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.
Texas state highway system
The United States Numbered Highways are a nationwide grid of highways, but unlike the Interstate Highway System, there is no minimum design standard for these highways. This is clearly evident as some stretches of the U.S. Highways in Texas are nothing more than a two-lane rural road, while others are urban freeways. Although the U.S. Highways have been replaced for the most part by Interstate Highways for through traffic, the U.S. Highways still serve as important regional connectors. Several notable examples of U.S. Highways that are built to freeway standards include US 75 and US 80 in Dallas, US 59 and US 290 in Houston, and US 90 and US 281 in San Antonio.