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41 CHAPTER 6: FIELD MEASUREMENTS A test plan for field measurements was developed and executed. First, portable field instruments capable of color measurements were identified. Then, a protocol was developed for characterizing, calibrating, and validating the field instruments. A climatically diverse set of states with NTPEP test decks were sampled for field measurements and field measurements were completed at the selected set of states. IDENTIFICATION OF THE INSTRUMENTS CAPABLE OF MAKING FIELD MEASUREMENTS For the NCHRP Project 5-18, two conditions were to be measured, nighttime and daytime chromaticity. For the nighttime condition the illumination and viewing geometry follows the 30-m geometry. The 30-m geometry is a set of angles that are determined from a condition where the source aperture is 65 cm from the road surface directly over the stripe and the observer aperture is 120 cm from the road surface directly over the stripe and the source. The resulting angles are 88.76° for the entrance angle, 1.05° for the observation angle and 0° for the presentation angle. The illuminating spectrum convolved with the spectral sensitivity of the detectors is equal to the CIE illuminant A multiplied by the CIE color matching functions [5]. At the time of this work only one commercially-available portable instrument was available to make this measurement. The instrument is based on three filters used to approximate the color matching functions. The instrument was provided to the researchers on a loan basis from the Federal Highway Administration. For the daytime chromaticity measurements, two geometries are used. The 0/45 geometry where the stripe is illuminated normal to the road surface and viewed at an angle of 45°, which is the geometry currently used in standards and thus to qualify a material. The material may also be measured with instruments that measure a 45/0 geometry which is illuminating the strip at 45° and viewing it normal to the road surface. Another distinction for this type of instrument is whether it has a point or annular system. A point system is uniplanar and measures in one direction. An annular system integrates either the illumination or the detection at 45° over the entire 360° possible. Depending on the optics of retroreflective material these two instruments typically produce different results. The illuminating spectrum multiplied with the spectral sensitivity of the detector equals the CIE D65 illuminant multiplied by the CIE color matching functions. Many varieties of these types of instruments are commercially-available. The instrument provided for this research by the Federal Highway Administration was an annular system that illuminated at 45° and viewed at 0°. The second geometry used for daytime chromaticity measurements is diffuse illumination and a viewing geometry which is based on the 30-m geometry, notated in this report as d/30m. The co-viewing angle for this measurement is 2.29°. The chromaticity coordinates determined using the d/30m geometry are inherently expected to be closer to the white point than the 0/45 geometry. The white point is the chromaticity coordinates of the illuminating source. The reason for this shift is that the 30-m viewing geometry and diffuse illumination allows a specular and retroreflecting component off of the pavement material to be measured, as demonstrated in Figure 20. The intensity of the specular component depends on the gloss of the sample. The illuminating spectrum multiplied with the spectral sensitivity of the detectors equals the CIE D65
42 illuminant multiplied by the CIE color matching functions. At the time of this work no commercially-available instrument was being produced. A prototype instrument under development was loaned to the research group. diffuse illuminating sphere 30-m observer specular component retroreflecting component Figure 20. A schematic of the diffuse/30-m viewing geometry shows that a specular (bold line) and retroreflecting (dashed line) component that is collected by the detector. DEVELOPMENT OF A PROTOCOL FOR CHARACTERIZING AND CALIBRATING THE FIELD INSTRUMENTS Since the nighttime instrument and the d/30m instruments used in this study have not been tested or the 0/45 instrument was not designed for measuring retroreflective material, the instruments were characterized for their optical properties. The first test performed was the measurement of BCRA ceramic tiles that were calibrated at NIST. The 0/45 instrument was constructed for the purpose of measuring ceramic tiles. The results of the NIST scale minus the instrument value are displayed in Table 6. Since the instruments were designed for this purpose, the results were quite good. The only deviations were the Black and Deep Blue tiles where the signal is low and the Red and Orange tiles which are difficult to measure because the spectral power distribution changes at the wavelengths where the color matching functions change.
43 Table 6. The color difference of the NIST scale minus the 0/45 instrument value. Color Îx Îy Color Îx Îy White 0.0004 0.0000 Red -0.0044 -0.0006 Black 0.0090 -0.0131 Deep Pink -0.0004 -0.0008 Pale Grey 0.0002 0.0002 Orange -0.0086 -0.0025 Mid Grey -0.0002 -0.0003 Yellow 0.0005 0.0004 Diff Grey 0.0000 0.0003 Green 0.0002 0.0023 Deep Grey 0.0001 -0.0020 Diff Green 0.0001 0.0026 Deep Blue 0.0057 0.0070 Cyan 0.0000 0.0005 The nighttime instrument was also characterized using the ceramic tiles. By placing the tiles normal to the light source in the device, as shown in Figure 21, the ceramic tiles can be measured and compared to NIST values. Table 7 presents the results of the NIST scale minus the instrument value. portable instrument ceramic tile source detector color matching filter Figure 21. The ceramic tiles were placed in the nighttime instrument approximately normal to the illumination and observation axis. The differences are significantly larger for the nighttime instrument versus the 0/45 instrument. The Black, Deep Blue and for the most part the Deep Grey have sensitivity issues. The majority of the colors compared to the grey scales have significant differences in the x coordinate. The only reasonable color measurement is the yellow tile.
