Key takeaways
- Re means: electric engine with increased curve speed – the R replaced the earlier A on newer high-speed engines.
- 4/4 means full drive on all four axles, i.e. a Bo'Bo' wheel arrangement.
- The Roman I marks the first series of the family and distinguishes it from the Re 4/4 II and Re 4/4 III.
- Lightweight design was the concept: the engine was built for light, fast passenger trains, not heavy loads.
- No longer a regular-service vehicle today – encounters come from special trains, museum runs or private-railway workings.
Contents
Fact file
| Vehicle type | Light electric locomotive for passenger services |
|---|---|
| Railway administration | originally Swiss Federal Railways (SBB) |
| Designation R | vehicle with increased curve speed |
| Designation e | electric drive |
| Axle ratio 4/4 | all four axles powered, Bo'Bo' wheel arrangement |
| Roman numeral I | first build series of the Re 4/4 family |
| Electrification system | 15 kV / 16.7 Hz AC |
| Current status | Withdrawn from SBB scheduled service; individual examples at private railways and heritage societies |
Identifying features
Is this really the class in front of you?
- Four axles in two bogies, all powered – no trailing axles
- Noticeably shorter and lighter body than the later Re 4/4 series
- Boxy early post-war styling without modern curves
- Designation with a Roman I after the fraction
- Often seen in a special or historic heritage-society livery
- Usually seen ahead of short trains, special services or empty stock moves rather than long-distance services
Updated: August 2026 – At the start of the best-known Swiss locomotive family stands a compact, light engine: the Re 4/4 I. It explains the Swiss designation system as clearly as almost no other vehicle – and shows how much information a single Roman numeral can carry. This page shows you how to read it, how to spot it, and where it can still turn up today.
Don't just see a rare engine – keep the record
Number, keeper, livery, date: with Traintrack, a complete sighting takes half a minute to log.
What is the Re 4/4 I?
The Re 4/4 I is a light four-axle electric locomotive of the Swiss Federal Railways with drive on every axle. It was procured in the second half of the 1940s and built for light, fast passenger trains – a deliberately lean vehicle concept, not a universal machine for heavy loads.
Historically, it is the starting point of a family that shaped the image of Swiss railways for decades: the first series was followed by the noticeably more powerful Re 4/4 II and Re 4/4 III, which took over regular service. The Re 4/4 I has vanished from SBB’s everyday operations. What survives today belongs to private operators, heritage societies and the museum world.
How to read the designation
Swiss locomotive designations are not a catalogue code but a short description of the vehicle. For the Re 4/4 I, there are four parts to it.
R – increased curve speed
The R marks vehicles permitted to take curves faster than the standard classes. It replaced the older A on newer high-speed engines, which is still found on machines such as the Ae 6/6.
e – electric drive
The lower-case letter describes the type of drive. An e stands for electric, an m for a combustion engine. If it is missing altogether, it is a steam locomotive.
4/4 – all axles powered
The numerator gives the powered axles, the denominator the total axles. Four out of four means: not a single wheel just runs along freely. In international notation, that corresponds to the Bo'Bo' wheel arrangement.
I – the first build series
Roman numerals separate successive series of the same basic design. The I comes first, followed by II and III – each a distinct vehicle with its own character.
Once you understand the principle, you can also read an Ee 3/3 or a steam locomotive like the A 3/5 without looking anything up. The general method for identifying unfamiliar vehicles is described in the guide to identifying locomotive classes.
Old fraction, new number – both are in use
In Switzerland, two layers of designation exist side by side. The classic fraction describes the vehicle, while the more modern three-digit series is fit for computers and databases. In practice that means you need to be able to read both forms.
| Classic designation | Modern series | What the number shows |
|---|---|---|
| Re 4/4 I | Re 410 | four powered axles, first series |
| Re 4/4 II | Re 420 | four powered axles, second series |
| Re 4/4 III | Re 430 | four powered axles, third series |
| Re 6/6 | Re 620 | six powered axles |
| Ee 3/3 | Shunting range | three powered axles, shunting class E |
A memory aid for the new numbers
For Swiss electric locomotives, the first digit of the three-digit series can be read as the number of powered axles: anything starting with 4 is four-axle, anything with 6 is six-axle. This does not work for every vehicle class, but it is reliable for the Re family.
Keep track of build series
I, II or III – whoever has already seen which series is only known to whoever wrote it down. Traintrack turns that into a sortable collection.
Where you meet the Re 4/4 I today
The class is no longer a regular-service vehicle. The search therefore works differently than for a current main-line engine: you plan around dates, not routes.
Events instead of the timetable
Railway festivals, anniversaries and announced special runs are the realistic opportunity. A chance encounter in regular service practically does not happen.
Keep an eye on keepers
Private operators and heritage societies run surviving engines with varying intensity. Who looks after which locomotive changes – treat lists as a snapshot in time.
Photograph the livery too
Historic vehicles often carry liveries from different eras. For them, the side is the real information, not just the front.
Only from public areas
Even at special events: tracks, sidings and operational railway land are off limits. Platforms, footpaths and bridges are enough for good photos.
Anyone wanting to get involved in preserving historic vehicles themselves will find the way in through the overview of heritage railway societies in Germany, Austria and Switzerland. And so that a rare sighting doesn’t end up lost in an unsorted photo folder, a properly kept sighting log pays off.
Why lightweight design was its own concept
A railway administration specially procuring a light express engine seems unusual from today’s perspective. In the post-war period it was an obvious answer to a real problem: not every passenger train is heavy, and an oversized engine costs more to buy, maintain and run than it earns back.
Light locomotives also have an operational advantage that is often overlooked: they put less strain on bridges, track and curves. On lines with older infrastructure, that can decide whether a vehicle is allowed to run at all. The downside is just as clear – low weight means low adhesive weight, and therefore limited starting tractive effort. Ahead of heavy trains or on gradients, a vehicle like this quickly reaches its limits.
