49 CFR § 393.91
Buses, aisle seats prohibited
November 18, 2020
No bus shall be equipped with aisle seats unless such seats are so designed and installed as to automatically fold and leave a clear aisle when they are unoccupied. No bus shall be operated if any seat therein is not securely fastened to the vehicle.
[53 FR 49402, Dec. 7, 1988]