44 Table 7. color difference of the NIST scale minus the nighttime instrument value. Color Îx Îy Color Îx Îy White -0.004 -0.001 Red -0.030 0.012 Black ----- ----- Deep Pink -0.046 0.010 Pale Grey -0.004 -0.003 Orange -0.022 0.001 Mid Grey -0.019 -0.016 Yellow -0.005 -0.002 Diff Grey -0.019 -0.011 Green -0.038 0.015 Deep Grey -0.076 -0.051 Diff Green -0.012 0.000 Deep Blue ----- ----- Cyan -0.033 0.004 To determine if the nighttime instrument could be improved, further characterization was performed. A true understanding of the instrument required the measurement of the spectral power distribution of the light source and the spectral sensitivity of the three filters and detectors. To measure the spectral power distribution of the nighttime instrument a calibrated diode array spectrometer was used with a diffusing opal glass as the input optic. Figure 22 shows the geometry of the light source measurement. To achieve an acceptable level of signal-to-noise the diode array system was placed in a dark environment, and was set to integrate for 60 sec. Thirty seconds was a total of 22 individual measurements by the nighttime instrument. The spectral power distribution is shown in Figure 23. The spectral power distribution should closely match the CIE illuminant-A distribution, which is reasonably matched except in the red region. The drop-off in the red region is most likely due to a cool mirror used to redirect the light from the halogen light source. A cool mirror is a broadband mirror that reflects visible and transmits heat or infrared. The spectral sensitivity of the three filters and the detector, which is a photomultiplier tube, was measured at the NIST facility for spectral irradiance and radiance responsivity calibrations with uniform sources (SIRRCUS) [6]. SIRRCUS is a laser-based facility that has been developed to provide high-flux, monochromatic, Lambertian radiation over the spectral range 0.2 μm to 18 μm. The facility was designed to reduce the uncertainties in a variety of radiometric applications, including irradiance and radiance responsivity calibrations.
45 portable instrument calibrated spectrometer opal glass Figure 22. The nighttime instrument source was measured at a normal geometry. 380 480 580 680 780 Wavelength (nm) R el at iv e Po w er D is tri bu tio n Instrument Illuminant A Figure 23. The illumination spectral power distribution of the nighttime instrument compared to CIE illuminant A.
46 The wavelength uncertainty is on the order of 0.001 nm and the spectral response uncertainty is limited by the resolution of the instruments tested in this study. The measurement geometry is shown in Figure 24. Briefly, when the measure button is pushed on the nighttime instrument, the nighttime instrument measures the dark signal, turns on the light source, and then measures the retroreflected light. A photodetector was used to detect the source illumination. The signal from the photodetector opened the shutter to the tunable laser allowing the sphere to illuminate. The source from the nighttime instrument was blocked and the flux from the sphere source was measured for each color matching filter compared to a calibrated trap detector. The trap detector spectral sensitivity is known; therefore, as the wavelength of light was changed the relative response of the instrument was determined. Figure 25 shows the relative response of the nighttime instrument for the three color matching functions. fiber sphere source trap detector portable instrument tunable lasers shutter Figure 24. The SIRRCUS facility is composed of lasers and sphere sources used to illuminate the portable instrument.
47 380 480 580 680 780 Wavelength (nm) R el at iv e R es po ns iv ity Green Blue Red Figure 25. The relative response of the nighttime instrument is plotted versus wavelength. Assuming that the pavement markings of interest are not fluorescent, the comparison to be made is the relative responsivity multiplied by the illuminant SPD, versus the CIE color matching functions multiplied by the CIE illuminant A. Figure 26 shows this comparison. The match is quite bad. The reason this instrument works is that a correction matrix is constructed from three calibration standards. Three standards, a diffuse white, a pale yellow and amber, are provided with the nighttime instrument. These standards are calibrated by the instrument manufacturer against color standards calibrated at a national laboratory. By measuring these three standards with the three color matching filters in the nighttime instrument, a 3 x 3 matrix is constructed. The three color matching filter measurements multiplied by the correction matrix gives corrected chromaticity coordinates. This correction matrix works quite well on test samples where the chromaticity coordinates fall within the triangle of chromaticity coordinates formed by the three standards. This correction matrix is examined further in the following section on validating the instruments.
