The design was complete enough to be frozen by July 2006. It had become formalised at basic train lengths of 7 or 14 cars, with the 3-car modules remaining part of the design. Each 3-car module had either a transformer or one of two traction modules (inverters) located beneath a carriage. Additional trailer vehicles (referred to as 'key' cars) were to extend the train size beyond multiples of three. The train is able to operate under all four European electrification systems, with a top speed specified at under 25 kV electrification, under 15 kV 16⅔ Hz supply, and further reduced to and under 3 kV and 1.5 kV respectively.