Key takeaways
- Am means: diesel locomotive of the fastest class. A is the speed class, m stands for the internal combustion engine.
- Main-line capable rather than a pure shunting tractor: the A sets the Am 843 apart from pure shunting vehicles like the Ee 3/3.
- Centre cab and bonnets are the typical look of a shunting and engineering-service locomotive.
- The range of duties is broad: shunting, engineering trains, transfer runs and work on non-electrified track.
- Its usual haunts are operational railway land – observed and photographed only from publicly accessible areas.
Contents
Fact file
| Vehicle type | Four-axle diesel locomotive for shunting, engineering and main-line duty |
|---|---|
| Railway administration | Swiss Federal Railways (SBB) |
| Designation A | highest speed class – the locomotive is main-line capable, not a pure shunting tractor |
| Designation m | powered by an internal combustion engine |
| Base type | Vossloh G1700-2 BB |
| Power transmission | diesel-hydraulic |
| Wheel arrangement | B'B' – two two-axle bogies, all axles powered |
| Number range | begins with 843 |
Identifying features
Is this really the class in front of you?
- No pantograph on the roof, but exhaust and radiator housing instead – diesel traction
- Four axles in two bogies
- Centre cab with long bonnets ahead of and behind the cab
- Walkway railings and access steps for shunting staff on both sides of the vehicle
- Conspicuous warning livery rather than passenger colours
- Vehicle number begins with 843
Updated: August 2026 – Two letters, three digits – and you already know what the vehicle can do. The SBB Am 843 is a four-axle diesel locomotive for shunting, engineering trains and main-line duty, and its designation says exactly that. This page shows you how to read it, how to recognise the vehicle in the field, and why diesel is still needed on the largely electrified Swiss network.
Document shunting and engineering-service locomotives
These vehicles rarely turn up in collections. If you spot one, note the number, location and date.
What is the SBB Am 843?
The Am 843 is a four-axle diesel locomotive of the SBB with diesel-hydraulic power transmission, built on the Vossloh G1700-2 BB base type. All four axles are powered, and the wheel arrangement is B’B’.
Its range of duties is deliberately broad: shunting at stations, engineering trains, transfer runs, and work on track without an overhead line. That’s precisely why a largely electrified network still needs diesel vehicles – not as a stopgap, but because siding connections, construction sites and operational railway land aren’t everywhere under wire, and a vehicle working during construction needs to be independent of the overhead line.
What the designation Am tells you
The Swiss letter system describes vehicles instead of just numbering them. With diesel vehicles it works exactly the same way as with electric locomotives – you just need to read the lower-case letter correctly.
A – the speed class
A is the fastest category. For a shunting and engineering-service locomotive, that means: it's main-line capable and not confined to station areas.
m – the internal combustion engine
The lower-case letter describes the type of traction. An m stands for internal combustion, an e for electric. If it's missing entirely, it's a steam locomotive.
E instead of A – the shunting case
An E in the first position marks pure shunting vehicles, as with the Ee 3/3. Knowing the difference tells you instantly whether a vehicle is allowed on the main line.
843 – the number block
The three-digit series places the vehicle within a number block. With diesel locomotives, the electric-locomotive rule of thumb that the first digit shows the number of driving axles doesn't apply – here the block determines the grouping.
The matching counter-examples often stand right next door: the electric shunting locomotive Ee 922 does the same job under wire, while the classic Ee 3/3 shows the same principle in an older vehicle generation. How to approach unfamiliar vehicles in general is described in the guide to identifying classes.
Diesel or electric? The five-second test
Before you get into vehicle types, you settle the basic question. It’s answerable from any distance.
| Observation | Diesel locomotive like the Am 843 | Electric locomotive |
|---|---|---|
| Roof | exhaust, radiator, ventilation louvres | pantograph, roof cabling |
| Body | centre cab with bonnets possible | continuous body with cabs at each end |
| Sound when starting | engine speed rises audibly | mostly fan and rolling noise |
| Operating location | possible even without overhead line | only under catenary |
| Typical livery | warning or signal colours | corporate or keeper colours |
Look at the roof first
The diesel-or-electric question is the fastest fork in the whole identification process. It halves the field of possible classes before you've even counted an axle.
Log sightings, don't just collect them
Shunting and engineering-service vehicles in particular are poorly documented. Your log entry helps other spotters.
Where you’ll find the Am 843 – and how to go about it
Shunting and engineering-service vehicles stand where scheduled traffic stops. That makes them hard to plan for and places different demands on the location than a main-line locomotive.
Look for stations with shunting operations
Wherever wagons are reshuffled or trains are formed, shunting locomotives are at work. Larger hub stations often offer a clear view from the ends of the platforms.
Keep an eye on engineering works
Construction sites mean engineering trains, and engineering trains mean diesel locomotives. It's one of the few reasonably predictable opportunities.
Work with focal length
Because these vehicles are almost always on operational railway land, you need distance. A longer telephoto brings the vehicle closer without you approaching the facility.
Record the number separately
For service vehicles, the number is the real piece of information. A second shot of just the data panel is worth more than three overview shots.
Operational railway land isn't a photo spot
Shunting facilities, storage sidings, construction areas and operating yards are operational railway land, and tracks are always out of bounds. That applies even if nothing has moved for an hour – shunting movements arrive quietly and often without warning. Observe only from publicly accessible areas.
How to spot sensibly and within the rules around large facilities is described in the guide to spotting at marshalling yards. And how to log a sighting so that others actually benefit from it is shown in the guide to logging sightings.
Why an electrified network still needs diesel locomotives
Switzerland is considered one of the most thoroughly electrified rail networks in Europe. Even so, the railways keep procuring diesel vehicles – for solid operational reasons that the Am 843 illustrates well.
