Pavement Marking Materials and Markers: Real-World Relationship Between Retroreflectivity and Safety Over Time (2006) / Chapter Skim
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7 2. Chapter 2 Literature Review This literature review is the result of a review of research conducted by various state DOTs, academic institutions, private and public sector materials testing laboratories, manufacturers and suppliers of materials, and the National Transportation Product Evaluation Program (NTPEP)
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8 2. Control traffic, for example, by reserving certain parts of the road for certain traffic groups (e.g., public transport)
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9 In 1994, the FHWA released a memorandum describing the impact of a new Environmental Protection Agency (EPA) regulation on the use of pavement marking material.
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10 2.1.2. Conventional Solvent Paints Conventional solvent paints are single-component paints that contain a binder resin, pigments or fillers, and solvents or additives.
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11 inconsistent performance of thermoplastic markings on concrete pavements in Texas and some other states, the findings of Ahmad et al.
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12 traditionally been viewed as a marking material that provides exceptional adhesion to both asphalt and concrete pavements when the pavement surface is properly cleaned before application (10)
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13 et al.
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14 transportation agencies is to reconcile the different service lives and costs of the various pavement marking materials with the remaining service life of the existing pavement surface, while maintaining an acceptable level of performance for road users. Given that longitudinal pavement markings provide visual guidance to drivers, the key issue is to understand what constitutes an effective visible pavement marking.
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15 Figure 1. Non-linear relationship between retroreflectivity and participant ratings, from Parker and Meja (17)
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16 Figure 2. Non-linear relationship between retroreflectivity and participant ratings, from Loetterle, Beck and Carlson (16)
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17 The use of Equation 1 for markings and markers should result in positive values from 0 to infinity. Using Equation 1 for targets with less luminance than the background will result in values ranging from 0 to -1.
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18 luminance contrast ratio (average of 14.3) compared to yellow markings (average of 9.2)
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19 submitted for testing. This fingerprinting allows states to ensure that once a product is approved for use by an agency, no changes have been made since testing.
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20 • Application information, including application equipment, equipment description, thickness, temperature of material, relative humidity, no-track time, and type and rate of application of beads; • Retroreflectivity values; • Durability ratings; • Appearance; and • Information on snowplow damage. Figure 4.
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21 Figure 5. ASTM D713 field test for pavement marking material (24)
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22 Figure 6. Retroreflectivity measurements on the left wheel path and centerline(25)
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23 retroreflectivity measurements for the same four waterborne paint markings shown in Figure 8 are illustrated in Figure 9. Figure 7.
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24 Figure 8. Four waterborne pavement markings retroreflectivity skip readings on concrete for a 12 month period from NTPEP (23)
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25 Figure 9. Left-wheel retroreflectivity pavement markings readings of the four markings in Figure 8, from NTPEP (23)
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26 Nearly all agencies that apply waterborne paint apply their markings on a yearly basis, although some may have 2-year cycles, and few agencies remark on a cycle of less than 1 year. Therefore, for most jurisdictions, the visibility of their waterborne paint pavement markings, the most common type of marking in use today, at night falls below what most practitioners would consider to be a minimum threshold.
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27 Figure 10. Entrance and observation angles for 30-meter geometry, from the Highway Innovative Technology Center (26)
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28 judgment, based on established guidelines, to assign a rating to it. A variety of subjective tests and the degree of usage for each of these tests are summarized in Table 3.
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29 degradation of older established markings may be sufficient. In Figure 11, "C" demonstrates how the retroreflectivity of a pavement marking can be dramatically affected by activities, such as remarking (marked improvement in retroreflectivity)
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30 A B C Figure 11. Retroreflectivity degradation pattern of new (A)
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31 2.2.6. Retroreflectivity Performance Requirements Visibility is often measured in terms of the detection of a target at a distance.
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32 Bowman's research shows a retroreflectivity threshold value in the range of 140-156 mcd/m2/lx based upon maintaining a crash rate below the overall average. In an attempt to structure the information deficiencies that can contribute to a crash, Taylor et al.
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33 be maintained by allowing the markings to fade if markers are installed. The first Molino et al.
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34 Table 4. Experimental design used by Molino et al.