48 380 480 580 680 780 Wavelength (nm) Ill um in an t x R es po ns iv ity Inst Blue Inst Green Inst Red Ref z Ref y Ref x Figure 26. The relative responsivity of the nighttime instrument multiplied by the nighttime instrument illuminant compared to CIE illuminant A multiplied by the CIE color matching functions. A similar analysis was done to the d/30m instrument. NIST does not currently have the facilities to calibrate the ceramic tiles with the d/30m geometry, so this comparison was not done. The d/30m instrument was characterized for illumination source and spectral sensitivity of the color matching functions. Figure 27 shows the geometry of the light source measurement. To achieve an acceptable level of signal-to-noise the diode array system was placed in a dark environment, and was set to integrate for 0.5 sec. The spectral power distribution of the light source is shown in Figure 28. The spectral power distribution is very similar to CIE illuminant A, but for this measurement the illuminant should approximate CIE D65. This difference can be corrected by shifting the spectral responsivity of the color matching filters. The instrument illuminant multiplied by the spectral responsivity of the instrument is shown in Figure 29. The match is considerably better than the nighttime instrument. The d/30m instrument also uses the three standards to create a correction matrix.
49 portable instrument calibrated spectrometer opal glass Figure 27. The d/30m instrument source was measured in the sample plane. 380 480 580 680 780 Wavelength (nm) R el at iv e Po w er D is tr ib ut io n Inst Illuminant D65 Figure 28. The illumination spectral power distribution of the d/30m instrument compared to CIE D65.
50 380 480 580 680 780 Wavelength (nm) Ill um in an t x R es po ns iv ity Inst Blue Inst Green Inst Red Ref z Ref y Ref x Figure 29. The relative responsivity of the d/30m instrument multiplied by the d/30m instrument illuminant compared to CIE D65 multiplied by the CIE color matching functions. DEVELOPMENT OF A PROTOCOL FOR VALIDATING THE FIELD INSTRUMENTS The characterization and calibration protocols show the capabilities of the instruments. Specifically, in some regions of the chromaticity diagram, the user would expect the instrument to produce accurate measurements. The ceramic tile measurements are sufficient to validate the 0/45 instrument because the retroreflective properties of the pavement marking materials to be measured do not significantly affect the 0/45 measurements. A few of the materials that are structured such as some of the tape materials have insignificant changes in the chromaticity but can affect the magnitude of the reflectance factor, which is not under study in this work. The nighttime instrument was validated by comparing the measured results to measurements made at the Center for High Accuracy Retroreflection Measurements (CHARRM) constructed and developed under NCHRP Project 05-16 and maintained by NIST [7]. The main question is whether the portable instrument, with its compactness, correlate to the laboratory values which represent the road viewing conditions more accurately. One concern is that the portable instrument integrates over a range of observation and entrance angles. As shown in Figure 30, a portable instrument must illuminate a large area of footprint that retroreflects a detectable amount of light. The collection angle from the illuminated area is also an integration over a set of angles.
51 portable instrument range of angles Figure 30. The nighttime instrument averages of a range of entrance and observation angles. In the road scenario when an observer is viewing a marking material 30 m away, the cone of light about the entrance angle and observation angle is quite small due to the distance. Another concern is the retroreflecting properties of the pavement marking materials at different distances. Figure 31 shows that the light seen by an observer is composed of diffuse scatter and retroreflected light. The diffuse scatter can be approximated by the inverse square law such that when the observer is twice as far away, the flux from diffuse scatter is one fourth. The retroreflected light follows a beam because it is illuminated by a beam of light. The optical properties act much like a mirror. Therefore, at different distances the light that reaches the observer has a different ratio of diffuse scatter and retroreflected light. The portable instrument measures over a distance of approximately 1 m. The road scenario is commonly from 10 m to 90 m. The correlation due to distance needs to be determined. cone of retroreflected lightdiffusely scattered light Figure 31. The ratio between the cone of retroreflected light and diffusely scattered light changes with observation distance. The CHARRM facility at NIST is composed of three components, the source, the goniometer, and the detector. The source composed of a 100 W strip lamp produces an image that under-fills the pavement marking sample. A variable aperture in the projection system is used to control the image such that the light does not hit the edges, most importantly the front edge, of the pavement marking sample. The goniometer of the reference retroreflectometer is mounted on a rail system.
