How to reach parking lots before the Liberty Bridge in Venice
After you get out of Mestre (mainland Venice) and head for the center of Venice just before the Liberty Bridge (the only bridge that connects Venice with the mainland) you will notice several streets on your right. These parking lots are located at the last right turn just before the Liberty Bridge, but do not worry since even if you turn right a bit earlier you will find a similar offer for the same price.
After you park your car, in order to get to Venice, you will need to get a bus, by which you will cross the Liberty Bridge and get to Piazzale Roma (one stop). The bus stop is located just around 50 meters from these parking lots which is quite convenient. Also, bus tickets can be purchased at the parking lots.
As for the bus lines you need to take in order to get to Venice, you can choose any of the lines (2, 4, 6, 7) that stop here, since they all stop at Piazzale Roma.