In the U.S. state of Arizona, Interstate 10 (I‑10), the major east–west Interstate Highway in the United States Sun Belt, runs east from California, enters Arizona near the town of Ehrenberg and continues through Phoenix and Tucson and exits at the border with New Mexico near San Simon. The highway also runs through the cities of Casa Grande, Eloy, and Marana. Segments of the highway are referred to as either the Papago Freeway, Inner Loop, or Maricopa Freeway within the Phoenix area and the Pearl Harbor Memorial Highway outside metro Phoenix.
Route description I-10 through Arizona is designated a "Purple Heart Trail", after the Purple Heart, the award received by American soldiers wounded in combat. The western terminus is located at the California border at the Colorado River in La Paz County where I-10 continues westward into California towards Los Angeles. Here, the highway is cosigned as I‑10 and U.S. Route 95 (US 95).
Western segment The highway runs east by northeast through Ehrenberg, the Dome Rock Mountains, and Quartzsite and then turns to an east by southeast orientation just before the junction for US 60. It continues this path entering Maricopa County and the Phoenix Metro area. The route turns east by northeast again at the junction for State Route 85 (SR 85) northwest of downtown Buckeye, and turns due east at Verrado Way (exit 120). Here, the speed limit drops from . The landscape by this point is largely urban.
Papago Freeway From there, I-10 traverses through the communities of Goodyear, Avondale, and Tolleson, meeting with local streets and area freeways such as Loop 303 (at the former Cotton Lane interchange, exit 124) and the Loop 101 Agua Fria Freeway along the way. By December 2019, the simple diamond interchange with 59th Avenue (exit 138) was totally rebuilt, transforming it into the first of two junctions with the Loop 202 Ed Pastor Freeway. As it makes its way through Phoenix, the highway meets with I‑17 and US 60 for the first time just northwest of downtown at The Stack.
Inner Loop East of The Stack, I-10 forms the north edge of downtown. Near 3rd Avenue, the highway enters a half-mile tunnel () that runs under a park and the central branch of the City of Phoenix Library. Emerging past 3rd Street, the highway continues due eastward for another before coming to another interchange for Route 51 and Loop 202 (second of three junctions with the latter), called the Mini Stack. At this interchange, I‑10 turns southward for about , passing near Sky Harbor International Airport and reaching the second junction with I‑17/US 60. Here, I‑17 terminates as I‑10 skews eastward again. After this junction, the highway is cosigned with US 60.
Maricopa Freeway
Continuing southeast over the Salt River and eastward, I‑10/US 60 enter Tempe and meets with SR 143. The freeway turns southward again at the Broadway Curve, with US 60 heading east towards Mesa. I‑10 continues southward through Tempe, Guadalupe, and Chandler on the east. Immediately north of the Gila River Indian Community, I‑10 has its third and final intersection with Loop 202. Past Loop 202, the highway heads southeast through the Gila River Indian Community and entering Pinal County.
Broadway Curve As of a 2006 estimate, the Broadway Curve portion of I‑10 in Tempe carried an average of 294,000 vehicles per day. This number was predicted to increase by over 150,000 to approximately 450,000 by 2025. The section of I-10 from I-17 to the Broadway Curve is the widest stretch of freeway in the valley and one of the widest in the United States, spanning 16 to 20 lanes, including two HOV lanes in each direction. A recent construction project added collector-distributor lanes and flyover ramps connecting SR 143.
Eastern segment After exiting the Phoenix metropolitan area, I‑10 continues primarily south-southeast towards Casa Grande intersecting I‑8 before heading southeast towards Marana and Tucson, paralleling the Santa Cruz River. After an interchange with I-19 in Tucson, I-10 heads in a more easterly direction towards Benson and Willcox, with a brief concurrency with US Route 191. The highway passes through the towns of Bowie and San Simon before entering New Mexico.
History
I‑10 in Arizona was laid out by the Arizona Highway Department in 1956–1958 roughly paralleling several historic routes across the state. Particularly east of Eloy, it follows the Butterfield Stage and Pony Express routes, and loops south to avoid the north–south Basin and Range mountains prevalent in the state. In fact, the route from its junction with I‑8 east to New Mexico is almost exactly the same route used by the old horse-drawn stagecoaches, which had to go from waterhole to waterhole and avoid the hostile Apache Indians. This is why I-10 is more of a north–south route between Phoenix and Tucson than east–west. The Southern Pacific Sunset Route line had to take the route of least hills, and in the 1920s highways were laid down next to the trains across southern Arizona.
When the project was being designed in the 1950s, the Arizona Highway Department fought for a nearly straight-shot west from Phoenix for the new freeway, instead of angling northwest out of Phoenix along US 60/US 70/US 89, through Wickenburg. Wickenburgers battled to bring the freeway through their city but lost that battle. The detour up through Wickenburg was logical decades earlier, when nearly all U.S. highways through Arizona were laid out along railroad tracks, and US 60/US 70 was routed mostly parallel to the Santa Fe rail tracks east of Wickenburg, and the Arizona and California Railway west to Vicksburg. The two old federal routes then struck west across the desert and state line, picking up the Southern Pacific mainline at Indio, California, and I-10 overlies the old roads most of that distance.
