Paris Line 18 opening at risk as partners blame Alstom's automation

Lire en français : Ligne 18 Grand Paris Express : Alstom livre les premières rames en 2025

The first section of Grand Paris Express Line 18, due to open in early December 2026, could slip into 2027 because of problems with its driverless train control system, according to AFP. Operator Keolis, infrastructure manager RATP and transport authority Île-de-France Mobilités point to Alstom, which denies any recurring fault.

The Société des grands projets (SGP), which built the line, handed the Massy-Palaiseau to Christ de Saclay section over to Île-de-France Mobilités (IDFM) and RATP on 13 October. Two months of trial running without passengers were meant to follow, but they had not started by 23 October, AFP reported that day. RATP said IDFM, Keolis and itself did not yet consider the technical and safety guarantees for those runs to be fully in place, and named the automation system coordinated by Alstom as the main issue, with some tests still to be completed.

IDFM said it regretted the new delay and held Alstom and the SGP responsible. The SGP did not comment. Alstom told AFP that the reports did not match reality: it said it had tested the automation with its partners for more than seven months, that "everything works", and that the SGP could not have completed the handover if failures had been recurring.

One supplier for trains and signalling

The dispute centres on a single contract. In October 2021 Alstom won a deal worth about 230 million euros for up to 37 trainsets, 15 of them firm, together with the line's driverless train control, data transmission and centralised supervision, according to the manufacturer. The signalling is its Urbalis Fluence communication-based train control (CBTC) system, run from Iconis control software, and Alstom also acts as general integrator for the line's systems.

The trains themselves arrived on time. The first three-car, 47-metre set reached the Palaiseau depot in May 2025, Urban Transport Magazine reported. What is now in question is how train, track-side equipment and control centre behave together under the operator's rules, which is precisely what trial running is designed to prove before passengers board.

The governance adds a layer of difficulty. An anonymous source quoted by AFP described Line 18 as the first new metro project in which infrastructure management and train operation are separated. The SGP built and financed it, RATP manages the infrastructure, Keolis, an SNCF subsidiary, runs the trains, and IDFM let the operating contracts. Four parties are now involved in explaining the delay, and their accounts differ.

A date that had already moved

The SGP announced on 25 June 2026 that the first section would open in the first week of December, after an earlier target of autumn, AFP reported at the time. The four stations, Massy-Palaiseau, Polytechnique, Université Paris-Saclay and Christ de Saclay, serve a plateau where about 70,000 students, researchers and employees work. The route includes a 6.7 km viaduct, which AFP describes as the longest rail viaduct in France.

Line 18 is not the only part of the network running late. On 24 September the SGP pushed back the first sections of Lines 16 and 17 to autumn 2028, AFP reported. The second section of Line 18, from Massy-Palaiseau to Orly airport and its connection with Line 14, is due at the end of 2027.

No new opening date has been announced. The next step is the start of the two-month trial running by Keolis on the RATP-managed infrastructure; until it begins, a December opening cannot be met. For the wider context, see the changes to Île-de-France transport in 2026 and the automation of Paris Metro Line 13.

Sources: AFP via La Gazette France (23/10/2026); AFP via La Gazette France (25/06/2026); AFP via Fortuneo (24/09/2026); Alstom, press release (11/10/2021); Urban Transport Magazine (18/05/2025); Île-de-France Mobilités, Line 18 project page.

Photo: construction of the elevated Orsay-Gif station on Line 18, January 2023. Jmex, CC BY-SA 4.0, via Wikimedia Commons.

Article written with the help of AI from the sources cited above, reviewed by the TrainsNews editorial team. Real photo, credited below the image. Spotted an error? contact@trainsnews.com – Our AI charter