Key takeaways
- SM42 and SU42 are the same class: the second letter describes the job, not the design.
- M stands for manewrowa – shunting duty; U for uniwersalna, meaning line service including passenger trains.
- Tamara is the established nickname and appears in Polish sighting reports more often than the official designation.
- No pantograph instantly separates it from every electric class.
- Operating locations change: shunting duties and regional services shift with contract awards and operating concepts.
Contents
Fact file
| Vehicle type | Diesel locomotive for shunting and line service |
|---|---|
| Designation system | S = combustion engine, M = manewrowa (shunting), U = uniwersalna (universal), 42 = class number |
| Manufacturer | Fablok (Chrzanów) |
| Wheel arrangement | Bo'Bo' – four axles in two bogies |
| Nickname | Tamara – firmly established in Poland |
| UIC country code | 51 for Poland |
Identifying features
Is this really the class in front of you?
- Markings reading SM42 or SU42 with a running number on the body
- Four axles in two bogies, a compact body with a long bonnet
- No pantograph – the machine operates independently of overhead line
- Shunting steps and grab handles at the vehicle ends
- As the SM42 in shunting and trip-working duties, as the SU42 hauling passenger trains on non-electrified lines
- UIC number with the country code 51 for Poland
Updated: August 2026 – SM42 and SU42 are two designations for the same vehicle family – and that’s exactly where the lesson lies. The Polish class system doesn’t describe the construction but the job. Understand this difference and you’ll read every Polish vehicle designation correctly from then on. This page shows how that works and how to recognise the machine in the field.
Spotted a Tamara? Read the letter too.
SM or SU – this one letter decides the identification. Log it straight away in Traintrack.
What are PKP SM42 and SU42?
The SM42 is a four-axle diesel locomotive from Fablok of Chrzanów, designed for shunting and trip-working duty. The name says it directly: S for a combustion engine, M for manewrowa – shunting or manoeuvring duty – and 42 as the class number.
The SU42 is the same basic class in a specification for line service. Here U stands for uniwersalna, meaning universal use including passenger trains on non-electrified lines – a segment served by regional operators such as Polregio. Constructionally the kinship is obvious; operationally these are two different jobs.
Why the letter matters more than the metal
The designation system of Polskie Koleje Państwowe differs fundamentally from purely technical designations. It answers two questions – and both concern the use, not the components.
| Character | Meaning | What follows from it |
|---|---|---|
| S (first position) | Combustion engine | no pantograph, independent of overhead line |
| M (second position) | manewrowa – shunting duty | short distances, low speeds, wagons rather than trains |
| U (second position) | uniwersalna – universal | line service, including passenger trains |
| T (second position) | towarowa – freight | heavy trains, larger machines |
| 42 | Class number | places the specific construction |
That gives a practical rule: if you only note “diesel loco seen”, you lose the decisive piece of information. Only the second letter tells you which role the vehicle was working in.
Two letters, two questions
First question: what powers the vehicle – E or S? Second question: what is it intended for – U, T, P, M or N? This order works for every Polish rail vehicle.
Identification in the field
Check the roof
No pantograph means a combustion engine and so a leading S in the markings. That rules out every electric class.
Assess the size
A compact body with four axles points to the shunting and trip-working class. Large six-axle machines belong to the heavy freight classes.
Watch the job
If the vehicle is moving individual wagons, SM is likely. If it's hauling a passenger train along the line, SU is more probable.
Read the markings
SM42 or SU42 plus the running number settles it for good. The running number identifies the individual machine and belongs in the logbook.
How to find and interpret such markings systematically is shown in the guide to decoding train numbers.
See what's being reported right now
Shunting locomotives turn up unannounced – community reports show you where something's happening.
Spotting: the underrated vehicle
Diesel shunting locomotives are among the most commonly overlooked vehicles of all. They stand at the edge of the frame, work unspectacularly and are rarely photographed deliberately – which makes them, in the long run, some of the most interesting archive subjects.
