Pavement Marking Materials and Markers: Real-World Relationship Between Retroreflectivity and Safety Over Time (2006) / Chapter Skim
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117 5. Chapter 5 Retroreflectivity Modeling and Safety Analysis This chapter on retroreflectivity modeling and safety analysis has three major sections.
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118 same age. Figure 23 shows the average retroreflectivity by age across all pavement marking materials in the NTPEP data.
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119 5 10 15 20 25 10 0 15 0 20 0 25 0 Average Retroreflectivity by Age Pavement Marking Age (months)
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120 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 10 0 20 0 30 0 40 0 50 0 Age vs Retroreflectivity by Color Age (months)
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121 Modified Urethane 40 0.09% Permanent Tape 2452 5.27% Poly-Cement 88 0.19% Polyester 210 0.45% Polyurea 40 0.09% Solvent 1315 2.82% Thermoplastic 18793 40.37% Waterborne 19110 41.05% Total 46554 100% Based upon the number of available observations, epoxy, methyl methacrylate, permanent tape, solvent, thermoplastic and waterborne have sufficient data to be modeled. It was concluded, based upon the number of observations and the high variance of the data, that there were insufficient data to reliably model the remaining five material types: 1.
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122 The goodness of fit of the models was examined graphically by plotting observed and predicted retroreflectivity and the corresponding cumulative residual (CURE) plot.
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123 0 5 10 15 20 25 0 10 0 30 0 50 0 White Epoxy Age (months)
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124 0 5 10 15 20 25 0 10 0 30 0 50 0 White Methyl_Methacrylate Age (months)
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125 0 5 10 15 20 25 0 10 0 30 0 50 0 White Solvent Age (months)
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126 Table 46. Number of observations by AADT for markings in NTPEP data AADT Number of NTPEP Observations Percent of NTPEP Observations 5000 8034 17.26% 5500 2308 4.96% 8000 4196 9.01% 9000 4254 9.14% 10000 8268 17.76% 11600 2450 5.26% 12000 5680 12.20% 12195 2694 5.79% 13100 2478 5.32% 15000 2790 5.99% 20000 2742 5.89% 160000 660 1.42% Total 46554 100.00% In Figure 31, epoxy and solvent have randomly distributed observed values indicating that the AADT effect on the retroreflectivity is not useful for improving the prediction of retroreflectivity.
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127 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Epoxy by AADT Age (months)
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128 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Waterborne by AADT Age (months)
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129 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Waterborne by Pavement Surface Age (months)
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130 models are based on the combinations of white and yellow thermoplastic hot dry and mixed humid, and two models are based on white and yellow waterborne mixed humid. Table 47.
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131 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Thermoplastic Mixed Humid Age (months)
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132 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Thermoplastic Hot Dry Age (months)
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133 values were consistently higher than the predicted. The parameter estimates from Table 45 for waterborne and thermoplastic materials of both colors were recalibrated to account for the effect of snow removal.
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134 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Thermoplastic Heavy Snow Removal Age (months)
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135 0 5 10 15 20 25 0 10 0 20 0 30 0 40 0 50 0 White Thermoplastic Low to Medium Snow Removal Age (months)
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136 can be seen by the line representing the average retroreflectivity at each age. Figure 41 also depicts the amount of variability in retroreflectivity for markers at the same age.
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137 5.1.2.2. Marker Type Effect Marker type refers to the marker being either plowable or non-plowable.
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139 The effect of pavement surface on retroreflectivity can be seen in Figure 44. No systematic pattern was noticed in the distributions of pavement surface for asphalt or concrete indicating that the effect of surface type on the retroreflectivity of pavement markers is not useful in improving the prediction of retroreflectivity.
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141 Table 53. Number of observations by AADT for markers in NTPEP data AADT Number of NTPEP Observations Percent of NTPEP Observations 37,200 30 14.29% 45,600 61 29.05% 61,800 30 14.28% 78,827 89 42.38% Total 210 100.00% 0 5 10 15 20 0.
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142 difference between the 24th month and the 25th month. The models were used to predict retroreflectivity until 48 months.
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143 0 10 20 30 40 50 0 10 0 20 0 30 0 40 0 50 0 Predicted Retroreflectivity for Epoxy Age (months)
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144 0 10 20 30 40 50 0 10 0 20 0 30 0 40 0 50 0 Predicted Retroreflectivity for Thermoplastic by Climate Region Age (months)
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145 thermoplastic approaches zero retroreflectivity by the 38th month. White and yellow thermoplastic low to medium snow removal approaches zero retroreflectivity after the 48 months.
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146 0 10 20 30 40 50 0 10 0 20 0 30 0 40 0 50 0 Predicted Retroreflectivity for Waterborne by Snow Removal Age (months)
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147 Figure 52. Predicted average retroreflectivity for plowable and non-plowable markers Table 54 to Table 56 summarizes all twenty six marking models developed in this study and their calculated parameter estimates needed for Equation 7.
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148 Table 55. Parameter estimates for color, material type, age, and climate region models Model λ δ Waterborne White Mixed-Humid Climate and No Snow Removal 3.49 164.99 Waterborne Yellow Mixed-Humid Climate and No Snow Removal 2.36 131.27 Thermoplastic White Mixed-Humid Climate and No Snow Removal 3.64 215.53 Thermoplastic Yellow Mixed-Humid Climate and No Snow Removal 2.80 111.00 Thermoplastic White Hot-Dry Climate and No Snow Removal 1.64 168.21 Thermoplastic Yellow Hot-Dry Climate and No Snow Removal 1.58 78.43 Table 56.
