Trailer types in special transport: visual guide

A 75 m wind blade does not fit on a 13 m semi-trailer. A 200-tonne transformer does not survive a standard platform. Every indivisible load leaving the Port of Barcelona needs specific equipment — and the choice is made in the route study, not when the cargo arrives at the quay.

This guide gathers the most-used trailer types in special transport operations from the Port of Barcelona: what problem each one solves, what cargo it carries, and when one is chosen over another.

The four variables that decide the trailer

Before choosing equipment, a special-transport company works with four operational variables:

1. Total mass: cargo weight plus the tare of the combination. The ordinary regime allows up to 40 t in general and up to 44 t for combinations with 5+ axles (Orden PJC/780/2025). Above those thresholds, the operation enters the special regime and requires a complementary circulation authorisation (ACC). Mass also dictates the axle count and the capacity needed per axle line.
2. Dimensions: length, width, height. The limits in the Spanish General Vehicle Regulation are 16.50 m articulated / 18.75 m road train, width 2.55 m, height 4.00 m. Any dimension above these forces processing an ACC. Orden PJC/780/2025 has also opened two specific regimes without need of ACC: height up to 4.50 m for defined types (combined transport, live animals, straw/forage, industrial supply ≤ 50 km, vehicle transporters, cranes) and length up to 18.00 m for articulated vehicles carrying longitudinal indivisible loads.
3. Centre of gravity: high or low. A load with a high CG requires a lowered platform or low bed to avoid exceeding the authorised height.
4. Cargo geometry: concentrated or distributed; uniform or irregular. This defines whether a standard platform is enough or a hydraulic modular with independent suspension per axle is required.

A 200-tonne transformer with a high centre of gravity forces a hydraulic modular with a lowered platform. A 75 m wind blade, with relatively uniform mass distribution but extreme length, requires a blade lifter or a specific extendable platform. A complete wind turbine (nacelle, blades, tower sections) is planned with three different trailers, not one.

Fig. 01 · RGV limits: length · width · height · mass. Above any of them, ACC.

Standard platform (flatbed semi-trailer)

When it is used: indivisible cargo compatible with standard clearance that exceeds another RGV limit (length, width above 2.55 m, mass above 40/44 t, or height). If the combination stays within the four RGV limits, it is not special transport and does not require ACC.

Fig. 02 · Standard platform. 3 axles · 13-15 m usable length.

• Common configuration: 3 axles; some models up to 4
• MAM of the combination under ordinary regime: up to 44 t (5+ axles, Orden PJC/780/2025); above that, special regime with ACC
• Usable loading length: 13-15 m
• Platform height from ground: 1.1-1.4 m
• Width of the semi-trailer itself: 2.55 m

Limitations: falls short for heavy loads or loads with a high centre of gravity. For lengths above 15 m, the next step up is the extendable platform.

Common variant: lowered platform with gooseneck. The central loading area sits lower than the rear axles, gaining 30-50 cm of usable height. Resolves elevated crossings at the limit without changing equipment.

Extendable platform

When it is used: loads between 16 and 30 m in length. Structural beams, wind tower sections, long cylinders, short blades.

Fig. 03 · Extendable platform. Up to 30 m extended · 30-50 t of cargo.

• Platform with a telescopic section that extends hydraulically
• Reachable length: up to 30 m extended
• Loading capacity: 30-50 t
• Allows adjustment of length to the exact size of the piece

Limitations: relatively high centre of gravity, not suitable for very tall pieces. Any width of the combination above 2.55 m already requires ACC (RGV limit). From 3 m on, a reinforced pilot vehicle and specific roundabout coordination are standard; above 3.50 m the ACC itself usually requires police escort.

Low bed (lowboy / conventional low loader)

When it is used: the limitation is the available height under elevated crossings or overhead lines. The cargo is tall but compact in weight. For indivisible cargo exceeding 4.00 m total height, the ACC remains mandatory — the 4.50 m specific regime of Orden PJC/780/2025 covers defined types (combined, animals, straw, cranes, vehicle transporters) that do not include indivisible cargo.

Fig. 04 · Low bed with gooseneck. Platform height 30-50 cm · ideal for tall, compact loads.

