41 C.F.R. § 301-10.420
Use of taxi, TNC, innovative mobility technology company, shuttle service, or other courtesy transportation
When authorized and approved by the agency, employee transportation expenses in the performance of official travel are reimbursable for the usual fare plus a tip which the agency determines to be reasonable for use of a taxi, TNC, innovative mobility technology company, shuttle service, or other courtesy transportation (if charges result). When selecting a TNC, first consideration should be given to the General Services Administration's Ridehail/Rideshare program.