INVESTIGATE THE ABILITY TO DETERMINE PAVEMENT MARKING RETROREFLECTIVITY

INVESTIGATE THE ABILITY TO DETERMINE PAVEMENT MARKING RETROREFLECTIVITY Evaluate the Advanced Mobile Asset Collection (AMAC) Mobile Pavement Marking Retroreflectivity Measurement System Report prepared by Adam Pike and Paul Carlson TEXAS A&M TRANSPORTATION INSTITUTE College Station, Texas 77843-3135 Report Prepared for AMAC DBI/Cidaut Technologies LLC April 213

TABLE OF CONTENTS List of Figures... ii List of Tables... iii Chapter 1: Background... 1 Chapter 2: Certification Test... 2 Conducting the Certification Test... 2 Data Submission... 4 Data File... 5 Map in Electronic Format... 6 Video... 6 Chapter 3: Evaluation of Mobile and Retroreflectivity Data... 7 Comparison Retroreflectivity Readings... 7 Mobile versus Evaluation... 8 Raw Retroreflectivity Data Plots... 13 Closed-Course Testing... 13 Open-Road Testing... 2 Chapter 4: Findings and Recommendations... 29 Summary of Test Results... 29 Additional Comments and Suggestions... 31 Page Page i

LIST OF FIGURES Figure 1. Closed-Course Pavement Marking Evaluation Area.... 3 Figure 2. Open-Road Pavement Marking Evaluation Route.... 4 Figure 3. Histogram of Percent Error for All Tests.... 11 Figure 4. Comparison of Mobile and Retroreflectivity Measurements.... 13 Figure 5. Runs 1, 7, 8, 16, 22: Yellow Solid Marking.... 14 Figure 6. Runs 1, 8, 16, 22: White Solid Marking.... 14 Figure 7. Runs 2, 9: Double Yellow Solid Marking, Left Line.... 15 Figure 8. Runs 2, 9: Double Yellow Solid Marking, Right Line.... 15 Figure 9. Run 3: White Solid Marking.... 16 Figure 1. Runs 4, 17, 18: Yellow Solid Marking.... 16 Figure 11. Runs 5, 6, 23: White Solid Marking.... 17 Figure 12. Runs 1, 15, 2: Yellow Skip Marking.... 17 Figure 13. Runs 11, 12, 19: White Skip Marking.... 18 Figure 14. Run 13: Double Yellow Broken/Solid Marking, Left Line.... 18 Figure 15. Run 13: Double Yellow Broken/Solid Marking, Right Line.... 19 Figure 16. Run 14: Double Yellow Solid/Broken Marking, Left Line.... 19 Figure 17. Run 14: Double Yellow Solid/Broken Marking, Right Line.... 2 Figure 18. Run A: White Edge Line Marking.... 21 Figure 19. Runs A and H: White Skip Line Marking.... 21 Figure 2. Run B: White Edge Line Marking... 22 Figure 21. Runs B and I: White Skip Line Marking.... 22 Figure 22. Run C: White Edge Line Marking... 23 Figure 23. Run C: Yellow Skip Center Line Marking.... 23 Figure 24. Run D: White Edge Line Marking.... 24 Figure 25. Run D: Yellow Skip Center Line Marking... 24 Figure 26. Run E: White Edge Line Marking.... 25 Figure 27. Runs E and J: White Skip Line Marking.... 25 Figure 28. Run F: White Edge Line Marking.... 26 Figure 29. Run F: Yellow Skip Center Line Marking.... 26 Figure 3. Run H: Yellow Edge Line Marking.... 27 Figure 31. Run I: Yellow Edge Line Marking.... 27 Figure 32. Run J: Yellow Edge Line Marking.... 28 Figure 33. Screenshot of Mapped Data.... 3 Figure 34. Screenshot of Data Collection Video.... 3 Page Page ii

LIST OF TABLES Table 1. Minimum Sample Size (n) Required to Estimate the True Mean Retroreflectivity to within B with 95 Percent Confidence.... 8 Table 2. Summary of Closed-Course Testing Data... 9 Table 3. Summary of Open-Road Testing Data... 1 Page Page iii

