices of the radial organisation of the RER and Transilien lines. Here, changes in global accessibility are huge. Accessibility measures are computed from a shortest path matrix, summarizing the total time necessary to go from each station to all other stations. Results show that the articulation of the GPE and other transport modes, especially trams and buses, significantly reduces the differential accessibility between the centre and periphery of the region, and, to a lesser degree, between the West/South-West and North/North-East. In other words, these results show that recent investments in public transportation aim to increase the area of ‘good rail accessibility’ from Paris and its inner suburbs beyond the limits of the Grand Paris region (and especially to the south-west), instead of trying to reduce inequalities between East and West (as aimed for by RER development in the past). The highest gains are obtained in the heart of the ring formed by lines 15 and 18 of the GPE to the south of Paris.