Southern bypass of Ernée on the RN 12 (Déviation sud d’Ernée par la RN 12).

Southern bypass of Ernée on the RN 12 (Déviation sud d’Ernée par la RN 12).

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

A public consultation was expected before the end of 2025. The supplied source does not confirm whether it took place.

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03

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).

Attributed to IGEDD environmental authority assessment and attributed developer synthesis.

Source: IGEDD environmental authority native opinion text · publication date not recorded · observed 2026-10-03