For the purposes of this Act, the overall levy target amount for an eligible levy period is the sum of:
(a) the total amount paid by TUSMA on behalf of the Commonwealth during the period under contracts made under section 13; and
(b) the total amount paid by TUSMA on behalf of the Commonwealth during the period by way of grants made under section 13; and
(c) the total amount of TUSMA's administrative costs incurred during the period;
reduced by the total of the amounts appropriated by Appropriation Acts for the purposes of:
(d) making payments under section 13 contracts during the period; and
(e) making section 13 grants during the period; and
(f) the administrative costs of TUSMA in relation to the period.