Amid the rapid increase in the world's population, the number of people living in "megacities" with populations of 10 million or more is expected to increase from the current 3.2 billion to 5.0 billion by 2030. While urbanization brings abundance and convenience to people and prosperity to cities, it also invokes a variety of problems, including environmental issues such as air pollution, waste, noise, and energy shortages, traffic issues such as congestion and accidents, and shortages of housing and medical facilities.