Since Boulder has operated under residential growth control ordinances since 1976, the growth of employment in the city has far outstripped population growth. Considerable road traffic enters the city each morning and leaves each afternoon, since many employees live in Longmont, Lafayette, Louisville, Broomfield, Westminster, and Denver. Boulder is served by US 36 and a variety of state highways. Parking regulations in Boulder have been explicitly designed to discourage parking by commuters and to encourage the use of mass transit, with mixed results.