I have undertaken many times but given the fact that the people in the wrong lanes do things without thinking, they can easily come back in - if, for example, you're coming up to an exit ahead which they want.
I've never had an accident because I drive defensively and try and look for things like this, and you never just fly down lane 1 at top speed (as some people do, and then it's not a non-existent 'undertaking' offence but driving without due care).
I can't see why you'd need to undertake in Germany. People move back in very quickly, obviously having been taught that lane 2+ are for overtaking only. If you know that, the problem is half solved - bar the odd bad driver that ignores all the rules. We have too many of these here.
Personally, I don't think people should be allowed to drive on the motorway until they have passed a test to show that they are capable of using them properly.
Obviously you incorporate it into test, but make it optional - like being able to do your test in an automatic but not being allowed to drive a manual if you do.
Clearly, it wouldn't be implemented overnight, but would have a date set some point, say 2 or 3 years later, to give people time to arrange and have the test done. It wouldn't need to be too long or expensive, as it would just need to cover staying to the left unless overtaking, practising overtaking others and using sliproads properly. I propose installing ANPR cameras at the start of motorways and all onramps (though not offramps as they are not to be average speed cameras), which will flag up cars registered to those who are not licenced to be using them (Obviously there shall be leniancy for those who have taken a wrong turn onto it by accident, but repeat offenders will get a fixed penalty notice and points on their licence).
Actually, that reminds me of something else that really irritates me about motorways; Sliproads.
So many people don't seem to understand that they're there and so that you can get up to a safe speed to join the motorway, not dawdle down them at 30 or 40 then accelerate when you get onto the motorway itself. It's not only annoying but sometimes dangerous as well.
I mean, my car isn't powerful (54bhp

), so it doesn't accelerate that quickly, but slip roads are fine for getting up to speed, however, I've had more than one occasion when I've almost had a crash because the person in front wouldn't accelerate down the slip road.
Mind you, the ones who slow down before pulling on are even worse, they shouldn't be allowed near motorways if they do that
/rant
