It is an imposing viaduct: 7 kilometers long, 200 piles, and a height ranging from 6.50 to 30 meters. The future metro 18 does not go unnoticed in its aerial part. However, the Grand Paris Society assures that everything has been done to make it as discreet as possible. It has just finished being assembled a few months ahead of time, an exception in the construction industry.
This passage in the air was decided primarily to reduce costs. A viaduct is much cheaper than a tunnel. The major disadvantage is that it creates a view of nearby buildings and does not contain the noise of a metro as a tunnel does. To reassure residents, measures have been taken: 2.50-meter noise barriers are installed in urban areas, foundations are also positioned under the rails to absorb the vibrations of trains traveling at 100 km/h.
Another feature designed to reduce visual nuisance is that there is no catenary (overhead contact wire) to power the trains but a third rail, laid on the ground and therefore less visible.
In the rest of the 35 km of the future automated metro, the primary work is also nearing completion. The tunnel boring machine Céline is being dismantled. It has successfully dug 20 km passing under Orly Airport and under the twenty or so railway tracks of Massy Palaiseau. The first rails are starting to be laid.
The first section will open in 2026 between Massy and the Saclay plateau, with a metro frequency of every 3 minutes. Then, in 2027, the 18 will reach Orly Airport to the east. And finally, Versailles Chantiers (Yvelines) in 2030.