23 C.F.R. § 450.220
(a) At least every 4 years, the State shall submit an updated STIP concurrently to the FHWA and the FTA for joint approval. The State must also submit STIP amendments to the FHWA and the FTA for joint approval. At the time the entire proposed STIP or STIP amendments are submitted to the FHWA and the FTA for joint approval, the State shall certify that the transportation planning process is being carried out in accordance with all applicable requirements of:
(b) The FHWA and the FTA shall review the STIP or the amended STIP, and make a joint finding on the extent to which the STIP is based on a statewide transportation planning process that meets or substantially meets the requirements of 23 U.S.C. 134 and 135, 49 U.S.C. 5303 and 5304, and subparts A, B, and C of this part. Approval of the STIP by the FHWA and the FTA, in its entirety or in part, will be based upon the results of this joint finding.
(1) If the FHWA and the FTA determine that the STIP or amended STIP is based on a statewide transportation planning process that meets or substantially meets the requirements of 23 U.S.C. 135, 49 U.S.C. 5304, and this part, the FHWA and the FTA may jointly: