Police stopped a woman as she drove down a busy main road on her mobility scooter.
The woman was reported to police by another driver who spotted her on the A30 near Bodmin in Cornwall at about 14:00 BST, said officers.
A patrol crew stopped the woman who was driving on the side of the road.
A spokesman for the Devon and Cornwall force said she was not breaking the law, but was given "appropriate advice not to do it again".
The A30 is the main highway into and through Cornwall.