Category O vehicles: what are they and what are their characteristics?

In the automotive and logistics sectors, the correct classification of vehicles is essential to define regulatory requirements, usage limits, and insurance obligations. Among the various categories established by European legislation are Category O vehicles, i.e., trailers.

In this article, we examine what the international vehicle classification system provides, which vehicles fall under Category O, and the differences between the O1, O2, O3, and O4 subcategories.

What does the international vehicle classification provide?

The international vehicle classification system is primarily governed by European legislation (EU Regulations and UNECE directives) and is also applied in Italy for vehicle type approval and registration.

Vehicles are divided into categories identified by letters, based on:

vehicle function;
maximum mass;
maximum speed;
engine power.

The main categories are:

Category L: two- and three-wheel vehicles (motorcycles and similar vehicles);
Category M: motor vehicles for the carriage of passengers;
Category N: motor vehicles for the carriage of goods;
Category O: trailers, i.e., vehicles without their own means of propulsion.

This classification makes it possible to establish technical requirements, speed limits, periodic inspection obligations, and specific road traffic rules for each type of vehicle.

Which vehicles fall under category O?

Category O includes all vehicles designed to be towed by another vehicle, such as passenger cars, commercial vehicles, or industrial vehicles. These are vehicles without an engine, designed for the transport of goods, equipment, or specific loads.

Category O includes:

light trailers;
goods trailers;
drawbar trailers;
semi-trailers;
industrial and agricultural trailers (if type-approved for road circulation).

The internal subdivision of Category O is mainly based on the maximum technically permissible mass (MTPM) of the trailer.

Difference between O1, O2, O3, and O4

Category O is divided into four subcategories, distinguished according to the trailer’s maximum mass.

Category O1

Maximum mass up to 750 kg

Includes light trailers, such as:

trailers for private use;
small trailers for transporting equipment or luggage;
drawbar trailers.

Category O2

Maximum mass exceeding 750 kg and up to 3,500 kg

Often used for professional purposes, including:

goods transport;
construction activities;
craft and trade activities.

Category O3

Maximum mass exceeding 3,500 kg and up to 10,000 kg

Includes medium-to-large trailers used in commercial and industrial transport.

Category O4

Maximum mass exceeding 10,000 kg

Includes heavy trailers and semi-trailers, typically used in industrial transport and large-scale logistics.

They are intended to be coupled with industrial vehicles and road tractors.

Category O vehicles play a central role in the transport of goods and equipment, both for private and professional use. Understanding the correct classification between O1, O2, O3, and O4 is essential to operate in compliance with current regulations, select the most suitable vehicle for specific operational needs, and ensure road safety.