Class 646 (Stadler GTW 2/6)

Updated: August 2026 – A railcar whose middle section looks like an inserted technology container: that’s Class 646, the Stadler GTW 2/6. Hardly any other vehicle in German regional services is so easy to identify. This page explains what’s behind the unusual layout, how to place the type, and how to photograph it well.

What is Class 646?

Class 646 is the Stadler GTW 2/6, a diesel-electric articulated railcar from Stadler Rail for regional services. Its layout is unique in German local rail transport: between two car body sections sits a narrow, taller drive module, which houses the engine, generator and cooling. The end cars themselves carry no drive technology and can therefore be built consistently low-floor.

The designation 2/6 follows the Swiss classification system and names the ratio of powered to total axles: two of six. The two axles of the centre module are powered. The vehicles are approved for 120 km/h. The principle has also been built in longer variants and in an electric version, for instance in the GTW vehicles of the Thurbo RABe 526 in Switzerland.

How to identify the GTW in seconds

If you want a systematic approach to identification, the guide to identifying classes explains the order in which to work through the features.

Why the drive sits in the middle

The GTW concept turns the usual arrangement on its head. Instead of spreading motors under the floor of the passenger areas, it bundles all the technology into its own module. That has several practical consequences.

Aspect	GTW layout	Usual underfloor layout
Location of drive technology	bundled in the centre module	spread under the passenger area
Floor height in the end cars	consistently low possible	raised above the motors
Maintenance access	central, in one place	at several points along the train
Recognisability in the field	very high	low
Roof housings	concentrated over the module	spread across the car body sections

For spotters, the last row is the one that matters most: a GTW’s silhouette is distinctive enough to work from a great distance and in poor light.

The concept does, however, have an operational downside that shows on the vehicle: the drive module takes up space in the train without carrying passengers. For a six-axle unit that’s a noticeable share of the overall length. That’s exactly why longer GTW variants were developed, in which the same module is spread across more seats – the ratio improves, while the basic principle stays the same.

For identification in the field that means: don’t just count the car body sections, count the axles too. A GTW with six axles is the short version; more axles mean a longer variant. The slash figure in the type name reflects exactly this ratio and is thus the most compact description a vehicle name can offer.

Where it fits in rail operations

The GTW occupies the same niche as other multi-part diesel railcars: regional lines without overhead wires, often with moderate demand. Because the type is used by several railway operators, you’ll find it in a wide range of liveries. These include companies of the Netinera group. Some of the lines it runs on belong to regional infrastructure managers such as the Bremen/Lower Saxony Railway Network (EBN).

Location	Chance of a sighting	Why
Non-electrified regional lines	high	core territory of the type
Networks of private railway operators	high	the type is widespread there
Regional hubs at the edge of diesel networks	medium to high	transition from electric to diesel operation
Electrified main lines	low	only diversions and transfer runs
S-Bahn networks	very low	purely electric operation

Spotting and photography

The GTW is photographically unusual: its most interesting part isn’t at the front, but in the middle. A pure front-on shot wastes exactly the feature that defines the type.

The guide to keeping a sighting log shows how to record your finds so they stay usable long-term. You’ll find suitable, publicly accessible locations in the overview of the best stations for trainspotting in Germany.

Common mix-ups

The type is also common abroad – for instance as the Arriva GTW in the Netherlands. Within Germany, the Regio-Shuttle RS1 of Class 650, also from Stadler, is the closest relative, but differs fundamentally: one car body, no drive module.

Conclusion

Class 646 is the simplest case among German diesel railcars. One look at the middle of the train is enough, and the type is identified. What makes it interesting is the variety of operators and liveries – which is exactly why it’s worth recording every sighting with number, date and colour scheme.