The far left lane on a highway with two lanes or more is for passing, according to the Missouri State Highway Patrol. If you're driving in the left lane and someone behind you wants to pass, the National Highway Traffic Safety Administration (NHTSA) recommends changing lanes to let them pass.

Remain a safe distance behind any vehicles in front of you so that you do not need to slam on the breaks. Keep an eye out for smaller vehicles and motorcycles and leave plenty of space when passing and merging in front of semi-trucks.