Out-of-gauge (OOG) cargo transport is the movement of loads that exceed the standard legal envelope for road vehicles — under Turkish road regulations and EU Directive 96/53/EC, roughly 4.0 m in height, 2.55 m in width and 40 tonnes gross vehicle weight — and therefore require special permits, an engineered route and specialised trailers. Voltim Global plans these operations end to end and carries them out with its partner network, moving heavy machinery, turbines, generators, transformers, prefabricated structural elements and industrial equipment on lowbed and modular trailer combinations sourced for each project.
The regulatory line: where Turkish and EU rules draw the OOG threshold
A load is out of gauge when the loaded vehicle combination exceeds the limits of the Turkish Highway Traffic Regulation (Article 128), which mirrors EU Directive 96/53/EC: 2.55 m width, a 4.0 m height ceiling and 40 tonnes gross weight (44 tonnes only for combinations carrying a 40-foot ISO container in combined transport). Because these thresholds concern the vehicle plus cargo, even a modest machine can become OOG once trailer deck height is added; this is why Voltim treats anything above 4.20 m loaded height, 2.55 m width, 13.60 m cargo length or 24 tonnes payload as a special transport case requiring a feasibility study before quotation.
Inside the KGM special load permit dossier
Indivisible loads that cannot be reduced to legal dimensions may only move under an Özel Yük Taşıma İzin Belgesi (Special Load Transport Permit) issued by the General Directorate of Highways (KGM). The permit, obtained for each movement, defines the exact vehicle configuration, axle load diagram, route and travel windows. Voltim prepares the full technical dossier and coordinates the supplementary approvals the permit depends on: municipal permissions for urban segments, traffic police clearance, and — where the route crosses utility infrastructure — arrangements with utility companies to lift or de-energise overhead power lines. Signage removal and overpass passages are planned in the same dossier, so the convoy never waits at an obstacle that could have been cleared in advance.
How is a route survey conducted for an oversized load?
Before any permit is filed, Voltim's team performs a physical route survey: driving the corridor, measuring bridge and tunnel clearances, checking junction turning geometry, and logging every overhead obstacle — power lines, gantries, signage, pedestrian overpasses. Bridge load ratings are compared against projected axle loads; weight-restricted structures are routed around or crossed at crawl speed. The survey output is a kilometre-by-kilometre route book fixing travel speeds, night-movement windows, escort positions and contingency lay-bys — the operational reference for the driver, escort crews and accompanying police units, and the best insurance against the classic OOG failure mode: discovering a low bridge with 300 tonnes already on the road.
How are axle loads calculated and kept within legal limits?
Axle load calculation distributes the combined weight of cargo, trailer and tractor across every axle line so that no single point exceeds what the pavement and bridges can carry. Turkey applies EU-aligned limits — 11.5 tonnes on a driving axle and 10 tonnes on a single non-driving axle, according to ITF country data — and the KGM permit is granted against a stamped axle load diagram. For heavy pieces, the solution is not a stronger trailer but more axle lines: hydraulically compensated modular trailers spread a 150-tonne transformer over 16 or 20 lines, keeping each line near ordinary legal loads. Voltim engineers the load position — centre of gravity, overhang, lashing points — so the calculated distribution matches reality at the weighbridge.
When is a lowbed enough — and when do you need modular trailers or SPMTs?
Trailer selection is driven by weight, deck height and manoeuvring space. Three- and four-axle lowbed trailers handle the bulk of construction machinery — excavators, dozers, mobile cranes — where low deck height solves the 4 m clearance problem. Above roughly 60–100 tonnes, hydraulic modular trailers take over: axle modules coupled side by side or in line, with steering and suspension on every line. For the heaviest and least accessible moves, self-propelled modular transporters (SPMT) add their own drive and millimetre-level manoeuvrability; standard SPMT axle lines carry up to 44 tonnes each according to Mammoet, and up to 60 tonnes in the strongest versions according to manufacturer TII Scheuerle. Voltim matches the configuration to the cargo, sources it from its partner network and pairs it with crane, jacking and forklift support at both ends.
How are power transformers and generators moved by road?
Large power transformers are among the most demanding OOG cargoes: according to the U.S. Department of Energy, they can weigh between approximately 100 and 400 tons (roughly 90 to 360 tonnes), and the active part is sensitive to shock and tilt. Road movement therefore relies on hydraulically suspended modular trailers that keep the deck level over uneven surfaces, strictly limited convoy speeds and, where required, impact recorders on the unit itself. Where site headroom is limited, loading and unloading use jacking-and-skidding systems rather than cranes. Voltim applies the same discipline to generators, industrial boilers and distillation columns; for supply shipments to the Akkuyu site region, see nuclear project transportation.
What do escort vehicles and route clearance teams actually do?
Escort is active traffic engineering in motion. Depending on load width and route class, the permit prescribes dedicated escort vehicles ahead of and behind the convoy, plus police or gendarmerie accompaniment. The lead escort verifies clearances and stops oncoming traffic at pinch points; the rear escort shields the convoy and manages overtaking. Ahead of the convoy, the route clearance crew arranged with our partners executes the obstacle plan: temporarily removing traffic signs, coordinating utility crews at overhead lines, and holding intersections during wide turns. Movements run at night or in permit-defined low-traffic windows, with multi-day corridors broken into stages with secured parking between them.
Key facts: out-of-gauge road transport at a glance
- Standard limits under EU Directive 96/53/EC and Turkish road regulations: 2.55 m width, 4.0 m height, 40 tonnes gross weight (44 tonnes only for 40-foot ISO container combinations in combined transport), per the European Commission and Article 128 of the Turkish Highway Traffic Regulation.
- Turkey applies EU-aligned axle limits: 11.5 tonnes driving axle, 10 tonnes single non-driving axle, according to ITF (OECD) data.
- Indivisible oversized loads in Turkey move only under a Special Load Transport Permit issued by the General Directorate of Highways (KGM).
- Large power transformers weigh approximately 100 to 400 tons (roughly 90 to 360 tonnes), according to the U.S. Department of Energy.
- SPMT axle lines carry up to 44 tonnes each according to Mammoet, and up to 60 tonnes according to TII Scheuerle.
Oversized moves are usually one leg of a wider industrial delivery. Voltim integrates OOG road transport with multimodal project cargo shipments and full-scope project logistics programmes, so permits, vessels, cranes and site delivery follow a single plan. Send us your cargo drawings and dimensions — let's discuss the details.
Frequently Asked Questions
What is Out of Gauge (OOG) transport?
Which cargo dimensions and weights are classed as out of gauge?
Which permits are required for oversized and heavy cargo transport?
How is an OOG transport operation planned?
How is the price of an oversized transport determined?
From the guide: questions about this service
- What is out-of-gauge cargo?
- How do you obtain a KGM special permit for out-of-gauge cargo?
- What is a reactor pressure vessel, and how is it transported?
- What is a lowbed trailer, and what cargo is it used for?
- What is an oversize load escort and when is it mandatory?
- What are the legal vehicle dimension limits on the road?
- What is ISO 45001?
- What is heavy cargo, and above what tonnage is a special permit required?
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