# Southern bypass of Ernée on the RN 12 (Déviation sud d’Ernée par la RN 12).
Publisher: CapexCue
Canonical dossier:
Dossier reference: release 1 (b3cb1806-7a2c-42eb-9dd1-c8db58175c8b)
Released project intelligence
Oldest supporting observation: 2026-10-03T18:21:35.508066+00:00
Dossier released: 2026-10-15T18:19:26.938693+00:00
Source report dates and capture dates are listed per fact below; neither establishes an event date.
## Project summary
Southern bypass of Ernée on the RN 12
The proposed project is a 5 km bidirectional road: 3.6 km of new alignment west of Ernée and 1.4 km of requalification of the RD 31 to the east. The works described include a viaduct across the Ernée valley, cycle-route sections and road-runoff treatment basins. The project owner is the French State, through the Pays de la Loire DREAL.
The project is intended to divert mainly transit traffic from Ernée’s centre and complement the north-east RD 31 bypass opened in 2019. The environmental authority notes that the existing RN 12 would still pass through the centre and that its requalification had not advanced; it considers requalification important to achieving the stated objectives. It also recommends recalibrating traffic projections using 2023 counts and experience from other bypasses.
The opinion describes seven compensation sites and measures including 7.3 km of hedge planting for 1.8 km destroyed. It also characterizes the project’s greenhouse-gas balance as unfavorable, with construction a major contributor, and says induced development around the bypass is not adequately assessed.
The source reports a total cost of €43.5 million and financing shares associated with the 2021–2027 State–Region plan; it does not establish disbursement or financial close.
The environmental authority’s opinion, deliberated on 10 October 2025, is advisory and is not an authorization decision. The source reports the project’s declaration of public utility and required authorization processes. Source: [IGEDD environmental authority opinion](https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf), dated 10 October 2025.
## Evidence limits and unknowns
- The opinion expected a public consultation before the end of 2025 but does not confirm whether it occurred or give later authorization outcomes. It records that the National Council for Nature Protection opinion was not available on 10 October 2025.
- The source does not establish whether traffic projections were recalibrated, whether the existing RN 12 through Ernée was requalified, or the project’s subsequent construction or opening status.
- The opinion does not identify construction contractors or procurement packages or report procurement status.
- The source does not establish whether the reported financing shares were fully committed or disbursed.
- The opinion includes maps and figures; their graphical details were not interpreted for this page.
Current purchasing availability: unknown.
Source-dated plans do not establish current progress or available supplier packages.
## Project metadata
Country: France
Region: Europe
Physical assets: Road
Derived from the exact released evidence; unresolved fields remain unclassified.
## Project category
Transport and logistics
Derived from the reviewed name statement; delivery stage remains unclassified.
Southern bypass of Ernée on the RN 12 (Déviation sud d’Ernée par la RN 12).
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
Project overview
Oldest decisive evidence: 2026-10-03T18:21:35.508066+00:00
Newest evidence: 2026-10-03T18:21:35.508066+00:00
Knowledge reviewed: 2026-10-15T18:19:25.475416+00:00
Publication reviewed: 2026-10-15T18:19:25.475416+00:00
## Name
Southern bypass of Ernée on the RN 12 (Déviation sud d’Ernée par la RN 12).
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Scope
A bidirectional 5 km road with a 2×1 carriageway: 3.6 km of new alignment west of Ernée and 1.4 km requalification of the existing RD 31 to the east. The described works include three overtaking sections, a viaduct across the Ernée valley, reinstatement of the RD 514, five roundabouts, four cycle-route sections, agricultural and ecological access/restoration structures, six natural-flow crossings, and road-runoff collection and treatment basins. The source also describes a carpooling area linked to a road access and coach stop.
Status: planned
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Ecology
The source describes effects on a bocage and watercourse setting, including destruction of 1.8 km of hedges, and impacts on habitats and agricultural land. It reports seven compensation sites and measures including hedge planting (7.3 km for 1.8 km destroyed), wetland and habitat restoration, watercourse work, ponds and ecological crossings. The environmental authority also reports an unfavorable greenhouse-gas balance, heavily affected by construction, and says induced development around the bypass is not adequately assessed; it recommends further consideration of these effects and related measures.
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Activity
Intended to divert mainly transit traffic from Ernée’s centre, with expected road-safety and quality-of-life benefits, and to complement the separate north-east RD 31 bypass opened in 2019. The environmental authority cautions that the current RN 12 will still pass through the centre and that its requalification has not advanced; it considers that requalification important to achieving the project’s stated objectives. It also recommends recalibrating traffic projections using 2023 counts and experience from other bypasses, rather than relying on the unrevised initial model.
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Location
Around Ernée, in the Mayenne department, Pays de la Loire, France, on the RN 12 corridor between Fougères and Alençon. The new section is west of Ernée and the RD 31 section to be requalified is to the east.
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Investment
The source gives a total project cost of €43.5 million and reports financing shares of 72.5% State, 12.5% Region, 10% Mayenne Department and 5% Ernée intercommunal community, in connection with the 2021–2027 State–Region plan. The source does not establish disbursement or financial close.
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Regulatory
The bypass was declared of public utility by prefectural order on 30 July 2021. The source says it requires authorization under water legislation and is subject to an application for derogation from prohibitions on destroying protected species and habitats. The National Council for Nature Protection opinion was not yet available when the environmental authority deliberated on 10 October 2025. That authority’s opinion is advisory, not an authorization decision, and is neither favorable nor unfavorable.
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Next Milestone
A public consultation was expected before the end of 2025. The supplied source does not confirm whether it took place.
Status: planned
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Implementing Agency
The French State, through the regional directorate for environment, planning and housing for Pays de la Loire (DREAL), is identified as the project owner (maître d’ouvrage).
Status: reported
Attribution: IGEDD environmental authority assessment and attributed developer synthesis
Source: IGEDD environmental authority native opinion text — https://www.igedd.developpement-durable.gouv.fr/IMG/pdf/2_-_deviation_sud_d_ernee_53_par_la_rn_12_2e_avis__cle77be15.pdf | published unknown | observed 2026-10-03T18:21:35.508066+00:00
## Cite this dossier
CapexCue — Southern bypass of Ernée on the RN 12 (Déviation sud d’Ernée par la RN 12). — dossier released 2026-10-15T18:19:26.938693+00:00, release 1 (b3cb1806-7a2c-42eb-9dd1-c8db58175c8b) — https://capexcue.com/projects/southern-bypass-of-ernee-on-the-rn-12-deviation-sud-dernee-par-la-rn-12-2a0bbcd4a8e700cc/.
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