41 CFR § 302-4.205
If my spouse or domestic partner and I travel on the same days along the same general route by using more than one POV, is my spouse or domestic partner considered unaccompanied?
June 9, 2020
No; for per diem purposes, you and your spouse or domestic partner are considered to be traveling together if you travel on the same days along the same general route by using more than one POV.
[FTR Amdt. 98, 66 FR 58196, Nov. 20, 2001, as amended by FTR Amdt. 2010-06, 75 FR 67631, Nov. 3, 2010]