Here in Newfoundland vehicles drove left until 1947 and then drove right to conform with the rest of North America. Then there's the British Ministry of Transport which has this useful advice: “Visitors are informed that in the United Kingdom traffic drives on the left-hand side of the road. In the interests of safety, you are advised to practise this in your country of origin for a week or two before driving in the UK.” Yes, I'll be sure to drive into oncoming traffic before I visit them.
All of this naturally brings up the question of how people decided what side of the road to drive on in the first place.