52 The illumination distance is variable from 3.5 to 33 m. The entrance angle components have an absolute expanded uncertainty of 0.02° (k=2) and both axes have a range of ± 95°. The largest retroreflective device the goniometer can accommodate is a device diameter of 95 cm, and it has a clear view to allow almost any length of pavement marking. The sample mounting plate uses vacuum cups to hold the retroreflective devices against a precision register. The precision register is two machined rails that are 150 cm in length. When the vacuum is applied the sample is pulled flat against these rails. The mounting bracket has an adjustable depth to accommodate different sample thicknesses. The detector is supported by the observation angle positioner, which is comprised of a 2 m translation stage, a rotation stage and a 0.2 m translation stage. Each of these motions has an optical encoder to ensure accuracy. The absolute expanded uncertainty of the entrance angle, α, is 0.0002° (k=2). The observation distance is maintained equal to the illumination distance to an absolute expanded uncertainty of 0.005 m (k=2). The detector is a single grating spectroradiometer with a back-thinned CCD. Researchers at NIST have developed a correction matrix for CCD array spectroradiometers that eliminates the stray light from the signal, therefore, increasing the stray light rejection to at least 105. This level of stray light rejection allows measurement of chromaticity coordinates with a standard uncertainty of roughly 0.002. The input optics consists of an observer aperture, a lens, a transmitting diffuser and a fiber optic bundle that directly attaches to the instrument. By spectrally measuring the light returned to the detector, and dividing it by the spectral power distribution of the source measured with the same detector, the spectral coefficient of retroreflected intensity is measured. Using the spectral coefficient of retroreflected intensity and any chosen light source the chromaticity coordinates for the pavement marking samples can be calculated. The first experiment performed was testing how the chromaticity coordinates change over a range of viewing geometries. The pavement marking samples used in this experiment are the panels described in the field experiments and others submitted by manufacturers, including thermoplastic, paint, epoxy and tape. The panels were positioned on the goniometer at a distance of 10 m. The panels were measured for spectral coefficient of retroreflected intensity at observation and entrance angles that correspond to viewing distances of 10 m, 20 m, 30 m, 60 m, 75 m and 90 m. The chromaticity coordinates were calculated based on CIE illuminant A and are plotted in Figure 32.
53 Figure 32. The shift in the chromaticity coordinates for the angles corresponding to viewing distances of 10 m, 20 m, 30 m, 60 m, 75 m and 90 m along with the ASTM nighttime color boxes. The arrow indicates that as the viewing distance geometry becomes larger, the chromaticity coordinates shift toward the white point, which is (0.45, 0.41) for CIE illuminant A. This shift is expected since at 90 m viewing geometry the entrance angle is very large, the returned light is predominantly from retroreflection and front surface reflection off of the glass beads which spectrally is similar to the illuminant used. The shift was consistent and rather independent of the material. The following polynomial equations are the results of a fit to all the data to determine a correction factor for this set of panels, 038.11099.11087.21044.1 32537 +â ââ +â â= âââ dddxacf (1) 012.11039.51046.61051.3 42638 +â ââ +â â= âââ dddyacf (2) where d is the viewing geometry distance. Using this correction factor a material can be measured at the 30m viewing geometry, and corrected for the actual viewing distance used in the field.
54 The second experiment performed was testing how the chromaticity coordinates change over a range of distances using the same viewing geometry. The panels were positioned on the goniometer at a viewing geometry of 30 m. The panels were measured for spectral coefficient of retroreflected intensity at actual distances of 3.65 m, 5 m, 10 m, 15 m, 20 m and 25 m. Not all of the panels could be measured at the 25 m distance with the current equipment. The chromaticity coordinates were calculated based on the CIE illuminant A and are plotted in Figure 33. Figure 33. The shift in the chromaticity coordinates for a 30-m viewing geometry with actual distances of 3.65 m, 5 m, 10 m, 15 m, 20 m and 25 m along with the ASTM nighttime color boxes. The arrow indicates that as the actual distance becomes farther away the chromaticity becomes more saturated that is moves away from the white point. This result was not expected and is currently being investigated at NIST to determine the underlying optical mechanisms that cause this chromatic shift. A possible explanation is that at 30m viewing geometry, the retroreflected light has more saturation than the scattered light by the pavement markings. The shift was consistent and rather independent of the material. The following polynomial equations are the results of a fit to all the data to determine a correction factor for this set of panels, 992.01027.31075.31024.1 32435 +â +â ââ = âââ dddxdcf (3)
55 989.01095.31032.41040.1 32435 +â +â ââ = âââ dddydcf (4) where d is the actual distance. Using this correction factor a material can be measured at a specific distance, 10 m, and corrected for the actual distance used in the field. NIST is continuing to investigate this correction factor. The last validation performed was a comparison between the portable nighttime instrument and the laboratory measurement at a 30 m viewing geometry with samples measured at 30 m. Figure 34 shows the comparison. Table 8 presents the CHARRM measurements minus the nighttime portable instrument measurements. The CHARRM measurements were made on samples that were 6 feet long. The nighttime instrument is an average of 4 spots on the sample. The white samples are in good agreement between the two devices. Sample White 6 (the purple circles) is slightly off, but White 6 was highly retroreflective sample and produced readings higher than the nighttime instrument was rated to measure. The yellow samples showed a consistent shift. Table 8. The CHARRM scale minus the nighttime instrument scale. Sample Îx Îy White 1 -0.004 -0.001 White 2 -0.002 0.000 White 3 0.001 0.000 White 4 0.001 0.000 White 5 0.000 -0.002 White 6 -0.006 -0.005 Yellow 1 -0.010 0.009 Yellow 2 -0.010 0.008 Yellow 3 -0.010 0.007 Yellow 4 -0.009 0.009 Yellow 5 -0.013 0.012
56 Figure 34. Shown is the comparison of the CHARRM measurements versus the nighttime instrument. The shift can be corrected by providing new values to the pale yellow and amber calibration standards. The new standard values will be applied to the field measurements. NIST currently does not have the facilities to validate the d/30m instrument as has been done with the nighttime instrument. We are attempting to obtain a 2-m sphere using funds not from this contract to setup a facility where pavement marking materials and signage material can be calibrated for diffuse illumination and various viewing geometries. Once this sphere is obtain and the source is constructed a complete validation and further research into the d/30m instrument can be completed. Accounting for all of the uncertainty contributions for the nighttime and the daytime instruments, which includes calibration plaque uncertainty, instrument resolution, transfer from actual 30 m measurements to 1 m portable measurement distance (angle acceptance, chromaticity shifts, distance dependence) among others, the overall expanded uncertainty for the two instruments is 0.018 (k=2) chromaticity units.
