Markings have definite and important functions in traffic control. Sometimes they supplement the regulations or warnings of other traffic control devices. Used alone they can produce results that other devices can't, effectively designating a lane, locating the road center, and locating a stopping point, information that could not otherwise be made understandable.
Pavement markings have limitations.
They are obliterated by snow, may not be clearly visible when wet, and may not be very durable under heavy traffic. It may be necessary to repaint them every year, or more often. White lines separate traffic flowing in the same direction or mark the right edge of the pavement. Line width indicates the degree of emphasis. Normal center lines and edge lines are four inches wide.