After moving to the USA from Europe I was quite shocked at the free-for-all on American freeways. The European model is followed very well in Switzerland, and it's extremely pleasant and practical to have the ability to cleanly overtake, overall reducing traffic and allowing different vehicles to go at their optimal speed without being stuck behind the lowest common denominators (trucks, busses, etc. clogging everything up)

Illegal ≠ does not happen, and actually from my experience of driving in Italy, passes on the right are almost as common as the one on the left

It’s illegal in much of the US and Canada as well. It’s just rarely enforced.

That’s the theory perhaps. The practice OTOH would disappoint.

I would invite the downvoters to try driving in southern France at their next opportunity. People pass on the right, drive slowly in the middle lane and tailgate dangerously in the left lane.

Then you also have the special letter of the law crazies who zig zag every minute across multiple lanes to pass people in the middle.

In some countries I know it generally works, in others it maybe doesn't. I can't speak for italy.

Yeah, having driven on Italian motorways - my experience is the exact-opposite of what the law supposedly encourages.

You are wrong. In the U.K., which drives on the left and is in Europe, it is not expressly forbidden to undertake (pass on the left) anywhere, including motorways. This is independent from the legal requirement to remain in the left-most lane if possible.

On designated one-way streets, and thus not on motorways, passing on either side is expressly allowed. Of course, reckless undertaking at high relative speed on the motorway may be interpreted as illegal under other more widely encompassing laws.

That is only in the UK. In the rest of the continent it is illegal.