Key takeaways
- ZW stands for Zweiwege (road-rail): the vehicle drives to site on rubber tyres and then switches onto the track via retractable flanged wheels.
- Type code 99 marks it out as a works or auxiliary vehicle – the clear distinction from a shunting locomotive, whose numbers start with 98.
- The excavator is the site all-rounder: it lifts, grabs, loads and clears, depending on the attachment fitted.
- Operating times fall within possessions, so often at night, at weekends or during off-peak periods.
- Sites in the track area are highly dangerous and off-limits to onlookers; the upper carriage also slews out without warning.
Contents
- 1.What is the Atlas 1604 ZW?
- 2.Road-rail technology: how an excavator gets onto the track
- 3.What a road-rail excavator does in the construction process
- 4.How to identify a road-rail vehicle reliably
- 5.Observing engineering trains without putting yourself at risk
- 6.Common mix-ups and how to rule them out
- 7.Verdict
Fact file
| Vehicle type | Road-rail mobile excavator for track construction and maintenance work |
|---|---|
| Manufacturer | Atlas, a German manufacturer of hydraulic excavators |
| ZW abbreviation | road-rail equipment – can run on road and rail |
| UIC type code | 99 – works or auxiliary vehicle |
| Typical use | Permanent-way and civil engineering work at the track, material handling, vegetation work |
| Mode of operation | used mostly during possessions, often at night and at weekends |
Identifying features
Is this really the class in front of you?
- Two sets of running gear, one above the other: rubber tyres for the road plus retractable flanged wheels for the track
- Slewing upper carriage with cab and boom – the silhouette of a construction machine, not a locomotive
- Bold warning livery in yellow or orange, beacon lights, reflective stripes
- Interchangeable attachments: bucket, grapple, sleeper tongs, magnet or mulching head
- Vehicle number begins with 99 – a works vehicle, not a shunting vehicle
- Often seen in a consist with material, ballast or engineering-train wagons, frequently within track possessions
Updated: August 2026 – A yellow excavator standing in the trackbed that still carries a twelve-digit vehicle number: the Atlas 1604 ZW is exactly that – construction machine and railway vehicle in one. This page explains how road-rail technology works, what the excavator is needed for in the construction process, and how to identify it beyond doubt as a works vehicle.
Spotted an engineering train? That's a rare find.
Works vehicles are rarely documented and constantly on the move. Log your sighting in Traintrack while you still have it in front of you.
What is the Atlas 1604 ZW?
The Atlas 1604 ZW is a road-rail mobile excavator: a hydraulic excavator on rubber tyres that is additionally fitted with rail-running equipment. Atlas is a German manufacturer of hydraulic excavators; the abbreviation ZW marks the road-rail version that turns the construction machine into an authorised railway vehicle. Rail-running equipment and matching attachments for it come from specialist suppliers such as PACTON.
That has an important consequence for classification: as soon as such a vehicle is permitted to work on the track, it’s registered as an auxiliary vehicle and gets a twelve-digit vehicle number starting with 99. That places it systematically alongside tamping machines, rail-mounted trolleys and railway cranes – and explicitly not among shunting locomotives, whose numbers start with 98.
Road-rail technology: how an excavator gets onto the track
Switching from road to rail is the actual trick behind these vehicles – and the reason they’re so popular in the construction process.
Approach by road
The excavator drives to the site on rubber tyres. That saves the construction process the cost of transport on low-loaders or a dedicated engineering train run – a considerable time saving for short jobs.
Setting onto the track at a crossing point
At a suitable level crossing or site access point, the vehicle aligns itself over the track. This happens exclusively in closed-off areas and under supervision.
Lowering the flanged wheels
Smaller flanged wheels are lowered hydraulically. They guide the vehicle on the track, while the road wheels either continue to transmit power or are relieved, depending on the design.
Working on the track
Once on the track, the excavator moves independently between work locations. The slewing upper carriage allows it to work to the side without repositioning the vehicle.
