Key takeaways
- SU45 means diesel universal locomotive: S stands for combustion traction, U for universal duty, 45 is the design number.
- It descended from the SP45 – during conversion, the second letter changed from P (passenger train) to U (universal).
- Fastest route to identification: six axles, full-width body, no pantograph.
- Greatest risk of confusion is with the similarly proportioned SU46 – only the markings help here.
- Deployment and fleet size are changeable: this generation of large diesel locomotives is increasingly being displaced by railcars and electric traction.
Contents
Fact file
| Vehicle type | Six-axle diesel-electric line locomotive for universal duty |
|---|---|
| Origin | Polish design, derived from the SP45 class |
| Wheel arrangement | Co'Co' – two three-axle bogies |
| Body design | Full-width body with a cab at each end |
| Designation | S = combustion engine, U = universal duty, 45 = design number |
| UIC country code | 51 for Poland |
Identifying features
Is this really the class in front of you?
- Six axles on two three-axle bogies
- Continuous body over the entire vehicle length – no separate bonnet
- A cab at each end of the vehicle, large front windows
- No pantograph on the roof, instead radiator and exhaust sections
- Vehicle number begins with the code SU45
- Visually closely related to the SU46 – if in doubt, the markings decide
Updated: August 2026 – A large, boxy diesel locomotive with six axles, a cab at each end and no pantograph: that is the typical picture of the SU45. It belongs to the generation of Polish line diesels that work where there is no overhead wire. This page shows you how to identify it, what its code means, and how to tell it apart from the closely related SU46.
Spotted an SU45? Don't forget the number.
With closely related designs, the vehicle number decides – log it on the spot in Traintrack.
What is the PKP SU45?
The SU45 is a six-axle diesel-electric line locomotive of Polish design for universal duty. It has a continuous, full-width body with a cab at each end, clearly setting it apart visually from locomotives with a separate machine bonnet.
Operationally it is a machine for non-electrified main lines. It descended from the SP45 class; during conversion, the second letter changed from P for passenger train to U for universal. That very letter change is the beauty of the Polish system: it documents an operational change directly in the designation.
Decoding the SU45 code
At the Polskie Koleje Państwowe, traction vehicles carry two letters and a design number. Once you have understood the system, you can immediately say what you are dealing with for any Polish vehicle.
| Character | Meaning | Examples |
|---|---|---|
| First letter | Traction type | E = electric, S = combustion engine |
| Second letter | Use | U = universal, P = passenger train, T = freight train, M = shunting duty, N = railcar |
| Number | Design number | 45 for the SU45, 46 for the SU46, 44 for the ST44 |
That gives you a clean map: the ST44 is the freight diesel locomotive, the SM42 and SU42 cover shunting and light line duty, and in the electric sector the EP07 or EU07 family handles passenger service. The twelve-digit international number comes on top of that, with country code 51; how to read it is explained in the article on the UIC number on the vehicle.
Confident identification in three steps
Look at the roof
No pantograph? Then the code begins with S. All electric locomotives are ruled out.
Count the axles
Six axles on two three-axle bogies. Four-axle vehicles belong to other designs.
Check the body
Full-width body over the entire length rather than a narrow central bonnet. That's how you tell the SU45 apart from the ST44.
Read the markings
The final authority. Only the markings reliably separate the SU45 and SU46 – note them in full.
If you take this sequence to heart, you’ll identify even unfamiliar vehicles quickly. The methodical groundwork for it is in the guide to identifying classes: first coarse features visible from a distance, then details, and finally the lettering.
One picture for the subject, one for the number
Get into the habit of taking a second, unspectacular photo of the vehicle number after the main shot. It costs two seconds and saves any doubtful match in your archive.
Why the letter system is so valuable for spotters
If you come from Germany, you’re used to a class number only becoming information once you know it: whether 218, 232 or 245 is a diesel locomotive, you simply have to know by heart. The Polish system takes that work off your hands. Two letters are enough to know traction and purpose – even for a vehicle you’ve never seen before.
That is especially valuable abroad. You’re standing at an unfamiliar station, an unknown vehicle pulls in, and instead of guessing you read the code: if it starts with S, it’s a combustion-powered vehicle. If a T follows, it belongs to freight traffic. If a U follows, it’s universally deployable. That gives you more information in three seconds than a glance at a vehicle list would in five minutes.
The one catch: the system describes the design intent, not the day-to-day deployment. A universal locomotive can run exclusively ahead of freight trains for years without its code ever changing. So take the letters as design intent, not as a timetable statement.
