(a) The commission may not raise a service standard applicable to the provision of local exchange telephone service by an electing company if the increased investment required to comply with the raised standard in any year exceeds 10 percent of the company's average annual intrastate additions in capital investment for the most recent five-year period.
(b) In computing the average under Subsection (a), the company shall exclude:
(1) extraordinary investments made during the five-year period; and
(2) investments required by Section 58.203.