57 SELECTION OF STATES FOR FIELD MEASUREMENTS To minimize expense and sample a wide range of field material with known background specifications, the research team decided to measure the NTPEP test decks that were currently available. The first site was outside of Tupelo, Mississippi on state road 78 going west. Pavement markings on concrete and asphalt surfaces were measured on June 24th and 25th of 2004. The data was collected using the three instruments available. The first set of data points was 36 samples that were one week old on a concrete test deck. The second set of data points was 78 samples that were two years old on an asphalt test deck. The second site examined was the test decks in Morgan, Utah on interstate 84 going east. The samples are 3 years old on concrete decks. Unfortunately the asphalt decks had already been removed. The data set includes 149 lines that were measured. There are 95 different materials on the deck so there are a few duplicated materials in this data set. The third site examined was the test decks in Sparta, Wisconsin on interstate 94. The asphalt set are on west bound lanes and the concrete set are on east bound lanes. The material was applied in early July 2004 so it is only a few months old. The data set includes 48 lines on concrete and 65 lines on asphalt. The last site to be examined was in Pennsylvania on Interstate 80 and was measured the end of October 2004. By measuring the material on the NTPEP test decks, we did the field tests economically and effectively because of the available manufacturer and aging information. A number of the materials are the same products applied in different parts of the country and have been on the road for different periods of time. We will be able to draw some conclusions about changes in chromaticity based on aging and weathering for these overlapping materials. EXECUTION OF THE TEST PLAN IN NTPEP TEST DECKS The first site is outside of Tupelo, Mississippi on state road 78 going west. The selection of Mississippi satisfies environmental aging due to the hot, humid, and rainy conditions. In June 2004, the researchers measured lines on concrete and asphalt surfaces. The data was collected using the three instruments available. The first set of data points was 36 samples that were one week old on a concrete test deck. The second set of data points was 78 samples that were two years old on an asphalt test deck. To establish the required protocol for the sampling of the lines the following procedure was performed. The instruments were fully charged the night before and allowed to come to equilibrium (several hours) with the hot and humid measurement environment. The instruments were calibrated following the manufacturers specifications and the standard blocks results were recorded. Each instrument was placed on the first line such that the active measuring region was the same for each instrument. Three measurements were made without moving the instrument for each filter setting. The instruments were then moved to a new spot on the line and the measurement was repeated. A third spot was chosen and the measurements repeated. This was done for ten lines. The results showed that the repeatability (three measurements without movement) of the instruments was exceptional. The quality of the repeatability was limited by the display resolution of the instruments. The reproducibility of the instrument or the uniformity of the line (three measurements on different parts of the line) revealed that by averaging three spots was no better than measuring one spot. The expanded uncertainty of the nighttime instrument and the Qd instrument is 0.018 (k=2) chromaticity units. The expanded uncertainty in
58 the daytime instrument is 0.005 (k=2) chromaticity units. The typical reproducibity of a pavement line was 0.005 chromaticity units. The researchers when choosing where to measure, selected an area that visually appeared to average for the line â not the cleanest spot and not the most worn spot. The average of three spots did not decrease the uncertainty of the chromaticity coordinates for the line. It only served as a sanity check. Therefore, for further line measurements: a single spot was chosen, the spot was measured once by the instrument, the instrument was moved slightly (re-seated) and the spot was measured again. The average value was recorded. The instruments typically reported the same values. The second measurement is simply a sanity check and does not decrease the uncertainty of the measurements. These repeatability and reproducibility measurements were performed in the laboratory environment (new material) with the same conclusions. After measuring for three hours, the instruments were recalibrated and measurements continued. The instruments were recalibrated at the end of field measurements. For all the field measurements the instrument recalibration showed no differences from the initial calibration or the final calibration. The overall line statistics are summarized in Table 9. The lines represent the product of over 21 companies. Unfortunately, none of the products are exactly the same from 2001 to 2004; therefore, an aging study on a particular product could not be conducted in this research. Table 9 â Overall Line Statistics Year and Location Surface Sample Age Yellow Lines White Lines 2001 Utah Concrete 3 years 32 45 2002 Mississippi Asphalt 2 years 29 21 2002 Pennsylvania Asphalt 2 years 51 67 2004 Wisconsin Concrete 3 months 27 21 2004 Wisconsin Asphalt 3 months 28 32 2004 Mississippi Concrete 2 weeks 10 5 Totals 177 191 DAYTIME MEASUREMENTS Figure 53 shows the daytime measurements of all the white lines on NTPEP test decks using the 0/45 instrument. The individual chromaticity points are plot on an enlarged (x, y) 1931 chromaticity diagram. The boxes represent the acceptable white and yellow chromaticities defined in the ASTM standard D6628-01.
