Some countries have followed the model of the demographic transition—they have reached large and stable population sizes and have increased life expectancies. Throughout history, and currently in many parts of the world, populations that have high rates of growth create environmental problems. A rapidly growing population uses resources at an increased rate and can overwhelm the infrastructure of a community. Infrastructure is the basic facilities and services that support a community, such as public water supplies, sewer lines, power plants, roads, subways, schools, and hospitals. The symptoms of overwhelming population growth include suburban sprawl, overcrowded schools, polluted rivers, barren land, and inadequate housing. You may have seen some of these problems in your community.