Here’s what you need to know about side markings on semi-trailers: mounting & regulations

For vehicle builders, trailer manufacturers and original equipment manufacturers, ECE R48 is the key regulation. This regulation specifies where side marker lights must be positioned on the vehicle. Side marker lights are mandatory for semi-trailers longer than 6 metres, and are therefore a standard component of the lighting plan for virtually all O3 and O4 semi-trailers.

In this article, you can find out when side markings are mandatory, what distances and mounting heights apply, what to look out for when choosing a light, and what the regulations on flashing side lighting mean for new O3 and O4 semi-trailers.

When is side marking on a semi-trailer compulsory?

According to ECE R48, side marker lights are compulsory on vehicles and semi-trailers longer than 6 metres. For a semi-trailer, you must take the total vehicle length into account. In practice, this means that virtually every heavy-duty semi-trailer in category O3 or O4 requires side marker lights.

For vehicles up to and including 6 metres, less stringent requirements apply. In such cases, at least one side marker light on each side, positioned in the first or last third of the vehicle’s length, is sufficient. For the lorry and trailer sector, however, this is the exception, as most semi-trailers are well above the 6-metre limit.

In short: a semi-trailer longer than 6 metres requires side markings. In practice, this is almost always the case for O3 and O4 semi-trailers.

The distance requirements according to ECE R48

ECE R48 stipulates not only that side markings must be present, but also where the lights must be located. This involves four points: the position of the front light, the distance between them, the position of the rear light and its distribution over the vehicle length. We will run through them in order.

Front side marker lights: up to 3 metres from the front

The front side marker light must be positioned no more than 3 metres from the front of the semi-trailer. This ensures that the front outline remains visible when another road user approaches from an angled position to the front, for example at a junction, roundabout or entrance. In the case of non-standard designs, such as special surface mountings or components that restrict positioning, please check during the design phase whether this position is feasible.

Spacing: up to 3 metres

There must be no more than 3 metres between any two consecutive side marker lights. For a long semi-trailer, this automatically means multiple marker lights per side. Do not wait until after the bodywork has been fitted to work this out; instead, incorporate the side marker lights directly into the chassis and cabling plan. This will prevent mounting points, mudguards, boxes or surface mounting components from turning out to be in exactly the wrong position later on.

Rear side marker lights: up to 1 metre from the rear

The rear side marker light is positioned within 1 metre of the rear of the vehicle. This is important for ensuring the full length of the vehicle is visible, particularly when overtaking, turning off and manoeuvring in the dark. This is a point to bear in mind for semi-trailers with tail lifts, bumper structures or protruding parts. You should therefore always check the actual rear of the vehicle and not just the theoretical chassis measurement.

At least one light in the middle third

For semi-trailers longer than 6 metres, there must be at least one side marker light on each side in the middle third of the vehicle’s length. This prevents a situation where only the front and rear are visible, whilst the middle of the semi-trailer is visually obscured. In practice, the number of lights is usually determined automatically by the combination of these requirements.

Distance requirement	Standard according to ECE R48
Spacing requirement: Front side marker light	Standard in accordance with ECE R48: maximum3.0 m from the front
Spacingrequirement: Distance between units	Standard in accordance with ECE R48: maximum3.0 m between two lights
Spacing requirement: Rear side marker lights	Standard in accordance with ECE R48: maximum1.0 m from the rear
Spacing requirementsfor lengths > 6 m	Standard in accordance with ECE R48: at least one light in the middle third
Distancerequirement: Mandatory	Standard in accordance with ECE R48 Forvehicles longer than 6 m

Mounting height and visibility

You normally install side marker lights between 250 mm and 1,500 mm above the road surface. If the body shape makes this impossible, the upper limit can go up to 2,100 mm under certain conditions. However, the standard height remains the starting point.

In doing so, pay attention not only to the measured value on paper. The light must also remain visible in practice within the prescribed angular field. A side marker light that is at the correct height but partly disappears behind a mudguard, support, profile or box can still lead to problems. Therefore, check the position on drawing, the actual mounting height, visibility from angled front and rear, any shielding by superstructures and the cable route. The latter points in particular often determine whether a mounting will continue to work practically well in series production.

Choosing the right side marker lamp

The mounting of side markings is covered by ECE R48, but the light itself must be separately approved. In current regulations, type approval of light and signal functions falls under ECE R148. In it, side-marker lamps are classified as SM1 and SM2. The difference is in the photometric requirements: an SM1 provides at least 4.0 candela in the reference axis, an SM2 at least 0.6 candela. Both have a maximum of 25.0 candela.

For heavy-duty O3 and O4 semi-trailers, you should opt for an SM1-approved side marker lamp. The higher light output ensures better visibility across a wider field of view, which is particularly important for long vehicles in the transport sector. When purchasing, ensure that the light bears a valid E-mark with the correct function designation. Without this type approval, mounting in accordance with ECE R48 is non-compliant.

Never simply use an approved side marker light for another light function. A light approved as a side marker light is not automatically suitable for use as a side marker light, indicator or contour light. The function specified on the product must correspond to the function on the vehicle.

Colour of side marker lights on semi-trailers

Side marker lights on the side of a semi-trailer are generally amber, or yellow-orange. This ensures the vehicle is recognisable from the side without causing confusion with white lighting at the front or red lighting at the rear. At the very rear, specific combinations with red light functions may occur, but for a standard lighting layout on semi-trailers, amber is the standard.

Ensure that the side markings are coordinated with the other contour lights, reflectors and rear lights. The aim is to ensure that the entire side profile of the semi-trailer remains clearly and continuously visible.

Flashing side lighting on new O3 and O4 semi-trailers

For new O3 and O4 semi-trailers, lateral visibility when indicating is particularly important. New heavy-duty semi-trailers must therefore be fitted with a side indicator function. This can be achieved using side marker lights that flash in sync with the indicators, or with separate side indicators. Both configurations are technically permitted.

The aim is clear: a vehicle travelling alongside the semi-trailer must be able to see sooner that the combination is about to turn or change lanes. Particularly with long semi-trailers, the rear indicator light is not always immediately visible to traffic travelling alongside the vehicle. This requirement stems from accident analysis of blind-spot situations, where a static side light failed to signal the manoeuvre.

For vehicle builders, this means that you should not view the side lighting in isolation from the indicator system. The control system, wiring harness, connectors and any control box must be incorporated into the design from the outset. There are a few key points to bear in mind:

• The side lighting operates in sync with the indicator on the same side;
• the function fits within the chosen ECE R48 solution;
• The lights and controls are suitable for 24V semi-trailer applications;
• the installation is reproducible for series production.

You do not automatically need to retrofit existing semi-trailers. The requirement is particularly relevant for new vehicles, new type approvals and new series.

What this means for vehicle builders and original equipment manufacturers

For semi-trailer builders and initial mounting, the profit lies mainly in early planning. Those who measure the side markings only after surface mounting run the risk that the distance requirements or mounting height are no longer practically feasible. Then adjustments have to be made afterwards, resulting in extra costs and delays. So include side markings in the chassis design, the position of mudguards and boxes, the wiring harnesses, the choice of connectors, the control of flashing side lighting and the type approval file.

TRALERT® supplies ECE-certified side marker lights and complete solutions for 24V trailer lighting. In doing so, we look not only at the light itself, but also at the practical mounting, the cable routing and the connection to the rest of the vehicle. For a wider range of applications within trailer construction and heavy haulage, you will find relevant information under ‘Lighting for bodybuilding ’ and ‘Lighting for heavy haulage’. You can read the full framework regarding semi-trailers in the regulations for truck and semi-trailer lighting.

Do you use light trailers rather than 24V semi-trailers? If so, different practical guidelines apply. Please read our explanation of marker lights with indicator function on trailers. If you drive frequently in Germany, be sure to check the regulations regarding flashing marker lights in Germany.

Frequently asked questions about side markings on semi-trailers

Are side markings compulsory on every semi-trailer?

Not on every semi-trailer, but on virtually all semi-trailers in the professional lorry and trailer sector. ECE R48 makes side markings compulsory for vehicles longer than 6 metres. Virtually every O3 and O4 semi-trailer exceeds this limit and therefore requires side markings as standard.

How many side marker lights must a semi-trailer have?

This depends on the length. The front light must be no more than 3 metres from the front, the rear light no more than 1 metre from the rear, and there must be no more than 3 metres between any two consecutive lights. For semi-trailers longer than 6 metres, there must also be at least one light in the middle third. For long semi-trailers, this means several lights on each side.

At what height do you fit side marker lights on a semi-trailer?

The standard mounting height is between 250 mm and 1,500 mm above the road surface. Only when the body shape makes this impossible is mounting up to a maximum of 2,100 mm permitted. In addition, always check that the light is not blocked by mudguards, profiles or other body parts.

What is the difference between ECE R48 and ECE R148?

ECE R48 covers installation on the vehicle: position, height, distance, visibility and electrical operation. ECE R148 covers the type approval of the light itself as a light-signalling function. Correct mounting therefore requires both: an approved light and correct positioning on the semi-trailer.

Plan your side marking before surface mounting

Planning a new semi-trailer series or want to make sure your side marking fits within ECE R48? Check out our 24V plug-&-play semi-trailer lighting or contact our technical consultants for a lighting plan that is right for mounting, inspection and delivery.

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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.