HRS §291C-127
No coasting downhill in neutral or with clutch out
This law says that when you drive a motor vehicle downhill, you must not let the car roll freely with the gear shift in neutral or with the clutch pressed down. You must keep the car in gear while going down a slope.
The statute, as written — Coasting prohibited
The driver of any motor vehicle when traveling upon a down grade shall not coast with the gears or transmission of the vehicle in neutral or with the clutch disengaged.
LawTrove is not legal advice. The summary above is a computer-generated restatement — the authoritative text is the official version linked above.