The metropolitan area of Phoenix in the U.S. state of Arizona contains one of the nation's largest and fastest growing freeway systems, boasting over 1,405 lane miles as of 2005.
Due to the lack of any form of mass transit besides bus prior to 2008, the Phoenix Metropolitan Area has remained a very automobile-dependent city, with its first freeway opening in 1958—a year preceding most cities' first freeway openings. Coupled with the explosive growth of the region and adequate funding, the result is one of the nation's most expansive freeway networks.
The backbone of Phoenix's freeway system is composed of three major freeways—Interstate 10, Interstate 17, and U.S. Route 60. Interstate 10, being a transcontinental route between California and Florida, is the most heavily traveled freeway in the Valley of the Sun. Interstate 17 runs down the center of Arizona, connecting Phoenix with Sedona, Prescott, Flagstaff and the Grand Canyon. U.S. Route 60 spans most of the country, but is only a controlled-access highway (i.e. freeway) for a few short stints, one of them being in the Valley. It shuttles travelers to cities such as Wickenburg, Globe, Kingman and Las Vegas (by way of a connection in Wickenburg with U.S. Route 93). In addition to these three freeways, two beltways, Routes 101 and 202, loop around Phoenix and Mesa respectively. State Route 51 connects Downtown with the northern reaches of the city, and Arizona State Route 143 is a distributor for Phoenix Sky Harbor International Airport.
Phoenix freeways are funded primarily by local sales tax dollars rather than federal money, so newer freeways were, and are, given state route designation as opposed to interstate designation. Primarily due to this, Phoenix is the largest city in the United States to have two Interstate Highways and no 3-digit interstates.