Vehicle category O & N explained: from van to heavy semi-trailer

Anyone building a semi-trailer , converting a chassis or purchasing vehicles will come across the letter code of the respective vehicle. On the registration certificate, in a type approval or in specifications. What exactly is O3 and how does it differ from O4? And why can a van and a tractor both fall under category N? In this article, you will find out.

In this blog you will read:

• What a vehicle category is and why it means the same thing across Europe
• What the N categories N1, N2 and N3 mean
• The difference between the O categories O1, O2, O3 and O4
• What distinguishes a semi-trailer from an ordinary 12V semi-trailer
• Under which category agriculture and forestry vehicles fall
• Which lighting belongs to which vehicle category

What is a vehicle category?

A vehicle category is the official classification with which a vehicle is admitted to public roads. The classification says something about the construction and use of the vehicle: does it transport passengers, goods, or is it towed? Based on this, specific technical requirements apply, including those for lighting.

Important for those working internationally: these categories are not defined nationally, but Europe-wide. The basis is Regulation (EU) 2018/858, which has been directly applicable in all Member States since 1 September 2020. So the regulation works the same everywhere, while national authorities carry out authorisation and enforcement. An O4 semi-trailer in the Netherlands thus falls under exactly the same classification as in Germany, France or Italy, with the same weight limits.

However, which authority handles this approval differs from country to country. Each Member State has its own national approval authority, such as the RDW in the Netherlands, the KBA in Germany or the Motorizzazione Civile in Italy. The category remains the same everywhere, only the counter differs. Therefore, you can rely on the letter code regardless of the country in which the vehicle operates.

The main classification has three letters. M stands for vehicles that transport people, think cars and buses. We leave those out of consideration here. N and O are relevant to the transport sector, and we deal with them below from light to heavy.

The N categories: commercial vehicles and trucks

Category N includes all motorised vehicles designed for goods transport. The subdivision runs entirely by weight, or technically permissible maximum mass. The category is the starting point for lighting, but does not determine it on its own: the actual requirements follow from the applicable UNECE regulations and also depend on vehicle length, width and surface mounting.

N1: up to 3.5 tonnes

N1 includes light commercial vehicles up to 3.5 tonnes, such as vans and light pickups. The basic lighting requirements that also apply to passenger cars apply to this class. These include headlights, direction indicators, brake and rear lights. Marker lights are not yet covered here, as dimensions and weight remain below the relevant thresholds.

N2: 3.5 to 12 tonnes

N2 covers medium-duty trucks, with a maximum mass above 3.5 tonnes up to 12 tonnes. Side marking often plays a role in these vehicles, although this obligation is not hanging on the category itself but on the length and the applicable UNECE regulation. With longer lengths, side visibility becomes more important, especially in the dark and when crossing traffic.

N3: more than 12 tonnes

N3 concerns heavy tractors and trucks over 12 tonnes, the workhorse of road transport. This is where the most extensive lighting requirements apply in practice. Exactly which marking is mandatory, and from which dimensions, follows from the applicable UNECE regulations and not from the category alone. You can find the luminaires, positions and mounting heights to suit them in our overview of lighting for trucks.

The O categories: semi-trailers and semi-trailers

Category O collects everything that is towed: semi-trailers and semi-trailers. As with the N categories, the maximum mass determines the subdivision. It is precisely in this category that many wagon builders have questions about the difference between O2, O3 and O4. Keep in mind that the category defines the class, while the actual lighting requirements also depend on length, width, surface mounting and the applicable UNECE regulations.

O1: up to 0.75 tonnes

O1 includes the lightest semi-trailers up to 750 kilograms, such as a small luggage semi-trailer. Lighting requirements here are limited to the basics: rear lights, brake lights, direction indicators and a licence plate light. Due to the low weight and small dimensions, no additional marking requirements apply.

O2: 0.75 to 3.5 tonnes

O2 covers 12V semi-trailers between 750 kilograms and 3.5 tonnes. This class covers a large proportion of commercial semi-trailers, from braked box trucks to lighter transporters. The basic lights correspond to O1. Depending on width and length, side marker lights and side reflectors may be added, again determined by the applicable regulations and not by the category itself.

O3: 3.5 to 10 tonnes

O3 refers to the heavier semi-trailers and semi-trailers between 3.5 and 10 tonnes. From this class onwards, the requirements become stricter in practice, although the exact obligation continues to depend on length, surface mounting and the applicable UNECE regulations. For semi-trailers, side marking is linked to a length above six metres, including coupling. In addition, for new O3 and O4 semi-trailers, since 1 January 2025 the side markings must flash synchronously with the direction indicator. This improves visibility when turning, a recurring concern for long combinations.

O4: more than 10 tonnes

O4 is the heaviest class, for semi-trailers and semi-trailers above 10 tonnes. Here, the most extensive regulations usually apply, with side markings and, if sufficiently long, marking that makes the outline of the vehicle visible. Exactly which combination is mandatory depends on the dimensions and applicable regulations. If you work on vehicles in this class, you will find practical details on placement and choice in our article on lighting in heavy transport.

