State Implementation Plan (SIP)

The portion (or portions) of the implementation plan (as defined in section 302[q] of the CAA), or most recent revision thereof, which has been approved under section 110 of the CAA, or promulgated or approved under section 301(d) of the CAA and which implements the relevant requirements of the CAA. Although the SIP is produced by the state environmental agency (not the MPO) to monitor, control, maintain, and enforce compliance with the NAAQS, it must also be taken into account in the transportation planning process.