What a road-rail excavator does in the construction process
A track construction project consists of many individual steps, and most of them have highly specialised machines. The excavator is the opposite: the all-rounder that closes the gaps between the specialists.
| Work step | Role of the road-rail excavator | Typical attachment |
|---|---|---|
| Excavation and bedding work | Digging, profiling, backfilling | Bucket |
| Material handling | Loading ballast, sleepers and old material | Grapple, sorting grapple |
| Sleeper replacement | Lifting and inserting individual sleepers | Sleeper tongs |
| Small fittings and scrap | Picking up metal parts from the ballast area | Load magnet |
| Vegetation work | Clearing growth in the trackside strip | Mulching head, branch shears |
| Clearing and cleaning | Removing deposits in the track area | Clearing blade, sweeping attachment |
Specialised machines, on the other hand, handle the major work steps: a railway slewing crane such as the Kirow KRC 810 / 1200 lifts heavy loads and complete points, while a rail-mounted trolley such as the Robel GKW 315 brings staff, material and cargo to the worksite.
See where engineering trains are currently being reported
Works vehicles appear without warning – community sightings are often the only trace of them.
How to identify a road-rail vehicle reliably
The decisive look goes downward. Between the road wheels and the track sits a second, smaller pair of wheels with flanges – front and rear, usually hydraulically foldable. Once you see that, the matter is settled, regardless of what body sits on top.
Three features that always go together
Retractable flanged wheels, a bold warning livery with beacon lights, and a twelve-digit vehicle number starting with 99. If one of these is missing, a second look is worthwhile: a pure construction machine has no vehicle number, and a locomotive has no road wheels.
The same logic applies to all road-rail machines, such as the Liebherr A 900 C ZW-Li/1031 – there too, the ZW abbreviation reveals the design. The guide to identifying classes shows how to narrow down vehicles systematically via such features rather than guessing from overall impression.
A second look at the attachment is worthwhile, because it tells you which phase of the construction process you’re witnessing. A sorting grapple points to handling and clearing work, sleeper tongs to work on the track panel, a mulching head to vegetation maintenance in the trackside strip. Because attachments are swapped during a job, the same vehicle can look completely different on two different days – one more reason to treat the vehicle number, not the appearance, as its identity.
The consist is also a clue. Road-rail vehicles rarely work alone: material, ballast or engineering-train wagons are usually nearby, often along with a rail-mounted trolley and lighting equipment. Such machine fleets are looked after by track construction firms and workshops such as Gleisbaumechanik Brandenburg. Documenting the surroundings as well makes your own sighting considerably more useful to others, because it lets them infer the type of construction work under way.
Observing engineering trains without putting yourself at risk
Engineering trains are fascinating and at the same time the most dangerous area of the whole hobby. At a track construction site, several vehicles move simultaneously, machines work with a slewing upper carriage, lighting dazzles, and the noise level makes warning calls inaudible.
Sites in the track area are off-limits
Track construction sites are operational installations and private land at the same time. Vehicles start moving without warning, engineering trains also run at night, and an excavator's slewing range extends well beyond the track. Entering is out of the question – even when a site looks abandoned. Observe and photograph only from publicly accessible land at a clear distance.
Because the work runs mostly at night, a sighting is usually a night shot. The article on safety when spotting at night describes what preparation and behaviour that requires; the basic distance rules are covered in the overview of safe distances at the track. For camera settings in poor light, the guide to camera settings for trainspotting at night helps.
Common mix-ups and how to rule them out
It points to a road-rail excavator if …
- road wheels and retractable flanged wheels are present at the same time
- a slewing upper carriage with a boom is fitted
- the vehicle number starts with 99
- the vehicle stands within a track possession or at a site storage area
Look more closely if …
- the vehicle stands on the road with its rail-running equipment folded away
- an unusual attachment changes the silhouette
- company livery and markings show no sign of the manufacturer
It isn't a road-rail excavator if …
- only rail wheels are present – then it's a pure rail vehicle
- no vehicle number is marked on it – then it's a pure construction machine
- the number starts with 98 – then it's a shunting or small locomotive
Verdict
The Atlas 1604 ZW shows why the works-vehicle category is so varied: purpose decides, not origin. A construction machine with rail-running equipment becomes an auxiliary vehicle with its own number and its own rulebook. Two observations are enough to identify it – double running gear and a leading 99 – and a single rule applies to observing it: keep your distance, don’t enter the site.
In short
Road wheels plus flanged wheels, a slewing upper carriage, a number starting with 99: that's a road-rail excavator. It's the all-rounder of the track construction site – and mostly works when nobody else is about.
Collect works vehicles systematically
Vehicle number, keeper, site and date in one app – for engineering trains, your own note is often the only source.
Summary
- The Atlas 1604 ZW combines a classic mobile excavator with rail-running equipment, turning it into a works vehicle.
- Its role in the construction process is that of an all-rounder for excavation, handling and clearing work right at the track.
