Answer :
Final answer:
In the U.S., the only round highway sign is the railroad advance warning sign, its purpose being to alert drivers of a railroad crossing ahead. It is the only round sign used on highways.
Explanation:
In the U.S., the only round highway sign is indeed the railroad advance warning sign. This sign is characterized by its round shape, a yellow background, and a black image of a railroad crossing. The purpose of this sign is to alert drivers that there is a railroad crossing ahead, prompting them to slow down and prepare to stop if necessary. It is the only round sign used on highways, making it easily recognizable among other warning signs. It's very important for drivers to understand and recognize this sign for safety reasons on the roads.
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