That is exactly why the family kept growing. The second series became a universal locomotive for a broad range of duties, the third was geared towards heavy train working. Three series, three answers to three different questions – but always the same basic idea of a four-axle, fully powered locomotive.
How to spot lightweight design in the field
Compare the length of the locomotive body with the coaches behind it. A light engine looks noticeably shorter next to a normal passenger coach, while later universal engines come close to matching coach length. That is no proof, but it is a good first impression.
Common mix-ups
It points to a Re 4/4 I if …
- you see a compact four-axle electric engine with a boxy body
- the marking carries a Roman I after the fraction
- it is running ahead of a special train or a short set of coaches
- the body looks shorter than on the familiar standard engines
Look more closely if …
- the engine carries a historic or heritage-society livery
- you have nothing to compare it against and the proportions are hard to judge
- only the modern series number is marked
It is not a Re 4/4 I if …
- you count six axles
- the marking shows II or III after the fraction
- the engine is scheduled ahead of a current regular service
Conclusion
The Re 4/4 I is today above all a teaching example. Read it, and you understand the whole Swiss system: R for the high-speed class, e for electric, 4/4 for full drive, Roman I for the first series. As a vehicle, it has vanished from regular service and lives on with heritage societies and private operators – every encounter is therefore planned, never accidental.
In short
A compact four-axle electric engine, a Roman I in the marking, no longer in regular service: that is the Re 4/4 I. To see one, plan around special runs and events – and document the sighting with number, keeper and livery.
Your Swiss collection grows with you
From the historic Re 4/4 I to today's main-line engines: in Traintrack, it all sits in one collection.
Summary
- The Re 4/4 I stands at the start of arguably the best-known Swiss locomotive family and explains its naming logic best.
- Its lightweight design clearly sets it apart from the later, more powerful Re 4/4 II and Re 4/4 III series.
- It has vanished from SBB's regular service; surviving examples are found with heritage societies and private operators.
- To see one, follow special runs and event dates – fleets and keepers change.
Frequently asked questions
What does the designation Re 4/4 I mean?
The R marks a vehicle with increased curve speed, the lower-case e the electric drive. The fraction 4/4 says that all four axles are powered. The Roman I marks the first build series of the family. Put together: a high-speed, fully powered electric locomotive in its first version.
How does the Re 4/4 I differ from the Re 4/4 II?
Chiefly in size and purpose. The Re 4/4 I was designed as a light express engine and is accordingly more compact. The later Re 4/4 II became SBB's universal standard locomotive and is more powerful and longer. In the field, a direct size comparison helps – and if in doubt, the marking on the vehicle.
Why do some Swiss engines carry A and others R?
The A belongs to the classic speed-class system and is found on older vehicles such as the Ae 6/6 or the Ae 3/6. For newer high-speed engines, the R was introduced, marking vehicles with increased curve speed. Both letters denote fast machines, but come from different eras.
Does the Re 4/4 I still run today?
No longer in SBB scheduled service. Surviving engines are held by private operators, heritage societies and in museum settings. Whether a particular engine is operational and where it is used changes with keepers, inspection deadlines and projects – so always check the current status.
What does Bo'Bo' mean for a Re 4/4?
Bo'Bo' is the internationally standard notation for two two-axle bogies in which every axle is individually powered. That is exactly what the Swiss notation 4/4 expresses – four powered out of four axles. The two systems describe the same thing from different traditions.
What does the new number Re 410 mean?
With the move to computer-readable numbers, many Swiss vehicles also received a three-digit series designation. For electric locomotives, the first digit can be read as the number of powered axles: Re 410, Re 420 and Re 460 are four-axle, Re 620 is six-axle. The old fraction survives alongside it in everyday usage.
Where do I have the best chance of a sighting?
At announced special runs, railway festivals and anniversaries, and around the operators that still maintain examples. A chance encounter in regular service is practically ruled out. Anyone searching deliberately works from event calendars and community reports rather than timetables.
Why is it worth documenting locomotives like this?
Because the surviving fleet is finite and its condition keeps changing. Liveries change, keepers change, engines go into overhaul or are withdrawn. A sighting with number, date, location and livery is therefore a genuine timestamp – and worth more in a few years than it is today.
Log your sighting of the Re 4/4I
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
SBB Re 420 (Re 4/4 II)
The Re 4/4 II is the standard electric locomotive of the SBB and is now called the Re 420. This page shows you how to recognise it and what the two designations mean.
Electric locoSBB Re 430
The Re 430 is the third series of the Swiss Re 4/4 family and is designed for tractive effort. This page shows you how to tell it apart from the similar Re 420.
Electric shunterSBB Ee 3/3
The Ee 3/3 is the classic electric shunting locomotive of the SBB: three powered out of three axles. Here's how to read the designation and identify it reliably.
Electric locoSBB Re 450
The Re 450 is the locomotive of the Swiss double-deck push-pull train in S-Bahn service. This page shows how the set is put together and what that means for spotting.
Electric locoSBB Re 460 (Lok 2000)
The Re 460 is the SBB's modern long-distance locomotive: 119 machines, 200 km/h, an unmistakably rounded front. Here's how to recognise it and its sister designs.
Electric locoSBB Re 465 (BLS)
The Re 465 is the BLS variant of the Lok 2000 family and is easily mistaken for the Re 460. This page shows you how to tell the two apart with confidence.
Who is behind it
Groups, brands, manufacturers and operators – who owns whom and how to recognise them out in the field.
Where to see the Re 4/4I
Specific viewpoints with lighting times, coordinates and an honest verdict on whether the trip is worth it.
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