First, the areas without overhead line. Siding connections to industrial sites, loading roads, workshop approaches and secondary tracks are often not wired. A wagon that needs collecting there requires a vehicle that runs without catenary. The same applies to the country’s few non-electrified lines, such as the connection maintained by the Verein zur Erhaltung der Bahnlinie Etzwilen–Singen.
Second, engineering works. When work is carried out on the overhead line, the wire is switched off and earthed. That’s exactly when an engineering train still has to be moved. A diesel vehicle isn’t just convenient for that – it’s a precondition.
Third, disruption. If the power supply fails on a section, a vehicle independent of the overhead line is the only way to move stranded trains. Such deployments are rare, but they help determine how many vehicles are kept in reserve.
What this means for your sightings
Diesel locomotives turn up wherever something out of the ordinary is happening: engineering works, diversions, disruptions, special movements. Keeping an eye on construction sites and closures significantly improves your chances – no insider knowledge required.
Common mix-ups
It points to an Am 843 if …
- there's no pantograph on the roof
- you count four axles in two bogies
- the vehicle has a centre cab with bonnets
- the number begins with 843
Look more closely if …
- a similar-looking shunting locomotive from another keeper is standing next to it
- you can't see the roof and exhaust or pantograph aren't visible
- the vehicle is running in a different keeper's livery
It isn't an Am 843 if …
- there's a pantograph on the roof – then you're looking for an Ee or Re
- you count only three axles
- the designation begins with Ee, Em or Re
The most obvious comparison is the shunting locomotive Em 840 – also powered by an internal combustion engine, but in a different speed class and therefore built for a different range of duties. Anyone wanting to go further can compare it with the main-line locomotive Re 430: the same number of axles, a completely different job.
Conclusion
The Am 843 is a vehicle that demonstrates the Swiss system particularly well. The A tells you it’s allowed on the main line, the m tells you it can do that without overhead line, and the centre-cab layout tells you what it spends the rest of its time doing. For spotters, it’s also one of the most rewarding sightings around – not because it’s rare, but because hardly anyone documents it properly.
In short
No pantograph, four axles, centre cab, number from 843: that's the Am 843. A main-line-capable diesel locomotive for shunting and engineering duty – usually on operational railway land, so photograph with focal length rather than by getting closer on foot.
Collect the underrated side of the railway
Shunting locomotives, engineering-service vehicles, special types: in Traintrack every sighting gets its place.
Summary
- The Am 843 is the SBB's do-everything diesel locomotive for every job where the overhead line is missing or isn't enough.
- Its designation fully explains its purpose: speed class plus type of traction.
- It's one of the few vehicle groups you're more likely to find stabled than running.
- Because it often sits on operational railway land, a telephoto lens matters here more than for almost any main-line vehicle.
Frequently asked questions
What does the designation Am 843 mean?
The capital letter A stands in the Swiss system for the highest speed class, the lower-case m for an internal combustion engine as the power source. Together: a main-line-capable diesel locomotive. The number 843 is the modern series designation marking the number block for this vehicle group.
Why isn't the Am 843 a pure shunting locomotive?
Because the A marks the fastest speed class. Pure shunting vehicles carry an E, as with the Ee 3/3 – they're designed for station operations, not for longer distances. The Am 843 can do both: shunt and run on its own, for instance ahead of engineering trains or transfer workings.
How can I tell a diesel locomotive at a glance?
By the missing pantograph. Where electric locomotives carry the pantograph frame on the roof, diesel locomotives have exhaust pipes, radiator grilles and ventilation louvres instead. Shunting types also typically have the centre-cab look with long bonnets – a shape you'll practically never find on a main-line electric.
What is a centre cab and what's it for?
A cab positioned in the middle of the vehicle with bonnets at both ends. During shunting, the direction of travel changes constantly, and the driver needs to be able to see both ways. A centre cab makes that possible without the locomotive having to be turned or the driver switching ends.
What does diesel-hydraulic mean?
The diesel engine's power is transmitted to the axles through a hydraulic gearbox, rather than via a generator and traction motors as with diesel-electric locomotives. Both concepts are common; hydraulic drives are frequently found on shunting and engineering-service vehicles because they're easy to control at low speeds.
What does the wheel arrangement B'B' mean?
Two two-axle bogies in which the two axles within each bogie are mechanically coupled to each other. All four axles are powered. The difference from Bo'Bo' is that there, each axle has its own individual drive, whereas with B'B' the axles of a bogie are mechanically linked.
Where can I see the Am 843?
At stations with shunting operations, around marshalling facilities, at siding connections, and during engineering works. These areas are, however, mostly operational railway land. Observation takes place from platforms, public paths and bridges – track areas and operating yards aren't accessible.
Why are engineering and shunting locomotives so rarely photographed?
Because they're hard to plan for and rarely sit where you can get to freely. That's exactly what makes good photos of them valuable: huge collections exist for main-line locomotives, far fewer for shunting and engineering vehicles. A clean sighting with number and date fills a genuine gap here.
Log your sighting of the SBB Am 843
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
SBB Em 840
The SBB Em 840 is a shunting locomotive with an internal combustion engine – and its name already says so. Here's how to read the Swiss code and identify the machine reliably.
Electric shunterSBB Ee 922
The Ee 922 is a modern electric shunting locomotive of the SBB. Its three-digit number shows how the Swiss classification system has changed – here's how to read both.
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.
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 SBB Am 843
Specific viewpoints with lighting times, coordinates and an honest verdict on whether the trip is worth it.
Related guides from the blog
