Is the driver obliged to apply the so-called "zipper merge" when there is no significant speed reduction ?

The principle of zipper merging applies only in conditions of a significant reduction in speed on the roadway, i.e., in a traffic jam situation. When traffic is moving smoothly, a driver changing lanes is obliged to yield the right of way to a vehicle already in the lane they intend to enter, based on general rules. According to Art. 22 para. 4a of the Road Traffic Act, the absence of a significant slowdown in traffic excludes the obligation to apply this rule.