systems have been built, with lowest car ownership rates in New York City (44%), Washington, D.C. (62%), Boston (63%), Philadelphia (67%), San Francisco (69%), and Baltimore (69%). With the development of the extensive Eisenhower Interstate Highway System in the 1950s, both long-distance trips and daily the commute were mostly by private automobile. This network was designed to exacting federal standards in order to receive federal funding. The system, , has a total length of , making it the world's second longest after China's, and the largest public works project in US history. The Interstate system joined an existing National Highway System (a designation created for the legacy highway network in 1995), comprising 160,000 miles (256,000 kilometers) of roadway, a fraction of the total mileage of roads. The Interstate system serves nearly all major U.S. cities, often through the downtown areas (a point which triggered freeway and expressway revolts in the 1960s and 1970s). The distribution of many goods and services involves Interstate highways at some point. Residents of American cities commonly use urban Interstates to travel to their places of work. The vast majority of long-distance travel, whether for vacation or business, is by the national road network; of these trips, about one-third (by the total number of miles driven in the country in 2003) utilize the Interstate system. In addition to the routes of the Interstate system, there are those of the U.S. highway system, not to be confused with the above-mentioned National Highway System. These networks are further supplemented by State Highways, and the local roads of counties, municipal streets, and federal agencies, such as the Bureau of Indian Affairs. The five inhabited U.S. territories also have their own road networks. There are approximately of roads in the United States, paved and unpaved. State highways are constructed by each state, but frequently maintained by county governments aided by funding from the state, where such counties exist as governing entities (mostly every state except the Northeastern). Counties construct and maintain all remaining roads outside cities, except in private communities. Local, unnumbered roads are often constructed by private contractors to local standards, then maintenance is assumed by the local government. All federal highways are maintained by state governments, although they receive federal aid to build and maintain freeways signed as part of the 46,000 mile (75,000 km) nationwide Interstate highway network. Changes by state initiative may be made with federal