 In the 1920s and 1930s, many nations began investing heavily in progressively more modern highway systems to spur commerce and bolster national defense.Major modern highways that connect cities in populous developed and developing countries usually incorporate features intended to enhance the road's capacity, efficiency, and safety to various degrees.Such features include a reduction in the number of locations for user access, the use of dual carriageways with two or more lanes on each carriageway, and grade-separated junctions with other roads and modes of transport.