(a) Whenever local authorities within their respective jurisdictions determine upon the basis of an engineering and traffic investigation that the absolute speed permitted under this chapter is greater than is reasonable or safe under the conditions found to exist, such local authority, subject to subsection (c) of this section, shall determine and declare a reasonable and safe absolute speed limit, which shall be effective when appropriate signs giving notice thereof are erected.
(b) Local authorities in their respective jurisdictions may at their discretion, but subject to subsection (c) of this section, authorize by ordinance higher absolute speeds than those stated in this chapter upon through highways or upon highways or portions thereof where there are no intersections or between widely spaced intersections provided signs are erected giving notice of the authorized speed, but local authorities shall not modify or alter the basic rule set forth in § 4168(a) of this title.
(c) Alteration of absolute limits on state-maintained highways in any municipality by local authorities shall not be effective until such alteration has been approved by the Department of Transportation.