59 Figure 53 â All daytime measurements of white lines on the NTPEP test decks. Also shown on the graph is the chromaticity coordinate for CIE Illuminant D65, the reference illuminant for the ASTM D6628-01 standard. The box around the Illuminant D65 mark represents the expanded uncertainty of the measurements. The overall conclusion for these measurements is that all the results, independent of the age or location, are within the acceptable limits. Figure 54 shows the daytime measurements of the white lines on NTPEP decks sorted by the type of material. Within the uncertainty of the measurement no conclusions can be drawn between material types. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 Utah - Concrete 2002 Mississippi - Asphalt 2002 Pennsylvania - Asphalt 2004 Wisconsin - Concrete 2004 Wisconsin - Asphalt 2004 Mississippi - Concrete
60 Figure 54 - All daytime measurements of white lines sorted by type. The daytime specification is based on the 0/45 geometry. A proposed method of measuring the daytime specification of pavement material is using the Qd geometry. The Qd geometry diffusely lights the sample and views it at a 30 m geometry, which would appear to represent the real world situation. Figure 55 shows the Qd measurements of same white lines shown in Fig. 53 sorted by location and Fig. 56 shows the Qd measurements sorted by type of material. For white material the Qd measurements show little difference compared to the daytime (0/45) measurements. The spread of Qd measurements compared to the daytime (0/45) measurements is slightly larger which is due to the larger uncertainty of the Qd measurements represented by the box around the Illuminant D65 mark. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 Paint MMA Tape Thermoplastic Preformed Thermo Epoxy
61 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 Utah - Concrete 2002 Mississippi - Asphalt 2002 Pennsylvania - Asphalt 2004 Wisconsin - Concrete 2004 Wisconsin - Asphalt 2004 Mississippi - Concrete Figure 55 â All Qd measurements of white lines on the NTPEP test decks. Figure 56 - All Qd measurements of white lines sorted by type. 0.40 0.38 0.36 0.34 0.32 0.30 x 0.380.360.340.320.300.28 y Illuminant D65 Paint MMA Tape Thermoplastic Preformed Thermo Epoxy
62 Figure 57 â All daytime measurements of yellow lines on the NTPEP test decks. Figure 57 shows the daytime measurements of all the yellow lines on NTPEP test decks using the 0/45 instrument. The two points approaching the green part of the chromaticity diagram are intended to be yellow-green pavement marking material. Since none of the lines are the exact same material used at different times, conclusions for an aging study must be general. One conclusion is as the material ages it becomes whiter, falling out of the ASTM box. Another possible conclusion is that the environmental conditions due to the different geographical locations do not make a difference in the chromaticity change over time. Figure 58 shows the daytime measurements of all the yellow lines sorted by the type of material. All of the materials are susceptible to the aging process shown by the fact that all of the materials had at least one measurement fall out of the ASTM box. The thermoplastic material had just one measurement out of 42 fall outside the ASTM box. It was located on a test deck in Pennsylvania applied in 2002. Table 9 shows the statistics for the daytime yellow measurements. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 Utah - Concrete 2002 Mississippi - Asphalt 2002 Pennsylvania - Asphalt 2004 Wisconsin - Concrete 2004 Wisconsin - Asphalt 2004 Mississippi - Concrete
63 Figure 58 - All daytime measurements of yellow lines sorted by type. Figure 59 shows the Qd measurements of the same white lines shown in Fig. 57 sorted by location and Fig. 60 shows the Qd measurements sorted by type of material. The Qd measurements for the yellow lines is significantly different from the daytime measurements using the 0/45 geometry. The difference is expected because the optical process for each measurement geometry is significantly different. The daytime of 0./45 geometry has light the interacts with the pavement material in one direction. The diffuse scatter is detected in the 45 degree direction. The retroreflective properties of the material have little effect on the chromaticity measured. The Qd measurement has many more optical process occurring. Figure 61 summarizes the general optical process for the 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 Paint MMA Tape Thermoplastic Preformed Thermo Epoxy
64 Table 9 â Daytime yellow line statistics Year, Location Surface Age Out of ASTM box Type breakdown 2001 Utah Concrete 3 years 7 out of 32 4 paint, 1 epoxy, 2 tape 2002 Mississippi Asphalt 2 years 11 out of 29 9 paint, 1 tape, 1 pre thermo 2002 Pennsylvania Asphalt 2 years 32 out of 51 20 paint, 2 epoxy, 1 tape, 1 thermo, 2 pre thermo, 3 MMA, 3 urea 2004 Wisconsin Concrete 3 months 0 out of 27 --- 2004 Wisconsin Asphalt 3 months 0 out of 28 --- 2004 Mississippi Concrete 2 weeks 0 out of 10 --- Total 50 out of 177
