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 East Valley. West of Phoenix, it shuttles travelers to cities such as Wickenburg, Kingman and Las Vegas (by way of a connection in Wickenburg with U.S. Route 93). In addition to these three freeways, three beltways, Routes 101, 202, and 303 loop around Phoenix, the East Valley, and the West Valley, 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 three-digit Interstates.
This is Arizona's widest and most congested freeway, entering the metropolitan area on its western edge in the city of Buckeye as the Papago Freeway. It continues eastward through the cities of Goodyear, Avondale, and Tolleson; where it has an interchange with northbound Loop 101. Following Tolleson, I-10 reaches Phoenix's western city limits, and as it approaches downtown, there is a four-level symmetrical stack interchange with Interstate 17 known by locals as The Stack.
There are numerous construction projects along the Papago Freeway spanning both east and westbound from around Dysart Road in Avondale, to Verrado Way in Buckeye. The projects are expected to convert the current 4 lane divided freeway into a 6 to 10 lane divided freeway. The main project is complete. Along with the anticipation of the completion of State Route 801, traffic coming in and out of Phoenix is anticipated to be less congested, and easier to manage.
Beyond The Stack, Interstate 10 proceeds eastward through a tunnel underneath Downtown. The tunnel is locally called the Deck Park tunnel, as Margaret T. Hance Park is located above. Following the tunnel, it reaches the Mini Stack interchange with Loop 202 and SR 51. Turning southward at this interchange, I-10 runs adjacent to Sky Harbor International Airport before an interchange with the southern terminus of I-17.
After this second I-17 interchange, I-10 occupies the eastern leg of the Maricopa Freeway, presumably named after the Native American tribe for which the county is also named. It regains its primary eastward direction as it crosses the Salt River, but after meeting SR 143 it turns south again via the Broadway Curve, where it enters the city of Tempe. There, an interchange with US 60 is located. The freeway enters its final city in the Valley of the Sun, Chandler, where Loop 202 intersects I-10 at another four-level symmetrical stack interchange before the Interstate enters the Gila River Indian Community and continues on through the undeveloped stretch of desert between Phoenix and the fast-growing town of Casa Grande before making its way southeast toward the Tucson metropolitan area.