<P> A passing lane (North American English) or overtaking lane (English) is the lane on a multi-lane highway or motorway closest to the center of the road (the central reservation). In some countries, lanes are described as being on the' inside' or the' outside' of a road - which one the passing lane is varies . </P> <P> In modern traffic planning, passing lanes on freeways are usually designed for through / express traffic, while the lanes furthest from the center of the road have entry / exit ramps . However due to routing constraints, some freeways may have ramps exiting from the passing lane; these are known as "left exits" in North America . </P> <P> A passing lane is commonly referred to as a "fast lane" because it is often used for extended periods of time for through traffic or fast traffic . In theory, a passing lane should be used only for passing, thus allowing, even on a road with only two lanes in each direction, motorists to travel at their own pace . </P>

What is the left lane of a motorway used for