Retroreflectivity! It's Important

Posted by Joanne Conrad on Feb 16, 2017 9:41:28 AM

As seen in the IMSA Journal, January/February 2017 Edition

As of late, I have received a number of calls asking about retroreflectivity.  No matter if you are a small town, large city or county, state DOT, federal lands or a site open to public travel, your agency must comply with the Manual on Uniform Traffic Control Devices (MUTCD) on retroreflectivity.

What is it? Where is it? How bright is it? Generally, it is not a part of any educational curriculum and is often acquired via on-the-job training. Your agency is now responsible to maintain sign retroreflectivity.

Retroreflectivity “It’s Required”

RetroreflectometerSection 2A.06 - Design of Signs 

The basis requirements of a sign are that it be legible to those for whom it is intended and that it be understandable in time to permit a proper response. Desirable attributes include:

  1. High visibility by day and night; and
  2. High legibility (adequately sized letters, symbols or arrows, and a short legend for quick comprehension by a road user approaching a sign).

Section 2A.07 – Retroreflectivity or Illumination:

Signs shall be retroreflective or illuminated to show the same shape and similar color by both day and night, unless specifically stated otherwise in the Manual. The requirements for sign illumination shall not be considered to be satisfied by street or highway lighting. The responsibility for the design, placement, operation, maintenance and uniformity of traffic control devices shall rest with the public agency or the official having jurisdiction.

Why is it required?

Simply for safety and accident prevention. Only about 20-to-25 percent of driving occurs at night but there are approximately three times as many accidents at night that account for 50 percent of traffic fatalities.

Some studies have shown that warning and regulatory signs are one of the most cost effective means of improving conditions — reducing the increase in crashes and improving driver awareness of hazards and driving conditions.

MUTCD Language

Section 2A.08- Maintaining Minimum Retroreflectivity

Support: 01; Retroreflectivity is one of several factors associated with maintaining nighttime sign visibility (see Section 2A.22).

Standard: 02; Public agencies or officials having jurisdiction shall use an assessment or management methods that is designed to maintain sign retroreflectivity at or above the minimum levels in Table 2A-3.


What is Retroreflectivity?

Retroreflectivity is measured by evaluating the amount of a premeasured value of light that returns to the source over a set measured distance; cd / lx / m2.

Coefficient of Retroreflection (or RA) RA = cd / lx / m2.

How does this translate?
Intensity of the light source: candela or cdI
Illuminance: the light falling on a unit area or lx
Lumiance: Intensity / unit area or cd / m2.

Methods of Maintaining Retroreflectivity

“…One or more of the following assessment or management methods should be used…“  You may also combine methods to suit your agency.

Assessment Methods

Assessment Method 1: Visual Assessment

“Calibrate” eyes with calibrations signs. Calibration signs are simple signs that are near the minimum acceptable RA. Signs are evaluated in comparison to these calibrations signs.

Compare minimum values with comparison panels. Panels are near desired retroreflectivity, they are clipped to the sign and viewed from a distance and you evaluate signs compared to the panels.

Evaluate signs using consistent parameters similar to those used to develop the minimum levels using an inspector — drivers over the age of 60, with an SUV type vehicle and cut-off headlamp.

Assessment Method 2: Measured by Sign Retroreflectivity

Retroreflectometer-Colors.jpgSigns read by use of a retrorefletometer and signs falling below the minimum levels in the MUTCD should be replaced.

This sample reading from a retroreflectometer indicates the brightness of a sign at different observation angles and only the .2 degrees reading is currently required. This value is the Retroreflectivity Coefficient or (RA) that was discussed earlier.

Taking Readings – Mean Calculation. The ASTM International standard accepted by the Federal Highway Administration (FHWA) requires that no less than four readings need to be taken for each retroreflective  color. To accomplish this, the “Mean Calculation” feature should be turned on through the menu or via the software connection of your device.

Reflective materials sometimes have gloss and sheen issues. Manual selection is an option for miss-identified colors.

Advantages of measured sign retroreflectivity are they provide the most direct means of monitoring the maintained retroreflectivity levels while removing subjectivity. You can record IDs (via bar codes and Radio-Frequency Identification tag systems) and Global Positioning System (GPS) locations recorded along with readings allowing quick identification of a sign within a quadrant.

Management Methods

Management Method 1: Expected Sign Life

When signs are installed the install date is labeled and recorded. Stickers should be placed on the front or back of the sign to show when fabricated or installed. When the sign reaches the expected life span or service life it is replaced regardless of condition. This is easy but may waste money by early replacement or result in signs past their expected life remaining in use.

All signs in an area or corridor, or of a given type, would be replaced at periodic intervals. This method eliminates the need to assess retroreflectivity of individual signs. To determine sign life you will need to build and use a weathering rack like the one shown using American Association of State Highway and Transportation Officials-National Transportation Product Evaluation Program (AASHTO-NTPEP) data and warranty information from the sheeting company and specify sign life. Measure existing signs with known install dates and compare to the minimum level. Use weathering data or a nearby jurisdiction’s weathering data.

Predicted sign age is provided in a warranty by sheeting manufacturers. Typical warranties apply to material integrity and do not always account for minimum retroreflectivity levels. Agencies could develop specifications with warranties based on a minimum retroreflectivity levels. Example: Warranty Type XI sheeting for xxx years in accordance with Table 2A-3 of the MUTCD and your performance data.

Advantages: This method requires that agencies track the installation date of their signs. Use a date sticker, bar code or computerized sign management system. Agencies can develop or copy local service life levels.

Disadvantages: It may be time consuming to inspect date stickers if the stickers are not easily viewable or identifiable on the sign. Another possible difficulty relates to marking signs that need to be replaced.

Management Method 2: Blanket Replacement

Divide your agency into areas/corridors or zones and relate them to a replacement cycle. Replace all signs in an area/corridor each replacement cycle.

Advantages: The major benefit of using this method is that if all signs are replaced there is a low likelihood of a given sign being skipped over or not being replaced. This ensures that all replaced signs are visible and meet minimum retroreflectivity levels.

Disadvantages: The major drawback to this method is the potential amount of waste than can be generated if signs that are relatively new are removed during a normal replacement cycle.

Management Method 3: Control Signs

Sign life is estimated using sample signs representing an agency’s inventory. Control signs can be in-service signs or signs in a maintenance yard or test area. Agency monitors control signs to estimate the condition of all their signs and periodically measure the retroreflectivity of control signs.

Management Method 4: Engineering Study

Other methods developed based on engineering studies can be used, combining methods or using methods to reinforce each other.

Agencies had until June 2014 to implement and continue to use an assessment or management method that is designed to maintain regulatory and warning sign retroreflectivity at or above the minimum levels in Table 2A-3 of the 2009 MUTCD.

Although guide signs are included in the minimum retroreflectivity levels table, there is not a specified compliance date for guide signs (including street name signs) to be addressed by an agency’s method. Guide signs are to be added to an agency’s management or assessment method as resources allow.

Agencies need to replace any sign they identify as not meeting the established minimum retroreflectivity levels. Agencies’ schedules for replacing signs are based on resources and relative priorities rather than specific compliance dates.

Subscribe to the Safe Travels Blog!

Recent Posts

Subscribe to the Safe Travels Blog & receive updates straight to your inbox.