Key takeaways
- The 423 is the successor to Class 420 and has defined the standard German S-Bahn vehicle since the late 1990s.
- The surest sign against the 420: four car sections and a fully walk-through interior instead of three separate car bodies.
- 423 and 433 belong together: 423 are the driving cars, 433 the intermediate cars of the same unit.
- It's the founding member of a family: 424, 425 and 426 are closely related designs for other platform heights and purposes.
- Against the near-identical 422, only the vehicle number helps in the field.
Contents
Fact file
| Vehicle type | Electric multiple unit for S-Bahn services |
|---|---|
| UIC type code | 94 – electric multiple unit or railcar |
| Train formation | Two Class 423 driving cars, two Class 433 intermediate cars |
| Design | Four-part articulated unit with Jakobs bogies, fully walk-through |
| Car body | Lightweight aluminium construction |
| Years built | from 1998 |
| Electrification system | 15 kV / 16.7 Hz AC |
| Maximum speed | 140 km/h |
| Typical use | S-Bahn services in conurbations with high-level platforms |
Identifying features
Is this really the class in front of you?
- Four car sections, fully walk-through – you can walk the length of the whole train
- Articulated unit: neighbouring car sections share a Jakobs bogie
- Level boarding at high S-Bahn platforms, with no steps
- Several wide double doors per side for fast passenger exchange
- Compact, softly rounded front end with a large windscreen
- Vehicle number starts with 423 (driving car) or 433 (intermediate car)
Updated: August 2026 – If someone says “S-Bahn” today and pictures something, there’s a high chance it’s a Class 423. The four-part articulated unit replaced the classic 420 from 1998 and became the standard vehicle of Germany’s conurbation S-Bahns. This page shows you how to recognise it – and how it relates to Classes 424, 425 and 426.
Spotted a 423? Note the number.
With S-Bahn classes, the number decides, not the shape – Traintrack logs it with place and date.
What is Class 423?
Class 423 is a four-part electric multiple unit for S-Bahn services, built from 1998. One unit consists of two powered Class 423 driving cars and two Class 433 intermediate cars. The train is an articulated unit with Jakobs bogies, built in lightweight aluminium construction, fully walk-through, and designed for 140 km/h under 15 kV / 16.7 Hz AC.
It succeeded the Class 420/421 and brought two innovations into everyday S-Bahn service that seem self-evident today: a fully walk-through interior along the whole length of the train and step-free boarding at high platforms. Both address the same operational problem – the shortest possible dwell times at the highest possible capacity.
The 423 family: one design, four classes
The most interesting part of this class is its family. Several classes come from the same construction family, differing mainly in purpose and platform height. Anyone who knows the family can place four classes with a single mental model.
| Class | Number of sections | Orientation | Recognisable by |
|---|---|---|---|
| 423/433 | four | S-Bahn, high platforms | step-free boarding, S-Bahn-typical door density |
| 424/434 | four | S-Bahn services with lower platforms | same basic shape, different boarding arrangements |
| 425/435 | four | regional services | boarding for lower platforms, regional-service seating |
| 426 | two | regional services, short units | noticeably short train with the same front end |
Practical tip: environment first, then number
Once you've recognised the family's basic shape, the environment already narrows things down a lot: a high platform and S-Bahn network point to 423 or 424, a regional platform and regional services to 425 or 426. The final answer, though, always comes from the vehicle number.
For the general order in which to work through features, see the guide to identifying classes.
Where it fits into S-Bahn operations
S-Bahn vehicles are consistently optimised for a single operating model. That makes them very common on their network and practically invisible outside it. On the trunk route through Munich Hauptbahnhof you can see this especially clearly. It belongs to the network of S-Bahn München, where the class has formed the backbone for years.
| Location | Likelihood | Why |
|---|---|---|
| S-Bahn trunk routes | highest | Densest timetable in the whole German rail network |
| Outer branches and terminus stations | high | Turnaround times, better vantage points and clearer light |
| Interchange hubs with regional services | high | Direct comparison with related classes possible |
| Regional lines without S-Bahn | low | Different platform heights and stop spacing |
| Long-distance routes | very low | No scheduled service |
Vehicle allocation changes
Which networks run which classes shifts with new deliveries, reallocations and tenders. Older network lists are therefore of little value. How to check the current picture live is covered in the article on tracking S-Bahn services live.
Check first, then head out
Live-reported sightings show you which units are currently in service.
