Zipper merging is not about 'when' you merge, but 'where'. It should be every-other car from each lane. Ideally this should be done before the end of the lane.

Zipper merging is not about 'when' you merge, but 'where'. It should be every-other car from each lane. Ideally this should be done before the end of the lane. It only ends up being the end of the lane and causing inefficiencies because of those who speed past their zipper spot, and are cheating. If I see that happening a few times, what I'll do is move along in sync with the other lane leaving space ahead of me where the lane ends.