(a) In this section, "electronic sign" means a sign that changes its message or copy by programmable electronic or mechanical processes.
(b) The department, in regulating outdoor advertising located in the corporate boundaries of a municipality with a population of more than 200,000 located in a county on the Texas-Mexico border with a population of less than 300,000, may not require an electronic sign owned by the municipality to be more than 500 feet from another sign.