65 Figure 59 â All Qd measurements of yellow lines on the NTPEP test decks. Figure 60 - All Qd measurements of yellow lines sorted by type. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 Utah - Concrete 2002 Mississippi - Asphalt 2002 Pennsylvania - Asphalt 2004 Wisconsin - Concrete 2004 Wisconsin - Asphalt 2004 Mississippi - Concrete 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 Paint MMA Tape Thermoplastic Preformed Thermo Epoxy
66 Figure 61 â A schematic of the diffuse/30-m viewing geometry shows that a specular (bold line) and retroreflecting (dashed line) component that is collected by the detector. Qd measurements. The primary signal comes from the diffuse illumination causing diffuse scatter that is viewed at the 30 m geometry. Two additional components affect the measurement of the chromaticity of the pavement marking sample. Since the material is designed to be retroreflective, light that emanates from the sphere wall close to the detector aperture is retroreflected. The chromaticity of the retroreflected light may be significantly different than the diffusely scattered light. This component does represent the real world because light does emanate from over the shoulder of the viewer. It critical concern is how the size of the detector aperture affects the signal. A smaller aperture will allow much smaller retroreflection angles and a larger aperture will preclude smaller retroreflection angles; therefore the retroreflected signal will depend on the instrument geometry. Dependence on the instrument geometry is not desired. The second component is the specular component. Light that emanates from the far edge of the sphere follows a specular path into the detector. The chromaticity of the specular light is the same as the source, CIE Illuminant D65. The magnitude of the specular light will depend on the gloss of the sample. The gloss of the pavement material depends on many aspects including how new the sample is, the type of material, and the moisture content on the surface. Once again this is a real world situation. One can image an open mid-west road where the light coming from the horizon is the predominant source of light. However, in a northeast tree lined road, a specular component may not exist because the trees block the specular source. For the portable measurements, the specular component is the reason the samples measure with a whiter chromaticity. Additionally, research is required that establishes correlations between the Qd measurements and the real world scenario. The geometry of the Qd measurement needs to be standardized based on the correlation research. The daytime data is graphed by type with respect to year of application. Graph 62 is for yellow paint lines. Graph 63 is for yellow epoxy lines. Graph 64 shows the yellow tape lines and Graph 65 shows the yellow thermoplastic lines. diffuse illuminating sphere 30-m observer retroreflecting component specular component
67 Figure 62 â All daytime measurements of yellow paint lines on the NTPEP test decks. Figure 63 â All daytime measurements of yellow epoxy lines on the NTPEP test decks. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 - Paint 2002 - Paint 2004 - Paint 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 - Epoxy 2002 - Epoxy 2004 - Epoxy
68 Figure 64 â All daytime measurements of yellow tape lines on the NTPEP test decks. Figure 65 â All daytime measurements of NTPEP test deck yellow thermoplastic lines. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 - Tape 2002 - Tape 2004 - Tape 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Illuminant D65 2001 - Thermoplastic 2002 - Thermoplastic 2004 - Thermoplastic
69 Figure 66 â All nighttime measurements of white lines on the NTPEP test decks. NIGHTTIME MEASUREMENTS Figure 66 shows the nighttime measurements of all the white lines on NTPEP test decks using the nighttime 30 m geometry instrument. The individual chromaticity points are plot on an enlarged (x, y) 1931 chromaticity diagram. The boxes represent the acceptable white and yellow chromaticities defined in the ASTM standard D6628-01 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A 2001 Utah - Concrete 2002 Mississippi - Asphalt 2002 Pennsylvania - Asphalt 2004 Wisconsin - Concrete 2004 Wisconsin - Asphalt 2004 Mississippi - Concrete
70 Also shown on the graph is the chromaticity coordinate for CIE Illuminant A, the reference illuminant for the ASTM D6628-01 standard. The box around the Illuminant A mark represents the expanded uncertainty of the measurements. The spread in the data points is along the red-green axis and is independent of the age or location of the material. The spread along the red-green axis is due to the fact that the RL values measured for the points outside the box have a magnitude less than 30 mcd/m2/lx. Figure 67 â All nighttime measurements of white lines sorted by type. Because of the resolution of the instrument read out, the uncertainty of the chromaticity measurement is 0.060 (k=2) for x and y. Figure 67 shows the nighttime measurements of the white lines on NTPEP decks sorted by the type of material. Table 10 presents the number of points outside of the ASTM boxes along with the types of materials that fall outside of the box. Within the uncertainty of the measurement no conclusions can be drawn between material types for the white lines. Figure 68 shows the nighttime measurements of the yellow lines on the NTPEP decks and Figure 69 shows the nighttime measurements of the yellow lines sorted by type of material. 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A Paint MMA Tape Thermoplastic Preformed Thermo Epoxy
