H-201 highlighted in red
|Auxiliary route of H-1|
|Maintained by HDOT|
|Length||4.10 mi  (6.60 km)|
|History||Signed in 2004|
|West end||Route 99 in Aiea|
|H-1 / H-3 in Hālawa|
|East end||H-1 in Honolulu|
Interstate H-201 (H-201) is the only auxiliary Interstate Highway located in the U.S. state of Hawaii, serving the island of O‘ahu. The H-201 designation is also known as the Moanalua Freeway. The 4.1-mile-long (6.6 km) loop route connects exits 13 and 19 on H-1, passing Fort Shafter, Tripler Army Medical Center, and Red Hill.
Despite being designated an Interstate in 1989, until mid-2004 the route was an unsigned Interstate, signed only as Route 78. The section of the Moanalua Freeway between Route 99 (Kamehameha Highway) and the western H-1 interchange remains designated as Route 78.
The length of H-201 was originally designated as Route 78. 
The Federal Highway Administration approved the addition of H-201 to the Interstate Highway System on November 1, 1989.  The Hawaii Department of Transportation (HDOT) asked that the Moanalua Freeway be reclassified as an Interstate so that the interchange with H-1 at the eastern end could conform to federal highway standards.[ citation needed] HDOT originally asked the American Association of State Highway and Transportation Officials (AASHTO) in June 1990 to approve the freeway as H-1A in an application to AASHTO's Special Committee on U.S. Route Numbering, the committee which approves Interstate Highway designations.  HDOT resubmitted a request later that year to number it as H-101, and AASHTO approved it as H-201 on December 8, 1990.  The highway was initially designated H-1A, but AASHTO policy does not generally allow alphabetic suffixes in Interstate numbers.  The final designation, H-201, conforms to the general rule for three-digit Interstate loop routes that uses an even initial digit. 
Until 2004, the state Department of Transportation chose not to sign H-201 as such, instead retaining the designation Route 78. Reasons given included the following:
- inability to render the new route number in a legible manner (because it has four characters, longer than the one to three characters of any other Interstate, it is necessary to use the thinnest font to render the number, and the shield is wider than the standard Interstate shield)
- encouraging motorists to use the newer and better designed H-1
- avoiding confusion with Interstate H-2 
In July 2004, in conjunction with a major resurfacing of both sides of the freeway, it was decided to bring the signage in line with the official designation. 
From east to west, H-201 starts after splitting from H-1 in Honolulu's Kalihi Kai neighborhood, spending most of its length as a six to eight-lane freeway, with a speed limit averaging 50 MPH. From this point it takes a gently curving path westward, interchanging with Funston Road to service Fort Shafter. Heading into the Monalua Gardens area, it serves as access to the eponymously named attraction, before interchanging with several more roads, coming to an end at Route 99.
|Length||0.739 mi (1.189 km)|
The entire route is in Honolulu County.
|Aiea||0.0||0.0||—||Route 99 west – Pearl City, Pearlridge||Continues as Route 99|
|Halawa||–||Stadium, Aiea||Westbound exit and eastbound entrance via Moanalua Road|
|0.5||0.80||1A||H-1 east – Honolulu International Airport, Pearl Harbor||No westbound exit|
|1C||H-1 west – Pearl City||No eastbound exit|
|0.9||1.4||1B||Halawa, Camp Smith, Stadium||Signed as exit 1E westbound; access via Kahuapaani Street|
|||1.4||2.3||1C||H-3 east – Kaneohe||Signed as exit 1D westbound; exit 1B on H-3|
|Honolulu||2.4||3.9||2||Moanalua Valley, Salt Lake, Red Hill||Access via Ala Kapuna and Ala Napunani Streets|
|3.7||6.0||3||Route 7310 (Puuloa Road) – Tripler Hospital, Airport|
|4.5||7.2||4||Ahua Street – Fort Shafter||No number designation on eastbound exit|
|4.6||7.4||—||H-1 east – Honolulu||Exit 19B on Interstate H-1|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi|
- Adderly, Kevin (December 31, 2014). "Table 2: Auxiliary Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways as of December 31, 2014". Route Log and Finder List. Federal Highway Administration. Retrieved June 8, 2015.
- Rand McNally (1989). "Hawaii" (Map). Rand McNally Road Atlas: United States/Canada/Mexico. Scale not given. Chicago: Rand McNally. p. 5. Oahu inset. OCLC 19224098. Retrieved September 9, 2007 – via Broer Map Library.
- Watanabe, June (July 27, 2004). "Kokua Line: Moanalua is actually part of interstate". Honolulu Star-Bulletin. Retrieved August 7, 2016.
- Special Committee on U.S. Route Numbering (June 4, 1990). "Report of the Special Committee on U.S. Route Numbering to the Executive Committee" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. Archived (PDF) from the original on October 16, 2017. Retrieved June 8, 2015.
- Special Committee on U.S. Route Numbering (December 8, 1990). "Report of the Special Committee on U.S. Route Numbering to the Executive Committee" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. Archived (PDF) from the original on October 16, 2017. Retrieved June 8, 2015.
- American Association of State Highway and Transportation Officials (January 2000) [Retained from August 10, 1973]. "HO2: Establishment of a Marking System of the Routes Comprising the National System of Interstate and Defense Highways" (PDF). AASHTO Transportation Policy Book. American Association of State Highway and Transportation Officials. Archived from the original (PDF) on January 1, 2014. Retrieved June 8, 2015.
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