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.
Speed limits in the United States by jurisdiction
New Mexico has six major freeway facilities, which include three lengthy Interstate routes. Part of US-70 (as a divided highway) between Las Cruces and Alamogordo is the only section of non-Interstate route as well as being the only road in New Mexico that's not a freeway to have the 75 mph limit; as of January 2019, US 285 between Roswell and Vaughn will be raised to 75 mph as well. New Mexico, Nevada (US 95 south of US 93), and Texas are the only three states with 75 mph limits on roads that aren't freeways. There is no statutory requirement for reduced speeds on urban freeways so that, for example at Santa Fe and Las Vegas the speed limit remains 75 mph on I-25. New Mexico, Kansas, North Dakota, Colorado, and Texas are the only states to have a speed limit greater than 70 mph in urban highways. Nonetheless, there are 65 mph limits on freeways in more heavily urbanized areas such as Albuquerque and Las Cruces. Other reduced speed limits do exist, but the lowest speed limit under normal conditions on New Mexico's freeways is 55 mph, which can be found on two sections of Interstate 25: The first section being three miles from the Big I to Gibson Boulevard in Albuquerque, and the second being a short stretch near Raton Pass. These particular stretches of I-25 were originally built as relocations of US-85, whose design and construction predate the interstate highway era. As such, these stretches do not meet modern interstate highway standards, and have closely spaced interchanges, sharp curves, and/or limited sight distances.