Trailers have no friction.

[TachyonGMZ]

All trailers in version 0.45.2 are unable to decelerate when disconnected while moving. This happens when being moved by a player or a vehicle. They can only be stopped by a 2 high wall that the trailer can't get over or they keep moving indefinitely . Tested with forge 36.1.16 in mc version 1.16.5 without any other mods whatoever.

[TurklerRS]

can confirm this happens in the current latest version