This communication reports a research on the effects of pairing of heavy infrastructures such as motorways and high speed lines railways on the functioning and perception of the territory. The ecological impact, effects on the evolution and perception of landscapes as well as governance issues and social acceptability in nearby areas have been specifically studied in three representative of the major types of land pairing observed in France : pairing of the East European LGV with the A4 between Reims and Château-Thierry, the A432 coupled with the LGV Rhône-Alpes to the east of Lyon, and the conventional railway line to the RN 113 to the east of Arles. The first justification of these pairings is to minimize fragmentation and reduce disturbance to biodiversity and impact on agriculture. The comparison of the different elements from the research shows in reality an apparent contradiction on scales of analysis of the appropriateness of the pairing. If it offers an overall benefit for land management with space saving and limiting fragmentation, it also causes a consumption of land with the creation of interstitial spaces, and a strong polarization of space. Regarding biodiversity, “pairing” shows benefits for 2 of the 3 investigated fields. Interstitial spaces can provide with development habitat opportunities as far as common habitat background are concerned. The richness and the abundance of some species (eg. For plants, reptiles, butterflies) in those spaces are equivalent to the quality of the external edge areas. Moreover, the habitat fragmentation increase caused by the 2nd infrastructure is also reduced due to “pairing”. For some species of open areas, a longitudinal corridor effect could even be highlighted. Nevertheless, incoherent location and design of ecological connectivity structures of both infrastructures leads to deep physical filters for some species spatial scattering. Landscape and Land use analysis on the studied sites show much less changes induced by the implementation of the second infrastructure than from the first: land redevelopment is indeed much more limited. Paired infrastructures integration into landscape and final layout more or less depend on important technical obligations (relief, curvature radii). Those involve distance variations between infrastructures which determine contrasted situations for the use of the interstitial spaces and the emergence of a new landscape through the development of semi-natural habitats (fallow, hedges, copses). These significant direct effects of infrastructures contrast with the very low indirect influence of infrastructure on the social-demographic developments of the studied territories. From the societal perspective, the advantages and disadvantages of the pairing are also related on scales thinking and posture of the actors interviewed vis-à-vis spatial or organizational cuts, or perception of nuisances. Pairing is therefore more a process than a technical solution. Directed downstream, it does not allow for synergies with the territory, but only responds to some isolated subjects like space consumption. The need to improve consistency between infrastructures, the appropriate management for interstitial spaces, global space fragmentation, better adaptation of pairing for each territory, pros and cons for “pairing” depending on territorial scales and local actors.
: pairing; landscape integration; fragmentation; interstitial space; synergy