When you pass a merging lane and you have the priority, it is courteous to move to the overtaking lane to allow traffic to merge. Do not flash at cars - this indicates that you are not allowing them priority and are coming trough. If Italians want to show that they are giving you permission, they might use their hands (but you probably won't see them!).
The autostrada, signposted on a green background, is always a toll road in Italy. At the entry to the system, you collect a ticket from any of the lanes showing a ticket (unless you have the automatic transponder charging system called "Telepass". These roads are well signposted and surfaced, the main advantage being top speed (130k for cars) and ease of use. When you enter an autostrada, it helps to know in what direction you are heading, ie., the principal city in your general direction. It also helps to know the cities in the opposite direction, so you can avoid them! Excepting entry to an autostrada at the beginning of the road, you frequently discover that a division is usually found following clearance of the toll barrier (upon taking your ticket) where you need to make your quick decision.
While toll prices vary slightly, the average price is about 1 euro for 17.5 kilometres [price correct at December 2006].
The majority of autostrade have two lanes, an inside lane where you shoudl spend most of your journey (depending upon speed and traffic) and an overtaking lane. Remember that you should indicate constantly when using the overtaking lane - there is no need to indicate when finishing your manouevre and returning to the inside lane.