Managing Selected Transportation Assets: Signals, Lighting, Signs, Pavement Markings, Culverts, and Sidewalks (2007)

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67 OVERVIEW Pavement markings encompass lane striping, raised lane markers, and painted symbols and messages on the road sur- face that provide information and warnings to road users. Pavement markings help to channel and guide traffic flow in an orderly, safe stream. They play an important role in traffic separation when it is necessary to identify distinct lanes or crossings for particular modes; for example, bus-, taxi-, automobile-, or truck-only lanes; bicycle lanes; and pedestrian crosswalks. They are used, often in conjunction with warning signs and signals, where particular attention is demanded of motorists; for example, at major crosswalks; when advance alert is needed approaching intersections, rail crossings, changes in speed, required stops, and so forth; and for in- formational guidance in school zones, in areas with elderly, disadvantaged, or handicapped populations; and for turning movements in intersections of multilane roads. Pavement markings are applied using a variety of materi- als, including various types of paints, thermoplastics, reflec- tive tapes, and raised markers. Because they are applied on top of the pavement surface, their performance is judged in several ways; for example, by their visibility in daytime, nighttime, under various weather conditions, and against the background color and texture of the pavement itself; by their durability—their ability to withstand damage resulting from traffic, weather, and actions such as snow plowing; and their skid resistance and avoidance of impediment to any form of traffic, including cyclists and pedestrians. Because paints may contain volatile organic compounds (VOCs), there may also be an environmental aspect to their application. Pave- ment marking materials may be applied by hand-operated machines or mechanized vehicles, and may entail preparatory work. For example, raised markers or reflective tape may require prior grooving or machined insets in the pavement surface to recess the markings, protecting them from snow plows. Thicker thermoplastics can be used to form rumble strips, providing visual as well as aural warnings of vehicles leaving the travel lane. It is estimated that in the year 2000, state and local trans- portation agencies in the United States and the 13 Canadian provinces and territories spent more than $1.5 billion on pavement markings. On a unit dollar-per-mile basis among levels of government, U.S. state DOT expenditures are the highest, given their greater inventory of multilane freeways and highways. State agencies also use the greatest variety of marking materials, including the more expensive durable markings and pavement markers (Migletz and Graham 2002). Agencies participating in the survey conducted for this study ranked the transportation objectives that are served by pavement markings in priority order, as given in Table 15. Meeting these objectives calls on agencies to observe stan- dards, technical recommendations, and guidelines from a variety of sources. Figures 53 and 54 present agencies’ judg- ments of those sources of guidance that are the important drivers of engineering and management decisions regarding pavement markings. These results are shown for two key aspects of asset management: new construction and installa- tion, and maintenance and rehabilitation, respectively. The importance of national standards, and especially of individual agency policies, standards, guidelines, and procedures, is evident in these results. Nationally recognized U.S. policies and standards for pavement markings are found in Part 3 of the Manual on Uniform Traffic Control Devices (2003). A summary of the MUTCD warrants for the use of longitudinal pavement mark- ings is given in Table 1 of NCHRP Synthesis of Highway Practice 306 (Migletz and Graham 2002). These standards, guidelines, supporting discussions, and allowable options specify the functions and accepted meanings of recognized markings; requirement for standardized application, materi- als, colors, widths, patterns, locations, and lengths or dimen- sions of usage; and illustrations of examples. The MUTCD also recognizes other sources, including legal citations (in this case, MUTCD Section 1A.11, which cites 23 CFR Part 655, Subpart F, Appendix regarding color specifications for retroreflective sign and pavement marking materials), and supporting documents by the FHWA (discussed here) and AASHTO (A Policy on Geometric Design . . . 2004). One of these referenced sources is the FHWA’s Roadway Delineation Practices Handbook (Migletz et al. 1994), which supplements the policies and standards of the MUTCD. This Handbook describes the devices and materials used in pave- ment markings and other delineators. It presents findings on their installation, performance, maintenance, and removal, drawing on the experience of agencies at different levels of government, field trials, laboratory experiments, and ongoing research. The FHWA Handbook includes guidelines for CHAPTER FIVE PAVEMENT MARKINGS

No Response Other Agency Guidelines Public Policy Natíl. Standards Statutes Percentage of Responses 0 20 40 60 80 100 FIGURE 54 Technical management guidance for maintenance of pavement markings. conducting engineering economic evaluations of competing pavement marking materials. Its information will be cited in several upcoming discussions. The FHWA has also compiled guidelines for the use of raised pavement markers (RPMs) (Guidelines for the Use of Raised . . . 1998). The FHWA is in the process of developing minimum retroreflectivity requirements for pavement markings, in response to a Congressional mandate (Department of Trans- portation and Related Agencies Appropriations Act 1993). Threshold values that could serve as candidate proposals have been developed through research (e.g., Migletz and Gra- 68 ham 2002). However, the FHWA has signaled its intention to issue an NPA for minimum levels of pavement marking retroreflectivity only after the corresponding rulemaking process for sign retroreflectivity is completed (“Traffic Con- trol Devices . . .” 2006; refer to discussion in chapter four). Individual agencies have likewise developed guidance based on their particular needs and experience. This guidance should be viewed as supplementary to the policies and stan- dards of the MUTCD and may appear in general highway design manuals, including bikeway design. Some agencies have developed specific pavement marking manuals, Texas No Response Other Agency Guidelines Public Policy Nat’l. Standards Statutes Percentage of Responses 0 20 40 60 80 100 FIGURE 53 Technical management guidance for new installation of pavement markings. Rank Factor 1 Public safety; accident and accident risk reduction 2 More efficient travel; maintain intended flow and operating speed; reduce travel time 3 Preservation of the existing road infrastructure; reduced agency life-cycle costs 4 Comfort and convenience of the traveling public (motorists, pedestrians, cyclists) 5 Road aesthetics and appeal TABLE 15 PRIORITY OF TRANSPORTATION OBJECTIVES SERVED BY PAVEMENT MARKINGS

69 (Signs and Markings Manual 2006) and Wyoming (Pavement Marking Manual 2002), intersection design guides that in- clude markings (Florida DOT 2000), and separate guidelines for pedestrian crosswalks Utah (Cottrell and Mu 2004) and Vermont (Guidelines for the Installation . . . 2004). A manual for pavement markings is under development for cities and counties in Iowa (Andrie et al. 2001). Agencies may also issue unpublished guidelines in the form of internal agency policies and directives. The focus of these guidelines is typically on criteria for the installation of pavement markings and other delineators (e.g., road class, average daily traffic, and pedes- trian traffic) and techniques and materials that have been found to work well in the particular jurisdiction. Experience with the service life of materials and maintenance replacement cycles may or may not be included in these agency docu- ments; however, if so, it is typically in general form. MANAGEMENT PRACTICES Synthesis and AASHTO–FHWA Survey Findings Among the agencies responding to the synthesis survey, main- tenance of pavement markings is accomplished as shown in Figure 55. A different survey of local governments in Iowa showed a similar pattern among small and large cities, although Iowa’s participating counties reported that they rely on contractors virtually 100% of the time, as indicated in Table 16 (Andrie et al. 2001). Other aspects of asset manage- ment practice are revealed through agencies’ methods of budgeting for preservation and maintenance of pavement markings, and their approaches to preserving and maintaining pavement markings once in service. Survey results obtained in this study for the budgeting methods used by agencies are shown in Figure 56. Explana- tions of the abbreviated budgeting process descriptions in this figure are given in chapter two. Because agencies could select multiple choices, the percentages in Figure 56 do not sum to 100%. Addressing their methods of budgeting, the largest number of responding agencies at all levels of government chose the “previous budget plus adjustments” option as best describing their processes, although other options were also well represented in the responding agencies’ results. The selections in Figure 56 were often specified in combination with one another. The survey results in Figure 56 show that the number and target performance of assets are used to a degree in budget- ing, but that they are not necessarily the primary drivers of budget processes among survey respondents. Approaches based on Target [Asset Performance] Drives Budget and Budget [Asset Performance] Drives Target each were identi- fied in about one-third of the responses, and those based on Percent of Inventory Budgeted Annually, in less than 20% of responses. By contrast, methods based on Adjustments to the Previous Budget were selected in almost one-half of the responses, whereas those that involve Staff Professional Judgment, Political Priorities, and Citizen Demands, in approximately one-third of responses (bearing in mind that agencies could select more than one approach). The general thrust of these results is complemented by a January 2000 AASHTO survey of roadway safety hardware (Hensing and Rowshan 2005). When asked whether asset inventory and asset condition were used as the basis of funding allocation, 9 of 39 states (23%) responded affirmatively for pavement markings inventory, and 11 of 39 (28%), for pavement mark- ings condition—again, well less than a majority in each case. Local Jurisdiction Small Cities Large Cities Other Groups 2 0 8 Counties In-House Staff 72 68 0 Contractors 21 24 95 No Response 5 0 5 Notes: Small cities, those with populations of less than 5,000; large cities, those with populations of greater than 5,000. Adapted from data in Andrie et al. (2001). TABLE 16 RESPONSIBILITY FOR REPLACING MARKINGS AMONG LOCAL GOVERNMENTS IN IOWA (percent of responses) 0 20 40 60 80 100 Own Agency Private (Outsourced) Other Gov’t. Unit Other Entities No Response Pe rc en ta ge o f R es po ns es Mgmt. Resp. No Mgmt. Resp. FIGURE 55 Responsibility for maintaining pavement markings once in service.