CHAPTER 1: BACKGROUND The Advanced Mobile Asset Collection (AMAC) system (operated by DBI/Cidaut Technologies LLC) has been enhanced to include mobile measurements of pavement marking retroreflectivity. The Texas A&M Transportation Institute (TTI) has experience evaluating various mobile pavement marking retroreflectivity technologies, and certifying equipment and operators for the Texas Department of Transportation (TxDOT). In this effort, TTI evaluated the AMAC mobile pavement marking technology, following the protocol that TxDOT and TTI have established to certify mobile systems used on TxDOT highways. The next three chapters in this document describe the certification test, the certification results, and the findings and recommendations, respectively. Page 1

CHAPTER 2: CERTIFICATION TEST The certification test of the AMAC system was conducted in January 213. This chapter describes the data collection efforts during the certification process. CONDUCTING THE CERTIFICATION TEST Currently there is not a national specification or test method for evaluating mobile pavement marking retroreflectometers. TTI and TxDOT have developed a certification program to evaluate the ability of an operator and his or her equipment to collect accurate mobile pavement marking retroreflectivity data. The certification test of the AMAC system followed the TxDOT and TTI certification process. TTI maintains a number of markings in standard and nonstandard configurations along the runways (closed-course testing) at the Texas A&M University s Riverside Campus. TTI also regularly evaluates several sections of markings on the TxDOT-maintained roadway system (open-road testing) near the Riverside Campus. The certification test evaluated both white and yellow pavement markings in solid and skip patterns. The certification test also evaluated markings on different road surfaces: concrete, asphalt, and seal coat. The markings evaluated covered a range of retroreflectivity levels so the AMAC system s ability to detect the different levels could be evaluated. Figure 1 shows the typical layout of the markings at the Riverside Campus. The majority of the closed-course markings are thermoplastic, but paint and tape are also part of the markings evaluated. The solid line areas on the closed course are approximately.4 miles (644 meters) long. The skip line areas are approximately.5 miles (85 meters) long. In general, the markings are evaluated as they would be under normal data collection operation. This means that yellow markings are evaluated on the left side of the vehicle and white markings on the right, except for skip markings, which can be evaluated on both sides. The AMAC system was evaluated in the standard measurement positions, with several runs in the nonstandard positions (i.e. yellow markings on the right, or solid white markings on the left) for comparison purposes. A total of 26 pavement markings were evaluated during the closed-course testing. All measurements on the closed-course markings were on a concrete road surface. Page 2

Figure 1. Closed-Course Pavement Marking Evaluation Area. Figure 2 indicates the road course for the open-road test area. The open-road course was approximately 2 miles (32 kilometers) long and contained 2 pavement marking test areas. All of the markings on the open-road test area were thermoplastic. Retroreflective raised pavement markers were present on the open-road test area along center and skip lines. Measurements on the closed-course markings were on either an asphalt road surface or a seal-coat road surface. During the certification test, the AMAC van and operator followed the evaluation course while measuring the retroreflectivity of the pavement markings. Pavement markings on the closed-course area were evaluated at approximately 35 mph. Pavement markings on the openroad test area were evaluated as close to the speed limit as possible. For the higher speed openroad test areas with a posted speed limit of 75 mph, the speed of data collection was lower than the posted speed to allow the system to have 1 percent data coverage through the evaluation sections. A researcher from TTI rode with the AMAC operator to direct the operator to the correct pavement markings to measure. Some test sections were read more than once to test the repeatability of the measurements. All testing was conducted at night. Page 3

Figure 2. Open-Road Pavement Marking Evaluation Route. DATA SUBMISSION Upon completion of the certification test, the data were processed, and the results were delivered to TTI for analysis. The data were submitted separately for the open-road course and the closed-course testing. Data for the closed-course testing were separated by the certification trial run number and the associated pavement marking identifier number for the specific marking evaluated. Data for the open-road testing were based upon the global positioning system (GPS) coordinates of the start and end points of the evaluation area. The data were further separated by the run identifier and the position (left or right) of the marking being evaluated. All data were continuously recorded through each measurement section. These raw data, as well as the data aggregated over.5 miles (8 meter) intervals, were submitted for analysis. All retroreflectivity measurements were in units of millicandelas per meter squared per lux (mcd/m 2 /lux). To comply with TxDOT Special Specification 894: Mobile Retroreflectivity Data Collection for Pavement Markings, additional data are also required to be submitted. These data include a formatted data file, an electronic map of the retroreflectivity data, and video of the data Page 4

