Unless specifically defined in the TCAA or in the rules of the Texas Natural Resource Conservation Commission (commission), the terms used by the commission have the meanings commonly ascribed to them in the field of air pollution control. In addition to the terms which are defined by the TCAA, the following words and terms, when used in Subchapter G of this chapter (relating to Transportation Planning), shall have the following meanings, unless the context clearly indicates otherwise:(1) Implementing agency - An entity, transportation provider, organization, agency, or individual responsible for the design, procurement of funds, construction, operation, maintenance, management, monitoring, and, in conjunction with the metropolitan planning organization, compliance with transportation control measures.(2) Metropolitan Planning Organization - As defined under the Intermodal Surface Transportation Efficiency Act,