A forklift keeps the warehouse occupied for the entire shift; a tugger train serves ten stations in a single tour. Anyone who watches the traffic in an assembly hall for an hour sees the pattern immediately: forklifts drive out empty, collect a pallet, drive back empty. The tugger train runs a fixed loop, drops off full containers at each station, takes empties with it and returns to the supermarket warehouse on a fixed cycle. This logic is not new — it comes from the Toyota Production System — but in 2026 it is still untapped potential in many German factory halls. This guide shows when switching to the Milkrun really pays off, which regulations (DGUV Information 208-057, VDI 5586) must be observed and which components you need.
What is a tugger train (Milkrun) really?
A tugger train is an in-plant transport system in which a towing vehicle (tug) pulls between two and five trailers — so-called trolleys or frames — through the plant on a defined route. Unlike the forklift, which responds to every single request individually, the tugger train serves several supply points one after the other according to a fixed timetable, drops off full goods and takes empties back with it on a single tour. Guideline VDI 5586 Part 1 (April 2016) defines tugger trains as an “in-plant transport system in which transport units are moved bundled in a train formation” and thus describes them as the tool for connecting the supermarket (central buffer store) and the point of consumption.
Three characteristics fundamentally distinguish the tugger train from the forklift model:
- Fixed route: The route is defined, signposted and marked where necessary. No ad-hoc trips.
- Timed schedule: Tour start 06:30, 07:00, 07:30 … — supply does not take place on demand, but in a rhythm.
- Bundled load: Instead of one pallet per trip, 3–5 trolleys transport the material for 6–12 stations at the same time.
Lean origins and the Toyota principle
The term “Milkrun” comes from the US milk collection rounds: a tanker drives a fixed route across several farms, loads milk and puts empty churns back. Taiichi Ohno, father of the Toyota Production System (TPS), transferred this principle to in-plant material supply in the 1950s — known at Toyota as Mizusumashi (“water spider”), a person who carries material to the assembly stations in a fixed cycle.
In Lean vocabulary, the tugger train is therefore inseparably linked to two concepts:
- Just-in-Time (JIT): Material only arrives at the station when it is needed — in the quantity required, not stockpiled.
- Kanban: Empty containers (or physical cards) signal demand to the tugger train driver. The tugger train is effectively the physical transport medium of the Kanban loop.
Anyone who wants to introduce Kanban without putting material transport on a fixed cycle will fail. Here the tugger train is not an end in itself, but the operational prerequisite for lean, low-inventory supply.
When is it worth switching from the forklift model?
Not every operation needs a tugger train. An 800 m² warehouse with three goods receipts per day and pallet dispatch is perfectly well served by pallet trucks and a reach truck. However, as soon as assembly lines, short distances and high supply frequency come together, the economics tip in favour of the tugger train. Four indicators provide reliable guidance.
Small lot sizes (small load carriers instead of pallets)
Anyone who delivers in small load carriers (KLT, typically 600×400 mm or 400×300 mm) instead of full pallets generates a large number of small transport orders. A forklift is oversized for this — it deploys 1 t of load capacity to move an 8 kg KLT. A tugger train with 5 KLT trolleys handles in one trip what would take the forklift 15 individual journeys.
High supply frequency
According to industry figures, typical cycles in practice are 30 minutes for high-frequency assembly lines and 60–120 minutes for areas with medium demand. If you have to serve stations more often than every two hours, the tour logic of the tugger train is more efficient than the zigzag trips of a forklift.
Short distances several times a day
Tugger trains play to their strengths on routes between 100 m and 1 km. For shorter distances the pallet truck is often the better choice; for significantly longer ones (several plant areas, external connections), AGVs (driverless transport systems in accordance with VDI 2510) or even truck shuttles are more economical.
Labour-intensive assembly lines
The more workers stand at a line, the more expensive downtime caused by material shortages becomes. The timed tugger train eliminates waiting time because it covers demand before the request is made. Studies from automotive OEM practice show that line supply in the assembly plants of BMW, Audi and Daimler is based almost exclusively on tugger trains — not out of fashion, but because the cost of line stoppages amortises every tour optimisation.
