(a) Except where indicated clearly to the contrary by the context, the word "member" as used in this article shall mean any employee who first or again becomes a member of the Employees' Retirement System of Georgia on or after January 1, 2009. From and after January 1, 2009, every person first or again becoming an employee entitled to a new membership in the Employees' Retirement System of Georgia shall become a member subject to this article. Any provision of this chapter providing that a class of employees shall be subject to Code Section 47-2-334 shall be deemed to have been amended by this subsection.

(b) Membership under this article shall be optional for any persons who are within the membership of the Employees' Retirement System of Georgia on December 31, 2008. Any such persons may elect in writing on a form to be provided by the board of trustees to become a member subject to this article at any time on or after January 1, 2009. This written election shall become effective upon the approval of the application by the board of trustees as provided in rules and regulations promulgated by the board of trustees and shall be final and cannot be later changed or rescinded. Upon such election, a member shall be subject to all the provisions, terms, and conditions of this article; provided, however, that the calculation to determine retirement allowances for any person exercising such option shall be made as follows:

(1) The retirement allowance shall be computed fully as if all creditable service of the member were acquired and calculated under the provisions of this article;

(2) Then the retirement allowance shall also be computed fully as if all creditable service of the member were acquired and calculated under the provisions of this chapter contained other than in this article and the rules and regulations of the board of trustees;

(3) Then a benefit amount shall be determined based upon a fractional part of each retirement allowance computed in paragraphs (1) and (2) of this subsection, which fractional part shall be computed by using the actual years of creditable service established under either this article, for paragraph (1) of this subsection, or the provisions of this chapter contained other than in this article, for paragraph (2) of this subsection, which number of years shall be the numerator of the fraction, over the total actual years of creditable service established under both this article and the provisions of this chapter contained other than in this article, which number shall be the denominator of the fraction;

(4) The two benefit amounts so determined shall then be added together to produce the actual retirement allowance; and

(5) Projected years of service shall not be used in the computation of the retirement allowances under this subsection.