aaaaargh!!!! if the police finds you with a bike on an autoroute in Italy you'll go directly into JAIL!!! I've been in Chile and I was very scared when we moved on an motorway, and also surprised... but the cyclists that were with me told me: "it's normal... we do not have as many routes as in Europe, we have a recent history of motorization..."
In Italy you must pay (and a lot of money...) to use motorways; there's a gate with tickets when you enter a motorway, there's a cashier to pay when you exit (you pay depending on the distance...)