Phase 1 of the project opened June 30, 2023 and lies entirely outside of the Urban Honolulu census-designated place, linking East Kapolei (on the ʻEwa Plain) and Aloha Stadium.

The 18.9-mile (30.4 km), automated fixed-guideway line was planned, designed, and constructed by the Honolulu Authority for Rapid Transportation (HART), a semi-autonomous government agency.

Controversy over the rail line was the dominant issue for local politics in the late 2000s,[6] and culminated in a city charter amendment which left the final decision to a direct vote of the citizens of Oʻahu.

In 1966, then-mayor Neal S. Blaisdell suggested a rail line as a solution to alleviate traffic problems in Honolulu, stating, "Taken in the mass, the automobile is a noxious mechanism whose destiny in workaday urban use is to frustrate man and make dead certain that he approaches his daily occupation unhappy and inefficient.

"[4] Frank Fasi was elected to office in 1968, and started planning studies for a rail project,[11] named Honolulu Area Rapid Transit (HART), in 1977.

[13][14][15] Fasi defeated Anderson in their 1984 rematch and restarted the HART project in 1986,[16] but this second effort was stopped in a 1992 vote by the Honolulu City Council against the necessary tax increase.

[19] The City and County of Honolulu Department of Transportation Services released the first formal study related to the HHCTCP on November 1, 2006, the Alternatives Analysis Report.

The DEIS indicated that impacts of the rail project would include land acquisition from private owners on the route, displacement of residents and businesses, aesthetic concerns related to the elevated guideway, and noise from passing trains.

[23][24] The anti-rail advocacy group Stop Rail Now criticized the report for not further discussing bus rapid transit and toll lanes, options studied earlier by the city in its Alternatives Analysis.

Three construction projects in the area since 2002 have each encountered unforeseen human remains that led to delays, and archaeologist Thomas Dye stated, "The council is absolutely right that you should expect to find burials on Halekauwila Street".

[30] In response to the Burial Council's concerns, the city agreed to begin conducting an archaeological survey of the area in 2010, two years earlier than originally planned.

[31] The city's decision to conduct the archaeological survey in phases subsequently led to a lawsuit filed on February 1, 2011, by the Native Hawaiian Legal Corporation on behalf of cultural practitioner Paulette Kaleikini.

[10] The suit was initially dismissed on March 23, 2011, after Circuit Court Judge Gary Chang ruled that state and federal laws allow the archaeological surveys to be conducted in phases.

Prevedouros, on the other hand, opposed any type of mass-transit project, favoring construction of a reversible tollway over the H-1, similar to the Managed Lane option which the Alternatives Analysis studied and rejected as unworkable, and reworking existing road systems to ease congestion.

Honolulu City Council Member Charles Djou, former mayor Peter Carlisle, and incumbent Kirk Caldwell all ran with the stated goal of finishing rail.

[51] In January 2010, Republican Governor Linda Lingle publicly recommended that the city alter plans for the rail line after news reports on FTA documents where the federal agency raised issues over declining tax revenues in connection with a global economic recession,[52] and commissioned a study by the state to review the project's finances in March.

[67][68] In November 2021, Roger Morton, director of Honolulu's Department of Transportation Services, stated that a required three months of field testing and certification (to be carried out by Hitachi) was scheduled to begin in January 2022.

[70] Due to the lack of local companies able to complete the work, the state's Department of Commerce and Consumer Affairs granted HART an exemption allowing mainland contractors to be hired.

After major cost overruns, the tax surcharges were extended in 2016 by five years to raise another $1.2 billion; however that additional funding was only sufficient for construction out to Middle Street in Kalihi.

[82][83][84] The tax increase legislation passed in 2017 also requires the State auditor carry out an audit of the project's accounts[85] and to consider alternatives for completing the system.

[88] The following May and upon prompting by the city, the Hawaii State Legislature passed a bill (Act 247) to allow counties a one-half percent increase in the Hawaiʻi General Excise Tax (GET), from 4% to 4.5%, to fund transportation projects.

[90] The Legislature considered a bill in the 2009 legislative session that would have redirected income from the half-percent increase back to the state to offset a $1.8 billion projected shortfall in the following three fiscal years.

[97][98][99][100] The bill was opposed by Mayor Hannemann and other city leaders who believed that redirecting the money would jeopardize federal funding for the project,[101] and was eventually dropped after U.S.

An alternative "Plan B" to build only 14 stations within the already funded $6.5 billion budget, was ruled out because of lower ridership, legal risks, insufficient contingency and other reasons.

[116] An estimate released in November 2020 put the total cost of the project's construction and financing at $11 billion, and pushed back its expected completion date to 2033, with delays due to the COVID-19 pandemic and utility relocation work.

[120] Skyline consists of an almost entirely elevated rapid transit line from the eastern edge of Kapolei, near the University of Hawaiʻi–West Oʻahu campus, to the Hawaii Capital Historic District, with a future expansion planned to Ala Moana Center (east of downtown Honolulu).

[144] The second phase of the route to be completed will be the 5.1 mi (8.2 km) Airport section east from Aloha Stadium to Middle Street (the site of Kalihi Transit Center, an existing major bus transfer point).

[148] Originally, the line was to fork near Aloha Stadium into two routes, one passing further south via Honolulu International Airport, and the other through Salt Lake, before reuniting at Middle Street in Kalihi.

[170][171] Kūkuluaeʻo (Kakaʻako) and Kālia (Ala Moana Center) stations were included in the original plan for Skyline but had to be eliminated from the initial phases of construction due to a severe funding shortfall.

[173][133][174] Past Kālia (Ala Moana), the alignment travels to a station at the Hawaii Convention Center, then splits into two branches – one to the University of Hawaiʻi at Mānoa campus and the other to Waikīkī on Kuhio Avenue.