Spotting and photo tips
The 423 is so ubiquitous that it’s easily overlooked. That’s exactly where the opportunity lies: you get plenty of chances to really work on a shot. On the S-Bahn tracks at Köln Hauptbahnhof the next one comes along every few minutes.
Use the frequency to practise
On trunk routes a train comes every few minutes. A perfect chance to work systematically through framing, focus plane and exposure.
Perspective at platform height
High S-Bahn platforms put you almost at vehicle height. That gives an unusually flat view – ideal for clean side-on shots, tricky for dramatic front-on ones.
Capture the design too
A shot that shows at least one gangway with a Jakobs bogie documents the design – a pure front portrait doesn't.
The number as a must-have shot
A tight extra shot of the side markings costs two seconds and makes the sighting permanently unambiguous.
Platform edge, safe distance, track area
S-Bahn platforms are narrow and busy, with trains arriving in close succession. Staying behind the safety line is mandatory; track areas, tunnels, operational railway land and stabling sidings are off limits. No shot justifies an exception.
For the photography side – shutter speed, dealing with station-hall light, composition – the guide on taking good photos of trains is worth reading. If you’d rather have daylight than hall light, head to the Hohenzollern Bridge.
Why this design changed S-Bahn operations
On an S-Bahn trunk route, the bottleneck isn’t top speed but dwell time. Every extra second a train stands at the platform costs capacity across the whole line – because the following train can only pull in correspondingly later. This is exactly where the design of the 423 comes in.
Three design decisions pay into this. Step-free boarding at high platforms makes passenger exchange both faster and more accessible. High door density spreads passengers along the length of the train instead of creating queues at a few doors. And the fully walk-through interior lets people spread out through the train – with the three-part 420 and its separate car bodies that was impossible; you’d be stuck in a packed carriage while there was room next door.
For spotters this is more than theory: it explains why this design won out over the old one and why later S-Bahn classes adopted the same basic features. Anyone who understands the logic can work backwards from door arrangement and boarding height to figure out what service an unfamiliar vehicle was built for.
Practical tip: watch the dwell time
Deliberately stand at a busy stop and watch a complete passenger exchange. Within a minute you'll see why door count and boarding height are the single most important design features in S-Bahn operation – and you'll spot the difference from regional vehicles instantly afterwards.
Common mix-ups
The 423 is almost exclusively confused within its own family. With the underground vehicles of the Münchner Verkehrsgesellschaft (MVG), on the other hand, it has nothing in common, even though both run in the same city. For each case there’s exactly one reliable feature.
It points to the 423 if …
- the train has four car sections and is fully walk-through
- there's only one bogie between each pair of car sections
- boarding is step-free at a high S-Bahn platform
- the number starts with 423 or 433
Look more closely if …
- the basic shape fits but boarding involves steps – then you're looking at a 425 or 426
- you can't decide between 422 and 423 – here only the number helps
- several units are coupled together and counting cars gets confusing
It isn't a 423 if …
- the train consists of three separate car bodies with no gangway – that's the 420
- the train has only two car sections – then the 426 is a candidate
- a separate locomotive is pulling or pushing the train
Conclusion
Class 423 is the vehicle that shows the shift from old to modern S-Bahn operation: fully walk-through, step-free, tuned for fast passenger exchange. Once you can identify it confidently, the family logic lets you place three more classes at once – and you also know the limits of looking alone: against the 422, only the number decides.
In short
Four car sections, a walk-through interior, Jakobs bogies, step-free boarding at a high platform: that's the 423. Three cars with no gangway would be the 420 – and steps at the entrance point to the regional variant.
Collect a whole family
423, 424, 425, 426 – with Traintrack you keep track of which units you're still missing.
Summary
- Class 423 is a four-part S-Bahn articulated unit in lightweight aluminium, built from 1998 and designed for 140 km/h.
- It replaced the three-part Class 420 in many networks and brought the fully walk-through interior to S-Bahn services.
- Classes 424, 425 and 426 come from the same construction family, built for different platform heights.
- For a clear sighting, the full vehicle number counts – not the livery or the network.
Frequently asked questions
How do I tell Class 423 apart from Class 420?
By the number of car sections and the gangway. The 423 is four-part and fully walk-through, the 420 consists of three separate car bodies with no gangway. This feature is visible from outside, works at a distance and reliably resolves the most common mix-up in the S-Bahn world.
What's the difference between 423 and 433?
