Andrzej Duda signed the new traffic rules into effect after they passed in a 84-0 vote with no abstentions in the upper house of parliament last month.
Under the new “zipper merging” approach approved by the Polish head of state, drivers will be required to merge at a late stage in places where two or more lanes of traffic narrow to one.
Experts say zipper merging helps relieve road congestion and is preferred to early merging because studies show that leaving a lane unoccupied is inefficient and only makes traffic heavier.
The zipper method is based on the idea of a zipper smoothly coming together.
In another new traffic rule signed into law by the Polish president on Wednesday, drivers will be required to move aside and create "emergency corridors" to allow emergency services to reach the scene of a road accident as fast as possible in case of traffic congestion.
An emergency corridor enables faster progression of emergency service vehicles such as ambulances and fire trucks and ensures their access to accident sites.
The new rules are expected to kick in later this year, public broadcaster Polish Radio’s IAR news agency reported.