Passing lane

A passing lane (North American English) or overtaking lane (British, Irish and Australian English) is the lane on a multi-lane highway or motorway closest to the center of the road (the central reservation). In Californian terminology, the passing lane is often known as the number one lane,left lane, or leftmost lane, due to left hand drive (driving on the right), and the rightmost slow lane is sometimes called the "outside lane", because the lane nearest the center of the roadway is considered "inside". Some regions of the world reverse the definitions of "inside" and "outside", as described under #Regional terminology.

In modern traffic planning, passing lanes on freeways are usually designed for through/express traffic, while the outer lanes 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.

A passing lane is often colloquially 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.