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35 H ig h M ar ki ng s Lu m in an ce M ed iu m M ar ki ng s Lu m in an ce Lo w M ar ki ng s Lu m in an ce N on e M ar ki ng s Lu m in an ce M arker Luminance None M arker Luminance Low M arker Luminance M edium M arker Luminance High 0 10 20 30 40 50 60 70 Meters 60-70 50-60 40-50 30-40 20-30 10-20 0-10 Figure 12. Mean curve recognition distances, from Molino et al.
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36 Table 5. Experimental design used by Molino et al.
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37 Addressing their initial experimental goal, Molino et al.
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38 The limited contrasts available with their simulator in both Molino simulator experiments (34,36) were 150:1, which is "far below those likely to be experienced on a real roadway at night." This limitation in contrasts emphasized the need for a field validation study.
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39 Table 6. Experimental design used by Molino et al.
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40 Low luminance centerline with low edgeline 0 20 40 60 80 100 120 None Low High Edge Line Luminance M ea n C ur ve R ec og ni tio n D is ta nc e (m et er s) Center Line Luminance High Center Line Luminance Low Center Line Luminance None Figure 15.
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41 consisting of paint and large beads were found to provide longer detection distances, compared with profiled tape with high-index beads under wet conditions as prescribed by the American Society for Testing and Materials (ASTM)
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42 Table 7. Minimum required retroreflectivity levels (RL)
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43 methods are closely tied to a jurisdiction's snow-removal policy. An example of one state's policy is in Section 95.6 of the California Streets and Highways Code: "Snow removal and ice control shall be performed as necessary in order to facilitate the movement and safety of public traffic and shall be done in accordance with the best management practices outlined herein with particular emphasis given to environmentally sensitive areas."(42)
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44 1. The effects of MgCl2 on reinforcing steel; 2.
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45 markings. Cottrell and Hanson (3)
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46 2.2.10. Summary of Visibility and Retroreflectivity To summarize, the performance of pavement markings in terms of retroreflectivity over time is understood to follow basic patterns that can be modeled.
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47 Parker and Meja (17) found that driver age has a significant impact on the visibility (which was quantified using detection distances)
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48 Figure 17. 90-degree curve showing the trajectory drivers actually drive.
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49 Figure 18. Retroreflectivity requirements by vehicle speed, from Zwahlen and Schnell (55)
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50 a change (e.g., installation of edgelines, change in the type of pavement materials) has been made.
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51 The use of longitudinal pavement markings is generally accepted as effective in reducing the number of crashes. Potters Industries (58)
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52 Also in Great Britain, Charnock and Chessell (60) conducted a thorough analysis using the before-and-after with control methodology to assess the safety impact of adding edgelines.
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53 Charnock and Chessell (60) further examined one section of road which consisted mostly of curves of sharp radii.
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54 (63) selected states with careful monitoring and maintenance schedules.
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55 benefit from having more expensive marking installed at no additional cost. However, the Migletz et al.
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56 ⎥⎦ ⎤⎢⎣ ⎡⎥⎦ ⎤⎢⎣ ⎡ − = months days DateDate CTP SLSL InstallFinal Final CTP Months 12 25.365 Equation 2 where SLMonths = Service life in elapsed months, SLCTP = Service life in cumulative traffic passages (millions of vehicles) , CTPFinal = Cumulative traffic passages (millions of vehicles)
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57 Migletz et al.
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58 respect to contrast and resolution of picture. The results of the survey were that motorists were more satisfied with retroreflectivity readings greater than 600 mcd/m2/lux and less satisfied with retroreflectivity readings less than 300 mcd/m2/lux.
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59 Table 10. Estimated service life by roadway type, pavement marking material, and color for sites without roadway lighting and permanent raised pavement markers, from Migletz et al.
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60 2.4.1. Driver Response, Delineation and Safety Effects Many researchers have hypothesized that if pavement markings are an effective safety treatment for sober drivers, then they should also be effective for impaired drivers.
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61 positional variability, while the presence of edgelines serves to decrease this variability." Potters Industries (65) did not look at left and right curves separately.
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62 Johnston cited previous research showing that the point of maximum lateral acceleration is a critical point for control when driving on a curve. Johnston's curve driving performance metric is based on the idea that: • Higher instantaneous path radii indicates better performance; and • Path radii below the geometric radii indicate undesirable performance.
