|Motorways:||A1, E70, E61|
Trieste is a city in the very east of Italy.
Most traffic going to Rijeka is passing a small village called Basovizza. You can take the bus #39 to get there. The bus starts at the main rail station inside the city, passing the university, then uphill. When the bus is leaving the main road, then it is the right time to get out. Go back to the road and start hitchhiking from there. It's an average place there, because it is behind a curve, but you will be seen soon enough to get away.
Take a tram to Opicina (cost 1.15eur, August 2012), which is a town almost at the border. The main village road becomes the road to the border, getting out of town there are places where vehicles can stop. Recommended place is in front of NLB bank at the end of the town and where cars can stop easily. Just after the border there is a gas station on the motorway, or you can stand by the old road.
Or you can ask at the train station for a bus to Sežana,ask for timetable because there aren't many buses per day. Once you are in Sežana walk down a little through the city until you see the signal of Ljubljana. You'd better hitch hike before getting in the the highway, there are not many cars but usually one of that few will stop.
Take a bus that goes to Aquilinia, for example bus #20 departing from the city centre, direction Muggia. Get off at the first stop in Aquilinia, which is more or less the first stop after passing an industrial district. Walk towards the second stop (if you aren't already there). The second stop is located right after a traffic light and a zebra crossing. In front of you you will see a blue sign which encourages drivers to slow down. A couple of hundred meters further the roads splits, one can either enter the motorway or drive towards Muggia. Probably good to have a sign (KP for Koper). Average waiting time 45 minutes (Italy is not very hitchhiking friendly).
Your best option is to get to a Area Servizio (petrol station) on the motorway. The easiest way to do that is to take bus line 51 from Trieste bus station (around 2 Euro), and get out some 30 minutes later in the first station after Sistiana - the station is called Duino Bar Bianco. You will get off in a milk bar with great ice creams, behind the building you will see the motorway. Get to the motorway cross it with the tunnel, some 50 meters, to your left. Then turn again left and walk to the Agip petrol station (150m away), where you can ask for rides.
One other option is to take bus #36 from the center of Trieste. It follows the road along the coast and this road (Viale Miramare) is the one leading to the motorway. Get out of the bus at the stop before the last one. There's no ideal spot on this road but if you walk a bit more on this road you can find a couple of acceptable places. You will need some luck though but it's probably your best bet. You should probably ask to get dropped at a petrol station on the motorway since you probably won't find a straight ride to Venezia.
There is sometimes a controller but when some anonymous hitchhiker got controlled he just told the controller that he thought he would be able to buy a ticket from the driver (which is not possible) and the conductor just walked away. This is just his own experience though and maybe you won't be lucky. If you speak Italian, don't show it to the conductor!
You can sleep in Barcola - a big park on the coast about 5 km far from city center. You can reach Barcola with a bus C from the railway station or with a tram from Obedram (tram station not far from center). You can also sleep in a tent there: in the morning there are many people coming to swim, but nobody pays attention to the tent. If it's getting late and you didn't find a place for the night, the train station is also a good option. Just find a quiet spot, between the others that already did, and you'll get a rather quiet sleep for the night; Until 6:20, when the guard came and woke everybody up, I wasn't bothered at all.