What does "sunken grade" on a road sign mean?

A sunken grade is a place where the road has literally sunk down, either into a sinkhole or because the underlying ground has shifted, according to MarieGale.com.

Sunken grades occur when the earth moves slowly beneath the road, creating a depression in the roadway.

The term "grade" is used in several different ways with respect to roads and highways. The "sub-grade" lies beneath a roadway and serves as a supporting base. "Grading" a road means to smooth out the roadbed using earth-moving equipment during the construction phase.

The grade of a highway is a measure of its incline or slope. The amount of grade indicates how much the highway is inclined from the horizontal. For more information, see Encyclopedia.com - Grades, Highway.

For a comprehensive listing of the most commonly used traffic signs in the United States, visit www.trafficsign.us and mutcd.fhwa.dot.gov.... Show More