Components of a tugger train
A tugger train is not a product but a system of three modules: towing vehicle, trailers and coupling. Each module must fit the application.
Towing vehicle (tug)
Tugs for in-plant tugger train use are available in the DACH region in three performance classes:
- Compact class: towing capacity 3–5 t, suitable for light KLT tugger trains in assembly and order-picking supply.
- Mid-range class: towing capacity 5–7 t, designed for multi-shift operation with exchangeable battery or lithium-ion.
- Heavy-duty class: towing capacity up to 10 t, used in industrial line supply with large E-frame trailers.
With all tugs you should look for an electronic parking brake, speed control for ramp travel and a turning circle < 2 m — the latter is decisive for narrow plant aisles.
Trailers / trolleys
The trailers are the real differentiator — this is where it is decided whether the system works.
- E-frame: frame trolley with electro-hydraulic lifting gear, lifts load carriers up to 1,000 kg, ground-level loading and unloading without a ramp; loading direction variable left/right.
- B-frame: floor-roller trolley for trolley pick-up — the KLT trolley rolls into the frame from the side or from behind.
- KLT trolleys: hand-guided trolleys for 600×400 small load carriers, often in 2- or 4-tier versions with side panels and castors.
Minimum aisle widths with three trailers are 2.5 m; the required outer turning radius for a 90° curve is 4–6 m. These values must be verified in the hall layout planning before procurement.
Coupling systems
The coupling determines tracking accuracy and safety. Three designs are established on the market:
- Rigid drawbar coupling: simple, but with several trailers it “drifts out” in curves.
- Virtual path-following coupling: each trailer follows the track of the vehicle in front under electronic guidance — significantly tighter cornering is possible.
- Mechanically steered tandem coupling: mechanical solution with steering linkage, robust and low-maintenance.
All couplings must comply with the relevant DIN and EN standards (e.g. DIN 15170 for trailer couplings on industrial trucks) as well as the manufacturer's specifications.
Economics: forklift vs. tugger train
The most reliable calculation comes from a direct comparison over five years. The following example (source: industry expertise / SME practice example) shows a typical switch from a three-person forklift crew to a two-person tugger train system.
| Cost item | Current state: 3 forklifts | Target state: 1 tugger train |
|---|---|---|
| Vehicle leasing/depreciation p. a. | 3 × 650 €/month = 23,400 € | 1 tug (18,000 €, 5 yrs) = 3,600 € |
| Trailers / trolleys p. a. | — | 5 E-frames + 20 KLT trolleys = 5,500 € |
| Personnel costs (incl. employer contributions) | 3 × 42,000 € = 126,000 € | 2 × 42,000 € = 84,000 € |
| Maintenance / energy (estimate) | ≈ 5,000 € | ≈ 1,800 € |
| Total costs p. a. | ≈ 154,400 € | ≈ 94,900 € |
Savings: around 59,500 € per year with a one-off investment of about 56,500 € — payback in approx. 12–14 months. Industry figures also cite a reduction in individual trips of up to 80 %, which additionally reduces wear and accident risk.
Important: the calculation only pays off above a critical number of supply points. For fewer than six stations with multiple requirements per shift, the ROI is typically not achieved — here, pallet trucks or a single forklift remain the right choice.
Safety and regulations
Tugger trains are industrial trucks within the meaning of DGUV Vorschrift 68. This means: the driver must be appointed in writing and trained in accordance with DGUV Grundsatz 308-001 — there is no shortened “forklift licence” route for tugger train tugs. Specifically, DGUV Information 208-057 “Einsatz von Schleppern und Anhängern als Routenzüge” (use of tugs and trailers as tugger trains) sets out the requirements for design, operation, driver qualification and instruction as well as safety technology.
The most important points:
- Maximum speed: Industrial trucks with a design speed of more than 16 km/h must not be used to carry people on standing platforms. In practice, the majority of in-plant tugger trains run at 6–12 km/h.
