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chapter two
Description of Sign Retroreflectivity Maintenance Methods
The 2009 MUTCD states that an agency "shall use an assess- · Expected Sign Life--When signs are installed, the
ment or management method" (1) to maintain sign retroreflec- installation date is labeled or recorded so that the age
tivity. The manual does not dictate the method, but provides of a sign is known. The age of the sign is compared
agencies the flexibility to implement one or more methods with the expected sign life. The expected sign life is
that best fit their needs, expertise, and level of resources. The based on the experience of sign retroreflectivity deg-
intent of the methods and guidance outlined in the MUTCD radation in a geographic area compared with the mini-
is to provide support to the agencies and offer them sys- mum levels. Signs older than the expected life need to
tematic procedures to maintain traffic sign retro reflectivity. be replaced.
Again, compliance is achieved by having a method in place · Blanket Replacement--All signs in an area or corridor,
and being able to document active implementation. Confor- or of a given type, are replaced at specified intervals.
mance does not require or guarantee that every individual This eliminates the need to assess retroreflectivity or
sign will meet or exceed the minimum retroreflectivity levels track the life of individual signs. The replacement inter-
at every point in time. This chapter describes each method val is based on the expected sign life, compared with
and concludes with a section on sign service life for different the minimum levels, for the shortest-life material used
sheeting materials. on the affected signs.
· Control Signs--Replacement of signs in the field is
Sign Retroreflectivity based on the performance of a sample of control signs.
Maintenance Methods The control signs might be a small sample located in
a maintenance yard or a sample of signs in the field.
Section 2A.08 in the MUTCD offers five traffic sign meth- The control signs are monitored to determine the end of
ods for maintaining nighttime sign visibility and an "Other" retroreflective life for the associated signs. It is impor-
method, which must be supported by an engineering study tant that all field signs represented by the control sam-
(1). The five methods are categorized as either assessment ple be replaced before the retroreflectivity levels of the
or management. Assessment methods evaluate the retrore- control sample reach the minimum levels.
flectivity of individual signs and include visual nighttime
inspection and measured sign retroreflectivity. Management It can also be pointed out that FHWA has a full report
methods incorporate an expected retroreflective life period of detailing each of the sign retroreflectivity methods listed in the
individual sheeting materials within the sign inventory. The MUTCD. The FHWA report also includes a useful descrip-
retroreflective life of signs can originate from manufactur- tion of how to conduct the assessment methods. Finally, it
ers' warranties, demonstrated performance, or control sign also specifies the advantages and disadvantages of each of
assessments. The management methods include expected the sign retroreflectivity methods listed in the MUTCD. The
sign life, blanket replacement, and control signs. Assess- FHWA report can be found at the following web address:
ment and management methods may be combined in many http://safety.fhwa.dot.gov/roadway_dept/night_visib/policy_
different ways to accommodate an agency's needs and objec- guide/fhwahrt08026/.
tives. The MUTCD description of each method is provided
here and additional details of each method are provided in
this chapter. Visual Nighttime Inspection
· Visual Nighttime Inspection--The retroreflectivity of Visual nighttime inspection is a common method for main-
an existing sign is assessed by a trained sign inspector taining traffic sign retroreflectivity and guidelines for the
conducting a visual inspection from a moving vehicle inspection procedure have been documented for approxi-
during nighttime conditions. Signs that are visually iden- mately 50 years (10). The method is simple and requires a
tified by the inspector to have retroreflectivity below the trained or experienced inspector to view traffic signs from a
minimum levels are to be replaced. moving vehicle during nighttime conditions. The inspector
· Measured Sign Retroreflectivity--Sign retroreflectivity subjectively concludes if a given sign passes or fails. This is
is measured using a retroreflectometer. Signs with retro- a broad overview, but effective implementation does require
reflectivity below the minimum levels are to be replaced. expertise and attention to detail.
