We drive on the left. Why, well there are a number of different explanations. The US Virgin Islands were owned by Denmark until 1917 so it is not a carry-over from the way they drive in, say, England as may be the reason behind driving on the left in the British Virgin Islands.
One story is that it is because of the donkeys (we have lots of wild asses – tourists aside – residing on St. John) who were trained to walk on the left with other traffic and could never get over it. More likely it is the rum! In any case, not to worry, you cannot get going very fast on St. John so except for the forgetful tourist driving on the ‘wrong’ side of the road, driving on the left is nothing to be concerned about.