Where the SU45 fits operationally
Large line diesels follow the infrastructure: they have the advantage wherever electrification is missing or where diagrams run through both electrified and non-electrified sections.
| Environment | Chance of a sighting | Why |
|---|---|---|
| Non-electrified main lines | high | Classic territory for line diesels |
| Large junction stations with a system changeover | medium | Locomotive changes and dwell times at the platform |
| Special and replacement services | medium | Scheduled at short notice, hard to plan for |
| Fully electrified main routes | low | Electric locomotives and multiple units work there |
| Purely urban transport hubs | very low | No deployment area for heavy line diesels |
Deployment keeps shifting
With every electrified kilometre of line and every new railcar series, the territory of large diesel locomotives changes. Statements about specific diagrams age quickly – rely on current sightings and real-time data.
Current sightings instead of outdated lists
In Traintrack you see which vehicles the community is reporting right now – the best basis for planning your own trip.
Photo tips for a large boxy locomotive
The full-width body is a photographic challenge: from the front, the locomotive looks like a wall, from the side it loses its front end. The compromise is what decides it.
Three-quarter view as the default
Around 30 to 45 degrees to the vehicle axis shows front and side at once and gives the body depth.
Look for flat light
Mornings and late afternoon bring out edges and panel lines. Midday light flattens large surfaces.
A slightly raised viewpoint
A somewhat higher public vantage point – such as a bridge – separates the locomotive from the background better than a view from track level.
Stick to public areas
Track areas, depots and stabling sidings are off limits. Photograph from platforms, paths and bridges.
The technical basics – shutter speed, panning, plane of focus – are covered in the guide to taking good photos of trains. And because distinguishing closely related designs is a real issue here, a consistently kept sighting log pays off twice over: it forces you to note the number. You’ll see how similar the direct sister design makes things on the page for the PKP SU46.
Common mix-ups
It points to the SU45 if …
- you count six axles
- the body is full-width over the entire length
- no pantograph sits on the roof
- SU45 is on the vehicle
Look more closely if …
- the locomotive fits in shape and proportion but you can't read the number – then it could be the SU46
- an unfamiliar livery obscures the familiar lines
- you only see the vehicle from a great distance or against the light
It is not an SU45 if …
- a narrow machine bonnet lies between the cabs
- you only count four axles
- a pantograph sits on top – then the code begins with E
Verdict
The SU45 is a good practice case for the Polish designation system: two letters supply traction and purpose, the number the type, and the change from SP45 to SU45 shows that the system reflects operational changes. Visually you identify it by axle count and body shape – the fine work against the SU46 is done by the markings.
Quick verdict
Six axles, full-width body, no pantograph: that is the SU45. It's found wherever there is no overhead wire – and always documented with the full number, because its sister design SU46 looks confusingly similar.
Collect and compare Polish diesel locomotives
Log your sightings with number and location – and see straight away which designs are still missing from your list.
Summary
- The SU45 is a six-axle Polish-built diesel locomotive for mixed duties on non-electrified lines.
- Its code follows the PKP system of a traction letter, a use letter and a design number.
- Identification works via axle count and body shape – the fine distinction from the SU46 comes down to the number.
- Because large diesel locomotives in passenger service are becoming rarer, it's worth documenting every sighting with date and location.
Frequently asked questions
What does the designation SU45 mean?
It follows the Polish letter-and-number system. The first letter S stands for the combustion engine, the second letter U for universal duty, meaning use ahead of both passenger and freight trains. The 45 is the running design number. Unlike in Germany, the designation directly conveys a technical statement.
What is the difference between the SP45 and SU45?
It is the same base design in a different state of equipment. During conversion, the second letter changed from P for passenger train to U for universal – the locomotive was upgraded for a broader range of duties. The basic shape of the vehicle remained unchanged.
How do I tell the SU45 and SU46 apart?
Both are six-axle diesel locomotives of Polish origin with a full-width body and look very similar at first glance. The reliable distinction comes down to the markings on the vehicle. If in doubt, photograph the number too, rather than relying on the overall impression.
How many axles does the SU45 have?
Six, distributed across two three-axle bogies in the wheel arrangement Co'Co'. That clearly distinguishes it from the four-axle shunting design SM42, which is far more common in Poland.
Where is the SU45 deployed?
On non-electrified lines and wherever a powerful line diesel locomotive is needed. Specific diagrams change with traffic contracts, timetable years and the progress of electrification – always check the current status via sightings rather than older lists.
Can you see the SU45 in Germany too?
Diesel locomotives are not tied to an electrification system, but cross-border deployments depend on approvals and specific services. At crossings along the Oder and Neisse, checking current sighting reports is more useful than any blanket statement.
How do I identify the exact machine?
By the full vehicle number. Alongside the Polish code, every vehicle carries a twelve-digit UIC number, whose country code for Poland reads 51. This combination is unambiguous and belongs in every clean sighting note.
Is the SU45 purely a freight locomotive?
No, that is exactly what the letter U tells you: universal duty. Pure freight locomotives carry a T in the Polish system, as with the ST44 or the electric ET22. The SU45 is deliberately designed to be more broadly deployable.
Log your sighting of the PKP SU45
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
PKP 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.
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Diesel locoPKP 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.
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