Haw. Rev. Stat. § 101-7: Superior public use.

Property already appropriated to some public use may be taken by the State or a county in the manner and under the conditions provided by part III. An easement over, across or under property not owned by the State or a county and devoted to public use may be taken by any other person enjoying the right of eminent domain where such taking will not substantially impair the use for which the property has previously been appropriated.