List of Interstate Highways
There are 70 primary Interstate Highways in the Interstate Highway System, a network of controlled-access freeways in the United States. They are assigned one- or two-digit route numbers, whereas their associated "auxiliary" Interstate Highways receive three-digit route numbers. Typically, odd-numbered Interstates run south-north, with lower numbers in the west and higher numbers in the east; even-numbered Interstates run west-east, with lower numbers in the south and higher numbers in the north. Highways whose route numbers are divisible by "5" usually represent major coast-to-coast or border-to-border routes (ex. I-10 travels from Santa Monica, California, to Jacksonville, Florida, traveling from the Pacific to Atlantic oceans). Additionally, auxiliary highways have their numbering system where a different number prefixes the number of its parent highway.
Transportation in the United States
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 virtually all 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.