collection. Not all aspects of the additional data are necessary for the certification trial, but the capabilities to include them must be demonstrated. Some aspects of the additional data may only be applicable to certain pieces of equipment and thus may not be required for the AMAC system. The requirements of each of these areas are described below. Data File The formatted data file must contain the following information: date; district number; county; route number with reference markers or other reference information provided by the engineer to indicate the location of beginning and ending data collection points on that roadway; cardinal direction; line type (single solid, single broken, double solid, etc.); line color; file name corresponding to video; data for each center line listed separately; average reading taken for each.1-mile interval or interval designated by the engineer; accurate GPS coordinates for each interval; color coding for each interval indicating passing or failing, unless otherwise directed by the engineer (passing and failing thresholds will be provided by the engineer); graphical representation of the retroreflectivity data (y-axis showing retroreflectivity and x-axis showing intervals) corresponding with each data file; distance in miles driven while measuring the pavement markings; event codes (pre-approved by the engineer) indicating problems with measurement; portable retroreflectometer field-check average reading and corresponding mobile average reading for that interval when applicable; and upper validation threshold (may be included separately with the raw data). Page 5

Map in Electronic Format The map in an electronic format, giving a visual representation of the retroreflectivity data plotted on the roads with color-coded retroreflectivity levels, must contain the following information: date; district number; county; color-coded 1-mile intervals (or interval length designated by the engineer) for passing and failing retroreflectivity values or retroreflectivity threshold values provided by the engineer; and percentage of passing and failing intervals, if required by the engineer. Video The video of the data collection must be provided on a high-quality DVD and include the following information: date and corresponding data file name; district number; county; route number with reference markers or other designated reference information to indicate the location of beginning and ending collection points on that roadway; and retroreflectivity values presented on the same screen with the following information: o date, o location, o starting and ending mileage, o total miles, o retroreflectivity readings, and o upper validation thresholds (may be included separately with the raw data). Page 6

CHAPTER 3: EVALUATION OF MOBILE AND HANDHELD RETROREFLECTIVITY DATA The goal of this research project was to assess the ability of the AMAC system to collect accurate mobile retroreflectivity data. This was accomplished by collecting mobile retroreflectivity data with the AMAC system and comparing that data to handheld retroreflectivity data collected along the same pavement marking test sections. This chapter of the report describes the collection of the comparison handheld retroreflectivity data and the comparison between the handheld and mobile readings. COMPARISON HANDHELD RETROREFLECTIVITY READINGS To assess the accuracy of the AMAC mobile pavement marking retroreflectivity evaluation system, comparison handheld readings were taken. These handheld readings are considered the true measure of the pavement marking retroreflectivity. Properly calibrated handheld pavement marking retroreflectometers measuring at the standard 3-meter geometry were used. A sufficient number of handheld readings are needed in each test section to be confident of the reported values that are compared to the AMAC values. Table 1 provides a comparison of the number of readings (n) necessary to be within B of the true retroreflectivity of the evaluation area. The standard deviation (σ) of the evaluation areas impacts the range in which the estimated true mean will fall for any given number of readings. Because the standard deviations of the evaluation areas were unknown prior to the data collection, a standard data collection plan was adopted. For the closed-course skip line pavement markings, one reading was taken on each skip line, which resulted in approximately 7 measurements per test line. For the closed-course solid pavement markings, one reading was taken at approximately 3-foot (9.1-meter) intervals, which resulted in approximately 75 measurements per test line. For the open-road pavement markings, all measurements were made at approximately 4-foot (12.2-meter) intervals. Due to the varying length of the open-road test sections, the number of handheld readings ranged from approximately 4 to 75 for each pavement marking. The handheld retroreflectivity readings were taken along some of the test sections the day before, the day of, and the day after the certification testing. All handheld retroreflectivity readings were taken within the three-day range and were taken on representative locations of the pavement Page 7