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Visual nighttime inspection requires one individual, but In 2001, to build on the previous studies findings, Hawkins
is more effective with two; a dedicated inspector monitoring and Carlson evaluated the accuracy of experienced TxDOT
and recording sign failures and a focused driver following sign personnel (10). In this study, TxDOT staff subjectively
a predetermined inspection route. It is important that visual assessed 49 test signs during nighttime conditions and rated
inspection take place during typical nighttime conditions them as "Acceptable," "Marginal," or "Unacceptable."
and that viewing not be affected by adverse or inclement TxDOT observers viewed test signs on a closed-course track
weather such as fog or rain. Interior vehicle lighting should at speeds of 30 to 40 mph. Only one test sign within the
be minimized so that the inspector's vision is not affected. sample failed to meet the MUTCD minimums; however, the
The inspection can emulate how a normal driver would view TxDOT observers rejected a total of 26 signs. The research-
a typical sign: at normal roadway speeds, from an appropri- ers determined that for sign assessment the overall appear-
ate travel lane, and at an adequate viewing distance. Sign ance and uniformity of the sign face were as important as
failures and noteworthy comments are to be documented in the retroreflectivity levels. The TxDOT observers identified
a standardized procedure. The inspector can document his sign inconsistencies and blemishes that rendered the sign
or her evaluations by means of written notes on an agency un acceptable despite meeting the retroreflective minimums.
form, audio recording, or laptop computer. The duration of a The researchers concluded that "visual nighttime sign inspec-
nighttime inspection session must not exceed a period where tions should be a critical component of any process that evalu-
inspector fatigue becomes an issue or where roadway condi- ates the nighttime visibility of traffic signs" (10).
tions change, such as frost forming on a sign. Throughout
the inspections, it is important to be consistent with agency Another visual sign inspection study was conducted in
procedures and be able to document when the nighttime sign North Carolina in 2006. Rasdorf et al. (13) evaluated the accu-
inspections have been completed. racy of North Carolina DOT (NCDOT) staff evaluations by
comparing the visual nighttime inspection pass or fail deci-
There have been several research studies that have evalu- sions with retroreflectivity measurements. The study collected
ated the visual nighttime inspection method. One of the first retroreflectometer measurements of 1,057 inspected signs
research studies to assess and document the accuracy of visual on various types of state roadways in five different counties.
sign inspection was conducted in the state of Washington in Overall, the analysis determined that the NCDOT sign inspec-
1987 (11). The first part of the study surveyed state DOTs and tors were effective in identifying and removing signs that were
determined that 35 of 44 responding states used some type of below the minimum values, and that accuracy levels ranged
visual inspections in the daytime and/or nighttime. The prac- from 54% to 83%. The incorrect inspection decisions included
tices varied between DOTs, but all states replaced signs if there a mix of both type I errors (failing adequate signs) and type II
were visual physical defects or inadequate retroreflectivity. (passing inadequate signs). Despite the wide accuracy range,
The second part of the Washington study evaluated the accu- the researchers concluded that the NCDOT inspectors were
racy of 17 trained sign observers (11). The researchers trained proficient and that nighttime visual inspection was reliable.
the observers to rate STOP and warning signs in two environ-
mental settings: a controlled gymnasium and a stationary car Finally, Kilgour et al. (7) at the Indiana LTAP Center com-
on a simulated road. After training, the observers were driven pleted a study similar to the North Carolina study during the
on two highway courses where they rated a total of 130 traf- same time period. Again, researchers compared the pass or fail
fic signs. Overall, the observers made correct ratings for 75% decisions of sign inspectors with the infield retroreflectometer
of the signs. Within the total incorrect responses, observers measurements. There were 1,743 signs measured on road-
were more likely to replace an adequate sign than to accept ways that were recently inspected by local agency personnel
a sign with insufficient retroreflectivity. Despite the incorrect throughout different counties, cities, and towns in Indiana.
