In some U.S. states (such as Louisiana, Massachusetts and New York), although there are rules covering all traffic on a public way to use the right-most lane unless when overtaking, this law is usually ignored and seldom enforced on multi-lane roadways. Some states, such as Colorado, use a collection of laws and signs restricting speeds or vehicles on certain lanes to emphasize overtaking only on the left lane, and to avoid a psychological condition which is commonly called road rage.
In California, cars may use any lane on multi-lane roadways. Drivers moving slower than the general flow of traffic are required to stay in the right-most lanes (by California Vehicle Code (CVC) 21654) to keep the way clear for faster vehicles and thereby speed up traffic. However, faster drivers may legally go through the slower lanes if conditions are permitted (by CVC 21754). But the CVC also requires trucks to maintain the right lane, or in the right two lanes if the roadway has four or more lanes going in their direction. The oldest freeways in California, and some freeway interchanges, often have ramps on the left, making signs like "TRUCKS OK ON LEFT LANE" or "TRUCKS MAY USE ALL LANES" necessary to override the default rule. Lane splitting, or riding motorcycles in the space between cars in traffic, is allowed as long as it is done in a safe and prudent manner