- You can recognise it by the double running gear, the warning livery and the vehicle number starting with 99.
- Keeper, livery and site of use change with the construction contracts – every sighting is a snapshot.
Frequently asked questions
What is a road-rail excavator?
A mobile excavator with additional rail-running equipment. It drives on rubber tyres by road to the site, sets down onto the track at a suitable crossing point and lowers its flanged wheels. It can then move and work on the track. The ZW in the type name stands for exactly that: Zweiwege (road-rail).
Why does the vehicle number start with 99?
The first two digits of the twelve-digit vehicle number are the UIC type code. 99 marks works and auxiliary vehicles, i.e. machines used for building and maintaining the network. A 98 would denote a diesel shunting locomotive, a 92 a mainline diesel locomotive.
What does the excavator actually do at a track site?
It's the all-rounder: excavation in the trackbed, loading ballast and old material, lifting and inserting individual sleepers with the matching tongs, handling cable protection ducts, clearing vegetation and general clearing work. Which of these it's doing at any moment is revealed by the attachment fitted to the boom.
Can a road-rail excavator pull wagons?
Depending on its equipment, it can move loads on the track and work alongside engineering or material wagons. That doesn't replace a locomotive, though: road-rail vehicles are designed for short moves within the site, not for train runs over longer distances. What's specifically permitted depends on the individual vehicle's authorisation.
When are such machines out and about?
Mostly during possessions, because work on the track can only happen when no train traffic is running. In practice that often means night and weekend work. During the day the vehicles then often stand at site storage areas or loading points – that's where you're most likely to see them at rest.
How do I tell a road-rail vehicle apart from a normal construction machine?
By the flanged wheels. They sit as an additional, smaller pair of wheels in front of and behind the road axles and can be lowered hydraulically. Add to that rail-specific equipment such as a warning horn, railway radio and the twelve-digit vehicle number – features a pure construction machine doesn't carry.
Am I allowed to photograph a track construction site?
From publicly accessible land, generally yes, with the usual restrictions. Entering it is out of the question: construction sites in the track area are operational railway installations, vehicles move there without warning, and an excavator's upper carriage slews out a long way. For detailed legal questions, the individual case always applies.
Do the keeper and livery of such excavators change?
Constantly. Road-rail vehicles mostly belong to construction firms or hire companies and change colour and markings with contracts, sales and company mergers. Only the design, type plate and vehicle number stay constant – so always note the date with your sighting.
Log your sighting of the Atlas 1604 ZW
Date, location and vehicle number logged in seconds – and visible to the community.
Related classes
Liebherr A 900 C ZW-Li/1031
A road excavator standing on rails: the Liebherr A 900 C ZW-Li/1031 combines rubber tyres with retractable rail gear. Here's how to spot a road-rail vehicle on the track.
DepartmentalKirow KRC 810 / 1200
Kirow railway slewing cranes lift points, bridge parts and derailed vehicles. Here's how to identify a KRC 810 or 1200 and understand its role on the worksite.
DepartmentalRobel GKW 315
The Robel GKW 315 is a track motor car: load deck, loading crane, crew cab. Here's how to recognise it and place it correctly among departmental vehicles.
DepartmentalPlasser & Theurer 08-275/4 ZW-Y
Tamping means restoring track geometry: the Plasser & Theurer 08-275/4 ZW-Y lifts, aligns and compacts the ballast under the sleepers. Here's how to recognise the machine.
DepartmentalPlasser & Theurer 09-4X Dynamic
Tamping and stabilising in one pass: the 09-4X Dynamic works continuously using the satellite principle. Here's how to recognise the machine on the track.
DepartmentalPlasser & Theurer EM-SAT 120
The EM-SAT 120 measures where the track actually lies – and hands the correction values to the tamping machine. Here's how the survey technique works and how to recognise the vehicle.
Who is behind it
Groups, brands, manufacturers and operators – who owns whom and how to recognise them out in the field.
Gleisbaumechanik Brandenburg
Gleisbaumechanik Brandenburg belongs to the businesses that don't build trains but the machines that build the track underneath. These vehicles never appear in a timetable, rarely carry a logo, and are still one of the most rewarding subjects around.
ManufacturerPACTON
PACTON, based in Ennepetal, trades in secondhand diesel locomotives, road-rail vehicles and railway construction equipment, and transports rail vehicles by road. A small company in a niche that explains why some locomotives change operators without covering a single mile of track.
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