responses, replacing signs that are questionable or borderline Overall, the study determined that the inspectors were accurate
is a more cautious but preferable approach for drivers. The in 88% of the pass or fail decisions. Within the type I errors,
researchers concluded that "trained observers can make accu- inspectors failed 1.2% of the signs despite adequate retrore-
rate and reliable decisions to replace traffic signs" (11). flectivity values. Type I errors were most common for signs
with red sheeting material. The red color in the sign would
In 1996, Hawkins et al. (12) conducted a similar study fade before the retroreflectivity resulting in inspectors failing
that built on the Washington study's survey. In a statewide the signs as a result of poor appearance. The overall type II
survey of Texas DOT (TxDOT) district sign maintenance error rate was 10.8% and the highest occurrence of this type
offices, the researchers found that 80% of the districts con- of error was observed for yellow warning signs. Ultimately,
ducted nighttime visual inspections and 65% also performed the study acknowledged that visual nighttime inspection
daytime inspections. Approximately 83% of the districts was a "reasonably accurate" method with "minimally trained
would implement visual inspection training when the pro- personnel" (7).
posed FHWA requirements took effect. The researchers also
conducted a costbenefit analysis of several different sign Despite the high accuracy nighttime retroreflectivity
maintenance methods and determined that at that time visual inspection rates noted previously, the visual nighttime inspec-
inspection was one of the least expensive methods. tion method is still a subjective process and dependent on the
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xperience and knowledge of the sign inspectors. FHWA offers
e Does not require advanced equipment or sophisti-
three different sign inspection procedures to assist inspectors, cated computer programs.
reduce the subjective nature of inspections, and develop a link Limits the low amount of waste because only failed
to the minimum retroreflectivity requirements. The details are signs are targeted for replacement.
contained in the 2007 publication Maintaining Traffic Sign · Issues to consider:
Retroreflectivity (14), which is referenced in the MUTCD and Sign evaluation is subjective.
contained in Appendix A. The procedures are a recommended Inspectors need to be properly trained and one of the
practice to comply with the MUTCD standard. If an agency three supportive techniques be used correctly.
chooses not to use at least one of the supportive techniques, it Because nighttime inspection occurs during non
is important that they be able to justify the deviation with an regular work hours, overtime and next-day schedul-
engineering study that describes another procedure linked to ing may be a concern.
the minimum MUTCD levels. One or more of the following There are outside aspects that are difficult to control
procedures can be used to support visual inspections: such as weather, moisture in the air, and oncoming
vehicles headlights.
· Calibration Signs: An inspector views a calibration sign Agency procedures need to be followed consistently.
each time before conducting a nighttime field review.
The calibration signs have known retroreflectivity lev-
els at or above the specified minimums. The calibration Measured Retroreflectivity
signs are set up in a maintenance yard where the inspec-
tor can view the signs in a manner similar to nighttime The measured sign retroreflectivity method directly obtains
field inspections. The inspector uses the visual appear- retroreflectivity values with specialized equipment. Sign mea-
ance of the calibration sign to establish the evaluation surements remove the subjective nature by acquiring a specific
threshold for that night's inspection activities. retroreflectivity value. Repeatable and adequate measurements
· Comparison Panels Procedure: This procedure involves require both a calibrated instrument and a knowledgeable oper-
assembling a set of comparison panels that represent ator. As with the visual nighttime inspection method, standard
retroreflectivity levels above the specified minimums. operating procedures need to be established.
Inspectors then conduct a nighttime field review and when
a marginal sign is found a comparison panel is attached There are two types of devices that measure sign retro
and the sign/panel combination is viewed. Signs found to reflectivity in the field: contact instruments, which require the
be less bright than the panel would then be scheduled for operator to place the device in direct contact with the sign face,
replacement. and noncontact instruments, which can measure sign retro
· Consistent Parameters Procedure: The nighttime inspec- reflectivity from a distance and where devices can be either
tions are conducted under conditions similar to those used hand-held or vehicle-based systems. Noncontact instruments
in the research to develop the minimum retro reflectivity can expedite the sign measurement process and offer a sig-
levels. These factors include: nificant amount of flexibility; however, the trade-off is higher
Using a sport utility vehicle or pick-up truck to con- levels of uncertainty. The current technology of vehicle-based
duct the inspection. systems is not yet at the level of practical implementation;
Using a model year 2000 or newer vehicle for the therefore, agencies must use hand-held contact units.
inspection.
