Quantification of Smoothness Index Differences Related To
Long-Term Pavement Performance Equipment Type
Appendix A: LTPP Profiler Comparison
Studies
1990 COMPARISON: AUSTIN, TX
This comparison was conducted in February 1990. The information
presented in this section was obtained from a paper written about
this comparison.(10)
The four LTPP DNC 690 profilers were used in this comparison.
Six test sections, each 322 m (1056 ft) long were established for
testing. Reference profile measurements along both wheelpaths at
the test sections were obtained using Dipstick. The profilers
performed five repeat runs at each test section at speeds of 56 and
80 km/h (35 and 80 mi/h). The left wheelpath was marked at the test
sections and the profiler drivers were asked to align the profiler
along this path. Each test section was divided into two sections
for analysis, resulting in the availability of 12 sections for
comparing the profiler and Dipstick IRI. The following are the main
findings from this study:
- In most cases, better agreement between profiler IRI and
Dipstick IRI was obtained for the left wheelpath than for the right
wheelpath. It was noted that the IRI for the right wheelpath
usually was higher than that for the left wheelpath. Poor agreement
between profiler IRI and Dipstick IRI usually occurred at the rough
sections.
- Significant differences between profiler IRI and Dipstick IRI
were noted for several cases, with the profiler IRI being much
higher than the Dipstick IRI. Most of the cases where these
significant differences occurred were along the right wheelpath at
extremely rough sections that had Dipstick IRI values in excess of
4 m/km (254 inches/mi). An evaluation of the profiler data for such
cases indicated saturation spikes in the data, which was the cause
of the high IRI value. It was concluded that the side-to-side
rocking motion induced on the profiler when traversing these rough
sections caused sunlight to seep under the shroud covering the
sensors and contaminate the profile data.
- Evaluation of the profiles also indicated instances where lost
lock occurred. This was another factor contributing to differences
between Dipstick and profiler IRI values.
- An evaluation of the Dipstick IRI values obtained for the 12
sections indicated the following IRI distribution:
- Left Wheelpath: Seven sections had IRI values between 1.2 and
2.4 m/km (76 and 152 inches/mi), three sections had IRI values
between 2.4 and 4.7 m/km (152 and 298 inches/mi), and two sections
had IRI values exceeding 4.7 m/km (298 inches/mi).
- Right Wheelpath: Five sections had IRI values between 1.2 and
2.4 m/km (76 and 152 inches/mi), five sections had IRI values
between 2.4 and 4.7 m/km (152 and 297 inches/mi), and two sections
had IRI values exceeding 4.7 m/km (298 inches/mi).
As seen from these IRI values, many sections had extremely high
IRI values. The side-to-side rocking motion of the profiler on some
of these extremely rough sections caused sunlight to seep under the
shroud covering the sensors and contaminate the profile data. The
majority of the LTPP test sections will not have such high
roughness values. Thus, contamination of profile data by ambient
light probably is not a major issue at the majority of the sections
if the shroud covering the sensors is in good condition. However,
at extremely rough sections, sunlight seeping under the shroud
could contaminate the data by causing saturation spikes to appear
in the data.
1991 COMPARISON: ANN ARBOR, MI TX
The four LTPP DNC 690 profilers participated in this comparison.
Details about this comparison were obtained from reference 11.
Eight test sections were used in this study-four AC sections and
four jointed PCC sections. When selecting the test sections, two
levels of roughness were considered-IRI less than 2.0 m/km (127
inches/mi) and IRI between 2.0 and 4.7 m/km (127 and 298
inches/mi). The goal was to establish two sections for each
pavement type that fell into each of these roughness levels.
Dipstick measurements were obtained along both wheelpaths on all of
the test sections. Profile testing was performed at speeds of 64
and 80 km/h (40 and 50 mi/h). The left wheelpath was marked on all
of the test sections, and the profiler drivers were asked to align
the profiler along this path when collecting data. Each profiler
operator was instructed to obtain six error-free profile runs on
each test section at each test speed.
The left- and right-wheelpath IRI values computed from the
profiler data collected at the 80 km/h (50-mi/h) test speed and
from the Dipstick data are presented in tables 17 and 18,
respectively. The IRI values presented in these tables are the
average IRI values computed from the six repeat runs. The Dipstick
IRI values presented in these tables are the average IRI obtained
for the two sets of measurements that were available for each
wheelpath.
Table 17. IRI values along the left wheelpath
(1991).