West of Phoenix
Moving east from the California line at Ehrenberg, I-10 follows the old route of US 60/US 70 for the first east from Blythe, California. In 1960, this westernmost stretch of I-10 was built from near the Colorado River east to the future spot where the "Brenda Cutoff" section of I-10 would connect a decade later. Until the early 1970s, this was the last freeway stretch until Phoenix. The "Brenda Cutoff" was named for a gas station on the old road just east of the fork where US 60 now terminates at I-10. Now an obscure name, "Brenda Cutoff" was the working title that the Arizona Highway Department called the stretch of freeway from US 60 to near Buckeye. The Brenda Cutoff paralleled old sand roads used in the 1920s for Phoenix-Los Angeles traffic, but mostly abandoned after US 60/US 70 was built to the north, through Wickenburg.
The Brenda Cutoff's opening on June 18, 1973 was eagerly awaited and was a big deal in newspapers in Phoenix and Los Angeles. It saved motorists from having to drive through Glendale, Sun City, Wickenburg and Salome, about out of the way, and it eliminated about of two-lane highway. But the freeway was opened only as far east as Tonopah, and heavy traffic was routed down narrow county roads through the desert and fields between Tonopah and Buckeye. In addition, there was only one very-small gas station on the very-long route between Buckeye and Quartzsite, on the old county road at the tiny crossroads of Palo Verde. Signs warning "No Services Next 106 Miles" were posted at either end of the Brenda Cutoff those first few years.
The freeway was extended past Tonopah as far east as Phoenix's western fringes (at Cotton Lane) in about 1974. I-10's freeway section ended in Goodyear until the controversial Papago Freeway was finished across the western Valley of the Sun in 1990. During the "west valley gap" years, westbound I-10 traffic was routed off the Maricopa Freeway at 19th Avenue in Phoenix, and stayed on the access road as it curved past the Durango Curve. Los Angeles-bound traffic then turned left on Buckeye Road and followed the "TO 10" signs down Buckeye Road (first marked US 80 until 1977, then SR 85) for nearly 15 years.
Phoenix metropolitan area The interstate's route through Phoenix was hotly contested in the 1960s, 1970s, and early 1980s. A plan proposed by the Arizona Department of Transportation involved monstrous block-sized 270-degree "helicoil" interchanges at Third Avenue and Third Street that would connect motorists to freeway lanes in the air, but voters killed it in 1973 as a result of opposition from the Arizona Republic newspaper and a growing nationwide anti-freeway sentiment. Voters on election day were treated to a photo depiction on the front page of the newspaper that in later years was shown to have drastically overstated the freeway's height, but there is no question the proposed viaducts and helicoils would have been a visual gash across central Phoenix.
Beginning in 1961, a stub of what is now the Inner Loop portion of I‑10 was built northward from the Maricopa Freeway (then I‑10) along 20th Street, ending north at Buckeye Road. This stub was originally designated I-510. The Inner Loop name was given to it in 1969, at which time the highway changed numbers, to I-410. The I-10/I-510 interchange was the first multilevel interchange in Arizona and lasted until the Inner Loop was built as a real freeway in the 1980s. This putative freeway was two lanes in each direction and would have been hopelessly inadequate as a leg of the Inner Loop as it was intended.
After 1973, Arizona engineers favored a more-modest plan to link I-10 with I‑17 at the "Durango Curve" near 19th Avenue at Buckeye Road, and avoid the "Moreland Corridor" alignment of the Papago Freeway by adopting a route south of Buckeye Road. In 1983, ADOT unveiled the current below grade plans on Moreland Street, three blocks south of McDowell Road. Despite some local opposition, I-10 was finally completed in central Phoenix on the Inner Loop alignment, north of Van Buren Street, on August 10, 1990. The state is now considering a reliever freeway in West Phoenix, parallel to I-10 on the old Durango Street corridor, and was originally designated as Route 801, which has since been changed to SR 30.
The original 1962 alignment of I-10 through Phoenix was on the Black Canyon and Maricopa Freeways, now signed as I-17 and US 60, starting at about Grand Avenue. From 1962 to 1974, I‑10 in Phoenix ended at 40th Street, and truck traffic through Phoenix and Mesa was directed to use Arizona Route T-69 via 40th Street south and Baseline Road east to connect to SR 87 and SR 93, the shortcuts to Tucson. The I-10 signs were moved from the Maricopa Freeway to the Papago Freeway/Inner Loop alignments when it opened in 1990—the last gap of I-10 to be completed between Santa Monica and Jacksonville. This was the only time in Arizona where the posted freeway was moved from one road to another: the state never posted interstate signs on older state or U.S. highways. ADOT instead made frequent use of interstate shields with the word "TO" above and arrows below the shield.
For several years in the early 1970s, an orphan section of I-10 was opened between Baseline Road and Williams Field Road (now Chandler Boulevard) but was not marked as any highway, nor was it connected to the rest of the Interstate Highway System. ADOT, it seems, did not want to divert trucks down from T-69 in Guadalupe down into the cotton fields west of Chandler. This section got its interstate signs when the freeway south to Tucson was completed in about 1970, and the "Broadway Curve" was connected a year or so later—for almost two years, I-10 traffic used Baseline Road and 40th Street through the Japanese flower gardens until the last link between Tucson and Phoenix opened in about 1972.