Using an inspector who is at least 60 years old with There are two common types of hand-held retroreflectom
20/20 vision (corrected). eters and both instruments express measurements, the co
efficient of retroreflection (RA), in units of candelas per lux per
With the aid of one or more of these techniques, visual meters squared (cd/lx/m2). Measurements need to be taken at
nighttime inspection can be an effective method for maintain- an observation angle of 0.2 degrees and an entrance angle of
ing sign retroreflectivity and monitoring sign quality. When -4.0 degrees to be comparable to the minimum levels in the
an agency is considering strategies, this is one method that MUTCD.
might be closely examined. Before making a decision, there
are some advantages and issues to consider: Sign retroreflectivity measurement procedures are rela-
tively straightforward; however, it is important that proce-
· Advantages: dures be followed consistently. ASTM Standard Test Method
Evaluates more than sign retroreflectivity, such as face E1709 outlines the procedures for operating and taking mea-
uniformity, message legibility, sign support integrity, surements with a retroreflectometer (15); it specifies that a
damage, knockdowns, vandalism, obscuring vegeta- retroreflectometer operator acquire a minimum of four retro
tion, genera sign visibility, etc. reflectivity measurements per retroreflective sign color.
Provides the opportunity to observe other roadway The measurement locations are in different parts of the sign
items such as raised pavement markers, pavement and the readings can be averaged when compared with the
striping, delineators, and object markers. MUTCD minimum levels.
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The measured sign retroreflectivity method can be expen- life represents the length of time that a certain sign sheeting
sive and time-consuming. Individual retroreflectometer units material will be used in the field while remaining in com-
can cost between $10,000 and $12,000; therefore, assigning pliance with the minimum retroreflective requirements. Sign
one to each sign technician is typically not feasible. Also, service life can be based on sign sheeting warranties, test deck
some measurements can be difficult to obtain because the or field measurements, or empirical data from other regional
lower edge of many signs is 7 ft above the road surface. studies.
Readings may require the use of a ladder, and overhead signs
may call for a truck with a boom lift. The readings may also The key is being able to identify the age of individual
expose sign technicians to more potential roadway hazards signs, which may be accomplished through a scientific sys-
and place them in undesirable locations. Widespread imple- tem and/or advanced technology. The level of complexity and
mentation of this method at a large agency may not be prac- sophistication depends on an agency's needs and available
tical because of the cost, time requirements, and roadway resources. Implementation of the expected sign life method
exposure. The advantages and issues to consider are: can vary significantly; however, there are three main com-
ponents to most successful systems. These components, in
· Advantages: a hierarchical order, are establishing sign installation dates,
Readings can be directly compared with MUTCD identifying signs for replacement, and organizing sign data.
minimum levels.
A retroreflectometer removes the subjective nature The first component is establishing a sign's installation
of the visual nighttime inspection. dates, which is the foundational base to the expected sign
Data collected throughout the years can provide life method. The majority of the agencies employing this
sheeting material deterioration rates for localized method use installation date stickers to track sign age (16).
conditions. An installation date sticker may contain the fabrication and/
Sign compliance can be thoroughly documented and or installation dates, sheeting type, unique sign identifica-
there is a minimal amount of waste because only tion number, and/or other agency specific information. The
failed signs are targeted for replacement. stickers are typically placed on the back of signs in a visible
The MUTCD minimum contrast ratios for red/white area. Figure 1 shows several examples of sign installation
signs can be obtained. date stickers. Barcode labels can also be used and serve the
Measurements can be obtained during normal day- simple purpose of linking important information physically
time work hours. to the sign. Another simple technique to establish sign age
· Issues to consider: is through digital images. Most digital cameras record the
Retroreflectometers can cost between $10,000 and date and time stamp noting when a picture was taken, and
$12,000. some cameras can also associate latitude and longitude
Signs may be difficult to access because of physi- coordinates with the image, which transitions into the next
cal barriers, sign height, and certain roadway condi- component.