Device |
Left-Wheelpath IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
North Atlantic Profiler |
1.42 |
3.45 |
2.40 |
0.91 |
2.41 |
2.65 |
1.94 |
0.84 |
North Central Profiler |
1.14 |
3.33 |
2.35 |
0.99 |
2.67 |
2.62 |
1.91 |
0.91 |
Southern Profiler |
1.29 |
3.63 |
2.48 |
0.93 |
3.14 |
2.84 |
2.05 |
0.98 |
Western Profiler |
1.18 |
3.31 |
2.27 |
0.87 |
2.74 |
2.62 |
1.86 |
0.84 |
Dipstick |
1.20 |
3.44 |
2.10 |
.84 |
2.65 |
2.43 |
1.81 |
0.98 |
1 m/km = 5.28 ft/mi
Table 18. IRI values along the right wheelpath
(1991).
Device |
Right-Wheelpath IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
North Atlantic Profiler |
1.29 |
4.64 |
2.63 |
1.63 |
3.09 |
2.62 |
1.77 |
0.96 |
North Central Profiler |
1.34 |
4.29 |
2.54 |
1.01 |
2.89 |
2.65 |
1.74 |
0.96 |
Southern Profiler |
1.26 |
4.37 |
2.59 |
0.99 |
2.97 |
2.59 |
1.72 |
0.91 |
Western Profiler |
1.26 |
4.43 |
2.54 |
0.98 |
2.89 |
2.57 |
1.75 |
0.95 |
Dipstick |
1.26 |
3.91 |
2.48 |
0.93 |
2.65 |
2.41 |
1.75 |
1.10 |
1 m/km = 5.28 ft/mi
The differences between the average profiler IRI and the
Dipstick IRI at the test sections for the left and right wheelpaths
are presented in tables 19 and 20, respectively.
Table 19. Differences between profiler IRI and Dipstick
IRI: Left wheelpath (1991).
Device |
Profiler IRI – Dipstick IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
North Atlantic Profiler |
0.22 |
0.02 |
0.30 |
0.08 |
-0.24 |
0.22 |
0.13 |
-0.14 |
North Central Profiler |
-0.06 |
-0.11 |
0.25 |
0.16 |
0.02 |
0.19 |
0.09 |
-0.06 |
Southern Profiler |
0.09 |
0.19 |
0.38 |
0.09 |
0.49 |
0.41 |
0.24 |
0.00 |
Western Profiler |
-0.02 |
-0.13 |
0.17 |
0.03 |
0.09 |
0.19 |
0.05 |
-0.14 |
1 m/km = 5.28 ft/mi
Table 20. Differences between profiler IRI and Dipstick
IRI: Right wheelpath (1991).
Device |
Profiler IRI – Dipstick IRI (m/km) |
Surface Type and Section Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
North Atlantic Profiler |
0.03 |
0.73 |
0.16 |
0.09 |
0.44 |
0.21 |
0.02 |
-0.14 |
North Central Profiler |
0.08 |
0.38 |
0.06 |
0.08 |
0.24 |
0.24 |
-0.02 |
-0.14 |
Southern Profiler |
0.00 |
0.46 |
0.11 |
0.06 |
0.32 |
0.17 |
-0.03 |
-0.19 |
Western Profiler |
0.00 |
0.52 |
0.06 |
0.05 |
0.24 |
0.16 |
0.00 |
-0.16 |
1 m/km = 5.28 ft/mi
The standard deviations of the IRI values for the 80-km/h
(50-mi/h) testing for the left and right wheelpaths are presented
in tables 21 and 22, respectively.
Table 21. Standard deviations of IRI for 80-km/h (50-mi/h)
runs: Left wheelpath (1991).
Device |
Standard Deviations of IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
North Atlantic Profiler |
0.08 |
0.07 |
0.08 |
0.02 |
0.05 |
0.03 |
0.01 |
0.03 |
North Central Profiler |
0.03 |
0.03 |
0.03 |
0.02 |
0.04 |
0.07 |
0.04 |
0.01 |
Southern Profiler |
0.00 |
0.02 |
0.02 |
0.01 |
0.01 |
0.05 |
0.03 |
0.01 |
Western Profiler |
0.01 |
0.02 |
0.00 |
0.02 |
0.02 |
0.05 |
0.04 |
0.03 |
1 m/km = 5.28 ft/mi
Table 22. Standard deviations of IRI for 80-km/h (50-mi/h)
runs: Left wheelpath (1991).
