There are busses from other major Corsican towns, and ferries from other locations. If driving to town in the summer months, it is best to arrive very early, before 10 (or even 9 in August) to ensure parking near the town center. On cloudy or rainy days in August traffic jams may stretch 2 hours long getting into or through town.
Porto Vecchio is best navigated on foot, as the town has a one-way traffic system that makes it virtually impossible to navigate my auto.
The town has dozens of excellent restaurants, some with beautiful views over the harbour, and a main square where you can sip your latte while people watching.