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 Interstate Highways in New York
There are 31 Interstate Highways—9 main routes and 22 auxiliary routes—that exist entirely or partially in the U.S. state of New York. In New York, Interstate Highways are mostly maintained by the New York State Department of Transportation (NYSDOT), with some exceptions. Unlike in some other states, Interstate Highways in New York are not directly referenced by NYSDOT with their number; instead, the letter "I" is suffixed to the number of the route on reference markers and in internal documents. On the surface, there appears to be numerical duplication between several Interstate Highways and state routes—such as I-86 (I-86) and NY 86—but the "I" suffix that is appended to Interstate Highway numbers allows the Interstate Highway and state route to co-exist ("86I" versus "86", respectively).