Final answer:
Backing up is not allowed on highways or interstate roads unless the driver of an emergency vehicle must do so while doing their job.
Step-by-step explanation:
Backing up is not allowed on highways or interstate roads unless the driver of an emergency vehicle must do so while doing their job. This is because backing up on these types of roads can be dangerous and cause accidents. Emergency vehicles may need to back up in certain situations to reach their destination or to ensure the safety of others.