A related question in the AASHTO survey asked whether state DOTs have a separate budget line item for maintenance of pavement markings; 28 of 39 agencies (72%) responded affirmatively. Although there was no corresponding question for the budgeting of new pavement marking installations, the survey did address tracking and updating of asset inventory. These additional responses are reported in a later section of this chapter. Agencies often described their approaches to preservation and maintenance as well in terms of multiple selections of the items shown in Figure 57. A review of the survey responses showed that different preservation and maintenance ap- proaches were often associated with different pavement marking materials. 70 Materials Usage Agencies use a number of materials for pavement markings. NCHRP Synthesis 306, for example, identifies 16 types of materials used by U.S. state DOTs, with subsets of these applied by U.S. cities and counties and Canadian provinces and territories (Migletz and Graham 2002). NCHRP Report 392 lists the major types of markings with their estimated service lives, advantages, disadvantages, and levels of VOCs (see Andrady 1997, Table 1). Table 17 identifies comparative DOT usage of a number of marking materials based on information in NCHRP Synthesis 306, as summarized in NCHRP Report 484 (Hawkins et al. 2002). Local government practices in the United States show a somewhat narrower range of materials selections, but nevertheless a mix of products. 0 20 40 60 80 100 No Response No Specific Approach Other Pct. of Total Budget Judgment, Politics Previous + Adjustments Pct. Inventory Annually Budget Drives Target Target Drives Budget Percentage of Responses FIGURE 56 Annual budgeting method for maintenance and rehabilitation of pavement markings. 0 20 40 60 80 100 No Response Other No Maintenance Responsibility Deferred Maintenance Worst First Prioritized—Avail. Res. Corrected Immediately Preventive—Schedule Percentage of Responses FIGURE 57 Approach to maintaining and preserving pavement markings.

71 For example, local governments responding to the synthe- sis survey indicated a number of materials used, including non-epoxy and epoxy-based paint, thermoplastic, cold plastic, and raised pavement markers. Findings reported in NCHRP Synthesis 306 documented a number of paints, durable mark- ings, and pavement markers used by U.S. counties and cities responding to that study’s survey; the results also showed ex- clusive use of solvent-based paint among the five Canadian provinces reporting (see Migletz and Graham 2002, Table 31). Statistics on the materials most frequently used (i.e., more than 50% of the time) by local governments in Iowa are shown in Table 18 (Andrie et al. 2001). Based on the findings in NCHRP Synthesis 306 and other studies, the general trend in the United States across all levels of government is toward wide use of water-based paint and thermoplastic, with significant use of other materials (mostly by states, and to a lesser degree by counties, then by cities), declining use of solvent-based paints, and the continuing search for better performing, longer-lasting, and environ- mentally friendly materials. In terms of pavement marking performance, research in the past several years conducted by DOTs in Alaska, Michigan, Ohio, Pennsylvania, and South Dakota, among others, all reinforce a broad understanding that although paint is the least expensive material, it wears the fastest. More durable markings such as thermoplastic and tape have higher retroreflectivity over a longer life, prompt- ing the need to compare the performance and costs of alter- nate materials on a life-cycle basis. Color also has an effect: white markings are more retroreflective than yellow mark- ings (Thomas and Schloz 2001). More detailed examinations of these general findings are presented in the following sections. MEASURING ASSET PERFORMANCE Synthesis Survey Findings The information provided by agencies on performance mea- surement of pavement markings is summarized in Figure 58, based on categories of performance factors similar to those described in chapter two. Physical as well as qualitative mea- sures of pavement marking condition, asset age, and cus- tomer complaints were cited the most often by responding agencies. The frequencies with which physical measures are addressed are shown in Figure 59. Almost 85% of the reporting agencies assess pavement marking condition at least annually. The methods used by responding agencies to assess pavement marking condition and performance are reported in Figure 60. All of the responding agencies reported using visual inspections; physical measurements and customer complaints were also identified as common methods used. Physical measurements of pavement markings typically include assessments of reflectivity, color, and durability. Pavement Marking Material Water-Based Paint Alkyd-Based Paint Tape Epoxy Thermoplastic Other No Response Small Cities (%) 37 44 2 0 0 2 14 Large Cities (%) 84 12 4 0 0 0 0 Counties (%) 91 5 0 0 0 2 2 Adapted from data in Andrie et al. (2001). TABLE 18 PAVEMENT MARKING MATERIALS MOST COMMONLY USED BY LOCAL GOVERNMENTS IN IOWA (percent of responses) Longitudinal Pavement Marking Material Water-Based Paint Thermoplastic Preformed Tape—Profiled Preformed Tape—Flat Epoxy Solvent-Based Paint Methyl Methacrylate Thermoplastic—Profiled Polyester Polyurea Cold-Applied Plastic No. of Statesa 33 30 20 19 19 13 9 9 5 2 1 Using Materialb 89% 81% 54% 51% 51% 35% 24% 24% 14% 5% 3% aA total of 37 state DOTs responded to the survey. bMultiple responses were allowed; totals therefore sum to more than 100%. Adapted from data in Migletz and Graham (2002), as reported by Hawkins et al. (2002). TABLE 17 PAVEMENT MARKING MATERIALS USED BY STATE DOTs

More Than Once A Year Annually Biennially Less Freq Than Biennially FIGURE 59 Frequency of physical condition assessments of pavement markings. 72 PHYS: Abrasion, Wear, Delam. PHYS: Broken, Missing RPMs PHYS: Loss of Reflectivity PHYS: Use- or Time-Related PHYS: Other Asset Age Performance or Health Index QUAL: Abrasion, Wear, Delam. QUAL: Broken, Missing RPMs QUAL: Loss of Reflectivity QUAL: Use- or Time-Related QUAL: Other Asset Value Customer Complaints Customer Surveys Other No Response 0 20 10 40 60 80 30 50 70 90 100 Percentage of Responses FIGURE 58 Measuring performance of pavement markings. PHYS = physical; QUAL = qualitative; RPMs = raised pavement markers.