- Towed load: The permissible towed load for the respective place of use must be determined by the employer and communicated to the driver in writing — it results from gradient, friction coefficient and vehicle design.
- Coupling: Trailer couplings must be DIN-compliant, secured against unintentional release and visually/functionally checked every day before the start of the shift.
- Route layout: Route marking, crossing signs and, where applicable, priority rules for pedestrians are required. Pedestrian routes must be separated from tugger train routes structurally or by means of markings.
The planning of the route itself should follow VDI 5586 Part 2 (tugger train systems — planning and dimensioning). For the overarching material flow design, the VDI Handbook of Technical Logistics (Volume 7 Material Flow I) is relevant, as is VDI 3578 (attachments) for trailer elements.
Common implementation mistakes
Most failed tugger train projects do not fail because of the technology, but because of the planning. Four recurring mistakes can be derived from project reviews and recommendations of the Fraunhofer IML on intralogistics.
- Routes with crossings: Anyone who routes the tugger train through central plant intersections produces waiting times and safety conflicts. The route should be consistently planned as a clockwise loop (or consistently anticlockwise), ideally without reversing.
- Trolleys without side-panel retention: KLT trolleys without side panels lose material when cornering. The investment in sturdy frames with defined retention pays for itself within a few weeks because dropped items and search work are eliminated.
- Missing route marking: Without a marked travel path, stop markings at stations and warning signs for workers crossing the route, near-accidents occur. Floor markings should be included in the initial investment, not added “once everything is running”.
- Wrong cycle time: Cycle too slowly and you fail to achieve JIT supply at the point of consumption; cycle too fast and you waste personnel. Rule of thumb: the tour cycle must be shorter than the Kanban range of the smallest container at a line.
Frequently asked questions
How many trailers may a tugger train pull?
Technically between 2 and 5 trailers, more in exceptional cases. Legally, the permissible towed load and number of trailers specified by the manufacturer of the towing vehicle for the specific place of use must not be exceeded. In practice, 4–5 trailers are the most economical.
How fast do tugger trains travel in the hall?
6–12 km/h is usual. Higher speeds are technically possible, but are limited by DGUV requirements (carrying people at > 16 km/h is not permitted) and by the safety assessment of the route.
Do I need separate tugger train training for my drivers?
Yes. Tugs are industrial trucks under DGUV Vorschrift 68; qualification is governed by DGUV Grundsatz 308-001. Forklift training alone is not sufficient — the tugger-train-specific topics (trailer tracking behaviour, coupling checks, tour discipline) must be added.
Is an automated tugger train (AGV) worthwhile?
Automated systems (driverless transport systems in accordance with VDI 2510) typically only pay off from three-shift operation (24/7). Investments are in the range of 150,000–350,000 € with payback in 2–3 years. For one- and two-shift operation, the conventional tugger train is usually more economical.
Can we operate forklifts and a tugger train in parallel?
Yes, and this is often the realistic approach. Forklifts remain responsible for goods receipt, pallet movements and heavy loads; the tugger train takes over the timed line supply with KLTs and small loads. This division corresponds to typical OEM practice in the DACH automotive sector.
What hall dimensions does the tugger train need?
At least 2.5 m aisle width for three-part trains, 4–6 m outer turning radius for 90° curves. Narrower halls can partly be used with mechanically steered or virtually guided trailers; a walk-through with the supplier is mandatory.
Conclusion
The tugger train is not a trend, but a solution for timed, lean line supply that has been proven at Toyota since the 1950s and has been standard in the DACH automotive industry for two decades. As soon as you supply assembly lines with KLTs in your plant, have to serve several stations several times per shift and observe a significant amount of empty forklift runs, switching to a tugger train is economically plausible — with payback typically within a year.
Before procurement you should take three steps: first, a route and frequency analysis in accordance with VDI 5586; second, a suitability check of the hall (aisle widths, curve radii, crossing points); third, personnel planning including training in accordance with DGUV. Anyone who does this homework is not just bringing in another forklift replacement, but the tool that makes Kanban and Just-in-Time work in in-plant operations in the first place.