This study examined deterioration of reflective sign sheeting in New York State, and assessed the effectiveness of sign washing and clear-coating for restoring or preserving reflectivity of enclosed-lens engineer-grade sheeting. Generally, little benefit was achieved by washing all signs in the fall. However, changes in sign brightness, as measured by a retroreflectometer, indicate that significant brightness loss may occur during winter due to dirt accumulation, but that most signs recover after spring rains. Those few that do not recover are readily identified by daytime visual inspection, and would be the best candidates for washing. A large portion of these chronically dirty signs are located along high-volume highways, close to the pavement, and in industrial areas. The practice of clear-coating could not be shown to help maintain sheeting brightness. In fact, for the small sample included in this study, it had a detrimental effect. Candidates for replacement can be determined by a nighttime visual inspection. Daytime cosmetic appearance alone should not determine need for replacement, because signs with cracked or otherwise deteriorated sheeting may still provide adequate night visibility. Average sheeting life could not be determined in this study because no records were available of signs that had been replaced. An examination of those still in service determined that service lives of 15 years in New York State are not unusual for enclosed lens sheeting. Sign replacement rates reported by maintenance engineers confirm that engineer-grade sheeting may retain adequate reflectivity for 15 years or more.
Abstract