The primary purpose of a transportation system is to provide the accessibility through which individuals and businesses can exercise mobility. That is, transportation systems provide the accessibility by which people get to jobs and recreation, trade in goods and services, interact with other regions, and develop land. A region's transportation system is a critical factor in its economic viability. The extent, use, cost, and impacts of transportation systems are often considered key factors of production in facilitating growth and economic health. In short, transportation systems provide a key base on which the economy of a nation rests.