- Work from the end of the platform. The only legal spot with a view into the yard is often the end of a publicly accessible platform. You can’t go further.
- Bring a telephoto lens. Shunting vehicles are rarely close. The distance isn’t negotiable, so the lens has to bridge it.
- Wait for movement. A working machine with wagons attached tells more of a story than a static shot.
- Include the surroundings. With shunting locomotives especially, the setting is part of the story – the yard, the signal box, the industrial backdrop.
The photographic basics are covered in the guide to taking good photos of trains; if you’re out and about in the freight sector, you’ll find further approaches in the article on tracking freight trains.
Shunting areas are off limits
You may not enter yards, shunting areas, siding tracks or operational railway land – regardless of whether there's a fence. Shunting movements move unannounced and in both directions. Observe only from publicly accessible locations.
Understanding shunting duty: what’s actually happening there
Watching shunting locomotives, at first glance you see only movement with no obvious goal. In fact, shunting follows a clear logic, and once you know it, you can read the sequences – and better judge when waiting is worthwhile.
At its core, there are three tasks: sorting wagons from arriving trains, assembling groups of wagons into new trains, and delivering or collecting individual wagons to and from customers. Each of these tasks has a typical rhythm. Trip workings often fall in the morning and evening, sorting happens once a train has arrived. Most of this work in Polish freight service is handled by PKP Cargo.
Watch for arrivals
When a freight train arrives, a shunting movement almost always follows. That's the best moment to see a shunting locomotive in action rather than stabled.
Expect direction changes
Shunting movements frequently change direction. Choose a vantage point with both directions of travel in view – and never try to follow a movement.
Plan for waiting time
Minutes or hours can pass between two movements. Shunting duty isn't timetabled operation but work as needed.
For safety, this exact point is decisive: shunting movements are unannounced, change direction, and are sometimes propelled from behind. So it applies without exception that yards and shunting areas must not be entered – not briefly, not at the edge, not even when nothing is currently moving.
The patience pays off photographically all the same. A shunting locomotive with wagons attached in the yard is a subject that tells the story of railway operations – unlike the usual locomotive portrait on the platform. And because hardly anyone documents these vehicles, the archive value is above average.
Common mix-ups
It points to an SM42 or SU42 if …
- there's no pantograph on the roof
- you count four axles in two bogies
- the markings start with SM42 or SU42
- the vehicle is moving wagons or hauling a short train
Take a closer look if …
- you can't read the letters – SM and SU are visually very close
- the vehicle is running for an industrial or private operator
- it's been modernised and differs in detail from the standard look
It isn't a 42-class if …
- pantographs sit on the roof
- you count six axles – then it's more likely an ST43 or ST46
- the vehicle is a railcar with no separate locomotive
Anyone wanting to go through the Polish diesel fleet systematically will find the heavy PKP ST43 and the PKP Cargo ST46 (Class 66) as the two freight representatives – and, among the diesel railcars, the PKP SA132 / SA133 / SA134 as the vehicles that take their place in regional services.
Verdict
The SM42 is the workhorse of Polish shunting duty and, at the same time, the best example of the logic behind the PKP system: a single letter decides whether the same machine is classed as a shunting locomotive or a line locomotive. Understand that, and you’ll stop identifying by looks and start identifying by job – and get it right noticeably more often.
In short
S for diesel, M for shunting duty, U for universal, 42 for the class. Four axles, no pantograph, a compact body – and the second letter as the real piece of information.
Shunting vehicles deserve a logbook
They're rarely photographed and even more rarely documented – which is exactly why every clean sighting counts.
Summary
- The SM42 is Poland's most widespread diesel shunting locomotive and a standard vehicle at freight and siding tracks.
- As the SU42, the same class takes on line services – a lesson in how the PKP scheme encodes purpose rather than technology.
- For identification, axle count, the missing pantograph and the markings you read off are enough.
- Because shunting locomotives are rarely photographed, clean sightings with the number are especially valuable.
