(a) At intersection. -- Whenever local authorities within their respective jurisdictions determine upon the basis of an engineering and traffic investigation that the speed permitted under this chapter at any intersection is greater than is reasonable or safe under the conditions found to exist at such intersection, such local authority subject to subsection (e) of this section shall determine and declare a reasonable and safe speed limit thereat, which shall be effective at all times or during hours of daylight or darkness or at such other times as may be determined when appropriate signs giving notice thereof are erected at such intersection or upon the approaches thereto.

(b) Authority to increase twenty-five mile limit. -- Local authorities in their respective jurisdictions may in their discretion, but subject to subsection (e) of this section, authorize by ordinance higher speeds than those stated in section one of this article upon through highways or upon highways or portions thereof where there are no intersections or between widely spaced intersections, which higher speed shall be effective at all times or during hours of daylight or at such other times as may be determined when signs are erected giving notice of the authorized speed, but local authorities shall not have authority to modify or alter the basic rule set forth in subsection (a), section one of this article or in any event to authorize by ordinance a speed in excess of fifty-five miles per hour.

(c) Authority to decrease fifty-five mile limit. -- Whenever local authorities within their respective jurisdictions determine upon the basis of an engineering and traffic investigation that the speed under this chapter upon open country highway outside a business or residence district is greater than is reasonable or safe under the conditions found to exist upon such street or highway, the local authority may determine and declare a reasonable and safe limit thereon but in no event less than thirty-five miles per hour and subject to subsection (e) of this section, which reduced limit shall be effective at all times or during hours of darkness or at other times as may be determined when appropriate signs giving notice thereof are erected upon such street or highway.

(d) Authority to decrease twenty-five mile limit. -- A municipality may in its discretion, but subject to subsection (e) of this section, authorize by ordinance lower speeds than those stated in subdivision (2), subsection (b), section one of this article upon local dedicated rights-of-way in a residential district or portions thereof, which lower speed shall be effective at all times or during hours of daylight or at such other times as may be determined when signs are erected giving notice of the authorized speed.

(e) Alteration of limits on state highways in municipalities. -- Alteration of limits on state highways or extensions thereof in a municipality by local authorities shall not be effective until such alteration has been approved by the commissioner of highways.