It considers that the project, which supporters say will “free up” an area lacking major road infrastructure, will detract from a new commuter rail route.
Environmentalists also say it will increase pollution.
Work on the future A412, already cancelled in 1985 and 2006, is due to start in 2024.
Stay informed:
Sign up to our free weekly e-newsletter
Subscribe to access all our online articles and receive our printed monthly newspaper The Connexion at your home. News analysis, features and practical help for English-speakers in France