If a Federal action would result in total direct and indirect emissions above the applicable thresholds which would be emitted beyond the time period covered by the SIP, the Federal agency can:

(a) Demonstrate conformity with the last emission budget in the SIP; or

(b) Request the State or Tribe to adopt an emissions budget for the action for inclusion in the SIP. The State or Tribe must submit a SIP or TIP revision to EPA within 18 months either including the emissions in the existing SIP or establishing an enforceable commitment to include the emissions in future SIP revisions based on the latest planning assumptions at the time of the SIP revision. No such commitment by a State or Tribe shall restrict a State's or Tribe's ability to require RACT, RACM or any other control measures within the State's or Tribe's authority to ensure timely attainment of the NAAQS.