What about side marking on semi-trailers: mounting & legislation

Side marking on a semi-trailer seems simple at first glance: mount and connect lights along the side. In practice, the challenge lies mainly in the position. A light may be technically approved and work perfectly, but still raise questions during inspection or delivery when the distance, height or visibility are just not right.

For wagon builders, semi-trailer manufacturers and initial mounting, ECE R48 is particularly decisive. This regulation prescribes where side marker lights must be on the vehicle. Side marking is mandatory for semi-trailers longer than 6 metres, and therefore it is a standard part of the lighting plan for almost all O3 and O4 semi-trailers.

In this article you can read when side marking is mandatory, which distances and mounting heights apply, what to look out for when choosing the light and what the rules round flashing side lighting mean for new O3 and O4 semi-trailers.

When is side marking on a semi-trailer mandatory?

Side marking is mandatory according to ECE R48 on vehicles and semi-trailers longer than 6 metres. In the case of a semi-trailer, you are looking at the total vehicle length. In practice, this means that almost every heavy semi-trailer in category O3 or O4 requires side marker lights.

Lighter principles apply to vehicles up to 6 metres long. Then at least one side marker light on each side is sufficient in the first or last third of the vehicle length. However, this is the exception for the truck and semi-trailer sector, as most semi-trailers are well above the 6-metre limit.

In short: a semi-trailer longer than 6 metres needs side marking. With O3 and O4 semi-trailers, this is almost always the case in practice.

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 lights should be a maximum of 3 metres from the front of the semi-trailer. This keeps the front contour visible when another road user approaches angled from the front, for example at an intersection, roundabout or driveway. In the case of non-standard designs, such as special surface mounting or parts that limit the positioning, check whether this position is feasible at the design stage.

Spacing: up to 3 metres

There should be a maximum of 3 metres between two consecutive side marker lights. With a long semi-trailer, this automatically leads to several marker lights per side. Do not calculate this only after surface mounting, but include the side markings directly in the chassis and cable plan. This prevents attachment points, mudguards, boxes or body parts from turning out later to be exactly in the desired position.

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

The rear side marker lights are within 1 metre of the rear. This is important for recognition of the entire vehicle length, especially when overtaking, turning and manoeuvring in the dark. For semi-trailers with tailboards, bumper structures or protruding parts, this is a concern. Therefore, always check the actual rear of the vehicle and not just the theoretical chassis size.

At least one light in the middle third

On semi-trailers longer than 6 metres, there is at least one side marker light per side in the middle third of the vehicle length. This prevents only the front and rear from being visible, while the centre of the semi-trailer is visually lost. In practice, the number of lights usually follows naturally from the combination of these requirements.

Distance requirement	Standard according to ECE R48
Front side marker lights	Up to 3.0 m from the front
Mutual distance	Up to 3.0 m between two lights
Rear side marker lights	Up to 1.0 m from the rear
Distribution for lengths > 6 m	At least one light in the middle third
Obligation	For vehicles 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, steer clear of an SM1-approved side marker lamp. The higher light output ensures better visibility over a wider angular field, which matters especially for long vehicles in the transport sector. When purchasing, make sure the light bears a valid E-mark with the correct function designation. Without that type approval, mounting under ECE R48 is not compliant.

Never just use an approved side marker lamp for any other light function. A light approved as a side marker light is therefore not automatically suitable as a side marker light, indicator or contour light. The function on the product and the function on the vehicle must match.

Colour of side markings on semi-trailers

Side marker lights on the side of a semi-trailer are basically amber, or yellow-orange. This keeps the vehicle recognisable from the side without confusion with white lighting at the front or red lighting at the rear. There may be specific combinations with red light functions at the extreme rear, but for a standard lighting plan on semi-trailers, amber is the starting point.

Consciously combine the side marking with the other contour lights, reflectors and rear lights. The aim is that the entire side view of the semi-trailer remains logically and continuously visible.

Flashing side lighting on new O3 and O4 semi-trailers

For new O3 and O4 semi-trailers, lateral visibility when indicating direction is especially important. New heavy semi-trailers should therefore be equipped with a side indicator function. You can fit these with side marker lights that flash synchronously with the direction indicators, or with separate side direction indicators. Both versions are technically permitted.

The goal is clear: a vehicle next to the semi-trailer should be able to see earlier that the combination is about to turn or change lanes. Especially on long semi-trailers, the rear indicator light is not always immediately visible to traffic next to the vehicle. This requirement stems from accident analysis of blind spot situations, where a static sidelight did not announce the manoeuvre.

For wagon builders, this means that you should not consider side lighting separately from the indicator system. You include the control system, wiring harnesses, connectors and any control box in the design from the outset. There are a few fixed points to bear in mind:

• The side lighting works synchronously with the direction 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.

Existing semi-trailers do not automatically have to be converted. The requirement is particularly relevant for new vehicles, new type approvals and new series.

What this means for wagon builders and initial mounting

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 semi-trailer lighting. Here we not only consider the light itself, but also the practical mounting, cable routing and connection to the rest of the vehicle. For broader applications within semi-trailer construction and heavy transport, you will find relevant information under lighting for bodybuilding and lighting for heavy transport. You can read the complete framework round semi-trailers in the rules for truck and semi-trailer lighting.

Do you work with light semi-trailers instead of 24V semi-trailers? Then other practical principles apply. Read our explanation on marker lights with indicator function on semi-trailers. If you frequently drive in Germany, also check the rules round flashing marker lights in Germany.

Frequently asked questions about side marking on semi-trailers

Is side marking mandatory on every semi-trailer?

Not on every semi-trailer, but on almost all semi-trailers in the professional truck and semi-trailer sector. ECE R48 makes side marking mandatory on vehicles longer than 6 metres. Almost every O3 and O4 semi-trailer exceeds that limit and therefore requires side marking as standard.

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

It depends on the length. The front light sits a maximum of 3 metres from the front, the rear a maximum of 1 metre from the rear and there should be a maximum of 3 metres between two consecutive lights. For semi-trailers longer than 6 metres, there is also at least one light in the middle third. For long semi-trailers, this means several lights per side.

At what height do you install side markings 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 is about installation on the vehicle: position, height, distance, visibility and electrical operation. ECE R148 is about type approval of the light itself as a light signal 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.