|Motorways:||A1, A3, A16|
Napoli (Naples) is a city in the south of Italy.
North towards Rome A1
Right behind the central station is a road that leads to the autostrada towards the north. Hitching in this kind of area is really quite difficult because of its central location and perhaps fear of other seemingly dangerous locals. Jason and his friend waited almost two hours for a real ride not asking for money -- It was the first time in a month of hitching the south of Europe had they been asked for currency.
A much better option according to Fedcas is catching a train to Caserta (3,40€ and 00:40 min). The station it's just in front of the Reggia di Caserta (which it's worth having a look btw, and the gardens are free [updated at april 2011]). From there you can either ask if there is any big parking lot around (there would probably be lots of tourists leaving in the afternoon so you could ask for a ride directly) or have a 2 Km walk East to the A1 ramp.
Instead of taking the train, take the bus which leaves just behind the Mcdonalds from the main station, the bus will say Caserta for its final destination, cost 3,40€ , leave every hour, and you can get off at Via Largo Rotunda(ask the bus driver as the actual stop name might be a bit different or hard to see) which is just a few minute walk from the petrol station that leads North. Once off the bus walk two blocks back in the direction the bus came from, take a right(West)and you arrive at the petrol station. Julian waited with a girl and a guy for 30 minutes and found a ride direction North.
Another hint: if you're visiting some touristic spots around Naples at the end of your stay (such as Pompei, Vesuvio, Pozzuoli ecc) you can try to ask for a ride directly to the tourists coming back to their car for leaving as all of these spots are very crowded most of the time.
Naples is really walkable. Scour those fantastic narrow streets in the Spanish quarter. There are some metro lines and buses.