Evaluation of effects of the pairing between road and rail infrastructures on the functionning and the perception of the crossed territories

The research project deals with the effects of “pairing” between road and rail infrastructures on the functioning and the perception of the crossed territories. Questioning “pairing” goes beyond the raw juxtaposition of two infrastructures to reach a net benefit for crossed territories. The assumption aims at finding less impacts, synergetic functions between infrastructures and global benefits for population in that case. Three themes have been particularly focused on: the ecological impact on biodiversity, the effects on the evolution and the perception of landscapes and land use as well as governance issues and social acceptability in nearby areas. Three areas have been selected in rural and suburban zones to represent the major types of pairing observed in France: a railway built after a motorway in a rural field near Reims; a motorway built after a railway in suburban field near Lyon; a motorway built after an historical railway and a main road close to Arles. For each theme, methodology crossed bibliographic reviews about the main impacts of infrastructures, feedbacks from experts and former experiences, and field analysis. From the beginning, a cross-thematic approach linked all those elements.

As for the results, benefits were shown for 2 of the 3 investigated fields depending on species. The habitat fragmentation, caused by the 2nd infrastructure, is reduced thanks to pairing. Nevertheless, needs for consistency with location and design of ecological connectivity structures of each infrastructure are highlighted. Regarding landscape and land use analysis, less changes are induced by the implementation of the second infrastructure than from the first when pairing is created. However, paired infrastructures integration into landscape and final layout more or less depend on important technical obligations.

From the societal perspective, the lack of spontaneous and specific view of pairing is significant for the different actors of the crossed territories. This notion is globally misunderstood or is not associated with infrastructures. No special link between crossed territories and paired infrastructures was noticed. Moreover, actors mobilizations don’t seem to be as much dependent on the pairing characteristics as on the territorial context (social, economic, politic) or more precisely their view of their territory. Disparities in the perception and the feeling of the nuisances by local residents were observed to be dependent on personal characteristics and scale analysis (different benefits at national, regional or local level). However, a certain acceptation of paired infrastructures was shown on the medium and on the long term.

Thanks to a cross-thematic approach, comparison between different contributions and pros/cons analysis highlight the complexity of “pairing” implementation. Some observations are shared beyond each specific conclusion : the need to improve consistency between infrastructures, the appropriate management for interstitial spaces, global space fragmentation, better adaptation of pairing for each territory, pros/cons for “pairing” depending on territorial scales and local actors. Thus, this complex and multi-focal notion goes beyond technical approach for an infrastructure project manager. The only impact assessment doesn’t make it possible to reach beneficial “pairing” for crossed territories due to the decisive relations between scales, stakeholders and inhabitants.

pairing; impacts; biodiversity; landscapes; governance; social acceptability