After overtaking, the truck behind you flashes briefly once: this is what the driver wants to tell you.

Motorists can also get such a flash.

The signal is primarily used between truck drivers. However, you may also encounter it as a car driver. This happens, for example, when you are traveling with a caravan or trailer. With just a passenger car, you can usually clearly see when you have passed a truck. With a caravan behind the car, that is much more difficult. Your  vehicle combination  is suddenly several meters longer.

A truck driver may therefore also briefly signal to you with his headlights. By doing so, he lets you know that not only your car, but also your caravan, has passed him. This occurs regularly on busy German motorways, for example. However, this does not mean that you must immediately steer to the right. Always check your own mirrors first. You alone remain  responsible  for a safe lane change.

Sometimes a thank you follows.

Anyone paying close attention may see something else happen after the light signal. Truck drivers regularly thank each other for this help. For example, a driver who has moved back to the right might briefly use their hazard lights. Sometimes, the  left and right turn signals are also  used for just a moment. By doing so, the driver is essentially simply saying: thank you.

It is a kind of informal language among  road users . There are various types of these signals. However, they are not all officially defined and can differ from country to country. Therefore, if you see such a signal, you must always assess the situation. After all, a flash of light can mean something else at other times.

It is not official permission

Although many truck drivers understand these signals, they are not official traffic rules. In the Netherlands, according to traffic regulations, flashing and audible signals primarily serve a function in the event of imminent danger. Therefore, legally, a brief flash of light does not mean you are granted permission to change lanes. Nor does it give you the right of way. At most, the driver behind you can indicate that he sees sufficient space.

That difference is important. Therefore, always keep looking yourself before moving to the right. Check your mirrors and maintain sufficient distance from the  truck . Also, do not drive directly in front of the truck. Heavy vehicles require much more distance to come to a stop. Extra space between your car and the truck is therefore always wise.

Not every flash of light means the same thing.

If you see a truck flashing behind you, pay close attention to the moment it happens. Does the flash occur exactly after you have overtaken the truck? Then there is a good chance the driver is trying to help you. If the signal occurs at a different time, something else might be going on. Perhaps the driver wants to warn of danger. It could also mean that another  traffic situation  requires his attention.

That is why you can never rely blindly on a single light signal. View it primarily as additional information from another road user. Ultimately, you must always judge for yourself whether a maneuver is safe. So, the next time a truck briefly flashes its lights after overtaking, you don’t need to panic immediately. Chances are there isn’t an irritated driver behind you at all. He is probably just trying to tell you that you have completely passed him. A small gesture, but one that can make driving behind long  vehicle combinations  a lot easier.