73 Reflectivity may be measured by handheld or mobile reflectometers. Agencies may use reflectivity readings to verify visual inspections. Performance Attributes Several characteristics of pavement marking materials are important to the ease and safety of installation, perfor- mance, and cost, and may be considered by agencies in deciding among competing marking materials (Migletz et al. 1994; Andrady 1997; Thomas and Schloz 2001; Hawkins et al. 2002). • Visibility, retroreflectivity—The visibility of pavement markings is critical to the safety and orderly movements and interactions among motor vehicles, bicyclists, and pedestrians. The MUTCD requires that retroreflective marking materials be used unless adequate nighttime visibility is otherwise provided by illumination. Given the relatively small percentage of well-illuminated roadways, agencies tend to have all pavement markings retroreflective. Retroreflectivity is the ability of mark- ing materials to reflect light back to its source, the same property explained in chapter four for sign sheeting. Technical discussions of retroreflectivity are contained, for example, in the FHWA Roadway Delineation Prac- tices Handbook (Migletz et al. 1994) and the synthesis of pavement markings research performed for the Iowa DOT (Thomas and Schloz 2001). The issue of the min- imum level of reflectivity needed for safe and effective traffic movements has been a subject of continuing re- search, and agencies have adopted different approaches and threshold values. Other aspects of visibility to which drivers are sensitive include the apparent bright- ness or luminance of markings, the contrast between pavement markings and the pavement surface, loss of color of the marking material [e.g., owing to exposure to ultraviolet (UV) light or contamination by dirt, grime, exhaust, etc.], conspicuity or detection distance (the ability of a driver to notice a marking at a certain dis- tance), and the ability to see the markings clearly at dif- ferent times of day and in different weather conditions. • Durability—Durability refers to the lasting power of pavement marking, often interpreted as the time inter- val between placement and need for replacement; that is, its service life. The durability of a pavement marking depends not only on the marking material, but also on traffic average annual daily traffic (AADT), weather, and resulting activity (e.g., snowplowing and applica- tion of abrasives), the type of base under the marking surface and damage as a result of chipping and abrasion, and the type and condition of the pavement surface. An issue in assessing durability is defining when a marking has degraded to the threshold that requires replacement. Agencies have adopted different approaches and thresh- old values for evaluating durability. • Volatile organic compounds—VOCs are one of the environmental measures of interest for pavement markings. VOCs contribute to ozone and smog forma- tion in urban areas. Solvent-based traffic paint has 25% to 30% VOCs by weight, all of which are released into the atmosphere, contributing a considerable quan- tity of VOCs nationwide. Solvents used in cleaning pavement marking equipment add to this total. Agen- cies are subject to EPA regulations limiting the VOCs in their pavement marking applications, and state reg- ulations may also apply. These regulations have caused DOTs to shift from solvent-based paints to water-based paints and durable markings (see Table 18). VOC emissions by pavement marking materials No Response No Info. Collected Other Customer Complaints Customer Surveys Non-Destructive Testing Physical Measurement Photo, Video Visual Inspection 0 20 40 60 80 100 Percentage of Responses FIGURE 60 Data collection methods for pavement marking condition and performance.

are covered in greater depth in NCHRP Report 392 (Andrady 1997). • Toxicity during marking operations—Paints contain com- pounds that can be harmful to crews applying pavement markings. One problem concerns VOCs that are also haz- ardous air pollutants, including toluene, methanol, xylene, methyl ethyl ketone, and aromatics. A second problem is lead chromate pigment that has been used in yellow water- based and alkyd paints; both lead and this form of chromium are toxic. Problems associated with both appli- cation of these paints and their removal and disposal when replacing markings (residues must be tested for the potential for leaching of lead, chromium, and other heavy metals) have prompted agencies to look at alternate pig- ments such as organic dyes (Hawkins et al. 2002). • Life-cycle cost—Initial costs include the labor, equip- ment, and materials costs associated with preparation (pretreatment) and placement of the marking material. However, costs should be evaluated on a life-cycle basis and equivalent levels of performance, because different marking materials have different service lives. The FHWA Roadway Delineation Practices Handbook pro- vides guidance on the conduct of a benefit–cost analy- sis that considers agency and road-user cost streams through a material’s service life (Migletz et al. 1994). Other examples are given later in the chapter. These are the major attributes considered for general mark- ing applications. Other characteristics that may be considered for particular materials, locations, or situations include skid resistance and the potential to interfere with pedestrian, disabled, or bicycle traffic (e.g., owing to the thickness or slip- periness of the marking material); material stability during storage; and ease of application and removal. Proper specifi- cations and quality control during installation are also impor- tant to good performance. ASSET SERVICE LIFE Retroreflectivity Retroreflectivity is the ability of a material to reflect light back toward its source. It is a property of the pavement marking material used. In the case of markings that are not lit by road or street lighting, the source of light is the vehicle headlamps. The pavement marking material redirects this light back toward the vehicle, where it is perceived by the driver’s eyes. The coefficient of retroreflected luminance, RL, compares the light returned to the driver’s eyes (luminance) with the light from headlamps incoming to the marking surface (illumi- nance). Units of measure are millicandelas per square meter per lux in the metric system (abbreviated mcd/m2/lx, or equiv- alently mcd/lx/m2) and millicandelas per square foot per foot- candle in U.S. customary units (abbreviated mcd/ft2/fc, or equivalently mcd/fc/ft2). The FHWA Roadway Delineation Practices Handbook provides a technical explanation of retroreflectivity and RL using principles of solid geometry 74 (Migletz et al. 1994). Additional information is contained in other sources (e.g., King and Graham 1989; Clark and Sanders 1993; Thomas and Schloz 2001). The literature describes other approaches to measuring driver perceptions of pavement marking visibility that are either now used or proposed for future consideration. For example, the ability of drivers to notice the start or stop (or the number of skip marks) of pavement markings on the road ahead are gauged by their detection distance (or visibility distance) measured in meters or feet. This measure has been used in studies of pave- ment marking visibility in different day–night and dry–wet conditions (Aktan and Schnell 2004; Gibbons et al. 2004). Furthermore, potentially greater use of wider longitudinal strip- ing in the future has prompted consideration of other ways to understand pavement marking visibility beyond those now applied. For example, drivers in tests have noted that wider stripes are more visible and “look better” (Gates et al. 2002). This perception is not explained by traditional characteristics such as retroreflectivity, color, and contrast, because the same longitudinal marking and pavement surface materials are involved as for conventional width striping. Researchers have therefore proposed alternate measurement concepts; for exam- ple, to consider the increased peripheral visibility of wider strip- ing, resulting in increased driver comfort and reduced visual workload, and allowing more attention to other driving tasks. Further work is recommended to develop these concepts quan- titatively as part of a broader understanding of pavement mark- ing visibility (Gates et al. 2002). Although laboratory procedures are often used in research and calibration, it remains that RL readings of in-service mark- ings are influenced by field conditions, including dirt, grime, moisture, dried salt, and other contaminants on pavement markings, as well as the wear of the marking itself. Retrore- flectivity varies with weather; specifically, RL of wet pavement markings is much lower than that of dry markings (Migletz and Graham 2002; Aktan and Schnell 2004). For consistency in comparing data across a number of sources, all the data on RL in the remainder of this chapter will refer to dry road surface conditions unless explicitly stated otherwise. Field measurements further depend on the type of retroreflectome- ter used, which affects how the readings are taken and how adjustments for ambient conditions are made (Thomas and Schloz 2001). Different instruments can give varying readings of the same object (Research Results Digest 297 . . . 2005) and be affected by ambient conditions at the test site, such as tem- perature, humidity, and background glare. As a result, evalu- ating field readings against a minimum retroreflectivity threshold may be difficult to do reliably (Thomas and Schloz 2001; Migletz and Graham 2002; Kopf 2004). Variability in Retroreflectometer Readings NCHRP Synthesis 306 reviewed several correlation studies of different models of handheld and mobile retroreflectometers. The results across all these studies were mixed. For example,