markings at the approximate distances indicated above. There was no rain or other precipitation between the times the handheld readings and mobile readings were made. Table 1. Minimum Sample Size (n) Required to Estimate the True Mean Retroreflectivity to within B with 95 Percent Confidence. B N σ 4 1 σ 16 2 1 σ 35 3 1 σ 62 4 1 σ 385 1 MOBILE VERSUS HANDHELD EVALUATION To evaluate the accuracy of the AMAC mobile pavement marking retroreflectivity system, the mobile retroreflectivity data were compared to handheld retroreflectivity data collected along the same pavement marking test sections. The average mobile retroreflectivity value for each pavement marking test section was determined from the data provided by the operator. The average handheld retroreflectivity value was determined by averaging the handheld retroreflectivity readings taken along the pavement marking section. These two average values were then compared, considering the handheld value to be the true retroreflectivity. The percent error was then calculated. Table 2 provides the results of the closed-course testing. Table 3 provides the results of the open-road testing. Both tables indicate the run number or run identifier and the type of marking being measured. The average mobile and handheld values as well as the associated standard deviations (Stdev) of the measurements are also included. The percent error of the mobile reading from the handheld reading is provided for each pavement marking. The cells highlighted yellow are the readings that were outside the ±15 percent error range that is used to assess the quality of the mobile data collection. TxDOT wants mobile readings that are within ±15 percent error in order to be confident in the data collected. Page 8

Table 2. Summary of Closed-Course Testing Data Closed-Course Testing Line 1 Line 2 % Error Run Number Line Type Mobile Average Average Mobile Stdev Stdev Mobile Average Average Mobile Stdev Stdev Left Right 1 Yellow solid/white solid 156 148 29 26 237 22 41 34 5.41 7.73 2 Double solid yellow 179 154 29 26 188 159 34 31 16.23 18.24 3 White solid 144 135 37 3 6.67 4 Yellow solid 164 145 24 17 13.1 5 White solid 228 195 51 44 16.92 6 White solid 225 195 49 44 15.38 7 Yellow solid 151 148 35 26 2.3 8 Yellow solid/white solid 162 148 31 26 244 22 44 34 9.46 1.91 9 Double solid yellow 18 154 31 26 182 159 36 31 16.88 14.47 1 Yellow skip 186 179 52 37 3.91 11 White skip 26 227 58 44 14.54 12 White skip 262 227 63 44 15.42 13 Double yellow broken/solid 194 166 43 27 158 142 3 21 16.87 11.27 14 Double yellow solid/broken 188 17 33 32 184 152 38 24 1.59 21.5 15 Yellow skip 189 179 45 37 5.59 16 Yellow solid/white solid 157 148 31 26 242 22 44 34 6.8 1. 17 Yellow solid 156 145 23 17 7.59 18 Yellow solid 14 145 25 17 3.45 19 White skip 252 227 66 44 11.1 2 Yellow skip 197 179 43 37 1.6 22 Yellow solid/white solid 16 148 3 26 242 22 41 34 8.11 1. 23 White solid 218 195 43 44 11.79 Empty cells are due to only one marking being evaluated during that run. Run 21 was skipped and thus was not included. Page 9

Table 3. Summary of Open-Road Testing Data. Open-Road Testing Line 1 Line 2 % Error Run Identifier Line Types Mobile Mobile Average Average Stdev Stdev Mobile Mobile Average Average Stdev Stdev Left Right A White skip/white solid 435 453 48 4 36 353 39 26 3.97 1.98 B White skip/white solid 42 441 54 53 349 37 48 41 4.76 13.68 C Yellow skip/white solid 89 68 18 1 257 234 49 53 3.88 9.83 D Yellow skip/white solid 73 6 14 1 193 186 29 24 21.67 3.76 E White skip/white solid 4 421 55 28 417 431 66 38 4.99 3.25 F Yellow skip/white solid 92 87 18 1 182 169 43 32 5.75 7.69 G Yellow solid/white skip 192 182 48 45 231 239 63 37 5.49 3.35 H Yellow solid/white skip 195 198 35 33 395 453 53 4 1.52 12.8 I Yellow solid/white skip 28 23 34 27 396 441 7 53 9.57 1.2 J Yellow solid/white skip 23 248 43 23 387 421 52 28 7.26 8.8 Page 1

