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. 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 ...
The Massachusetts Institute of Technology's website on "Keep Right Laws" points out that:
This law refers to the "normal" speed of traffic, not the "legal" speed of traffic. The 60 MPH driver in a 55 MPH zone where everybody else is going 65 MPH must move right..."[3]
It is also illegal in many states in the U.S. 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 or more unless such person is passing other motor-vehicles that are in a non-passing lane...[4]
Other examples, such as Massachusetts (General Statute 89-4B),[citation needed] New Jersey, Maine, Illinois, Pennsylvania, and others, make it illegal to fail to yield to traffic that seeks to overtake in the left lane,[citation needed] 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. Many areas which make it illegal to fail to yield to faster traffic, also have exceptions to those rules. Some of these exceptions include preparing to make a left turn, taking an exit located on the left side of the roadway, avoiding traffic merging onto the roadway, or overtaking and passing another vehicle.
A common problem arising from misuse of the "fast lane" is that it forces faster moving traffic that wishes to overtake on the left to change lanes, do so on the right, and then change lanes again. Further, if the vehicle misusing the passing lane is going slower than the flow of other traffic, it forces those using the middle "travel" lane (but who are moving faster) to pass on the right as well, even though they have no intention of doing so.