75 a study by the FHWA showed divergences among different instrument models, suggesting either that the different instru- ments were measuring different phenomena or the same phe- nomena on different scales. A study by AASHTO reported good correlation for individual retroreflectometers, but a lack of correlation between different types of instruments. A South Carolina DOT study reported comparable results among three retroreflectometer models, a mobile unit and two handheld units. A study by the Texas Transportation Institute’s Highway Innovative Technology Evaluation Center evaluated four handheld instruments (MX30, LTL 2000, FRT01, Mirolux Plus MP-30) and two mobile instruments (Laserlux and ECO- DYN). Measurements were conducted at six test sites: three types of longitudinal striping on each of two highways. The results showed good agreement (within 10%) in many cases between the readings of the six instruments and the composite mean RL at each test site. (The composite mean RL for each test site was computed as the average of the readings by all six instruments at that site.) In several cases, however, an instru- ment reading varied by 10% to 15% from the composite mean and, in two cases, by 15% to 25% from the composite mean (Migletz and Graham 2002). Missouri DOT District 7 has found that retroreflectivity readings from three instruments (Mirolux 30, LTL 2000, and Laserlux) “do not directly corre- late with each other and should not be compared to each other” (Weinkein et al. 2002). These findings and assessments predate the recent establish- ment of the Center for High Accuracy Retroreflective Measure- ments national retroreflectometer calibration center that was discussed in chapter four (Research Results Digest 297 . . . 2005). It remains to be seen to what degree the variability in retroreflec- tometer measurements can be reduced through nationally standardized calibration of retroreflectometers supported by the Center. Lacking a nationally recognized retroreflectivity bench- mark, one cannot say that a particular retroreflectometer is “more correct” or “more accurate” than another. One can only compare readings between instruments, or against some value such as the composite mean described above, to see to what degree they pro- duce similar results. Durability Durability is judged by the lasting power of the marking material. It is often based on a physical measure such as the percentage of the stripe remaining and may be somewhat subjective. The Quebec Ministry of Transport defines five durability classes, each associated with a percentage range of material remaining, and each also associated with a color for use on maps. A guidebook includes photographs that illustrate examples of how each durability class appears in the field (Tremblay and Eng 2004). Durability measures that are com- monly applied to thermoplastic include remaining thickness and the percentage of retained area. However, a 1969 survey of highway agencies reported a wide variation in estimated service life based on this concept (Migletz et al. 1994). Mis- souri DOT District 7 is trying to determine an acceptable limit for chipping of pavement markings; although it is considering a maximum in the range of 20% to 40% of sporadic chipping, the matter has not been resolved (Weinkein et al. 2002). NCHRP Report 392 includes examples of subjective appear- ance ratings on 1–10 scales that were used in studies by the Northeast Association of State Highway and Transportation Officials (NASHTO) and the Southeastern Association of State Highway and Transportation Officials (SASHTO), as well as ratings of the percentage material retained after 12 months in use to reflect damage, debonding, or physical dete- rioration (Andrady 1997). The durability of raised retroreflective pavement markings (RRPMs) depends on several aspects of performance (Migletz and Graham 2002): • Retroreflectivity, which can be reduced by dirt, abrasion, and weathering; • Proper marking color, which can be degraded by UV rays, heat, traffic, and road surface grime; • Proper adhesion to the pavement, which must resist wear resulting from traffic, especially in weaving areas and in streams having significant truck traffic; and • Proper support of the pavement surface, which can be softened by hot temperatures as in desert climates. Threshold Retroreflectivity Levels Threshold values of retroreflectivity are used in two ways with regard to pavement markings: • As an acceptance criterion for newly installed markings, to ensure that marking materials meet the minimum values established by agency procurement require- ments. Satisfying this threshold does not indicate any information about the service life that will be delivered by the pavement markings. • As a minimum acceptable value of in-service pavement markings. For a material with a given initial retroreflec- tivity when new, and an annual decay rate in retrore- flectivity, this minimum level does affect the service life of the pavement markings. Examples of the variability in both types of threshold val- ues are given here. Minimum Level When Newly Installed Data gathered by the FHWA regarding the minimum initial values used by state DOTs to evaluate the quality of newly applied pavement markings resulted in a range of 175 to 700 mcd/m2/lx for white markings and 100 to 350 mcd/m2/lx for yellow markings. The variability in these thresholds depended on the particular agency, the type of marking material, and the time frame in which the retroreflectivity was measured (Hawkins et al. 2002).

Minimum Level In-Service In its research, South Dakota used 120 mcd/m2/lx as the min- imum acceptable value of retroreflectivity for white paint and 100 mcd/m2/lx for yellow paint, based on the experiences of the NYSDOT (Thomas and Schloz 2001). Research on several types of painted pavement markings for the Washington State DOT (WSDOT) used a minimum threshold value of 100 mcd/m2/lx to define the need for repainting (Kopf 2004). Establishment of this value was preceded by a literature review identifying the following minimum threshold values by other researchers (references cited in Kopf 2004): • New Jersey: Between 80 and 130 mcd/m2/lx for drivers below age 55, and between 120 and 165 mcd/m2/lx for drivers older than 55 (Parker and Meja 2003). • Study of needs of older drivers: Based on subjective judgments of the adequacy of the visibility of pave- ment markings, 85% of subjects 60 years or older found a value of 100 mcd/m2/lx to be adequate or more than adequate for nighttime driving (Graham et al. 1996). • MnDOT: Research indicated a threshold value between 80 and 120 mcd/m2/lx based on drivers’ nighttime driving experiences on state and county roads. MnDOT adopted a value of 120 mcd/m2/lx for its pavement marking management program (Loetterle et al. 2000). In a study of relative cost and service life of paint and ther- moplastic, researchers inferred a threshold value of 150 mcd/m2/lx based on prior correlations of retroreflectivity readings and vehicle crash data for Alabama highways (Abboud and Bowman 2002). Missouri DOT District 7 used preset levels of minimum retroreflectivity as a basis for comparing field readings. The preset levels were 80 mcd/m2/lx for yellow markings, and 100 mcd/m2/lx for white markings. Based on its expe- rience, District 7 regards readings above 250 mcd/m2/lx for new, white, water-based paint markings as “a good stripe”; and above 175, a good value for yellow (Weinkein et al. 2002). In a study of the service life of durable pavement mark- ings in 19 states sponsored by the FHWA’s Turner–Fairbank Highway Research Center, researchers specified a range of threshold retroreflectivity values that would define end of ser- vice life. These values were a function of type and color of marking material, lighting situation, class of roadway (free- way, nonfreeway), and nonfreeway road speeds (≤ 40 mph and ≥ 45 mph). For example, the threshold values for white markings ranged from 85 mcd/m2/lx on nonfreeway roads with speeds ≤ 40 mph to 150 mcd/m2/lx on freeways (Migletz et al. 2001). 76 Effect of Minimum Retroreflectivity Threshold on Service Life In comparing service-life data for different pavement marking colors, highway classes, AADT and vehicle speed ranges, road- way lighting conditions, presence or absence of RRPMs, and other situations, one must be aware of the minimum threshold retroreflectivity that applies to each case. For example, when comparing white and yellow pavement markings: • If the threshold RL is the same in each case—for exam- ple, 100 mcd/m2/lx—then the white markings will ap- pear to have a longer service life than the yellow mark- ings, all other factors equal. • If the threshold RL values differ—for example, 100 mcd/m2/lx for white markings, 80 mcd/m2/lx for yel- low—the yellow markings may appear to have a longer service life because of the lower threshold. In the case of white and yellow marking color, different thresholds enable agencies to replace all of the longitudinal markings on a highway at the same time, recognizing that for a given installation date and equal period in-service, yellow markings will generally have a lower RL than white markings. Nonetheless, the basic principle applies to other comparisons of pavement marking service life on different roadways: the threshold RL value, as well as potential differences in high- way geometric, traffic, pavement, and other environmental and operating characteristics need to be factored into the comparison. Service-Life Estimates Synthesis Survey Findings Information on service life was obtained in the study survey for three aspects of pavement markings: lane or edge striping, RPMs, and other pavement markings (e.g., arrows and mes- sages). Responding agencies were also asked to identify how they would determine service-life values. Responses to this question are shown in Figure 61. The majority of responses emphasized collective organizational knowledge, repre- sented by agencies’ experience with pavement markings and the professional judgment of their staffs. The remaining responses were distributed fairly evenly among the other choices. A comprehensive statement of most of the items for which estimated service lives were reported is given in Table 19. Examples of histograms showing service-life distributions for those items with the most numerous responses are given in Figures 62 through 67. The labels on the horizontal axis in these figures give the upper values of each range of service- life data. For example, if these labels are 0, 1, 2, 3 . . . , then the column labeled 1 shows the number of responses for es- timated service life of zero to 1 year; the column labeled 2, the number of responses for estimated service life of more

