[pmontra]

The rules in France are probably different but passing on the right is legal on Italian highways, in one circumstance: if one keeps driving on the lane on the right and somebody slower happens to be driving on the lane on the left. The rationale is that it normally happens when traffic is packed, so it's ok even if there is little traffic. Everybody keep driving straight and there is no danger.

It's not legal if somebody is following the slower car on the left and steers to the right to pass. However some drivers stick to the left at a speed slower than the limit and if they don't yield what happens is that eventually they get passed on the right.

The two cases have different names. The normal pass is "sorpasso", the other one (passing by not steering) is "superamento", which is odd but they had to find a word for it.