I’m making a train game, which has basically the same requirements.
Simplified I currently use Path3D with a RemoteTransform3D that points at a RigidBody3D.
The RigidBody3D is set to freeze = true and freeze_mode = FREEZE_MODE_STATIC. I manually calculate velocity and use that to update the progress along the Path3D.
To enable crashing I set the RigidBody3D to freeze = false and the RemoteTransform3D update_position = false. This let’s the physics engine take over and collide with everything.
This seems to be working pretty well so far.