77 No Response Do Not Use Service Life Other Manufacturer’s Data Professional Judgment Literature Agency Experience LCC Analyses Model Develop, MIS 0 20 40 60 80 100 Percentage of Responses FIGURE 61 Sources for determining service lives of pavement marking materials. MIS = management information systems; LCC = life-cycle cost. Component and Material No. of Responses Minimum (Years) Maximum (Years) Mean (Years) Median (Years) Mode (Years) Lane and Edge Striping Non-epoxy paint 22 0.5 2 1.1 1 Epoxy paint 13 1 5 3.3 4 Thermoplastic 16 2 10 4.2 4 Cold plastic 8 1 10 4.9 5 Polyester 2 2 3 2.3 2.3 — Tape 5 5 10 6.3 6 Thin thermoplastic 1 — — 1–2 — Preformed thermoplastic 1 — — 3 — Pavement Markers Ceramic pavement markers 2 3 3 3 3 Raised pavement markers 10 1 5 3.2 3 Recessed pavement markers 6 1 5 3.2 2.5 2 Raised snowplowable markers 1 — — 4 — 1 4 5 6 5 — — 3 3 — Notes: —, value is undefined for the particular distribution. When distribution is based on only one data point, its value is shown in the Mean column. TABLE 19 ESTIMATED SERVICE LIVES OF PAVEMENT MARKING COMPONENTS

78 20 16 18 14 12 N o. o f R es po ns es 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 Estimated Service Life, Years 20 16 18 14 12 N o. o f R es po ns es 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 Estimated Service Life, Years FIGURE 63 Estimated service life of epoxy paint in centerlines and edge lines. FIGURE 64 Estimated service life of thermoplastic in centerlines and edge lines. 20 16 18 14 12 N o. o f R es po ns es 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 Estimated Service Life, Years FIGURE 62 Estimated service life of non-epoxy paint in centerlines and edge lines.

20 16 18 14 12 N o. o f R es po ns es 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 Estimated Service Life, Years FIGURE 67 Estimated service life of thermoplastic in pavement messages. 20 16 18 14 12 N o. o f R es po ns es 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 Estimated Service Life, Years FIGURE 66 Estimated service life of epoxy paint in pavement messages. 79 20 16 18 14 12 N o. o f R es po ns es 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 Estimated Service Life, Years FIGURE 65 Estimated service life of non-epoxy paint in pavement messages.

than 1 to 2 years; the column labeled 3, the number of responses for estimated service life more than 2 to 3 years; and so forth. It should be noted again that the data in Table 19 and Figures 62 through 67 may be derived in part from the professional judgment of agency personnel. Agencies also provided service-life information on other specific materials, as follows: • Urethane 4 years (Oregon) • Polyurea 4 years (North Carolina) • Acrylic-based paint 2 years (West Virginia) • Durable waterborne paint 3 years (Iowa). Service-Life Estimates in the Literature • The FHWA Roadway Delineation Practices Handbook includes the following estimates of service life (Migletz et al. 1994): – Paint—6–12 months. Service life is affected by traffic passages (AADT), traffic composition, and roadway geometry. – Thermoplastic—estimates are variable, but all show a long durability. Models show a hypothetical maxi- mum life of 10–12 years; however, this maximum value should be reduced owing to effects of annual snowfall (a surrogate for wear resulting from snow- plows), traffic volume, abrasion resulting from stud- ded tires, and pavement type. • Based on a minimum threshold of 100 mcd/m2/lx, MDOT found that water-based paints had a service life of 445 days, or approximately 15 months. However, the variability in this result was large (Lee et al. 1999, as reported by Kopf 2004). • Using data for rural highways in Alabama, researchers determined that paint had a useful service life of 4.5 to 22 months for high-to-low traffic volumes [>5,000 vehicle per day (vpd) to <2,500 vpd], whereas thermo- plastic had a service life of 10.5 to 53 months for the same traffic intervals. These results were expressed in both tabular form for three ranges of AADT and as functions relating service life in months to AADT for two-lane highways. The threshold RL used in this study was 150 mcd/m2/lx (Abboud and Bowman 2002). • The study documented in NCHRP Report 392 uses the symbol T100 to express service life related to retroreflec- tivity. T100 was defined as the time during which a pave- ment marking retains its retroreflectivity above the minimum threshold value of 100 mcd/lx/m2. An empir- ical function to estimate T100 was proposed and calibrated using two sets of data: one from NASHTO, the second from SASHTO. The values of T100 for dif- ferent materials according to the two sets of data are summarized in Table 20 (Andrady 1997). • In a study of durable pavement markings in 19 states for the FHWA’s Turner–Fairbank Highway Research Center, researchers applying threshold retroreflectivity values 80 based on road class and speed (among other factors) found that the service life for white paint on freeways, for example, averaged 10.4 months, but varied from 4 to 18 months. Other materials likewise showed considerable variability in service life, whether measured in months or by cumulative number of vehicle passes. An example of these results is shown in Table 21 for white lines on free- ways. Additional information for other road classes and for yellow lines is given by Migletz et al. 2001. • Research findings from several state DOT studies of RRPMs that were reported in NCHRP Synthesis 306 indicated the following (Migletz and Graham 2002, who also cite Ullman 1994 and Hofmann and Dunning 1995): – The Georgia DOT uses RRPMs to supplement pave- ment markings on all classes of its state highways. Its policy is to replace RRPMs every two years through- out most of the state, except in the northern counties where replacement is annual owing to snow plowing. – The Oregon DOT found that retroreflectivity of RRPMs could decline by as much as 70% in one year. – The Texas DOT studied the durability of 17 types of RRPMs on San Antonio freeways during a two-year period. One-directional traffic volumes during the two-year test period ranged from 3,300 to 4,500 vpd at the low-volume site, to 58,900 to 63,200 vpd at the high-volume site. Regression analyses demonstrated that cumulative vehicle exposure most strongly affects the decay in retroreflectivity. Many RRPMs on high-volume freeways failed to provide adequate retroreflectivity after only 6 months. More durable and expensive RRPMs become cost-effective when AADT reaches 10,000 vpd per lane. – The Texas DOT has issued guidelines on when to maintain RRPMs (i.e., replace selected missing markers) based on visibility during nighttime inspec- tions and frequencies of RRPM replacement based on highway AADT. For example, suggested replace- ment intervals range from 3 to 4 years for highways with AADT <10,000 to annual replacement for high- ways with AADT >50,000. Deterioration Modeling Researchers have attempted to incorporate the deterioration of pavement marking materials within models that would enable practitioners to forecast decay rates and the need for markings replacement. One attempt was based on the data reported in Table 21. However, the variability in the results in the table translated into inconsistent decay models when mean retroreflectivity was compared with the cumulative number of vehicle passes. Even when considering a single type of material (e.g., white thermoplastic), a single application (e.g., edge line), and a single road class (e.g., freeway), the shapes or the slopes and

