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.
Environmental Action
In 1956, the United States began constructing the interstate highway system, the largest public works project in history. In rural areas the highways were popular, but by the late 1960s many interstates had destructively begun to penetrate inner cities, destroying neighborhoods, adding pollution, and generating political resistance. Local anti-highway groups sprang up in dozens of locations from Boston to Seattle calling for changes to the Highway Trust Fund, an exclusive source of highway-only dollars from Washington.