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The Basics of Traffic Sign Reflectivity

Traffic sign reflectivity is essential to public safety.  Fortunately, a great deal of research has been done on this topic in recent years.  As a result, officials have an excellent understanding of the level of retroreflectivity that public signage requires.  The following is a basic introduction to the topic.  Additional information is available in the Manual of Uniform Traffic Control Devices (MUTCD).


On the most basic level, traffic reflectivity for signage can be achieved using one of two means:

1.      Adding reflector buttons or similar items to a sign’s surface.  These can be used to line a worded message, a symbol, or the border of the sign itself.

2.      Using a sign made with a reflective material over which a smooth, transparent, and protective outer surface has been applied.

Both methods are commonly used because MUTCD standards simply specify that roadway signs must be able to reflect light from oncoming headlights since street or highway lighting by itself is insufficient to illuminate important signage.


Measuring Traffic Reflectivity

Officials can measure retroreflectivity with a device known as a retroreflectometerThese are available from specialty manufacturers and dealers.  Instead of using a retroreflectometer, however, officials may also judge traffic reflectivity visually.  This method is described below.


Ensuring Adequate Traffic Reflectivity

Retroreflectivity declines over time due to factors such as sunlight exposure, weather-related wear, and dust accumulation.  This requires officials to routinely inspect and/or replace signs according to established guidelines.  Some options for ensuring adequate traffic reflectivity include the following:

·         Nighttime inspections – trained inspectors can measure traffic reflectivity after dark using the headlights of a moving vehicle as a reference point.  If the inspector judges that the sign no longer has minimal retroreflectivity, he or she can authorize its replacement.

·         Average sign life – with this method, officials log the dates on which new signs are installed.  When the expected life of their reflectivity has expired, crews replace the signs automatically.  Different areas use different methods to gauge how long a sign will maintain adequate retroreflectivity. 

·         Blanket sign replacement – this method is the simplest, but often most expensive, of all.  Crews simply replace all the signs in a given geographical area at specified times.  This is scheduled so that no sign will exceed the expected traffic reflectivity lifespan.

·         Control signs – with this method, a certain percentage of the total signs in an area are designated as “control signs” and are inspected on a regular basis to ensure adequate traffic reflectivity.  When they fall below the accepted standard, both they and all other signs in a given zone are replaced.  While this saves on the costs associated with inspection or blanket replacement, its effectiveness depends on the control signs accurately representing the retroreflectivity of all signage in the area.


Traffic Reflectivity and Budget Realities

In an ideal world where costs were not an issue, ensuring adequate sign retroreflectivity would be a simple matter.  However, budgets in the real world are limited, resources can be scarce, and public officials must juggle their responsibilities based on ever-shifting priorities.  This is as true of ensuring traffic sign reflectivity as of any other important public safety matter.


These problems can be mitigated somewhat by understanding what types of signs can be safely exempted from traffic reflectivity inspections.  The MUTCD specifically allows exemptions in the following cases:

·         Signs that designate stopping, standing, and parking zones.

·         Any signs with blue or brown backgrounds.

·         Signs meant to designate walking, crossing, or hitchhiking zones.

·         Signs meant for the exclusive use of pedestrians or bicycle riders.

·         Signs intended to mark points of historic interest or acknowledge groups or individuals.



Ensuring adequate traffic sign reflectivity is essential for public safety.  In an era of tight budgets and overworked personnel, doing so will require ever more vigilance and good judgment on the part of safety officials.  Given the potentially serious consequences of ignoring this important work, however, it is a task that we dare not overlook.