A physician traveling in response to an emergency call shall be exempt from the provisions of Sections 22351 and 22352 if the vehicle so used by him displays an insigne approved by the department indicating that the vehicle is owned by a licensed physician. The provisions of this section do not relieve the driver of the vehicle from the duty to drive with due regard for the safety of all persons using the highway, nor protect the driver from the consequences of an arbitrary exercise of the privileges of this section.