(a) All members of the Arkansas State Highway Employees' Retirement System shall be assessed six percent (6%) of their salaries and wages by payroll deductions, and the Executive Secretary of the Board of Trustees of the Arkansas State Highway Employees' Retirement System shall transmit the payroll deductions from the employees' salaries and wages to the bank designated as the depository for the funds of the system or to the Treasurer of State, as appropriate.

(b) (1) (A) As a means of increasing his or her annual annuity benefits, a member may elect, upon approval by the Board of Trustees of the Arkansas State Highway Employees' Retirement System, to pay into the Arkansas State Highway Employees' Retirement System Fund to the credit of his or her account an amount equal to four percent (4%) of his or her earnings for each year of his or her authenticated prior and current service not covered, plus such interest as the board may prescribe.

(B) Each year, or fractional part thereof, for which such prior and current service contributions are paid shall be added to the current service record of the member in computing his or her retirement benefits under the provisions of §§ 24-5-115 -- 24-5-118, subject to the provision that no member may accrue more than thirty-five (35) years of creditable service.

(2) (A) (i) As a means of increasing his or her annual annuity benefits, a member may elect, upon approval by the board, to pay into the fund to the credit of his or her account an amount equal to four percent (4%) of the amount that his or her earnings exceeded seven thousand five hundred dollars ($7,500) per annum for periods previously covered through June 30, 1969, plus such interest as the board may prescribe.

(ii) These earnings in excess of seven thousand five hundred dollars ($7,500) per annum on which supplemental contributions have been paid shall be credited to his or her average compensation in his or her service record in computing his or her retirement benefits under the provisions of §§ 24-5-115 -- 24-5-118.

(B) The plan for such payment shall be as prescribed by the board.

(c) It is expressly guaranteed that all member contributions shall be held in trust for the exclusive benefit of the individual contributor.