Taken from a isle of man guide site.
Driving a car in the Isle of Man is broadly similar to driving in the United Kingdom, and most traffic regulations are the same. As in the UK people drive on the left hand side of the road.
Unlike the UK there is no national speed limit. There are speed restrictions in built up areas, but after passing a 'National Speed Limit' sign there ceases to be any speed restriction, although people driving in a reckless manner may well be stopped by the police