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63 Table 11. Experimental design used by Johnston (54)
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64 consisted of roads without edgelines, and the 2-year after period included the same roads with edgelines. In the end, Willis et al.
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65 Figure 19. Screenshot of National Climatic Data Center (http://www.ncdc.noaa.gov/oa/ncdc.html)
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66 Table 12. WETTIME model from Harwood et al.
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67 under wet conditions, and in cases where the profile pattern is pronounced enough, drivers can feel a rumble effect when driving over the markings. A number of application methods are used for the elevation and recessed pattern.
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68 2.6. Survey of Relevant Practices This section documents relevant findings from a survey of selected states related to the application of longitudinal pavement markings and markers by their state Departments of Transportation (DOTs)
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69 As part of the NCHRP Project 5-17 in order to assess the safety effects of PRPMs and develop guidelines for their use, iTRANS Consulting conducted a survey of 29 states with known PRPM installations in 2002. The survey revealed that most states, in accordance with the guidelines in the MUTCD and Roadway Delineation Practices Handbook, install one 2-way yellow marker on the centerline of 2-lane roadways only.
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70 Table 13. PRPM guidelines based on traffic volume for Illinois, Indiana, and Kansas Roadway type State Rural 2-lane Multi-lane Illinois ADT > 2,500 veh/day ADT > 10,000 veh/day Indiana ADT > 2,500 veh/day ADT > 6,000 veh/day Kansas ADT > 3000 veh/day and TADT > 450 veh/day ADT: Average Daily Traffic (both directions)
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71 manager staff, and the traffic devices engineer. This work group meets monthly to share the best practices, with the goal of developing new practices and policies for maintenance and equipment.
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72 The 2002 PRPM survey by iTRANS showed that the majority of states implement PRPMs at locations with actual or potentially poor safety records. In Maryland, PRPMs are implemented where the crash rate for "correctable" guidance-related crashes is significantly higher than the statewide average on similar road types.
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73 used in Florida is similar, specifying replacement if 8 or more consecutive RPMs are missing. In Massachusetts, RPMs are replaced if 30% or more are missing in a section of roadway.
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74 Performance measurements conducted before the application of pavement markings and markers include tests on the marking materials and the various components of the markers (such as the lens and casing) to ensure they are qualified to provide long-term performance.
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75 Table 17. Summary of objective and subjective evaluations of pavement markings States Surveyed Evaluation Methods CA IL IA KA MD MI MN MO NV NJ NY NC OH OR PA TX UT Objective Evaluations using a Retroreflectometer Dry retroreflectivity measurement of pavement markings D D D D D D D D N/A D D N/A D D N/A N/A Wet retroreflectivity measurement of pavement markings D D N/A N/A N/A N/A Luminance contrast ratio1 D N/A N/A N/A N/A Laserlux Van D D D N/A N/A N/A N/A LTL 2000 D D D D D D D LTL-X D D D D D Mirolux D D D MX-30 D Model of retroreflectometer used2: Unspecified model D D D Subjective Evaluations Dry measurement of pavement markings (e.g., using a 10-point scale)
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76 Table 18. Minimum pavement marking retroreflectivity specifications Minimum Retroreflectivity Requirements (mcd/m2/lux)
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77 Discussions with industry experts and NTPEP RPM panel members indicated that few state highway agencies collect retroreflectivity data for pavement markers. This may be due to several reasons, including a lack of resources to collect the data and the need for special retroreflectometers that are restricted to measuring retroreflectivity of pavement markers only.
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78 Minnesota has specifications for different pavement marking material. For example, the epoxy resin pavement marking specifications include the following information: • Contractor qualifications; • Material classifications (Type I or Type II)
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79 Table 20. Minimum in-service retroreflectivity guidelines for pavement marking materials recommended by state, county, and city agencies (mcd/m2/lux)
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80 preventive maintenance and good budget planning become essential. Some state agencies have developed or integrated decision-making tools that assist in evaluating the multiple criteria regarding the life and serviceability of a pavement marking.
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81 retroreflectivity standards two ways: by recognizing that increased retroreflectivity equals increased visibility for drivers under nighttime conditions, and that increased visibility equals increased safety for road users. While the first assumption has been validated by field data, with visibility being defined as detection distance, increased detection distance has not always meant an increase in safety, especially for roads with lower design standards.
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