Both numbers belong to the same unit. 423 denotes the powered driving cars with a cab, 433 the two intermediate cars. Such double classes are the norm for German multiple units – the same logic applies to 420/421, 422/432 or 424/434.
How fast does Class 423 run?
Its maximum speed is 140 km/h. That's enough for S-Bahn operation: on trunk routes with stops every few minutes, acceleration is what counts; on outer branches the figure is enough not to hold up mixed traffic.
What does the 423 have to do with Classes 424, 425 and 426?
They come from the same construction family. The 423 is the S-Bahn variant for high platforms, the 424 an S-Bahn variant for lower platforms, the 425 the four-part and the 426 the two-part regional-service variant. The basic shape is recognisably the same.
What is a Jakobs bogie?
A bogie shared by two neighbouring car sections. Instead of two bogies at the gangway, there's only one. That saves weight and length, but turns the train into an indivisible unit. For identification it's a strong feature, because it shows up instantly when you look from the side.
Why does the 423 have so many doors?
Because passenger exchange is the scarcest resource in S-Bahn operation. On trunk routes, dwell time determines the capacity of the whole line. Many wide double doors and step-free boarding shorten the stop and are what makes a dense timetable possible in the first place.
What does type code 94 mean?
It sits at the first two positions of the twelve-digit UIC vehicle number and denotes electric multiple units and railcars. It doesn't distinguish between S-Bahn, regional and tram-train hybrid vehicles – only the class number does that.
Where does Class 423 run?
In S-Bahn services in major conurbations. Which networks and lines that means exactly shifts with vehicle deliveries, reallocations and network tenders. Use current real-time data and community sightings rather than older overviews if you're looking for a specific one.
Log your sighting of the Class 423/433
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
DB Class 420 / 421
The Class 420 is the original German S-Bahn train: three cars, no gangway between them, built from 1969. Here's how to recognise it – and tell it apart from the 423.
EMUDB Class 422 / 432
The Class 422 is the direct evolution of the 423 – and its near-identical twin. Here's what genuinely sets the two apart.
EMUClass 425/426/435
Class 425 is the regional variant of the 423 family, and the 426 its two-part short version. You'll recognise both by the same front shape – and by train length.
EMUClass 493 (Extertalbahn 21 and 22)
Behind Class 493 stand the electric railcars 21 and 22 of the Extertalbahn – vehicles of a light railway you don't spot on a platform but trace through history.
EMUClass 557 (CAF Civity BEMU)
A multiple unit with a pantograph running on a line without overhead wires: Class 557 from the CAF Civity family is a battery multiple unit – and that's exactly how you recognise it.
EMUClass 563 (Siemens Mireo)
Class 563 belongs to the Siemens Mireo family. How to recognise the Mireo, how the number blocks 463, 1463 and 563 relate, and what sets it apart from the FLIRT.
Who is behind it
Groups, brands, manufacturers and operators – who owns whom and how to recognise them out in the field.
Münchner Verkehrsgesellschaft (MVG)
In Munich, three abbreviations sit side by side and are constantly confused: MVG is the municipal operator, MVV the fare association, SWM the parent group. And the S-Bahn, which many people simply lump in with the rest, belongs to an entirely different company.
BrandS-Bahn München
The S-Bahn München depends on a single twin-track tunnel through which almost every line runs. That dependency shapes operations, the timetable and how vulnerable it is to disruption – and, as everywhere, the brand name says nothing about who runs the trains. The answer is written small on the vehicle frame.
Where to see the Class 423/433
Specific viewpoints with lighting times, coordinates and an honest verdict on whether the trip is worth it.
Hohenzollern Bridge Cologne
The Hohenzollern Bridge is the busiest railway bridge in Europe – and one of the few top-tier spots that costs nothing and is open around the clock. A public footpath runs directly alongside the tracks on both sides, with the cathedral standing in the background.
Junction stationKöln Hauptbahnhof
Few stations in Europe pack so much traffic into so little space: over 1,200 train movements a day, eleven platform tracks, and the Hohenzollern Bridge starting right behind the platform ends. Get Köln Hbf right, and you'll have more in the bag after two hours than elsewhere in a whole day.
Junction stationMünchen Hauptbahnhof
München Hauptbahnhof is one of the largest terminus stations in Europe – and, at the same time, a major building site that has dragged on for years. If you know where the Starnberg and Holzkirchen wing stations start and where the S-Bahn disappears to, you can still pull a complete cross-section of southern German traffic out of it.
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