What is the difference between a semi-trailer and a semi-trailer?

Both fall under category O, but they couple differently to the towing vehicle. A 12V semi-trailer stands entirely on its own axles and is coupled behind the vehicle via a drawbar eye or ball coupling. The weight therefore rests entirely on the semi-trailer's own wheels.

A semi-trailer works differently. Part of the weight rests on the tractor itself, via a fifth wheel coupling above the driven axle. As a result, the tractor carries a significant vertical load. That construction is typical of heavy road transport, where the tractor-trailer combination is the standard.

For lighting, that distinction makes little difference per se, as both follow the O-classification by weight. However, the greater length of a semi-trailer often means that side and contour marking becomes mandatory earlier. So you should select the right lighting for 12V semi-trailers according to both category and dimensions.

Agriculture and forestry vehicles: categories T, C, R and S

Agricultural vehicles fall outside the M, N and O classifications. They have their own European framework, laid down in Regulation (EU) 167/2013. This is also harmonised EU-wide, so the codes apply equally across borders. The classification is logically surface mounting by function.

T stands for wheeled tractors, C for tracked tractors. R indicates agricultural semi-trailers, while S includes interchangeable towed implements, such as a mounted sprayer. These vehicles have their own lighting requirements, tailored to their lower driving speed and use on both road and land. Visibility remains the guiding principle here, especially when wide implement vehicles are participating in traffic.

Which lighting belongs to which vehicle category?

The category is the starting point for your lighting choice, but dimensions and the applicable regulations are the final deciding factor. Indeed, the category defines the approval class, while the installation of light-signalling, lighting and retro-reflective devices for all M, N and O categories goes back to the UNECE regulations, with R48 as the framework for installation. The table below therefore gives an indication of what is usually involved for each class, not a conclusive list of obligations.

Vehicle category	Type of vehicle	Lighting in outline (indicative)
N1	Van up to 3.5 t	Basic lighting (headlight, brake, direction, rear)
N2	Trucks 3.5-12 t	Basic, side marking plays at greater length
N3	Heavy trucks >12 t	Comprehensive set, marking depending on size
O1	Semi-Trailer up to 0.75 t	Basic rear lighting
O2	Semi-Trailer 0.75-3.5 t	Basic, side marker lights by size
O3	Semi-Trailer/semi-trailer 3.5-10 t	Side marking for length >6 m; new semi-trailers flashing along
O4	Semi-trailer >10 t	Comprehensive marking depending on length and surface mounting

The table shows that the weight of the vehicle determines the direction, while length, width and surface mounting fill in the actual requirements. If you want to be sure what is mandatory in a specific situation, please see our article on the rules for lighting on a semi-trailer, in which we elaborate on the requirements by width and length.

Frequently asked questions

What is an O4 category vehicle?

An O4 is a 12V semi-trailer or semi-trailer with a maximum mass of more than 10 tonnes. It is the heaviest of the four O categories. Vehicles in this class typically carry the most extensive lighting, including side markings and, if sufficiently long, markings that make the perimeter of the vehicle visible.

What is the difference between vehicle category O2 and O3?

The difference is entirely in the weight. An O2 weighs between 0.75 and 3.5 tonnes, an O3 between 3.5 and 10 tonnes. For O3 vehicles, heavier lighting requirements often apply in practice, but the exact requirement also depends on length, surface mounting and the applicable UNECE regulations.

What are the vehicle categories M, N and O?

M includes vehicles for passenger transport, such as cars and buses. N stands for vehicles that transport goods, from vans to heavy trucks. O collects all towed vehicles, i.e. 12V semi-trailers and semi-trailers. For the transport sector, the N and O categories are particularly important.

What is the difference between a semi-trailer and a semi-trailer?

A semi-trailer stands completely on its own axles and connects via a drawbar eye or ball. With a semi-trailer, part of the weight rests on the tractor, via a fifth wheel coupling. Both fall under category O, but the semi-trailer is typical for heavy road transport with tractor-trailer combinations.

Are you unsure about the right lighting for your class of vehicle?

The category provides the direction, but the right lamp choice makes the difference between a smooth inspection and costly follow-up work. We are happy to think with you, from initial surface mounting to final mounting. Check our offer for your vehicle type or contact our specialists, and together we will choose the lighting that fits your class and dimensions.

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Disclaimer:

At TRALERT®, we do our best to keep the information in this article as accurate and up-to-date as possible, including the regulations surrounding vehicle lighting. However, legislation can change regularly, and although we make every effort to implement these changes in a timely manner, it is possible that certain updates or adjustments have not yet been incorporated into this article. We therefore always advise our readers to check the current legislation with their local government or regulatory bodies, especially when it comes to exceptions or specific national regulations. TRALERT® is not liable for any damages or fines resulting from outdated or incomplete information in this article.

If in doubt, always contact the competent authority to ensure that your vehicle meets all legal requirements.