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 2013
Page i
TABLE OF CONTENTS
Page
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 Handheld Retroreflectivity Data ................................. 7
Comparison Handheld Retroreflectivity Readings ..................................................................... 7
Mobile versus Handheld Evaluation ........................................................................................... 8
Raw Retroreflectivity Data Plots .......................................................................................... 13
Closed-Course Testing ...................................................................................................... 13
Open-Road Testing ........................................................................................................... 20
Chapter 4: Findings and Recommendations ............................................................................ 29
Summary of Test Results .......................................................................................................... 29
Additional Comments and Suggestions .................................................................................... 31
Page ii
LIST OF FIGURES
Page
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 Handheld 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 10. Runs 4, 17, 18: Yellow Solid Marking. ....................................................................... 16
Figure 11. Runs 5, 6, 23: White Solid Marking. ........................................................................... 17
Figure 12. Runs 10, 15, 20: 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. ..................................... 20
Figure 18. Run A: White Edge Line Marking. ............................................................................. 21
Figure 19. Runs A and H: White Skip Line Marking. .................................................................. 21
Figure 20. 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 30. 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. ........................................................................................ 30
Figure 34. Screenshot of Data Collection Video. ......................................................................... 30
Page iii
LIST OF TABLES
Page
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............................................................................ 10
Page 1
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 2
CHAPTER 2:
CERTIFICATION TEST
The certification test of the AMAC system was conducted in January 2013. 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 0.4 miles (644 meters)
long. The skip line areas are approximately 0.5 miles (805 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 3
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 20 miles (32 kilometers) long and contained 20 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 open-
road test area were evaluated as close to the speed limit as possible. For the higher speed open-
road 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 100 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 4
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 0.05 miles (80 meter) intervals, were submitted for analysis.
All retroreflectivity measurements were in units of millicandelas per meter squared per lux
(mcd/m2/lux).
To comply with TxDOT Special Specification 8094: 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 5
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 0.1-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 6
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 7
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 30-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 70 measurements per test line. For the closed-course solid pavement markings, one
reading was taken at approximately 30-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 40-foot (12.2-meter) intervals. Due to the varying length of the open-road test
sections, the number of handheld readings ranged from approximately 40 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 8
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
2
1σ 16
3
1σ 35
4
1σ 62
10
1σ 385
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.
Pa
ge
9
Table 2. Summary of Closed-Course Testing Data
Closed-Course Testing Line 1 Line 2 % Error
Run
Number Line Type
Mobile
Average
Handheld
Average
Mobile
Stdev
Handheld
Stdev
Mobile
Average
Handheld
Average
Mobile
Stdev
Handheld
Stdev Left Right
1 Yellow solid/white solid 156 148 29 26 237 220 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 30 6.67
4 Yellow solid 164 145 24 17 13.10
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 2.03
8 Yellow solid/white solid 162 148 31 26 244 220 44 34 9.46 10.91
9 Double solid yellow 180 154 31 26 182 159 36 31 16.88 14.47
10 Yellow skip 186 179 52 37 3.91
11 White skip 260 227 58 44 14.54
12 White skip 262 227 63 44 15.42
13 Double yellow broken/solid 194 166 43 27 158 142 30 21 16.87 11.27
14 Double yellow solid/broken 188 170 33 32 184 152 38 24 10.59 21.05
15 Yellow skip 189 179 45 37 5.59
16 Yellow solid/white solid 157 148 31 26 242 220 44 34 6.08 10.00
17 Yellow solid 156 145 23 17 7.59
18 Yellow solid 140 145 25 17 −3.45
19 White skip 252 227 66 44 11.01
20 Yellow skip 197 179 43 37 10.06
22 Yellow solid/white solid 160 148 30 26 242 220 41 34 8.11 10.00
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.
Pa
ge
10
Table 3. Summary of Open-Road Testing Data.
