Keeping the signs (especially regulatory and warning signs) clearly visible and unobscured by vegetation, snow, parked vehicles and other obstructions is an extremely important maintenance task.

Tree foliage, grass, and weeds are the most common obstructions to sign visibility on rural highways. When visibility cannot be maintained with normal right-of-way mowing operations, special mowing operations, trimming, or vegetation control with appropriate herbicides should be initiated. This should also include removing the growth obscuring STOP (R1‑1) and YIELD (R1‑2) signs on approach roads within the highway right-of-way.

Vegetative growth beyond the right-of-way that may obscure STOP (R1‑1) and YIELD (R1‑2) signs on approach roads should be called to the attention of the local authorities. These clearings should be of such width and length as to furnish maximum sign visibility to approaching traffic.