81 Pavement Marking Material T 100 Based on NASHTO Data Months (years) T 100 Based on SASHTO Data Months (years) Water-Based Paint—White 27.7 (2.3) 38.0 (3.2) Water-Based Paint—Yellow 26.1 (2.2) 17.5 (1.5) Solvent-Based Paint—White 12.2 (1.0) 9.1 (0.8) Solvent-Based Paint—Yellow 3.1 (0.3) 7.2 (0.6) Polyester Paint—White 39.7 (3.3) 165.9 (13.8) Polyester Paint—Yellow 4.0 (0.3) 47.2 (3.9) Methacrylate Paint 10.8 (0.9) 18.3 (1.5) Epoxy Paint 18.8 (1.6) — Therm oplastic—White Hydrocarbon type Alkyd type 13.9 (1.2) 13.0 (1.1) 40.6 (3.4) Therm oplastic—Yellow Hydrocarbon type Alkyd type 7.8 (0.7) 8.0 (0.7) 18.5 (1.5) Preform ed Therm oplastic 12.6 (1.1) 3.8 (0.3) Tape—White 14.1 (1.2) 31.2 (2.6) Tape—Yellow 12.4 (1.0) 30.4 (2.5) Adapted from data in Andrady (1997). —, denotes no data available. TABLE 20 MEASURES OF T100 ESTIMATED FOR MARKING MATERIALS BASED ON NASHTO AND SASHTO DATA Pavement Marking Material No. of Pavement Marking Lines Average Service Life Months (Years) Range of Service Life, Months (Years) Thermoplastic 14 22.6 (1.9) 7.4 –49.7 (0.6–4.1) Polyester 2 20.8 (1.7) 14.7–27.0 (1.2–2.3) Profiled Tape 5 19.6 (1.6) 11.7–27.3 (1.0–2.3) Profiled Thermoplastic 7 18.4 (1.5) 4.7–35.6 (0.4–3.0) Profiled Poly (methyl methacrylate) 6 14.0 (1.2) 7.8–33.5 (0.7–2.8) Epoxy 11 12.8 (1.1) 3.4–34.0 (0.3–2.8) Poly (methyl methacrylate) 6 11.9 (1.0) 6.8–17.5 (0.6–1.5) Water-Based Paint 3 10.4 (0.9) 4.1–18.4 (0.3–1.5) Adapted from data in Migletz et al. (2001). TABLE 21 ESTIMATED SERVICE LIFE FOR WHITE LINES ON FREEWAYS

intercepts of the curves that were derived from data on dif- ferent highways varied considerably (Migletz et al. 2001). The University of Washington’s Washington State Trans- portation Center (TRAC) conducted another study to develop retroreflectivity degradation models for the WSDOT. The study was beset by considerable variability in data, both within individual highway test sections as well as among highways with similar AADT. Scatter and incongruous trends in the data complicated model development. For ex- ample, in one test section for which data were collected by a mobile retroreflectometer 11 times during a 3-month period, average retroreflectivity varied from 76 to 97 mcd/m2/lx. The standard deviation of this average was 42 mcd/m2/lx: rela- tively large and thus significant, particularly because a durable striping material with a 15-year service life would be expected to exhibit little variability within a 3-month test in- terval. (The author noted that although this example was an extreme case, it is indicative of the inconsistency that can occur in retroreflectivity measurements.) Detailed analyses of all of the measurement runs on this test section showed little pattern similarity among them, and even yielded counterin- tuitive trends such as an increase in retroreflectivity by as much as a factor of three between one run and a later run (i.e., with increasing age of pavement marking) (Kopf 2004). Sub- sequently, the WSDOT determined that the mobile retrore- flectometer used in this study was substandard and did not pursue the modeling effort further. The department switched to handheld devices and has since obtained more reliable data, performance trends, and evaluations of different mark- ing materials under winter conditions (Lagergren et al. 2006; WSDOT n.d.). WSDOT has developed specific guidelines for conducting retroreflectivity readings on pavement mark- ings, organized personnel training, and related five ranges of retroreflectivity to the levels of service (A, B, C, D, F) used in its Maintenance Accountability Process (Lagergren and Baroga 2006). Studies have also looked at the performance of materials constituents as a basis for retroreflectivity trends—in this case, glass beads. The decline in the retroreflectivity performance of two sizes of glass beads in epoxy pavement marking is given in a graphic in the FHWA Roadway Delineation Prac- tices Handbook (Migletz et al. 1994, Figure 11). The curves show a decrease to roughly half the value of RL in a period of 22 months. MDOT researched methods to determine the glass bead content of pavement marking paint and developed two such procedures. It also documented two relationships: (1) between the percentage of glass beads on the paint surface and glass weight in the marking material, and (2) between glass weight and retroreflectivity (Rich et al. 2002). Impacts of Pavement Marking Performance The FHWA Roadway Delineation Practices Handbook cites several early studies (prior to 1980) of the benefits of pave- ment markings. One showed reductions in accidents when 82 pavement markings were added at particular locations in highway geometry where they had not existed before; for example, tangent sections, horizontal curves, no-passing zones, pavement-width transitions, and other geometric situ- ations. Other before-and-after studies of edge line applica- tions showed improvement in driver performance with mark- ings; for example, improved lateral placement of vehicles away from the edge, reduced centerline straddling, and reduced speed on curves. However, it was noted that some agencies do not allow edge striping on very narrow roadways because of driver tendency then to avoid the edge, and the resulting greater possibility of head-on collision. Yet other studies, however, showed little change in accident rates, with only minor changes in the way markings appear, and some were inconclusive, confounded by differences among sites in other factors such as lane width and presence or absence of shoulders. The Handbook includes a method for conducting a life-cycle cost analysis of alternate pavement marking materials, including road-user benefits related to reduction in accident costs (Migletz et al. 1994). More recent studies illustrate several ways in which pave- ment marking options are compared on the basis of initial cost, cost-effectiveness, or minimum life-cycle-cost criteria. • The most basic criterion is initial cost, typically pre- sented for material costs only on a dollar-per-foot basis (e.g., Thomas and Schloz 2001, Table 1; Hawkins et al. 2002, Table 11; Migletz and Graham 2002, Table 39). • The performance of marking materials is factored into comparisons by combining expected service life (e.g., in days) with initial cost (e.g., cents per foot) to derive the cost per stripe length per unit time (e.g., cents per foot per day) of the material. It is a simple, basic cost- effectiveness criterion. The calculation may exclude discounting (e.g., the South Dakota example in Thomas and Schloz 2001) or a discount rate may be used (e.g., the Oregon example in Migletz and Graham 2002, Tables 46 and 47). Initial cost and service life may also be considered together with other performance mea- sures such as durability and initial reflectivity without combining them into a single number (e.g., the Michi- gan example in Thomas and Schloz 2001). • A further refinement is to include the cost of traffic delay during the installation of pavement markings, plus the cost of subsequent measurement of retroreflectivity. The sum of these agency costs is divided by the expected ser- vice life to produce a cost per stripe length per unit time (e.g., dollars per mile per year) (Migletz and Graham 2002, Table 45). • A comprehensive economic approach considers life- cycle costs to both the transportation agency and road users. Road-user costs are based on estimates of striping- related crashes for each pavement marking material. Although a discounted approach is recommended in the FHWA Handbook, the example in the literature comparing paint and thermoplastic for longitudinal