71 Unfortunately the instrument does not have a small enough uncertainty to allow a complete analysis or accurate conclusions based on the material type, age and location. Some generalities can be made assuming the uncertainty causes a spread along the red-green axis. The spread along the blue-yellow axis is predominantly due to the fluctuation in the blue or z-channel. The blue channel has a typical magnitude of 2 â 6 for the measurement of the yellow lines. A change of one unit in the blue channel changes the chromaticity coordinates by roughly 0.008; therefore, conclusions or generalities can be drawn about the data between the white and yellow boxes. The yellow lines appear to become whiter with age as shown in Figure 68. Surprisingly, two of the yellow line measurements that are less than 3 months old fall within the ASTM white box. These two yellow line measurements that appears white under nighttime conditions fall within the yellow ASTM box for daytime measurements. The two yellow line measurements are all paint. Table 10 â Nighttime white line statistics Year, Location Surface Age Out of ASTM box Type breakdown 2001 Utah Concrete 3 years 6 out of 45 3 paint, 2 thermo, 1 pre thermo 2002 Mississippi Asphalt 2 years 2 out of 21 2 paint 2002 Pennsylvania Asphalt 2 years 1 out of 67 1 tape 2004 Wisconsin Concrete 3 months 2 out of 21 1 MMA, 1 epoxy 2004 Wisconsin Asphalt 3 months 2 out of 32 1 paint, 1 tape 2004 Mississippi Concrete 2 weeks 0 out of 5 --- Total 13 out of 191
72 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A 2001 Utah - Concrete 2002 Mississippi - Asphalt 2002 Pennsylvania - Asphalt 2004 Wisconsin - Concrete 2004 Wisconsin - Asphalt 2004 Mississippi - Concrete Figure 68 â All nighttime measurements of yellow lines on the NTPEP test decks.
73 Figure 69 â All nighttime measurements of yellow lines sorted by material type. The nighttime data is graphed by type with respect to year of application. Graph 70 is for yellow paint lines. Graph 71 is for yellow epoxy lines. Graph 72 shows the yellow tape lines and Graph 73 shows the yellow thermoplastic lines. 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A Paint MMA Tape Thermoplastic Preformed Thermo Epoxy
74 Figure 70 â All nighttime measurements of yellow paint lines on the NTPEP test decks. 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A 2001 - Paint 2002 - Paint 2004 - Paint
75 Figure 71 â All nighttime measurements of NTPEP test deck yellow epoxy lines. Figure 72 â All nighttime measurements of NTPEP test deck yellow tape lines. 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A 2001 - Epoxy 2002 - Epoxy 2004 - Epoxy 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A 2001 - Tape 2002 - Tape 2004 - Tape
76 Figure 73 â All nighttime measurements of NTPEP deck yellow thermoplastic lines. 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Illuminant A 2001 - Thermoplastic 2002 - Thermoplastic 2004 - Thermoplastic
77 LEAD AND LEAD FREE MEASUREMENTS Many manufacturers are producing pavement marking material that is lead free reacting to environmental concerns. An analysis was completed to determine if the pavement marking materials with lead had a significantly different chromaticity than the lead free products. Figure 74 shows the daytime measurements (0/45) and the Qd measurements for the yellow thermoplastic pavement marking lines for all the NTPEP test decks that were known to have lead pigment or known to be lead-free pigments. The daytime and Qd measurements shows that little chromaticity difference is measured between lead and lead-free pigments. Figure 75 shows the nighttime measurements for the yellow thermoplastic pavement marking lines for all the NTPEP test decks that were known to have lead pigment or known to be lead-free pigments. The materials with lead pigment appear to have a shift in the direction of orange-red compare to the lead-free material. However, due to the uncertainty of the nighttime instrument no conclusions can be made. Therefore, no measurable difference exists for lead-free materials versus materials that have lead pigment. Figure 74 â All daytime measurements of thermoplastic yellow pavement marking lines on the NTPEP test decks that were know to be lead-free or contain lead pigment. 0.55 0.50 0.45 0.40 0.35 0.30 x 0.550.500.450.400.350.30 y Lead - Thermo - 0/45 Lead Free - Thermo - 0/45 Lead - Thermo - Qd Lead Free - Themo - Qd Illuminant D65
78 Figure 75 â All nighttime measurements of thermoplastic yellow pavement marking lines on the NTPEP test decks that were know to be lead-free or contain lead pigment. 0.50 0.45 0.40 0.35 x 0.550.500.450.40 y Lead - Thermoplastic Lead Free - Thermoplastic Illuminant A