Frequently asked questions
What does SM42 mean?
S stands for a combustion engine, meaning diesel traction, M for manewrowa – shunting or trip-working duty – and 42 is the class number. An SM42 is therefore a diesel shunting locomotive of class 42. The Polish scheme names traction and purpose directly in the name.
What's the difference between SM42 and SU42?
The second letter. M stands for shunting duty, U for uniwersalna, meaning universal line service including passenger trains. It's the same basic class in a different specification and role. It's a good example of the Polish system encoding the use, not the construction.
Why is the SM42 called Tamara?
Tamara is the firmly established nickname for the class in Poland. Such short names are widespread in Polish railway circles and are often used in forums, conversation and sighting reports more naturally than the official designation – comparable to German nicknames for well-known classes.
How many axles does the SM42 have?
Four axles in two bogies, wheel arrangement Bo'Bo'. Together with the compact body and the missing pantograph, that gives a very characteristic look, clearly different from six-axle heavy freight locomotives like the ET22 or ST46.
Where do you see SM42 locomotives?
At freight yards, on siding tracks, at industrial railways and anywhere wagons are moved individually. As the SU42, additionally hauling passenger trains on non-electrified lines. Which locations and duties are currently served changes with contract awards, operating concepts and timetable years.
Can a shunting locomotive also run on the line?
In principle yes, and that's exactly what's behind the variant with U. For passenger duties, though, a vehicle needs additional equipment, such as for train heating. So the letter change in the Polish system isn't a pure formality but describes a genuinely different specification.
How do I tell SM42 and ST43 apart?
By the second letter and the size. M means shunting duty, T heavy freight. The ST43 is the considerably larger line locomotive for long freight trains, the SM42 the more compact shunting and trip-working locomotive. Both run on combustion engines and so carry the leading S.
Am I allowed to photograph shunting locomotives?
From a publicly accessible platform or from the street, generally yes. Track areas, shunting yards, siding tracks and operational railway land, on the other hand, are off limits – even though the best subjects stand there. Details on house rules and access depend on the operator and the individual case.
Log your sighting of the PKP SM42 / SU42
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
PKP ST43
The ST43 is a line diesel locomotive for Polish freight traffic. Its code names both traction and purpose – and sets it clearly apart from shunting and electric classes.
Diesel locoPKP Cargo ST46 (Class 66)
The ST46 is the Polish designation for the EMD Class 66 – a six-axle diesel locomotive whose shape is unmistakable right across Europe.
DMUPKP SA132 / SA133 / SA134
SA132, SA133 and SA134 are Polish diesel railcars from PESA's range. This page explains the SA designation system and how to identify them in the field.
Diesel locoPKP ST44 (M62)
The ST44 is Poland's version of the Soviet M62 – six axles, loud and unmistakable. Here's how to read the code and recognise the locomotive in the field.
Diesel locoPKP SU45
The SU45 is a six-axle Polish universal diesel locomotive. Its code reveals both traction and purpose – and three features are enough for a confident ID.
Diesel locoPKP SU46
The SU46 is a six-axle Polish universal diesel locomotive and looks confusingly similar to the SU45. Here's how to tell the two apart cleanly.
Who is behind it
Groups, brands, manufacturers and operators – who owns whom and how to recognise them out in the field.
PKP Cargo
PKP Cargo is the freight arm of the Polish state railway holding – and a special case: unlike most groups, the company runs trains itself while also holding stakes in subsidiaries at home and abroad. On the track you'll find one of Europe's oldest electric-locomotive fleets.
State railwayPolskie Koleje Państwowe (PKP)
Polish locomotive designations are the most clear-cut numbering system in Central Europe: two letters tell you the traction and purpose before you've even read the number. The group structure behind them is considerably less clear – a lot of what's called PKP no longer belongs to it.
Where to see the PKP SM42 / SU42
Specific viewpoints with lighting times, coordinates and an honest verdict on whether the trip is worth it.
Related guides from the blog