Open-Road Testing Line 1 Line 2 % Error
Run
Identifier Line Types
Mobile
Average
Handheld
Average
Mobile
Stdev
Handheld
Stdev
Mobile
Average
Handheld
Average
Mobile
Stdev
Handheld
Stdev Left Right
A White skip/white solid 435 453 48 40 360 353 39 26 −3.97 1.98
B White skip/white solid 420 441 54 53 349 307 48 41 −4.76 13.68
C Yellow skip/white solid 89 68 18 10 257 234 49 53 30.88 9.83
D Yellow skip/white solid 73 60 14 10 193 186 29 24 21.67 3.76
E White skip/white solid 400 421 55 28 417 431 66 38 −4.99 −3.25
F Yellow skip/white solid 92 87 18 10 182 169 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 40 −1.52 −12.80
I Yellow solid/white skip 208 230 34 27 396 441 70 53 −9.57 −10.20
J Yellow solid/white skip 230 248 43 23 387 421 52 28 −7.26 −8.08
Page 11
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
10.8 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.
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 seal-
coat 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-
0
2
4
6
8
10
12
14
Nu
mb
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of
Occ
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Percent Error Range Bins
Page 12
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, 30.9 and
21.7 percent for runs C left and D left, respectively, but the magnitude of the retroreflectivity
difference was 21 and 13 mcd/m2/lux, respectively. This retroreflectivity difference is not as
large as other differences seen that resulted in percent errors that were less than 10 percent. The
fact that the mobile system evaluated these markings as poor-quality markings (retroreflectivity
levels less than 100 mcd/m2/lux) when the markings are actually less than 100 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 0.3 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 R2 value of 0.9687, 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
R2 value of 0.519.
Page 13
Figure 4. Comparison of Mobile and Handheld 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
10 percent higher than the handheld data on the closed-course test area.
y = 1.1184x - 35.918
R² = 0.9687
y = 0.9813x
R² = 0.9519
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0 100 200 300 400 500 600
Ha
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AMAC Mobile Retroreflectivity (mcd/m2/lux)
Page 14
Figure 5. Runs 1, 7, 8, 16, 22: Yellow Solid Marking.
Figure 6. Runs 1, 8, 16, 22: White Solid Marking.
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Mobile Run 1 Mobile Run 7 Mobile Run 8
Mobile Run 16 Mobile Run 22 Handheld
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Mobile Run 16 Mobile Run 22
Handheld
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Figure 7. Runs 2, 9: Double Yellow Solid Marking, Left Line.
Figure 8. Runs 2, 9: Double Yellow Solid Marking, Right Line.
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Figure 9. Run 3: White Solid Marking.
Figure 10. Runs 4, 17, 18: Yellow Solid Marking.
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Page 17
Figure 11. Runs 5, 6, 23: White Solid Marking.
Figure 12. Runs 10, 15, 20: Yellow Skip Marking.
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Mobile Run 5 Mobile Run 6 Mobile Run 23 Handheld
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Figure 13. Runs 11, 12, 19: White Skip Marking.
Figure 14. Run 13: Double Yellow Broken/Solid Marking, Left Line.
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Figure 15. Run 13: Double Yellow Broken/Solid Marking, Right Line.
Figure 16. Run 14: Double Yellow Solid/Broken Marking, Left Line.
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Mobile Run 13 Handheld
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Mobile Run 14 Handheld
Page 20
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.
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Figure 18. Run A: White Edge Line Marking.
Figure 19. Runs A and H: White Skip Line Marking.
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Figure 20. Run B: White Edge Line Marking.
Figure 21. Runs B and I: White Skip Line Marking.
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Figure 22. Run C: White Edge Line Marking.
Figure 23. Run C: Yellow Skip Center Line Marking.
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Figure 24. Run D: White Edge Line Marking.
Figure 25. Run D: Yellow Skip Center Line Marking.
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Figure 26. Run E: White Edge Line Marking.
Figure 27. Runs E and J: White Skip Line Marking.
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Figure 28. Run F: White Edge Line Marking.
Figure 29. Run F: Yellow Skip Center Line Marking.
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Figure 30. Run H: Yellow Edge Line Marking.
Figure 31. Run I: Yellow Edge Line Marking.
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Figure 32. Run J: Yellow Edge Line Marking.
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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 8094: 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 closed-
course runs averaged about 10.8 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
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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.
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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 500 mcd/m2/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.
