18.—(1) The duration of concession contracts shall be limited.
(2) The contracting authority or utility shall estimate the duration on the basis of the works or services requested.
(3) For concession contracts lasting more than 5 years, the maximum duration of the concession contract shall not exceed the time that a concessionaire could reasonably be expected to take to recoup the investments made in operating the works or services together with a return on invested capital taking into account the investments required to achieve the specific contractual objectives.
(4) The investments taken into account for the purposes of the calculation of the time period referred to in paragraph (3) shall include both initial investments and investments during the life of the concession contract.