Retroreflectivity: The Basics 
Traffic signs provide important information to drivers at all times, day and night. In order to appear bright to drivers at night, signs need to be either directly illuminated, or have retroreflective surfaces so that the light striking them from the vehicle headlights is reflected back to the driver's eyes. To be effective, their visibility must be maintained. 

The 2009 MUTCD establishes minimum retroreflectivity levels that must be maintained for all traffic signs, including those on public property. The FHWA has proposed assessment and management methods that agencies can use to maintain traffic sign retroreflectivity at or above the minimum levels. The FHWA believes that this proposed change will promote safety while providing flexibility for agencies to choose a maintenance method that best matches their specific conditions.

Maintenance Options
Agencies are required to establish and implement a sign assessment or management method to maintain minimum levels of sign retroreflectivity. Assessment methods require evaluation of individual signs within an agency's jurisdiction. Management methods provide an agency with the ability to maintain sign retroreflectivity without having to assess individual signs. The FHWA has suggested five options for maintenance.

1. Visual Assessment: Nighttime Inspection 
The inspector assesses the visibility and retroreflectivity of the traffic signs as he or she approaches the signs. Signs need to replaced if they do not meet the comparison defined in the appropriate procedure. Calibration signs, comparison panels, or consistent parameters may be used. 

2. Measured Sign Retroreflectivity 
The retroreflectivity of a sign is measured and directly compared to the minimum level appropriate to that sign. A sign needs to be replaced if the average retroreflectivity value is less than the appropriate minimum level. 

3. Expected Sign Life
Individual signs are replaced before they reach the end of their expected service life. To do this, an agency will need to know the expected service life required for the retroreflective material to degrade to the minimum retroreflective levels, and will need a method of identifying the age of individual signs. Date Stickers are a great way to keep track of installation dates.

4. Blanket Replacement 
An agency replaces all the signs in an area/corridor, or of a given type, at specified intervals. An agency that uses this method does not need to track the age or assess the retroreflectivity of individual signs. 

5. Control Signs 
A control sample of signs is used to represent the total population of an agency's signs. The retroreflectivity of the control sign is monitored at appropriate intervals and sign replacement is based on the performance of the control signs. Agencies can choose to use either an assessment method or a management method or a combination of the two.

Have more questions about Retroreflectivity? Check out our blog post here.

The information in this blog post originated from the U.S. Department of Transportation Federal Highway Administration publication; "Know Your Retro 2007: New MUTCD Sign Retroreflectivity Requirements" and the ATSSA pamphlet "New National Requirements for Maintaining Traffic Sign Retroreflectivity."