(a) Each county, municipality, college, and university using speed detection devices shall erect signs on every highway which comprises a part of the state highway system at that point on the highway which intersects the corporate limits of the municipality, the county boundary, or the boundary of the college or university campus. Such signs shall be at least 30 by 30 inches in area and shall warn approaching motorists that speed detection devices are being employed. No such devices shall be used within 500 feet of any such warning sign erected pursuant to this subsection.

(b) In addition to the signs required under subsection (a) of this Code section, each county, municipality, college, and university using speed detection devices shall erect speed limit warning signs on every highway which comprises a part of the state highway system at that point on the highway which intersects the corporate limits of the municipality, the county boundary, or the boundary of the college or university campus. Such signs shall be at least 30 by 30 inches in area, shall warn approaching motorists of changes in the speed limit, shall be visible plainly from every lane of traffic, shall be viewable in any traffic conditions, and shall not be placed in such a manner that the view of such sign is subject to being obstructed by any other vehicle on such highway. No such devices shall be used within 500 feet of any such warning sign erected pursuant to this subsection.