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Methods for Gauging Traffic Sign Reflectivity

Safety officials can use a number of measures to judge traffic sign reflectivity.  These include assessment methods and management methods.

Assessment Methods for Gauging Traffic Sign Reflectivity

Assessment methods break down into two categories:

1.      Nighttime inspections.

2.      Use of a reflectometer.

Nighttime Inspections

With these methods, a human inspector gauges sign reflectivity.  The inspector should take the following steps to ensure accuracy:

·         Approach the sign at normal highway speeds.

·         Use low-beam headlights and minimal vehicle interior lighting.

·         Use adequate viewing distances to allow drivers time to respond to the sign.

Inspectors should use one of the following procedures to ensure the accuracy of visual inspections:

·         Viewing a calibration sign that is known to have minimum retroreflectivity levels.  This gives the inspector a gauge for judging traffic sign reflectivity.  To be effective, the inspectors should have access to calibration signs in multiple colors.  These signs should be stored between inspections to protect their retroreflectivity levels.  Officials should periodically verify the retroreflectivity of the calibration signs.

·         Using a comparison panel that is set at or above minimal retroreflectivity levels.  When an inspector feels that a particular sign’s reflectivity is suspect, then he or she should attach a comparison panel to the sign for a side-by-side comparison.

·         Using a car or truck built since the year 2000.  This is done to ensure traffic sign reflectivity when viewed from modern vehicles.

The traffic sign reflectivity inspector should be at least 60 years old; this will help to ensure that his or her vision is about the same as that of aging drivers.

Reflectometer Methods

A reflectometer is a device that measures sign retroreflectivity.  The MUTCD specifies the standard methods for using these devices.

Management Methods for Assuring Traffic Sign Reflectivity

These methods rely on replacing signs at regular intervals.  They fall into three categories: expected sign life, control signs, and blanket replacement.

1.      The expected sign life method replaces signage prior to the age at which retroreflectivity normally degrades below minimum levels.  Determining this time period can involve using sign warranties, measurements of example signs, or weather studies.  For this method to succeed, each sign must include a label marking its year of installation.

2.      The blanket replacement method changes out all signs in a given area based on estimated retroreflectivity levels.  This is one of the simplest methods to implement.  However, it can lead to premature sign replacement, making it financially wasteful.

3.      The control sign method judges traffic sign reflectivity for an entire area based on reflectivity levels of designated control signs.  Once the control sign’s retroreflectivity degrades sufficiently, officials replace all signs in the area.  Like the blanket replacement method, this option is simple to implement, but can also result in replacing signs prematurely.

Factors Affecting Traffic Sign Reflectivity

A number of factors affect how drivers perceive road signs, especially at night.  These include: driver age, headlight design, and vehicle size.

·         America’s population is aging.  Nearly 8,000 baby boomers turn 65 every day of the week. This trend is expected to continue for the foreseeable future.  The US population in 2020 will contain almost 56 million adults age 65 or older.  This number increases to 72 million by the year 2030.  Of these people, at least 80% are expected to continue driving.  This is important to public safety because as drivers age, their visual acuity, nighttime vision, and reaction speeds worsen.

·         Modern headlights are designed to reduce the amount of glare seen by opposing traffic.  This feature, though desirable, can negatively affect traffic sign reflectivity from the driver’s perspective.

·         Drivers of passenger cars are often less able to see an oncoming sign than owners of pickup trucks and SUVs.  This is a factor officials must consider when gauging traffic sign reflectivity.

For more information on traffic sign reflectivity or to purchase reflective signs, contact Impact Recovery.