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149 5.1.4.2. Retroreflectivity of Pavement Markings Beyond 25 months Continuing with the previous example to predict the average retroreflectivity for white waterborne markings under heavy snow removal conditions at the 30th month the parameter estimates are taken from Table 56.
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151 prediction of average retroreflectivity and as a result were not included in the prediction models. Color, material type, climate region and snow removal all improve the prediction of retroreflectivity, thus separate models can be found for these variables.
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152 All roads in California are marked or striped according to the California Manual on Uniform Traffic Control Devices (CMUTCD) , which is FHWA's MUTCD 2003 Edition Revision 1 Manual amended for use in California.
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153 Then for a given marking material, age, climate region, and snowfall, a retroreflectivity value was determined based upon the NTPEP retroreflectivity models. The number of miles for each road type was calculated as follows.
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154 markings and markers. An analysis for pavement markers was attempted, however, the sample for pavement markers available for California was too small to be conclusive regarding combinations of markers with markings.
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155 5.3.1. Retroreflectivity Bin Ranges The retroreflectivity values contained in the state database derived from the NTPEP retroreflectivity models range from 21 to 413 mcd/m2/lux for white pavement markings, and 15 to 238 mcd/m2/lux for yellow pavement markings.
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156 Table 63. Retroreflectivity bins apportioned by crashes and by miles for white markings Multilane Freeways Retroreflectivity Bins Apportioned by Equal Number of Crashes Retroreflectivity (mcd/m2/lux)
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157 If retroreflectivity affects safety, then bin ranges based upon the number of crashes will change with the safety effect. Since the number of miles does not change as a function of the safety effect of retroreflectivity, retroreflectivity bins were apportioned by equal number of miles.
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158 Table 67. Safety estimation results for yellow markings by non-daylight, non-intersection crash severity Multilane Freeways Retroreflectivity (mcd/m2/lux)
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159 Table 69. Estimation results of safety effects qr for white markings by total non-daylight, non-intersection crashes Multilane Freeways Retroreflectivity (mcd/m2/lux)
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160 Table 70. Estimation pm results of seasonal effect for white markings by total non-daylight, nonintersection crashes Months Highway Type Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Multilane Freeways 1.31 1.13 1.00 0.70 0.65 0.63 0.68 0.76 0.86 1.23 1.51 1.53 Multilane Highways 1.34 1.16 1.05 0.72 0.69 0.62 0.68 0.79 0.83 1.12 1.48 1.51 2-lane Highways 1.23 1.04 0.94 0.73 0.70 0.70 0.79 0.92 0.95 1.16 1.42 1.41 The safety effect of yellow pavement markings is given in Table 71.
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161 measurable safety effect as a function of the retroreflectivity of markers. The safety effect of seasonal variation for markers is given in Table 74.
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162 Table 73. Estimation results of safety effects qr for markers by total non-daylight, non-intersection crashes Multilane Freeways Retroreflectivity (cd/lux)
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163 The next stage in the analysis is the consideration of those road segments that there are 2 pavement marking colors, i.e., white and yellow. The remarking of each color may follows a different striping cycle/ In order to address multiple safety effect of markings, a matrix of safety parameters are estimated simultaneously.
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164 Table 76. Safety effect estimation results for white and yellow markings combined for multilane highways for non-daylight, non-intersection crashes Retroreflectivity of Yellow Markings (mcd/m2/lux)
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165 Table 77. Safety effect estimation results for white and yellow markings combined for 2-lane highways for non-daylight, non-intersection crashes with standard error estimates Retroreflectivity of Yellow Markings (mcd/m2/lux)
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166 month of new striping. For example, the retroreflectivity values of white markings for the first full month of new striping, are 313, 331 and 392, as shown in Table 79 extracted from Appendix A
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167 Table 82. Estimation results for yellow markings separating the safety effect of first full month of new striping for all non-daylight, non-intersection crashes Multilane Freeways Retroreflectivity (mcd/m2/lux)
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168 Table 84. Safety effect with artificially increased number of crashes on multilane freeways Additional Crashes Safety Effect 25-207 208-268 269-312 314-330 332-391 393-413 313 331 392 0 1.00 1.00 1.00 0.97 0.97 0.97 1.02 200 1.00 1.00 1.00 0.97 0.97 0.97 1.04 400 0.99 1.00 0.99 0.96 0.96 0.96 1.06 600 0.99 1.00 0.99 0.96 0.96 0.96 1.08 800 0.99 1.00 0.99 0.95 0.95 0.95 1.09 1000 0.99 1.00 0.98 0.95 0.95 0.95 1.11 1200 0.99 0.99 0.98 0.95 0.95 0.95 1.13 1400 0.99 0.99 0.98 0.94 0.94 0.94 1.14 1600 0.99 0.99 0.97 0.94 0.94 0.94 1.16 The safety effect multiplier estimated for the current study for white markings on multilane freeways during the first full month of new striping is 1.02, shown in the first row of data, far right column in Table 84.
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169 0 .95 1.00 1.05 1.10 1.15 1.20 0 200 400 600 800 1000 1200 1400 1600 Change in Crashes Sa fe ty E ffe ct Figure 55. Change in safety with change in number of crashes for multilane highways
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