(1) Except when a special hazard exists that requires lower speed for compliance with section 60-6,185, the limits set forth in this section and sections 60-6,187, 60-6,188, 60-6,305, and 60-6,313 shall be the maximum lawful speeds unless reduced pursuant to subsection (2) of this section, and no person shall drive a vehicle on a highway at a speed in excess of such maximum limits:
(a) Twenty-five miles per hour in any residential district;
(b) Twenty miles per hour in any business district;
(c) Fifty miles per hour upon any highway that is gravel or not dustless surfaced;
(d) Fifty-five miles per hour upon any dustless-surfaced highway not a part of the state highway system;
(e) Sixty-five miles per hour upon any four-lane divided highway not a part of the state highway system;
(f) Sixty-five miles per hour upon any part of the state highway system other than an expressway, a super-two highway, or a freeway;
(g) Seventy miles per hour upon an expressway or a super-two highway that is part of the state highway system;
(h) Seventy miles per hour upon a freeway that is part of the state highway system but not part of the National System of Interstate and Defense Highways; and
(i) Seventy-five miles per hour upon the National System of Interstate and Defense Highways, except that the maximum speed limit shall be sixty-five miles per hour for:
(i) Any portion of the National System of Interstate and Defense Highways located in Douglas County; and
(ii) That portion of the National System of Interstate and Defense Highways designated as Interstate 180 in Lancaster County and Interstate 129 in Dakota County.
(2) The maximum speed limits established in subsection (1) of this section may be reduced by the Department of Transportation or by local authorities pursuant to section 60-6,188 or 60-6,190.
(3) The Department of Transportation and local authorities may erect and maintain suitable signs along highways under their respective jurisdictions in such number and at such locations as they deem necessary to give adequate notice of the speed limits established pursuant to subsection (1) or (2) of this section upon such highways.