A broken rear windscreen is not considered a major issue in terms of visibility for the driver, but it may still be considered a safety hazard if it shatters while driving, potentially causing injury to occupants or other road users.

While specific statutes vary by country and state, the core requirement is and roadworthiness . Reddit·r/drivingUK

Driving with a broken rear windscreen is generally legal as long as your vehicle has two functional side mirrors to provide a clear view of the road behind you . However, there are significant regional variations and safety risks—such as carbon monoxide poisoning—that can turn a "legal" drive into a citable offense. Regional Legal Overviews