Without white and yellow lines on streets and roads, we wouldn't know where the lanes are, or where to turn or stop or walk, etc. Car accidents would be much more frequent, many with fatalities.
A specialized sector of the construction industry paints lane markings on roads. One company in Michigan, PK Contracting, estimates that one worker paints about 400,000 ft (122,000 m) of lines every day. Over the 6-month construction season, the company stripes and re-stripes about 50,000 mi (80,500 km) of roads. Put those markings end-to-end and you could cross America 16 times.