The first MI20 multiple unit, the future train for Paris’s RER B line, was unveiled at the Alstom plant in Crespin, northern France, where it completed its first test run ahead of dynamic testing. Île-de-France Mobilités is investing EUR 2.5 billion in 146 new trains, which will replace the current MI79 and MI84 multiple units on one of Europe’s busiest urban rail lines.
Île-de-France Mobilités is investing EUR 2.5 billion in the purchase of 146 new trains, which will gradually replace the current MI79 and MI84 multiple units in service. The new trains are being built by the Alstom/CAF consortium, in partnership with RATP and SNCF Voyageurs, the line’s operators.
RER B carries approximately 1 million passengers per day and is the second-busiest line in Europe, after RER A. The line connects Paris-Charles-de-Gaulle Airport and Mitry-Claye in the north to Robinson and Saint-Rémy-lès-Chevreuse in the south, crossing through central Paris.
146 new trains for one of Europe’s busiest lines
The new MI20 multiple units are part of a comprehensive program to modernize public transportation in the Île-de-France region. Since 2016, according to the regional transportation authority, 1,550 new or modernized trains, RER trains, metro cars, and trams have entered the Île-de-France network.
The EUR 2.5 billion investment in the MI20 trains is fully funded by Île-de-France Mobilités and is part of a broader plan, totaling nearly EUR5 billion, dedicated to the RER B line through 2030. The program includes, among other things, a single control center for the RER B and RER D lines and the implementation of the NExTEO automated driving system.
According to Île-de-France Mobilités, the delivery schedule was tightened following initial delays, and the project has become a priority for the Alstom/CAF consortium. The current goal is for the first trains to run on the Île-de-France network by the end of 2028.
Up to 35% greater capacity
The new MI20 trains are designed to increase capacity and comfort on a line where overcrowding is one of the main issues. Each multiple unit will be able to carry 1,063 passengers, up to 35% more than current trains.
The number of seats will reach 342, up to 22% more than currently. The trains will be 104 meters long, similar to current multiple units, but will consist of seven short cars instead of four long cars.
The train’s width will be 3 meters, up to 20 cm wider than current rolling stock. This allows for wider aisles and better passenger flow inside the train.
A mixed architecture, with single-level and double-level sections
The MI20 will feature an unusual architecture that alternates between single-level and double-level cars. This design is tailored to different types of journeys and passengers.
The areas at the same level as the platform will be designated for passengers with luggage, strollers, or limited mobility. The double-deck sections will offer more seating and greater comfort for longer journeys. The gangways between cars will feature subway-style spaces with wide aisles, handrails, and longitudinal seats for short trips between stations.
The wide inter-carriage passageways and continuous ceiling will allow for better visibility throughout the train and a more even distribution of passengers inside, without rigid partitions between carriages.
Accessibility, air conditioning, and USB-C
The new trains will be 100% accessible, with level access and a design that reduces the gap between the platform and the train—an important feature, especially at stations located on curves.
The multiple units will be equipped with air conditioning, heated floors, a video surveillance system with real-time image transmission, USB-C ports, and numerous passenger information screens.
Each train will have 92 dual USB-C ports, 44 video cameras—50% more than currently—and various types of screens for displaying the route map and travel information.
There will be 90 priority seats, representing 26% of the total seating capacity, as well as four spaces for wheelchair users.
14 doors on each side of the train
To reduce dwell times at stations, each MI20 multiple unit will have 14 doors on each side. The access areas will account for 22% of the train’s length, which should allow passengers to board and alight more quickly.
This feature is important for a high-frequency line with heavy passenger traffic, where every second spent at stations affects punctuality.
Île-de-France Mobilités notes that 25% of the materials used in the new trains are recycled, in line with goals to reduce environmental impact.
The first dynamic tests will follow the test run at Crespin
The presentation at Crespin marked the first test run of the MI20 test train.
The train was already equipped with interior fittings, and the next step will be the start of dynamic testing.
At this time, 10 trains are in production. The first multiple unit assembled in the spring of 2026 confirms that the project has entered an important industrial phase, following initial delays.
If the current schedule is maintained, the first MI20 trains are expected to run on the RER B network by the end of 2028, ushering in a new era for one of the most important transit lines in the Paris region.
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