Final answer:
A white, rectangular sign with black lettering marked 'ROAD CLOSED' indicates that the road is completely closed to all traffic. It is crucial for drivers to obey this sign and seek alternative routes.
Step-by-step explanation:
A white, rectangular sign with black lettering saying "ROAD CLOSED" is telling drivers that the road is completely inaccessible to all vehicles. It does not indicate that the road is only closed during certain hours or that only certain types of vehicles are restricted. Instead, it clearly states that the road is not open to traffic under any circumstances. This could be due to construction, an accident, a natural disaster, or any other number of reasons. It's important for drivers to heed this sign and find an alternate route to reach their destination.