When a project of a department, municipality, county, or authority to construct or improve a public road or airport does not exceed $100 million in costs, such project shall not constitute a proposed governmental action which may significantly adversely affect the quality of the environment and the requirements of this article shall not be applicable, except that an environmental evaluation shall be considered in the decision-making process, consistent with paragraph (3) of Code
Section 12-16-2, when it is probable to expect significant adverse impact on historical sites or buildings and cultural resources.