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.
Federal Aid Highway Act of 1956
Many limited-access toll highways that had been built prior to the Interstate Highway Act were incorporated into the Interstate system (for example, the Ohio Turnpike carries portions of Interstate 76, I-80 and I-90). For major turnpikes in New York, New Jersey, Pennsylvania, Ohio, Indiana, Illinois, Kansas, Oklahoma, Massachusetts, New Hampshire, Maine and West Virginia, tolls continue to be collected, even though the turnpikes have long since been paid for. The money collected is used for highway maintenance, turnpike improvement projects and states' general funds. (That is not the case in Massachusetts, where the state constitution requires the money be used for transportation.) In addition, there are several major toll bridges and toll tunnels included in the interstate highways, including four bridges in the San Francisco Bay Area, ones linking Delaware with New Jersey, New Jersey with New York, New Jersey with Pennsylvania, the Upper and Lower Peninsulas of Michigan and, and between Indiana and Kentucky. Tolls collected on Interstate Highways remain on segments of I-95, I-94, I-90, I-88, I-87, I-80, I-77, I-76, I-64, I-44, I-294, I-355 and several others.