HRS §291C-82
Turning around to go the opposite direction
This law limits where you can turn your vehicle around to go the opposite direction (a U-turn). You cannot do it on a curve or near a hilltop if oncoming drivers can't see you from far away. Officials can also ban U-turns in other dangerous spots and must post signs.
everyone
The statute, as written — Turning so as to proceed in the opposite direction
(a) No vehicle shall be turned so as to proceed in the opposite direction upon any curve, or upon the approach to or near the crest of a grade, where such vehicle cannot be seen by the driver of any other vehicle approaching from either direction within five hundred feet. (b) In addition to the prohibition in subsection (a), the director of transportation is authorized to and the counties may by ordinance with respect to highways under their respective jurisdictions prohibit the turning of any vehicle so as to proceed in the opposite direction on the highway at any location where such turning would be dangerous to those using the highway or would unduly interfere with the free movement of traffic. (c) The director of transportation and the counties by ordinance with respect to the highways under their respective jurisdictions shall place signs which are clearly visible to an ordinarily observant person prohibiting the turning of a vehicle to proceed in the opposite direction. The signs shall be official signs and no person shall turn any vehicle in violation of the restrictions stated on such signs.
LawTrove is not legal advice. The summary above is a computer-generated restatement — the authoritative text is the official version linked above.