Figure 3 provides a summary histogram of the percent errors from all of the markings measured. In the figure, the overall data are skewed to the right, indicating that the system typically measured the markings higher than did the handheld retroreflectometer. Further investigation into the percent errors indicates that the closed-course runs averaged about 1.8 percent high, whereas the open-road runs averaged about 1.5 percent high. After excluding the two high error markings (runs C left and D left) from the open-road runs, the average error was 1.2 percent low. Overall, the error averaged 7.1 percent high. Excluding runs C left and D left, the overall error averaged 6.3 percent high. 14 12 Number of Occurrences 1 8 6 4 2 Percent Error Range Bins Figure 3. Histogram of Percent Error for All Tests. Runs C left and D left were both yellow skip line markings on a seal-coat road surface that had a very low retroreflectivity level. Low retroreflectivity pavement markings are typically difficult to measure with a mobile system. Yellow skip line markings, especially those on sealcoat surfaces, are also some of the most difficult types of markings to accurately measure with a mobile system. The low retroreflectivity level combined with a yellow skip marking on a seal- Page 11

coat road surface is the most difficult type of marking to evaluate. Looking at the actual retroreflectivity values, the mobile system may have had a large percent error, 3.9 and 21.7 percent for runs C left and D left, respectively, but the magnitude of the retroreflectivity difference was 21 and 13 mcd/m 2 /lux, respectively. This retroreflectivity difference is not as large as other differences seen that resulted in percent errors that were less than 1 percent. The fact that the mobile system evaluated these markings as poor-quality markings (retroreflectivity levels less than 1 mcd/m 2 /lux) when the markings are actually less than 1 mcd/m 2 /lux can be considered a good thing for maintenance purposes. The percent error may be large, but the readings themselves are representative of the quality of the pavement marking. To look for trends in the AMAC data collection on the markings, the percent error for the marking colors and measurement location were also evaluated. These trends will not consider runs C left and D left based on the previous discussion. The AMAC system measured white markings 4.8 percent high and yellow markings 7.8 percent high. White markings measured almost equally on both sides of the vehicle, with white markings on the left measuring 4.5 percent high and white markings on the right measuring 4.9 percent high. Yellow markings were typically measured only on the left side of the vehicle with the exception of the marking measured in runs 17 and 18 where it was measured on both sides of the vehicle. The results indicate that the AMAC system measured the yellow line approximately 7.6 percent high on the left side but 3.4 percent low on the right side. Five white lines were measured on both sides of the vehicle. The measurements on the left averaged approximately 3.2 percent high, whereas the measurements on the right averaged approximately.3 percent high. Combining all measurements on the left resulted in measurements that were approximately 7.2 percent high, whereas measurements on the right were 4.4 percent high. Figure 4 is a plot of the comparison of the mobile to handheld retroreflectivity readings. The data had a strong linear correlation, which indicates the system can accurately measure across a range of retroreflectivity levels. The best fit trendline had an R 2 value of.9687, which shows strong correlation between the mobile and handheld values. A second trendline with a y-intercept of zero was also included. The second trendline also had a strong correlation with an R 2 value of.519. Page 12

6 5 4 3 2 1 y = 1.1184x -35.918 R² =.9687 y =.9813x R² =.9519 1 2 3 4 5 6 AMAC Mobile Figure 4. Comparison of Mobile and Retroreflectivity Measurements. Raw Retroreflectivity Data Plots In addition to the evaluation of the data based on the overall average and the percent error, the general trends of the data along the length of the evaluation area were also observed. The raw mobile retroreflectivity data were plotted for the length of each test section. In addition to the mobile data, the handheld retroreflectivity data were also plotted to compare the trends in the retroreflectivity data along the length of the test section. Closed-Course Testing Figure 5 through Figure 17 show all of the retroreflectivity data for the closed-course pavement marking test sections. In general, the mobile data very closely follow the handheld retroreflectivity data trends. The only difference is that on some plots the mobile data are higher than the handheld data. This is expected because the mobile data average approximately 1 percent higher than the handheld data on the closed-course test area. Page 13

35 3 25 2 15 1 5 Mobile Run 1 Mobile Run 7 Mobile Run 8 Mobile Run 16 Mobile Run 22 1 2 3 4 5 6 7 Figure 5. Runs 1, 7, 8, 16, 22: Yellow Solid Marking. 45 4 35 3 25 2 15 1 5 1 2 3 4 5 6 7 Mobile Run 1 Mobile Run 8 Mobile Run 16 Mobile Run 22 Figure 6. Runs 1, 8, 16, 22: White Solid Marking. Page 14

