(a) In lieu of the retirement on service allowance, a vested member who retires in accordance with § 45-21-16 may choose an optional form of retirement benefit known as the social security supplemental option.
(b) This option provides for the payment of a larger benefit before the attainment of age sixty-two (62) and a reduced benefit thereafter. The reduced amount is equal to the benefit before age sixty-two (62), including cost of living increases, reduced by the member's estimated social security benefit payable at age sixty-two (62). Benefits payable under this option before and after the attainment of age sixty-two (62) are actuarially determined to be equivalent to the lifetime service retirement allowance as determined in § 45-21-17.
(c) Election of this social security supplemental option is available only to those who elect the service retirement allowance set forth in § 45-21-17.