Outside lane

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.

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.

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.

Common practice and most law on United States highways is that the left lane is reserved for passing and faster moving traffic, and that traffic using the left lane must yield to traffic wishing to overtake. Evidence exists demonstrating the efficiency of this practice.

The United States Uniform Vehicle Code states:

Upon all roadways any vehicle proceeding at less than the normal speed of traffic at the time and place and under the conditions then existing shall be driven in the right-hand lane then available for traffic ...

It is also illegal in many states in the US to use the "far left" or passing lane on a major highway as a traveling lane (as opposed to passing), or to fail to yield to faster moving traffic that is attempting to overtake in that lane. For example, Colorado's "Left Lane Law" states:

A person shall not drive a motor vehicle in the passing lane of a highway if the speed-limit is sixty-five miles per hour

In other states, such as Massachusetts, New Jersey, Maine, Illinois, Pennsylvania, and others, it is illegal to fail to yield to traffic that seeks to overtake in the left lane, or to create any other "obstruction" in the passing lane that hinders the flow of traffic. As a result, heavy trucks are often prohibited from using the passing lane.

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Wikipedia