During the 1940s and 1950s, urbanization accelerated and the built-up area was increased to 68 km2 by 1962, an almost fourteen-fold increase compared to 1925. Under the premiership of Mohammad Daoud Khan in the 1950s, foreign investment and development increased. In 1955, the Soviet Union forwarded $100 million in credit to Afghanistan, which financed public transportation, airports, a cement factory, mechanized bakery, a five-lane highway from Kabul to the Soviet border and dams, including the Salang Pass to the north of Kabul. During the 1960s, Soviet-style microrayon housing estates were built, containing sixty blocks. The government also built many ministry buildings in the brutalist architecture style.