[Tomte]

It's actually the law in Germany.

We have a slightly different problem: people don't understand that the full capacity of the road should be used, zipping only shortly before the constriction. People switch lanes far too early, other people pass them (because the lane is free until the constriction), people who switched early feel cheated, everybody gets aggressive.

[cameronh90]

The thing is about the zipper rule is that it can genuinely be difficult in practice sometimes. If it's a simple example of a busy slow moving two lane road becoming a one lane road, it's absolutely simple and unquestionably the best practice to merge late. But in other situations, especially ones involving exits and junctions, it can be down to judgement.

In very low density traffic on high speed roads, waiting until the lane is actually closed to move over can create slow downs, but moving left earlier doesn't. The point where the optimum behaviour changes isn't always clear and can change rapidly.

In the UK, the rule is that in slow moving congestion you should late merge but in other cases you should stick in the left lane unless overtaking. There isn't a specifically defined point where one behaviour should take precedence over the other.

[radlad]

This occurs in the US too. It drives me crazy when a two-lane highway turns into a one-lane highway for miles, despite a free lane leading up to the accident.

And any attempts to use the free lane will result in cars dangerously cutting you off.