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.
List of highways in Harris County, Texas
There are currently four interstates located within Harris County. They consist of three major interstates (Interstate 10 (I-10), known as the Katy Freeway and the East Freeway, Interstate 45 (I-45), known as the Gulf Freeway and the North Freeway, and Interstate 69 (I-69), known as the Southwest Freeway and the Eastex Freeway) and one Auxiliary Interstate (Interstate 610 (I-610), known as "The Loop"). There are also three U.S. Routes located in Harris County. These highways consist of U.S. Route 59 (US 59, known as the Southwest Freeway and the Eastex Freeway), U.S. Route 90 (US 90, known as the Crosby Freeway), and U.S. Route 290 (US 290, known as the Northwest Freeway). There are nine state highways, eight spur and loop highways, one park highway, six toll roads (five independent), twenty-two farm to market roads, four bannered U.S. routes, two bannered state routes, and one bannered farm to market road.