Final answer:
The railroad advance warning sign is round and alerts drivers about an upcoming railroad crossing.
Step-by-step explanation:
The standard size for railroad advance signs is 36" x 36" for all roadways. This sign features two "R" symbols to signify the upcoming railroad along with an "X" to symbolize the crossing. The highly reflective yellow background allows for excellent day and night visibility.
The railroad advance warning sign is round. This sign serves as a notification to drivers that they are approaching a railroad crossing. It is usually yellow with a black X and the letters R R, signifying 'railroad.' Its round shape is designed to alert drivers of the upcoming crossing well in advance, so that they can slow down and proceed with caution.