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Final preparations for the opening of Grand Paris Express Line 18 are accelerating south of Paris, as testing, staffing and construction milestones align toward a first section entering service in late 2026.
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A flagship line poised to open first in the new network
Publicly available information indicates that Line 18 is now positioned to become the first of the four new Grand Paris Express metro lines to open, ahead of Lines 15, 16 and 17. A first operational segment between Massy-Palaiseau and the Saclay plateau is targeted for the autumn, with several sources pointing to October as the reference date for initial passenger service.
The line is part of the wider Grand Paris Express scheme, described by project documents as one of Europe’s largest infrastructure undertakings, adding more than 200 kilometers of new automated metro to the capital region. Line 18 will ultimately stretch roughly 35 kilometers between Orly Airport and Versailles, but its opening is being staged in phases through 2030.
Recent coverage of project timelines notes that the first phase of Line 18 will now precede the delayed Line 15 South, which has been pushed back to 2027. That shift makes the south-western corridor between Orly, Massy and the Saclay research and university cluster the first area to experience the new-generation orbital metro.
According to summaries of Grand Paris Express planning documents, subsequent sections of Line 18 are due to connect Orly to Massy-Palaiseau and then extend westward to Versailles Chantiers, giving the line a strategic role linking the airport, high-speed rail, and the growing innovation hub on the Saclay plateau.
Testing campaign intensifies on the first operational section
Reports from late 2025 and early 2026 describe a visible acceleration in on-track testing, particularly on the elevated segment between Massy-Palaiseau and Saclay. Trial runs with the new automated trainsets are underway, checking signaling, traction and braking systems, as well as platform screen doors and communications equipment across the first group of stations.
Technical documentation from the rolling stock supplier highlights ongoing “dynamic tests” designed to validate performance at line speed, integration with the automatic train control system, and energy consumption patterns. These tests also include simulated service scenarios, from routine operations to degraded modes, as engineers fine-tune software and equipment ahead of opening.
Project updates describe a progressive ramp-up: initial low-speed runs have given way to more intensive cycles, including night testing, as more trainsets are delivered. By the end of 2026, the full initial fleet of Line 18 trains is scheduled to be available, allowing a transition from testing to pre-operational trials that resemble real passenger service without the public on board.
In parallel, station systems are entering their own commissioning phase. Fire safety installations, ventilation, ticketing and passenger information systems are undergoing inspection and validation, coordinated by the Société des Grands Projets and its industrial partners.
Construction milestones between Saclay, Guyancourt and Versailles
While the first section is being prepared for operation, major civil engineering work continues further west. Recent regional coverage points to key milestones at Guyancourt, where a new underground connection toward the already built tunnel beneath the National Golf course at Saint-Quentin-en-Yvelines is now underway. That junction is considered a critical step for the western half of the line.
Engineering references describe a mixed profile along Line 18, with both underground and viaduct sections. Earlier design revisions brought part of the original elevated alignment down into a trench to limit visual impact and reduce costs, particularly around the CEA Saclay and Saint-Quentin areas. Those design choices are now materializing on-site as structures, track beds and station shells are completed.
Contract announcements from construction firms over the past two years have detailed the progressive handover from tunneling to systems installation on the western section. Work on tracks, power supply and signaling is following the completion of major civil works, with an eye on the next opening target in 2027 toward CEA Saint-Aubin.
Local planning documents underline that the full route to Versailles Chantiers is not expected to open before 2030. Even so, the current pace of work between Saclay, Guyancourt and Saint-Quentin suggests that the line is advancing in clearly defined stages, each aligned with separate commissioning and testing phases.
Operational model and workforce preparations for launch
While technical tests proceed on the infrastructure, preparations for day-to-day operation are also taking shape. News coverage of a late-May briefing in 2026 reported that Line 18 will introduce an operational model pairing Keolis as the operating company with RATP as infrastructure manager, under the authority of the regional transport organizing body.
According to a recent recruitment-focused press release, RATP Group is hiring several thousand employees in the Paris region this year, citing the imminent opening of the first Grand Paris Express lines, with Line 18 explicitly mentioned as a priority. Roles range from maintenance technicians and supervisors to passenger support staff and control center operators, reflecting the needs of a fully automated, high-frequency metro.
Training programs are being tailored to the new line’s technology, which uses platform screen doors, advanced automation and a distinct rolling stock type compared with many legacy Paris Metro lines. Operating staff are expected to undergo simulations and practice sessions on the new systems during the pre-opening trial phase.
Public information also points to coordination between the operator, infrastructure manager and regional transport planners to finalize service patterns, frequencies and integration with existing metro, RER and bus networks around key interchange hubs like Massy-Palaiseau and Orly.
Transforming connectivity for the Saclay plateau and Orly corridor
Strategic analyses of the Grand Paris Express project consistently highlight Line 18’s role in reshaping east-west mobility across the southern arc of the metropolitan area. The line will directly link Orly Airport with the Saclay plateau, where a rapidly expanding cluster of universities, research centers and corporate campuses has long been constrained by limited rail access.
Urban development agencies describe the new line as a catalyst for the Paris-Saclay innovation district, by significantly reducing travel times to existing hubs such as Massy, with its TGV and RER connections, and eventually to Versailles. Frequent automated metro service is expected to provide a more reliable alternative to road-based commuting in an area often affected by congestion.
Environmental assessments of the Grand Paris Express program cite Line 18 as a contributor to regional climate objectives, by encouraging a shift from private cars to electrified public transport. The phased opening from 2026 to 2030 is presented as part of a broader strategy to cut greenhouse gas emissions and rebalance growth away from central Paris.
As the first passenger trains prepare to run later this year, attention will increasingly turn to how quickly travelers, students, researchers and airport users adopt the new line. The performance of Line 18’s launch phase is likely to influence public perception of the entire Grand Paris Express program in the years leading up to the opening of Lines 15, 16 and 17.