see exactly where the rear of the truck ends from the cab. This plays an important role, especially during overtaking. Moreover, trucks often drive at approximately the same speed. As a result, the speed difference during an overtaking maneuver is sometimes only a few kilometers per hour. Consequently, a truck can drive alongside another truck for quite a long time.
The driver being overtaken often has a clear view of the end of the other combination. As soon as the entire semi-trailer has passed, he can briefly signal with his headlights. This indicates that there is sufficient room to move back to the right. Such a signal is therefore usually intended in a friendly manner. The truck driver is not trying to rush his colleague; he is simply helping him to better estimate the length of his vehicle.
Motorists can also get such a flash.
The signal is primarily used
