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.
Atlanta
Atlanta has a network of freeways that radiate out from the city, and automobiles are the dominant means of transportation in the region. Three major interstate highways converge in Atlanta: I-20 (east-west), I-75 (northwest-southeast), and I-85 (northeast-southwest). The latter two combine in the middle of the city to form the Downtown Connector (I-75/85), which carries more than 340,000 vehicles per day and is one of the most congested segments of interstate highway in the United States. Atlanta is mostly encircled by Interstate 285, a beltway locally known as "the Perimeter" that has come to mark the boundary between "Inside the Perimeter" (ITP), the city and close-in suburbs, and "Outside the Perimeter" (OTP), the outer suburbs and exurbs. The heavy reliance on automobiles for transportation in Atlanta has resulted in traffic, commute, and air pollution rates that rank among the worst in the country. The City of Atlanta has a higher than average percentage of households without a car. In 2015, 15.2 percent of Atlanta households lacked a car, and increased slightly to 16.4 percent in 2016. The national average is 8.7 percent in 2016. Atlanta averaged 1.31 cars per household in 2016, compared to a national average of 1.8.