35 3 25 2 15 1 5 Mobile Run 2 Mobile Run 9 1 2 3 4 5 6 7 Figure 7. Runs 2, 9: Double Yellow Solid Marking, Left Line. 35 3 25 2 15 1 5 Mobile Run 2 Mobile Run 9 1 2 3 4 5 6 7 Figure 8. Runs 2, 9: Double Yellow Solid Marking, Right Line. Page 15

3 Mobile Run 3 25 2 15 1 5 1 2 3 4 5 6 7 Figure 9. Run 3: White Solid Marking. 3 Mobile Run 4 Mobile Run 17 Mobile Run 18 25 2 15 1 5 1 2 3 4 5 6 7 Figure 1. Runs 4, 17, 18: Yellow Solid Marking. Page 16

5 45 4 35 3 25 2 15 1 5 Mobile Run 5 Mobile Run 6 Mobile Run 23 1 2 3 4 5 6 7 Figure 11. Runs 5, 6, 23: White Solid Marking. 4 35 3 25 2 15 1 5 Mobile Run 1 Mobile Run 15 Mobile Run 2 2 4 6 8 1 Figure 12. Runs 1, 15, 2: Yellow Skip Marking. Page 17

6 Mobile Run 11 Mobile Run 12 Mobile Run 19 5 4 3 2 1 2 4 6 8 1 Figure 13. Runs 11, 12, 19: White Skip Marking. 4 35 3 25 2 15 1 5 Mobile Run 13 2 4 6 8 1 Figure 14. Run 13: Double Yellow Broken/Solid Marking, Left Line. Page 18

3 25 2 15 1 5 Mobile Run 13 2 4 6 8 1 Figure 15. Run 13: Double Yellow Broken/Solid Marking, Right Line. 3 25 2 15 1 5 Mobile Run 14 2 4 6 8 1 Figure 16. Run 14: Double Yellow Solid/Broken Marking, Left Line. Page 19

35 3 25 2 15 1 5 Mobile Run 14 2 4 6 8 1 Figure 17. Run 14: Double Yellow Solid/Broken Marking, Right Line. Open-Road Testing Figure 18 through Figure 32 show all of the retroreflectivity data for the open-road pavement marking test sections. The exact locations of the handheld readings compared to the mobile readings for the open-road testing are not as precise as they are for the closed-course testing. This is due to using GPS for the start and end points of the mobile data and the reporting intervals used by the AMAC system. Due to the minor expected differences, it is possible that the handheld data may need to be adjusted slightly along the x-axis to better align with the mobile data. Similarly to the closed-course testing, the mobile data very closely follow the handheld retroreflectivity data trends. Unlike the closed-course testing, the mobile data are similar in magnitude to the handheld data. This is expected because the mobile data average only 1 percent higher than the handheld data on the open-road test area. Page 2

5 45 4 35 3 25 2 15 1 5 Mobile Run A Right 1 2 3 4 5 6 7 Figure 18. Run A: White Edge Line Marking. 7 6 5 4 3 2 1 Mobile Run A Left Mobile Run H Right 1 2 3 4 5 6 7 Figure 19. Runs A and H: White Skip Line Marking. Page 21

6 Mobile Run B Right 5 4 3 2 1 2 4 6 8 1 Figure 2. Run B: White Edge Line Marking. 6 Mobile Run B Left Mobile Run I Right 5 4 3 2 1 2 4 6 8 1 Figure 21. Runs B and I: White Skip Line Marking. Page 22

4 35 3 25 2 15 1 5 Mobile Run C Right 1 2 3 4 5 6 Figure 22. Run C: White Edge Line Marking. 14 12 1 8 6 4 2 Mobile Run C Left 1 2 3 4 5 6 Figure 23. Run C: Yellow Skip Center Line Marking. Page 23

35 3 25 2 15 1 5 Mobile Run D Right 1 2 3 4 5 6 Figure 24. Run D: White Edge Line Marking. 12 Mobile Run D Left 1 8 6 4 2 1 2 3 4 5 6 Figure 25. Run D: Yellow Skip Center Line Marking. Page 24