83 striping applies cost-per-stripe-length-per-unit-time calculations similar to the earlier examples, with no dis- counting (Abboud and Bowman 2002). • NCHRP Report 392 applies a multi-attribute utility analysis to evaluate competing pavement marking materials across dimensions of cost, several aspects of performance, and environmental and safety impact (An- drady 1997). Although the previous studies and methods are largely for longitudinal striping, corresponding work has also been done for pavement markers. The FHWA has compiled guidelines for the use of RPMs (Guidelines . . . 1998). A comprehensive review and economic analysis of the impacts of permanent RPMs (PRPMs) is provided in NCHRP Report 518. This study was prompted by safety con- cerns regarding PRPMs in New York, Pennsylvania, and Texas. A review of PRPM experience on different classes of highways was accompanied by a survey of current DOT practices, a review of human factor issues, aggregate and disaggregate safety analyses, and recommendation of guide- lines for PRPM implementation. Although positive impacts of PRPMs in reduced numbers of crashes were observed in some of the reviewed cases, other cases resulted in negative impacts in terms of inappropriate driver response to PRPMs—for example, increases in speed on curves after installation—and resulting higher crash frequency. Factors involving road standard and geometry, AADT, weather, PRPM spacing and visibility, and human perception and response, all intersect in complicated ways. Implications of these combinations are discussed in detail in NCHRP Report 518, which concludes with recommended guidelines for PRPM installation and a detailed analytic procedure for analyzing PRPM benefit–cost on a discounted, life-cycle basis (Bahar et al. 2004; Persaud et al. 2004). The ability of pavement markings to serve the needs of older drives has also been considered. The threshold contrast value—the minimum difference between the luminance of a target and the luminance of the background that is needed for detection—increases rapidly above age 65 (Adrian 1989, as cited in Migletz and Graham 2002). An FHWA study con- ducted laboratory simulations and field tests of several pave- ment marking treatments with three age groups of drivers. The field tests investigated the recognition distance of each treatment by the oldest and the youngest groups of drivers. As a general rule, treatments that were recognized more quickly (i.e., at greater recognition distances) by older drivers were also recognized more quickly by younger drivers. How- ever, on average, the recognition distances of older drivers were 14% less than those of younger drivers, and the reduction in recognition distance may actually be greater among the elderly in the general population (Pietrucha et al. 1995, as cited in Bahar et al. 2004). The impacts of pavement markings have also been studied with respect to pedestrian traffic. Case studies in four U.S. cities reviewed the effect marked crosswalks had at unsignalized intersections, with the finding that such markings are a desirable practice and induced no undesirable behavior on the part of vehicle drivers or pedestrians (Knoblauch et al. 2001). Another study, looking at 5 years of experience in 30 cities, found that improvements such as raised medians, adding traffic signals, and applying speed-reduction measures, were more beneficial than marked crosswalks at uncontrolled locations (i.e., no signals or Stop signs) on multilane roads. If marked crosswalks were to be installed, companion safety improvements were also recom- mended. On two-lane roads, there was no difference in the pedestrian crash rate between marked and unmarked crosswalks. The study also documented that older pedestrians had a crash rate that was high in relation to their relative exposure (Zegeer et al. 2001). A third study found that advance warnings before crosswalks at uncontrolled approaches on multilane roads were likewise beneficial (Van Houten et al. 2001). Several jurisdictions in Australia use a thermoplastic audio tactile line marking for edge markings to help counter the effect of driver fatigue. Even though it is initially more expensive than a competing tactile marking product, its life- cycle costs are lower. Experience has shown it to be effective in reducing single-vehicle, run-off-road crashes (Woolley and McLean 2006). Determining Current Service-Life Status To apply the service-life concept in asset management, a method is needed to determine where an asset is in its service life—that is, how much life is consumed and how much remains. Agencies were presented with a number of ways to determine the current status of an asset regarding its service life, and asked to rank each method by relevance to their agency. The result is shown in Table 22. On the related issue of identifying the extension in service life as a result of maintenance, 3 of the 33 reporting agencies responded affirmatively. Quebec presents this information in a pavement markings guide it has prepared. Iowa noted that measuring retroreflectivity provides them with a more objective basis for determining whether existing stripes are still above the restriping threshold, potentially extending their projected service life. Portland described its economic analysis of using thermoplastic for longitudinal striping. The pay-back analysis considered material service life, striping inventory, and estimated productivity of thermoplastic application, including purchase of a thermoplastic long-line striping vehicle. For assumed conditions, it was estimated that an efficient, high-capacity thermoplastic application could reduce life-cycle costs of pavement markings by approximately 28%. Different operational scenarios were also tested, all showing a positive payback within 8 to 10 years. Results of these analyses led Portland to develop a transition plan from paint to thermoplastic (Portland Transportation . . . 2004).

INFORMATION TECHNOLOGY SUPPORT Agencies participating in the study survey identified their key IT capabilities as shown in Figure 68. A number of elements were ranked highly by responding agencies, including infor- mation on inventory, location, condition, and usage; asset age and anticipated service life; information on inspections and maintenance work done; and customer complaints. No strong distinctions in the findings represented by Figure 68 were observed among different levels of government. By compar- ison, responses to the January 2000 AASHTO survey indicated that 21 of 39 agencies (54%) had an inventory of pavement markings, and most of these updated their inven- tory by either manual surveys or semi-automated methods (Hensing and Rowshan 2005). Agencies characterized their IT systems for pavement markings as shown in Figure 69. Most agencies reported using broad-based management systems (such as mainte- nance management systems) and simple programs, followed by management systems for pavement markings and work- books or spreadsheets. The agencies that reported using a pavement marking management system or a maintenance management or transportation infrastructure asset manage- ment system that includes pavement markings are listed here. • Pavement Markings Management System – Iowa DOT – Kansas DOT – Minnesota DOT – Ohio DOT – Colorado DOT Region 4 – Ministry of Transport of Quebec – Saskatchewan Highways and Transportation – City of Tampa, Florida. • Maintenance or Asset Management System That In- cludes Pavement Markings – Florida DOT – Maryland SHA 84 – New Mexico DOT – North Carolina DOT – Ohio DOT – Texas DOT – Utah DOT – Colorado DOT Regions 2 and 5 – Dakota County, Nebraska – City of Portland, Oregon. The need for IT support of pavement marking manage- ment has been recognized in the literature. A pavement marking inventory management system has been developed by the MnDOT to track several aspects of pavement mark- ings (Pavement Marking . . . 1999; Migletz and Graham 2002). NCHRP Synthesis 306 discusses key elements of the MnDOT system: a description of each installation in terms of its location, the date of application, the type of line, and the type and quantity of material used; tracking of inventory on a daily basis, entering changes as soon as they are installed; tracking of retroreflectivity measurements; records of specific actions taken (e.g., reviews of situations and remedial activities in the field), as well as pertinent commu- nications such as complaints and responses thereto; costs of activities in terms of labor, equipment, and materials; and tracking of suppliers and even material batch numbers for quality control (Migletz and Graham 2002). Missouri DOT District 7 has also been using computerized programs to track pavement marking inventory for several years, particularly after responsibility for this task devolved from the DOT General Headquarters to the districts (Weinkein et al. 2002). Local governments also have used inventory systems to serve similar objectives: current and accurate information for management, performance accountability, quality control of materials and installation, and reduction of potential liability (Andrie et al. 2001). Agencies are also investigating other IT capabilities beyond inventory management to better support their pavement mark- ing programs. Rank Factor 1 Monitor condition of the asset on a periodic schedule 2 Assets are repaired or replaced as soon as they fail without regard to service life 2 Assets are replaced on a preventive maintenance schedule without regard to where they are in their service life 4 Compare current age of asset with the maximum age that defines service life 5 Monitor condition of the asset occasionally 6 The agency does not use/does not monitor service life for this type of asset 7 Apply deterioration models to estimate where the asset is on “the curve” TABLE 22 RANKING OF METHODS TO DETERMINE WHERE PAVEMENT MARKINGS ARE IN THEIR SERVICE LIVES

