Stadler GTW is family of vehicles which differ externally, in the various designs of the head of the vehicle (from angular to streamlined), and also in the different designs and power units that drive them.
They also come in different gauges and as rack railway vehicles.
The basic version is the GTW 2/6, a railcar which conforms to UIC standards. "
2/6" means "two of six axles are powered".
The GTW 2/6 is used for example by Deutsche Bahn as Baureihe 646 (Series 646) and by Swiss railways as RABe 526.

The basic concept is rather unconventional: the car is driven by a central "power module", also known as a "powerpack" or a "drive container", powered on both axles.
 Two light end modules, each with a bogie, rest on the power module, which produces useful traction weight on the driving axles.
The end modules also use the space very effectively, although the railcar is divided into two halves by the power module.
Most units have a path through the drive container for passenger access.
The end modules can be delivered with standard pulling devices or buffer gears, or with central buffer couplings.
They are built with a low-floor design except above the bogies and at the supported ends (more than 65% of the railcar is low-floor).
All of the usual comforts to be expected in a modern local network railcar are provided, such as air conditioning, a multi-purpose room, vacuum toilets (in a washroom suitable for the disabled) and a passenger information system.
The GTWs can be Diesel-electric or electric-powered (via overhead wires or third rail).

Although the traction is good for the powered bogies the concept has the same problem as other light railcars with the brakes on the non-powered axles having lower grip than traditional railcars.
This has led to actual restrictions when leaves are on the rails as the wheel slide protection can not fully compensate the effect.
The central power module has limits with heat dissipation as well which can lead into situations where the power output needs to be limited which is automatically done in this construction concept.
Stadler GTW is family of vehicles which differ externally, in the various designs of the head of the vehicle (from angular to streamlined), and also in the different designs and power units that drive them. They also come in different gauges and as rack railway vehicles. The basic version is the GTW 2/6, a railcar which conforms to UIC standards. "2/6" means "two of six axles are powered". The GTW 2/6 is used for example by Deutsche Bahn as Baureihe 646 (Series 646) and by Swiss railways as RABe 526.
The basic concept is rather unconventional: the car is driven by a central "power module", also known as a "powerpack" or a "drive container", powered on both axles.  Two light end modules, each with a bogie, rest on the power module, which produces useful traction weight on the driving axles. The end modules also use the space very effectively, although the railcar is divided into two halves by the power module. Most units have a path through the drive container for passenger access. The end modules can be delivered with standard pulling devices or buffer gears, or with central buffer couplings. They are built with a low-floor design except above the bogies and at the supported ends (more than 65% of the railcar is low-floor). All of the usual comforts to be expected in a modern local network railcar are provided, such as air conditioning, a multi-purpose room, vacuum toilets (in a washroom suitable for the disabled) and a passenger information system. The GTWs can be Diesel-electric or electric-powered (via overhead wires or third rail).
Although the traction is good for the powered bogies the concept has the same problem as other light railcars with the brakes on the non-powered axles having lower grip than traditional railcars. This has led to actual restrictions when leaves are on the rails as the wheel slide protection can not fully compensate the effect. The central power module has limits with heat dissipation as well which can lead into situations where the power output needs to be limited which is automatically done in this construction concept.
Stadler GTW