6 Mobile Run E Right 5 4 3 2 1 1 2 3 4 5 6 Figure 26. Run E: White Edge Line Marking. 6 Mobile Run E Left Mobile Run J Right 5 4 3 2 1 1 2 3 4 5 6 Figure 27. Runs E and J: White Skip Line Marking. Page 25

35 3 25 2 15 1 5 Mobile Run F Right 1 2 3 4 5 6 7 8 Figure 28. Run F: White Edge Line Marking. 14 12 1 8 6 4 2 Mobile Run F Left 1 2 3 4 5 6 7 8 Figure 29. Run F: Yellow Skip Center Line Marking. Page 26

3 Mobile Run H Left 25 2 15 1 5 1 2 3 4 5 6 7 Figure 3. Run H: Yellow Edge Line Marking. 35 3 25 2 15 1 5 Mobile Run I Left 2 4 6 8 1 Figure 31. Run I: Yellow Edge Line Marking. Page 27

4 35 3 25 2 15 1 5 Mobile Run J Left 1 2 3 4 5 6 Figure 32. Run J: Yellow Edge Line Marking. Page 28

CHAPTER 4: FINDINGS AND RECOMMENDATIONS This report includes a description of the testing of the AMAC mobile pavement marking retroreflectivity measurement capabilities. The AMAC system s ability to collect accurate pavement marking retroreflectivity data was assessed by comparing the AMAC retroreflectivity data to handheld retroreflectometer data collected along the same measurement sections. The data submitted from the AMAC system were also compared to the requirements specified in TxDOT Special Specification 894: Mobile Retroreflectivity Data Collection for Pavement Markings. The data submitted from the AMAC system meet the requirements for TxDOT certification. SUMMARY OF TEST RESULTS Closed-course and open-road testing was performed as part of the evaluation of the AMAC system. Investigation into the percent errors indicates that the AMAC system s closedcourse runs averaged about 1.8 percent higher than the handheld retroreflectivity measurements. The open-road runs averaged about 1.5 percent higher than the handheld retroreflectivity measurements. When excluding the two high error markings (runs C left and D left) from the open-road runs, the average error was 1.2 percent low. Overall, the AMAC error averaged 7.1 percent higher than the handheld measurements. Excluding runs C left and D left, the overall error averaged 6.3 percent high. In general, the mobile data very closely follow the handheld retroreflectivity data trends along each measurement section for both the closed-course and open-road test areas. Beyond the retroreflectivity data, additional information is required in order to receive TxDOT certification. These data include a formatted data file, an electronic map of the retroreflectivity data, and video of the data collection. Not all aspects of the additional data are necessary for the certification trial, but the capabilities to include them must be demonstrated. Figure 33 provides an example of the data in mapped format. The retroreflectivity is plotted on the map using color to indicate the retroreflectivity of the markings measured. Included with the map is a plot of the data and the raw data themselves. Figure 34 provides a screenshot from the Page 29

video of the data collection. The video includes images of the markings measured, with the retroreflectivity and GPS coordinates of the measurement location on the same screen. Figure 33. Screenshot of Mapped Data. Figure 34. Screenshot of Data Collection Video. Page 3

ADDITIONAL COMMENTS AND SUGGESTIONS After evaluating the AMAC system, the researchers had several comments and suggestions. These comments and suggestions are based on the results of the testing and may provide areas for future testing to improve the AMAC system. Was the downward slope or the undulating surface of the jointed concrete of the closed-course test area responsible for the consistently high retroreflectivity readings on the closed-course area? What impacts would ambient light such as an urban environment or oncoming traffic have on the AMAC system? With large temperature changes typical in Texas, how would changes in ambient temperature affect the AMAC system? This evaluation looked at a range of pavement marking retroreflectivity levels, but high retroreflectivity markings were not evaluated. How accurate would the AMAC measurements be on pavement markings over 5 mcd/m 2 /lux? Minor differences were observed across the measurement window for the conditions tested during this evaluation. Measurements on the left were slightly higher than on the right. Would other conditions such as differing lane widths or markings of greatly different retroreflectivity levels on different sides of the vehicle impact the accuracy of the readings? Some of the data submitted had measurements that were likely missed when filtering the data. Readings included some abnormally high and low measurements with the data. This was especially noticeable on the skip line pavement markings where there were several low readings included with the submitted data. It would be advantageous to have the ability to have real-time data output for verification of measurements and demonstration purposes. Page 31