St. Thomas drives on the left — a legacy of the Danish colonial era that remained after the US took over in 1917, and which continues to surprise American visitors who instinctively reach for a steering wheel on the wrong side. Rental cars are available at the airport and in Charlotte Amalie; a car is the most practical way to explore the island independently, since the beaches and viewpoints are spread out.
Open-air safari buses (share taxis on fixed routes) run between Charlotte Amalie, Red Hook on the east end, and most points in between. They depart when full rather than to a timetable, but are frequent, cheap, and part of the local texture. Regular taxis also operate from the airport, the ferry docks, and the cruise ship terminals; agree the fare before you get in.
The ferry to St. John runs roughly every hour from Red Hook and several times daily from the Charlotte Amalie ferry terminal. Many visitors rent a car on St. Thomas and leave it there, taking only what they need for a day in the national park — vehicle ferries to St. John exist but are expensive and rarely necessary for a day trip.