(a) General rule.--Except as provided in subsections (b) and (c), this act shall preempt and supersede a local ordinance or rule concerning the subject matter of this act.

(b) Exception.--A local ordinance or rule concerning the subject matter of this act that has been adopted by a county of the first or second class shall remain in full force and effect to the extent that the local ordinance or rule is more restrictive than the requirements of this act if the local ordinance or rule was in effect prior to January 1, 2007, and it has not been amended, suspended or rendered invalid, in whole or in part, by a court decision.

(c) Procedure.--A county, city, town, township, borough or local air pollution control authority with idling regulations in existence before the effective date of this act may approve idling time limits for buses in excess of the time limits in this act if the approval applies only to the warm-up of buses outdoors at a bus depot when the temperature is below 40 degrees and the approval is designed to minimize idling.

(d) Department.--This act shall not prevent the department from regulating emissions from idling of motor vehicles, as appropriate, under the act of January 8, 1960 (1959 P.L. 2119, No. 787),¹ known as the Air Pollution Control Act.