Original construction Loop 101 was a part of the 1985 Maricopa County Regional Transportation Plan that was funded by a sales tax approved by Maricopa County voters that year. The freeway was originally assigned two different route numbers along its path: The Agua Fria Freeway portion was initially designated as SR 417, and the Pima/Price Freeway portion was initially designated as SR 117. The Loop 101 designation was first assigned on December 18, 1987, at which time the South Mountain Freeway and the portion of the San Tan Freeway between I-10 and Price Road were also designated to be part of Loop 101. On July 19, 1991, the proposed South Mountain Freeway was renumbered as part of Loop 202. The San Tan Freeway portion of Loop 101 was only officially renumbered when its opening took place. Loop 101 was built in stages from 1986 to 2002. The first segment of Loop 101 opened in November 1988, consisting of the two-mile stretch from Peoria Avenue to
Northern Avenue in Peoria. There had been much criticism of the program since its inception, and it ended in 2010.
Recent improvements Due to booming population growth in Phoenix's suburbs along the route of the freeway, the initial build-out of three general purpose lanes and one auxiliary lane proved to be inefficient, and therefore, the route has undergone many widening projects to accommodate the growth in the region. First, between 2007 and 2011,
HOV lanes were constructed along the entire route in different phases. It included construction of direct HOV ramps between Loop 101 east and SR 51 south in Northern Phoenix and Loop 101 north and Loop 202 east (Santan Freeway) in Chandler. The final phase, the Maryland Avenue HOV interchange in Glendale began construction in October 2013 and was completed in March 2014. Due to the nature of the project, the HOV lanes near the exit had to widened for extra lane width. Following the completion of the phased HOV-lane project, a phased project was launched to add a fourth-general purpose lane in both directions. As of 2025, the section of the freeway from Indian School Road to 75th Avenue, is the only section remaining to not yet at least release final design plans on its fourth lane.
Phased fourth-lane construction In August of 2014, construction began for the 11-mile segment from Shea Boulevard to Loop 202 in Scottsdale. Construction was completed in October of 2016. In February of 2019, construction began for the 13-mile segment from I-17 to Pima Road in Scottsdale and northeast Phoenix. Construction was completed in January of 2022. In May of 2019, construction began for the 6.4-mile segment from Baseline Road to Loop 202 (Santan Freeway) in the East Valley. Construction was completed in August of 2020. Construction began in January of 2024 for the 4.5-mile segment from Shea Boulevard to Princess Drive/Pima Road. Construction was completed in January 2026. Construction began in September of 2024 for the six-mile segment from 75th Avenue to I-17 in the northwest valley. Construction is expected to be completed in early 2027. As a part of improvements made to the I-10 / Loop 101 interchange, the design report for the project shows the segment from I-10 to Indian School Road being widened. Construction is planned to begin in 2025 and be completed in 2027.
New exit The 64th Street interchange in northeast Phoenix opened in May 2015 after being built in 2008 during the initial build-out of the freeway. ==Future==