• Very low platform height: 30-50 cm from ground
• Detachable gooseneck: allows loading pieces that would rise above the tractor
• Maximum combination mass: 50-70 t in 4-axle configuration; any mass above the ordinary regime (40 t general / 44 t for 5+ axles) requires ACC

Typical loads: self-propelled construction machinery (excavators, loaders), tall and compact industrial machinery, boilers, vertical tanks, short process columns.

Hydraulic modular

When it is used: masses between 80 and 200 t. The cargo can be heavy and geometrically demanding.

Fig. 05 · Hydraulic modular with twin tractors. 80-200 t · hydropneumatic suspension, independent per axle line.

• Modular configuration: modules of 2, 3, 4 or more axle lines that couple together
• Independent hydropneumatic suspension per axle line
• Capacity per axle line: up to 36 t in heavy models
• Independent steering per axle (in some models): allows reduced turning radii
• Hydraulically adjustable platform height: eases loading and unloading without crane

Typical loads: power transformers (90-200 t), chemical reactors, electrical generators, nuclear plant components, self-propelled heavy machinery.

Operations: for high masses, the push-tractor plus pull-tractor configuration is used. Two tractor units share effort and maintain traction on extended gradients.

SPMT (Self-Propelled Modular Transporter)

When it is used: extreme loads (200-500+ tonnes) or operations in confined spaces where a conventional tractor cannot enter.

Fig. 06 · SPMT — top and side views. 200-500+ t · self-propelled platform, 360° steering.

• Self-propelled platform with integrated diesel-hydraulic motors
• Each axle line with independent hydraulic suspension and height adjustment
• 0-360° steering: the combination can rotate on its own axis, move sideways or diagonally
• Modular: two or more SPMTs couple side-by-side or end-to-end to distribute extreme loads
• Travel speed: very low (1-5 km/h in heavy-load operations)

Typical loads: nuclear reactors, very high-voltage transformers (250+ t), heavy prefabricated structures, quay movements, industrial plant, construction site; direct loading and unloading of heavy-lift vessels at the Port of Barcelona.

Limitations: not suitable for long-distance circulation on conventional roads. High operating cost. Typical use is intra-port or at the destination site.

Blade lifter

When it is used: transport of wind blades. Single piece, extreme length (60-90 m), moderate mass (15-25 t).

Fig. 07 · Blade lifter. Up to 60° elevation to clear lateral obstacles on the route (poles, overhead lines, trees) with blades of 60-90 m.

• Specific vehicle with a hydraulic system that lifts the rear end of the blade up to 60° of inclination
• Allows clearing lateral obstacles (overhead line poles, trees, signage), tight curves and roundabouts that would otherwise be impossible
• Independent rear suspension and steering from the front tractor
• Operation at reduced speeds (10-30 km/h)

Operations: the most complex trailer to coordinate. Blade elevation is executed at specific points of the itinerary, identified during the route study, and requires stopping the convoy. Each critical point adds 15-30 minutes to the total operation time.

Quick decision table

Premise: every row describes cargo that already exceeds at least one RGV limit and therefore requires ACC. The left column adds the decisive factor.

What is not a trailer but is part of the convoy

No special-transport convoy travels alone. Accompanying the trailer:

• Pull tractor: the main tractor unit. For masses above 80 t, a power of 600 hp or more is required.
• Push tractor: second tractor coupled at the end of the combination. Provides push on gradients and shares effort. Used from around 100 t.
• Front / rear pilot vehicle: car or derivative, equipped with omnidirectional amber lights and "TRANSPORTE ESPECIAL" panel. Leads the convoy signalling obstacles and coordinating roundabouts.
• Private escort vehicle: function equivalent to the pilot but for more complex operations or when the ACC requires more than one accompaniment. Formally provided by special-transport security companies.
• Police escort: Mossos d'Esquadra (Catalonia) or Guardia Civil de Tráfico (rest of Spain), mandatory above certain thresholds or at identified critical points.

The complete convoy of a 150-tonne transformer easily consists of 7-8 vehicles: 2 tractors, hydraulic modular, 2 pilot vehicles, police escort, technical support vehicle. The route study plans every one of them.

The final criterion

The question is not which trailer you have available, but what cargo you have and where it is going.

Equipment selection combines three inputs: the technical sheet of the piece, the route analysis, and the company's equipment availability. Companies with their own fleet of hydraulic modular and SPMT take the technical decision on the spot. Those that subcontract wait for an external quote.