tions. Obtaining some measurements with hand-held
contact units can be difficult and time-consuming. The second component is identifying and locating individ-
Dew, light rain, and moisture on a sign can impede ual signs that require replacement. Large agencies with size-
the data collection process. able sign inventories need to be able to identify the locations
Agencies must decide if sign measurements are to be of signs slated for replacement. Two effective forms of sign
collected when the signs are washed or unwashed. location information are spatial data and benchmark-based
Units only account for retroreflectivity readings and data. Spatial coordinates could be collected with a hand-held
this method does not consider overall sign appear- Global Positioning System (GPS) unit and benchmark-based
ance and uniformity. data could be measured with a Distance Measurement Instru-
Obtaining measurements may expose sign techni- ment from the nearest cross street or mileage marker.
cians to potential roadway hazards and place them in
undesirable locations. The third component deals with organizing and managing
the sign data. A large sign inventory may generate a signifi-
In general, sign retroreflectivity measurements appear to cant amount of data and agencies need to be able to access
be best suited to complement another method. information in a timely and efficient manner to schedule
sign replacement. The sign location and installation data can
be linked and stored in either a spreadsheet form or a geo-
Expected Sign Life graphic information system (GIS)-based platform. Microsoft
Excel is one type of spreadsheet software and Google Earth
The expected sign life method is the first of the three different and ArcGIS are two examples of spatial mapping platforms.
management methods. The main aspect of the expected sign A small agency could use Google Earth and the latitude and
life method is that it documents and tracks individual signs to longitude coordinates from the images of a digital camera to
be replaced before the service life period expires. Sign service populate an expect sign life system.
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FIGURE 1 Images of sign installation date stickers.
Agency needs and objectives vary considerably and there This method provides asset management capabili-
are many different options and levels of sophistication for ties and enhanced tools for planning, scheduling, and
expected sign life systems. These systems may have a sign budgeting purposes.
inventory component that allows agencies to query specific · Issues to consider:
sign information or asset management features that allow Service life periods need to account for the different
for enhanced planning, work scheduling, and budgeting types of sheeting materials and environmental condi-
capabilities. In all systems, the overall objective is to expe- tions that may affect retroreflectivity.
dite and streamline maintenance operations through the This method relies on accurate and up-to-date infor-
effective organization and management of the sign data. mation of individual signs.
Expected sign life systems or inventory programs could be Sophisticated and advanced systems may require a
developed in-house or acquired through an outside vendor. high level of technical support and expertise.
Several LTAP centers offer systems at a reasonable cost and Collecting sign inventory data and initially creating
there are many commercial companies that have developed an expected sign life system can be an expensive and
packages that include data-gathering equipment and sophis- time-consuming process.
ticated software. Administrative, maintenance, and upkeep cost can
be high.
Agencies considering this method need to thoroughly Computer-based systems are susceptible to technical
research the many different options available before select- problems and information loss.
ing a system or program. An agency could take into consid-
eration its level of resources, funding, staff demands, and
technical expertise. A system is selected that is compatible Blanket Replacement
with both short- and long-term agency goals. There also
needs to be general acceptance from all involved users and The blanket replacement method uses service life periods and
parties. If users are not willing to fully support the system is similar to the expected sign life method; the fundamental dif-
and keep the sign information up-to-date and accurate, then ference derives from targeting a large group of signs as opposed
the investment into the system could be wasted. The advan- to identifying individual signs. The replaced signs can be based
tages and issues to consider are: on either spatial or strategic data. The spatial sign replacement
removes all signs in a certain geographic area. The scale of the
· Advantages: spatial area can vary widely between agencies. The area could
Sign replacement can be thoroughly documented. be limited to a single road or corridor or as large as all signs in a
There may be only a small amount of waste because county. The strategic approach replaces all signs of a common
only those signs near the service life period are tar- characteristic such as sheeting type, sign classification, and
geted for replacement. sign content. Upgrading sign sheeting from Type I to Type III
This method can expedite and streamline signing is an example of strategic replacement. STOP signs are a major
operations. concern and may have a strategic priority for replacement over
This method keeps accurate records of the sign warning and guide signs. Blanket replacement could incorpo-
inventory and is easily able to access specific sign rate both spatial and strategic characteristics by removing spe-
information. cific sign types in a certain area.
