A. The governing bodies of counties, cities, and towns may adopt ordinances not in conflict with the provisions of this title to regulate the operation of vehicles on the highways in such counties, cities, and towns. They may also repeal, amend, or modify such ordinances and may erect appropriate signs or markers on the highway showing the general regulations applicable to the operation of vehicles on such highways. The governing body of any county, city, or town may by ordinance, or may by ordinance authorize its chief administrative officer to:
1. Increase or decrease the speed limit within its boundaries, provided such increase or decrease in speed shall be based upon an engineering and traffic investigation by such county, city or town and provided such speed area or zone is clearly indicated by markers or signs;
2. Authorize the city or town manager or such officer thereof as it may designate, to reduce for a temporary period not to exceed 60 days, without such engineering and traffic investigation, the speed limit on any portion of any highway of the city or town on which work is being done or where the highway is under construction or repair;
3. Require vehicles to come to a full stop or yield the right-of-way at a street intersection if one or more of the intersecting streets has been designated as a part of the primary state highway system in a town that has a population of less than 3,500;
4. Reduce the speed limit to less than 25 miles per hour, but not less than 15 miles per hour, on any highway, including those in the state highway system, within its boundaries that is located in a business district or residence district for which the existing posted speed limit is 25 miles per hour, and restore a speed limit that had been reduced pursuant to this subdivision to the speed limit that had been previously posted at that location, provided that such reduced or restored speed limit is indicated by lawfully placed signs. At least 30 days prior to changing a speed limit on any highway in the state highway system pursuant to this subdivision, the governing body shall provide written notice of the change to the Commissioner of Highways. If any provision of this subdivision is inconsistent with the provisions of § 33.2-310, 33.2-317, 33.2-326, or 46.2-878, this subdivision shall be controlling.
B. No such ordinance shall be violated if at the time of the alleged violation the sign or marker placed in conformity with this section is missing, substantially defaced, or obscured so that an ordinarily observant person under the same circumstances would not be aware of the existence of the ordinance.
C. No governing body of a county, city, or town may (i) provide penalties for violating a provision of an ordinance adopted pursuant to this section that is greater than the penalty imposed for a similar offense under the provisions of this title or (ii) provide that a violation of a provision of an ordinance adopted pursuant to this section is cause for a stop or arrest of a driver when such a stop or arrest is prohibited for a similar offense under the provisions of this title.
D. No county whose roads are under the jurisdiction of the Department of Transportation shall designate, in terms of distance from a school, the placement of flashing warning lights unless the authority to do so has been expressly delegated to such county by the Department of Transportation, in its discretion.
E. No law-enforcement officer shall stop a motor vehicle for a violation of a local ordinance relating to the ownership or maintenance of a motor vehicle unless such violation is a jailable offense. No evidence discovered or obtained as the result of a stop in violation of this subsection, including evidence discovered or obtained with the operator’s consent, shall be admissible in any trial, hearing, or other proceeding.