# TGV Duplex

The TGV Duplex is a French high-speed train of the TGV family, manufactured by Alstom, and operated by the French national railway company SNCF. They were the first TGV trainsets to use bi-level passenger carriages with a seating capacity of 508 passengers, increasing capacity on busy high-speed lines. While the TGV Duplex started as a small component of the TGV fleet, it has become one of the system's workhorses.
A total of 160 Duplex trainsets were built: the original order of 89 first constructed in 1995, an additional 19 Réseau Duplex trainsets created as an extension of the TGV POS project in 2006, and 52 second-generation Dasye trainsets were first delivered in 2007 with revised traction motors and safety systems.
The Duplex design was further refined into the third generation Euroduplex.

## Purpose

The LGV Sud-Est from Paris to Lyon is the busiest high-speed line in France. After its opening in 1981 it rapidly reached capacity. Several options were available to increase capacity. The separation between trains was reduced to three minutes on some TGV lines, but the increasingly complex signalling systems, and high-performance brakes (to reduce braking distance) required, limited this option. Another option is to widen the train but is generally not practicable due to loading gauge restrictions. Running two trainsets coupled together in multiple-unit (MU) configuration provides extra capacity, but required very long station platforms. Given length and width restrictions, the remaining option is to adopt a bi-level configuration, with seating on two levels, adding 45% more passenger capacity. TGV Duplex sets are often run with a single deck Réseau set or another Duplex set.

## History

The Duplex feasibility study was completed in 1987. In 1988, a full-scale mockup was built to gauge customer reactions to the bi-level concept, traditionally associated with commuter and regional rail rather than with high-speed intercity trains. A TGV Sud-Est trailer was tested in revenue service with the inside furnished to simulate the lower floor of a bi-level arrangement, and later that year another TGV Sud-Est was modified to study the dynamic behavior of a train with a higher center of gravity. Discussions with GEC-Alstom began soon after, and in July 1990 the company won the contract to build the "TGV-2N", as it was then known. The contract was finalized in early 1991, at which point the official order was made. The first tests of a bi-level trainset were in November 1994. Soon after their first run, the first rake of eight trailers was tested at 290 km/h (180 mph) on the Sud-Est line. The trainset was powered by TGV Réseau power cars at the time, as the Duplex power cars were not ready. The first Duplex power car was mated to the bi-level trailers on 21 June 1995.

## Innovations

Perhaps the most important innovation is the efficiency of the Duplex design. Comparing an original TGV Sud-Est and a Duplex trainset shows that the double-decker design has improvements in both power-to-weight ratio and weight-per-seat overhead:
| | Power-to-weight ratio (kW/tonne) | Weight/seat (tonne) | Power/seat (kW) |
| TGV Sud-Est | 17 | 1.10 | 18.34 |
| TGV Duplex | 23 | 0.7 | 16.15 |
In this comparison, "power" refers to installed power, not all of which is used when operating.
* Aluminium bodies: French high-speed lines have a 17-tonne (16.7-long-ton; 18.7-short-ton) axle load limit, so the larger double-deck trains needed to cut down on weight wherever possible. Alstom extensively used extruded aluminium to save weight.
* Improved aerodynamics: the nose of the power units and the gap between trailers were improved such that a Duplex train at cruise speed of 300 km/h (186 mph) experiences only 4% more drag than a single-level TGV. The nose, the first significant departure from Cooper's design of the original trainsets (TGV Sud-Est), was styled by industrial designer Roger Tallon, as was the rest of the trainset.
* Crashworthiness: crush zones and rigid passenger compartments protect safety in the event of a collision. The power units' frame is designed to take a (steady-state) 500 tonnes (492 long tons; 551 short tons) of force frontal load, and features structural fuses to absorb impact energy.
* Active pantograph: the Faiveley CX used on the Duplex has a pneumatically actuated active control system. Two small gas cylinders in the wiper armature can tune the stiffness of the pantograph's upper stage, to optimize contact at any speed.
* All wheel disc brakes: earlier TGVs (including Eurostar) used disc brakes only on unpowered axles. Weight gains on the Duplex power units allowed the installation of disc brakes directly on the wheels of powered axles (so-called "cheek discs"), instead of using the traditional tread brakes. This does not greatly improve braking performance, but it leaves the wheel tread smooth and considerably reduces rolling noise.
* Quiet roof fans: the cooling fans in TGV power units produce the most noticeable sound (a loud hum) when the train is in a station. The fans, located in the roof of the unit, were redesigned to be quieter.
* World's fastest train: in 2007 a short formation TGV Duplex was fitted with distributed traction as used in the future generation AGV (automotrice à grande vitesse) setting a new speed record of 574.8 km/h (357.2 mph). (see TGV world speed record#Record of 2007)
Also unique compared to single-level equipment, the lower level of the bar car is used for equipment, moving them out of passenger spaces.

## Réseau Duplex

The Réseau Duplex was part of the TGV POS project, a unique extension of the TGV Duplex order. For the POS project, Alstom delivered to SNCF 38 new tri-current power cars and 19 sets of double-deck Duplex passenger carriages in 2006. The new tri-current power cars were paired with the 19 sets of older single-level passenger carriages from TGV Réseau trainsets, while the new double-deck Duplex passenger carriages were paired with the 38 older dual-current power cars, creating the 19 Réseau Duplex trainsets.
The tri-current function was necessary for the LGV Est, which ends at the German border, where the electrification switches to the 15 kV  16.7 Hz AC system. Meanwhile, the heavily congested lines where the Réseau trainsets were used needed the additional passenger capacity provided by the Duplex passenger carriages.
The project allowed SNCF to receive the tri-current power cars needed ahead of the opening of the LGV Est, without slowing the production of the Duplex trainsets.

## Dasye

Dasye is a contraction of Duplex Asynchronous ERTMS and are the second generation of Duplex trains. In exterior design and passenger cabin experience, they are nearly identical to the first-generation Duplex trains, however, two major changes were made inside the power cars. First were the asynchronous motors, first used on the Eurostar e300 trainsets, which allow an individual motor in a bogie to be isolated (disconnected) in case of failure, allowing the train to continue to operate. Second was the addition of the European Rail Traffic Management System (ERTMS).
A total of 50 Dasye trainsets were ordered, with a prototype power car first delivered in late 2006 for testing, before entering service on 14 February 2008.
Starting in 2013, many of the Dasye trainsets have been reconfigured for use on SNCF's low-cost Ouigo service. These trains use a high-density layout, which can carry 20% more passengers (644 passengers, compared to 510 on a standard trainset). The extra seating is enabled by the elimination of the bar car and first-class cars, and the use of slimline seats. By 2021, 38 Dasye trainsets have been converted for Ouigo service, with all 50 trainsets expected to be converted by 2025.

## Eurotrain

Eurotrain was a consortium formed by Siemens and GEC-Alsthom (today Alstom) in 1996 to market high-speed rail technology in Asia. In 1997, it was one of two competitors to supply the core system of Taiwan High Speed Rail (THSR), and was awarded the status of preferred bidder by concessionaire THSRC.
In early 1998, the consortium created a demonstration train by combining cars of three existing French and German high-speed trains: the intermediate cars of TGV Duplex trainset #224 was joined with German Railways ICE 2 powerheads 402 042 and 402 046 at the two ends. On 4 May 1998, the Eurotrain demonstration train made a presentation run on the Hanover–Würzburg high-speed railway in Germany, achieving a maximum speed of 316 km/h (196 mph).
In December 2000, THSRC awarded the contract to the rival Taiwan Shinkansen Consortium, leading to a legal battle ending in damage payments for Eurotrain in 2004.