SNCF TGV Duplex - Why The Duplex?

Why The Duplex?

The LGV Sud-Est from Paris to Lyon is the busiest high-speed line in France, and after its opening in 1981 it rapidly reached capacity. When a railway line reaches its saturation limit, there are several options available to increase capacity. One way is to reduce train headways (the time between each train), i.e. to fit more trains onto the line at once. To achieve this, increasingly complex signalling systems and high-performance brakes (to reduce braking distance) are required. While these avenues have already been pursued to some extent by SNCF (headways have been reduced to three minutes on some TGV lines), the technical difficulties of continually improving signalling and braking make other solutions to the problem more attractive. Another option is to change the size of the train. Making the train wider is generally not practicable due to gauging restrictions. Running two trainsets coupled together in multiple-unit (MU) configuration provides extra capacity, but not enough in this case, and had the added disadvantage of requiring very long station platforms. If a train cannot be made longer or wider, then the remaining option is to make it taller, resulting in a bi-level configuration, with passenger seating on two levels, and 45% more passenger capacity than an equivalent single-level TGV. In addition, TGV Duplex sets are often run with a single deck Réseau set or another Duplex set.