The N87, also known as the southern ring road, is used daily by 50,000 vehicles in each direction. It bypasses Grenoble and joins the A480 motorway (Lyon-Vif) at the Rondeau interchange. This urban artery, which is close to saturation point, now passes through a 290-meter-long cut-and-cover tunnel, comprising two one-way tubes (with a gauge of over 3.5 m).

Transport & Mobility business manager Yann Grassart explains the origins of the project: "The Rondeau cut-and-cover tunnel is designed to relieve congestion at a busy intersection to the south of Grenoble. The DREAL aims to separate local flows from transit flows between the A480 and the N87, by burying part of the traffic. This redevelopment will also encourage soft mobility and improve user safety."

Our teams provided the tunnel's low-voltage power supply, technical rooms, safety niches, and emergency exits. They installed numerous devices, such as tunnel lighting, transmission networks, video surveillance, the emergency call network, dynamic signage, physical closure devices, pollution sensors and self-evacuation signage, as well as the fire network (dry columns). All these systems are supervised by a Centralized Technical Management System (CTMS) developed by our specialists, to ensure optimum tunnel operation in real time.

"This new structure mobilized a wide range of Eiffage's skills and involved several of the Group's expert entities in their respective fields. The project illustrates the Group's ability to offer a comprehensive, integrated and controlled solution for complex infrastructures in dense urban environments," added Yann Grassart.

Now that the operating, security, and building management systems are up and running, the covered trench, which was commissioned last June, still needs surface work. The trench slab, planted with green spaces, will be entirely dedicated to urban uses and roadways.