Interstates are long stretches of highway that typically travel through more than one state, and have a total of four or more lanes. Two of the lanes allow cars to go in one direction and the other two in the other direction. In metropolitan areas, these large highways can grow to sizes of six, eight or even ten lanes (three, four or five lanes per direction).
The Interstate System was conceived in 1956, when President Dwight D. Eisenhower signed the Federal Aid Highway Act, also known as the National Interstate and Defense Highways Act. This act appropriated $25 Billion towards the construction of approximately 41,000 miles of interstate around the country. One of the main objectives of the system, was that the United States needed to be able to rapidly respond to foreign threats if needed. The existing highways at the time simply did not allow for rapid movement of equipment, troops or supplies from coast to coast.
A naming and numbering system was created for these new highways as well. Each name would consist of the letter I followed by a dash and then a two-digit number. Large interstates traveling east to west would be given a two-digit number ending in zero, while those traveling north to south would be given a two-digit number ending in five. Some examples of the east to west names are I-10, I-20, I-40 and I-90. Examples of north to south names are I-5, I-15 and I-95.
Smaller interstates were built as well. Many of these were given two-digit numbers that ended in a seven or nine. In large, metropolitan areas, bypasses were required to circle or bend around the heavy traffic of the metropolitan areas' interiors. These bypasses were given three-digit numbers that typically ended with a five. One famous bypass is I-495 that circles around Washington, D.C., and is nicknamed "The Beltway".
Though many of the larger interstates have been completed, change is constant and new developments are always underway. A new project was just recently approved that will allow I-49 to be completed from Fort Smith to Kansas City. Another project currently in progress is called the I-4 Ultimate Highway, which will improve the road around Orlando and be completed by 2021.