85 Simple Program(s) for this Asset Broad-Based MMS, TIAMS, etc. Pavement Marking Mgmt. System Percentage of Responses Workbook, Spreadsheet Other Products or Procedures 0 20 40 60 80 100 FIGURE 69 Types of analytic tools to support pavement marking management. MMS = maintenance management system; TIAMS = transportation infrastructure asset management system. 0 10 20 30 40 50 60 70 80 90 100 No Response None of the Above Other Historical Database PMs, Dashboards, Accountability GIS Maps, Reports GIS Interface Est. Asset Impacts on Public Track Public Comments Cost Models for Treatments Other Optimization Procedures Benefit-Cost, LCC Decision Rules or Trees Inspector Recommendations Established Mntce. Schedule Deterioration Models Anticipated Service Life Dates of Inspections, Assess. Asset Age Usage, Traffic Volume Photograph Current Condition, Performance GPS Coordinates Location (e.g., Rte-Milepost) Number/Quantity of Asset Percentage of Responses FIGURE 68 IT capabilities to help manage pavement markings. GPS = global positioning system; LCC = life-cycle cost; GIS = geographic information system; PMs = performance measures.

86 • The Utah DOT is pursuing a Crash Avoidance Per- formance History effort by which managers can eval- uate the safety-related impacts of relevant programs, pavement markings among them. Safety-related performance measures under the Crash Avoidance Performance History will be supported by rapidly accessible crash data in the Utah DOT’s Crash Data Delivery System (Anderson et al. n.d.). • South Carolina DOT researchers have used their GIS to help develop models for predicting retroreflectivity of different materials, and displaying retroreflectivity lev- els in color-coded map displays. The scale of display can be adjusted to show overall results for long lengths of routes or to zoom in to see details (such as segments with low retroreflectivity) along short highway lengths. Another display also aids comparison of test results between mobile and handheld instruments (Migletz and Graham 2002). • A computer program, the Pavement Marking Assess- ment System, has been developed to implement the methodology developed in NCHRP Report 392. This methodology includes engineering performance (visi- bility, durability, convenience, and cost) as well as the environmental performance (VOC emissions and health and safety considerations) of pavement marking mate- rials (Andrady and Crowther 1998). KNOWLEDGE GAPS AND RESEARCH NEEDS Agencies at all levels identified a number of knowledge gaps and resulting needs for research. These comments have been organized by topic area and compiled and summarized here. • Basic information on performance—There is a need for basic information on the performance of pavement markings under the many different environments in which they operate. Several agencies addressed this point and identified several variables that need to be accounted for in understanding actual versus predicted service life, the relationship between the cost of striping and roadway traffic volume, and the life-cycle costs of different marking materials. Among the many variables listed by agencies were rural or urban location, traffic volume, weather, altitude and climate (Colorado reports shortened life at high altitudes), degree of snowplowing and type of winter maintenance, type of pavement, roadway classification, and pavement preparation. • Winter conditions—Special emphasis was given by sev- eral agencies to winter weather, with suggestions for research into cold weather pavement markings in addition to the considerations of winter maintenance noted earlier. Quebec reported that it is beginning to investigate this subject. • Urban conditions—Portland noted that a better under- standing of physical wear and tear and loss of retrore- flectivity in urban areas would streamline decisions on pavement marking needs. Variables that should be in- cluded in such a study include lane width, traffic volume, traffic mix, and roadway-use description (e.g., arterial/ commercial district versus collector/residential, arterial/ freight district). Results could be compiled within a ma- trix for ease of use in applying to different locations. • Technical—Agencies recommended investigating a number of technical aspects as well; for example, long- life materials for use on bridge decks and the moisture- proofing and adhesion qualities of glass bead coatings in waterborne and epoxy paints. • Standards—Edmonton noted that a standard definition and measurement of material failure is needed; that is, a minimum value for reflectivity and a threshold value for the number of markers that are missing. Minnesota suggested an objective determination of drivers’ needs for pavement markings in various environments. The TRAC study conducted for WSDOT (Kopf 2004) identified a number of potential sources of variability in retroreflectivity readings: environmental conditions, calibra- tion problems, variability in methods of marking application, varying depth of glass beads in paint, orientation of the laser reflection from the beads, contamination of the pavement marking surface, differences in contrast with the pavement surface, and inherent variability in the retroreflectometer it- self. Both the TRAC study and NCHRP Report 392 also noted that unless retroreflectivity data are collected through- out the life of pavement markings, agencies must extrapolate the trend line of existing, shorter-term data to estimate ser- vice life (Andrady 1997; Kopf 2004). This extrapolation can introduce another source of error if the mathematical form and parameter values of the predictive model are not accurate over the long term. Ongoing testing of pavement marking products is carried out by the NTPEP, sponsored by AASHTO and its member agencies. NTPEP conducts laboratory and field tests on var- ious pavement marking materials at sites in four climatic zones around the country, and publishes results on perfor- mance for participating agencies (Thomas and Schloz 2001). However, survey results reported in NCHRP Synthesis 306 present a mixed picture of current industry perceptions of, and reliance on, NTPEP for product testing data. Based on these findings, recommendations were developed to clarify NTPEP’s purpose and criteria for success, strengthen its base nationally, improve clarity and timeliness of its product test results, and instill greater flexibility to respond to new prod- ucts (Migletz and Graham 2002). The need for more reliable and standardized retroreflec- tivity measurements has been discussed many times throughout this chapter. There is a need for better informa- tion in several areas; for example, the approval of a national calibration standard for retroreflectometers; a better under- standing of how to achieve more repeatable, reproducible, and consistent readings; a better understood correlation

87 among different instruments; and protocols to measure retroreflectivity reliably and consistently under different conditions, particularly involving wet weather. More broadly, retroreflectivity needs to be understood in a performance context: how retroreflectivity affects driver performance in different highway situations (highway class, number of lanes, horizontal geometry, location of stripe, pavement marking material used, presence of lighting and RPMs, etc.); what are the visibility needs of elderly drivers; how retroreflectivity can be economically improved where needed to meet minimum thresholds, including for elderly drivers; role of pavement markings in reducing highway crashes (including pedestrian crashes); and better under- standing of situations where pavement markings have a neg- ative rather than positive impact on safety. Among the top 16 research priorities identified by the TRB Pedestrians Committee, one research problem state- ment addressed pavement markings: Evaluation of MUTCD Signing, Markings, and Traffic Signals for People with Visual Impairments, Children, and Elderly Adults (Trans- portation Research Circular E-C084. . . 2005). Other topics of interest in current or proposed research on pavement markings include: • Use of driving simulators to investigate driver perfor- mance and behavior when presented with different highway and pavement marking situations (Opiela et al. 2002). • Tests of different embedded roadway lighting systems and configurations, driver and pedestrian responses thereto, impacts on safety, and formulation of guide- lines for future usage (Ellis and Washburn 2003; Arnold 2004; Illuminated, Active, In-Pavement . . . in prep.). • Structured or textured pavement markings to improve wet night visibility (“Making Roads Much Safer by Night” Mar. 2005; “The Right Level of Safety” Mar. 2006).