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The major advantage of the blanket replacement method replaced before the retroreflectivity falls below the minimum
is that it is relatively easy and straightforward to implement. levels and reasons could be attributed to vandalism, vehicle
Operations and resources are minimal; it does not require knockdowns, road reconstruction, and changes in standards.
advanced personnel training, high administrative cost, or time- As a result, signs in a specific blanket replacement area will not
consuming maintenance procedures. A computer-based sign always have the same installation period. When the replace-
inventory and management system may not be a requirement, ment cycle is reached, there may be many signs with adequate
but it could greatly benefit this approach. When implemented, retroreflectivity that are removed. Not only do signs not reach
agencies typically stagger the blanket replacement schedule to full potential in the field, but maintenance costs for replacing
simplify planning and budgeting. adequate signs in the long term may be a substantial drain on
agency resources. The advantages and issues to consider are:
Consider an agency using Type III High-Intensity Beaded
Sheeting, which has a warranty period of 10 years. The agency · Advantages:
divides its jurisdiction into ten different areas. Each year, that Identifying signs and formulating the replacement
agency will replace all the signs in one of the ten different schedule is simple and straightforward.
areas and the replacement rate for each area is based on a regu- Administrative costs are low.
lar 10-year cycle. Planning, scheduling, and budgeting can be Regular replacement cycles can help with planning,
simplified when an agency knows that it will have to replace scheduling, and budgeting.
around 10% of the sign population each year. Figure 2 is a map There is the capacity to target certain sign types
of a blanket replacement schedule and the divided areas. such as placing a greater priority on STOP signs or
removing all Type I signs from the roadway.
The blanket replacement method documentation is simple Sign inventory and management systems may not be
and an agency can draft a short policy memo justifying the ser- necessary; however, they could provide support.
vice life period, defining the area boundaries, and outlining the · Issues to consider:
yearly sign replacement procedures. Because all of the signs in a There is a high possibility of premature sign
specific area are replaced on a regular cycle, the chances of hav- replacements.
ing signs that are below the MUTCD minimum requirements There remains the need to determine the replacement
are small. An agency can easily show that it is implementing its cycles.
method and working toward compliance through work orders Routine daily inspection and maintenance is still
and sign replacement schedules. Overall, the blanket replace- needed.
ment method has simple procedures, removes subjectivity, and Operating costs and additional sign installation labor
can simplify sign replacement documentation. could be higher than with other methods.
Conversely, the blanket replacement method can lead to
premature sign replacement and waste. Signs are sometimes Control Signs
The control signs method is the third sign management strat-
egy and it may utilize both sign assessment and management
techniques to maintain sign compliance. The MUTCD states
that sign replacement in the field is based on the performance
of a sample set of control signs (1). Specific sheeting types
in the controlled sample set represent the retroreflective val-
ues of a sign population in the field. The control signs may
be a sample in a secure maintenance yard or selected signs
on the roadway. Control signs are monitored and assessed
to determine retroreflective performance. When the control
signs approach the retroreflective minimums, all correspond-
ing signs in the field are replaced. The control signs method
requires a means of establishing a creditable sample set, sign
evaluation techniques, and a system to locate corresponding
signs in the field.
The first step is to establish an acceptable and effective
sample size. An agency should select a sample size that it
determines is appropriate and justifiable. The National Trans-
portation Product Evaluation Program conducts sign dete-
rioration studies for new sheeting products for AASHTO. It
FIGURE 2 Blanket replacement map and schedule. tests two panels for each new sheeting type in an accelerated