Device |
Standard Deviations of IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
North Atlantic Profiler |
0.03 |
0.11 |
0.04 |
0.01 |
0.04 |
0.04 |
0.04 |
0.02 |
North Central Profiler |
0.06 |
0.06 |
0.04 |
0.01 |
0.05 |
0.02 |
0.02 |
0.02 |
Southern Profiler |
0.03 |
0.08 |
0.03 |
0.01 |
0.02 |
0.03 |
0.02 |
0.03 |
Western Profiler |
0.04 |
0.15 |
0.06 |
0.01 |
0.05 |
0.03 |
0.02 |
0.01 |
1 m/km = 5.28 ft/mi
The main findings from this study are:
- An ANOVA performed on the IRI values indicated that the
left-wheelpath IRI from the Southern profiler was different from
the IRI values from the other three profilers. An ANOVA also showed
that the left-wheelpath IRI computed from the data collected by the
North Central, Western, and North Atlantic profilers were similar.
The overall mean IRI values for the profilers along the left
wheelpath computed by considering all of the profile runs at all of
the test sections at the 80-km/h (50-mi/h) test speed were 1.98,
1.97, 2.00, and 2.10 m/km (126, 125, 127, and 140 inches/mi) for
the North Central, Western, North Atlantic, and Southern profilers,
respectively. These values clearly show that the left sensor of the
Southern profiler is collecting data that have higher IRI values
than the data collected by the other three profilers.
- In the right wheelpath, the ANOVA indicated that the IRI values
obtained from profile data collected by the profiler combinations
of North Central, Western, and North Atlantic; North Central,
Western, and Southern; and North Central, North Atlantic, and
Southern, were similar. Although the right sensor of the North
Central profiler did not follow the same path as the other three
profilers (because of the difference in sensor spacing), all three
cases in which the profilers were not significant in the ANOVA
involved this profiler. Although the North Atlantic, Western, and
Southern profilers have similar sensor spacing, the ANOVA indicated
that at least one of the profilers was different from the rest. The
overall mean IRI values for the profilers along the right wheelpath
computed by considering all of the profile runs at all of the test
sections at the 80-km/h (50-mi/h) test speed were 2.18, 2.16, 2.26,
and 2.15 m/km (138, 137, 143, and 138 inches/mi) for the North
Central, Western, North Atlantic, and Southern profilers,
respectively. Although the ANOVA indicated that the IRI values for
the four profilers were not similar, an examination of the IRI
values obtained by the profilers at the test sections did not
indicate clear evidence that a particular profiler had a bias when
compared to the other profilers.
- The results of the ANOVA for the left-wheelpath IRI showed that
the speed of testing was not significant. For the right wheelpath,
the speed of testing was a significant factor for two of the
profiler combinations out of a total of five combinations that were
analyzed.
- All profilers showed excellent repeatability in IRI values
along both wheelpaths, except at a few sections that had spikes in
the profile data. It was observed that the repeatability of the
profilers was not affected by the surface type (asphalt vs.
concrete), the level of roughness, or the two speeds selected for
testing. Although the Southern profiler was producing higher IRI
values when compared to the other three profilers along the left
wheelpath, the repeatability of IRI values obtained by this
profiler was comparable to those obtained for the other three
profilers.
1992 COMPARISON: AMES, IA TX
The four LTPP DNC 690 profilers participated in this comparison.
The information presented in this section was obtained from a
document written about this comparison.(12)
Eight test sections were used in this study-four AC sections and
four PCC sections. When selecting the test sections, two levels of
roughness were considered (IRI less than 2.0 m/km (127 inches/mi)
and IRI between 2.0 and 4.7 m/km (127 and 298 inches/mi)). The goal
was to establish two sections from each pavement type that fell
into each of these roughness levels. Dipstick measurements were
obtained along both wheelpaths at all of the sections, with
replicate measurements obtained at seven sections. At six sections,
two sets of Dipstick measurements were obtained, with three sets of
Dipstick measurements being obtained at one section. Rod-and-level
measurements were also obtained at these test sections; however, at
some sections, only one wheelpath was surveyed. Two types of levels
were used to perform the rod-and-level measurements. The profilers
collected data at speeds of 64 and 80 km/h (40 and 50 mi/h). It was
requested that each profiler operator obtain six good profile runs
at ssection for each test speed.
During data analysis, it was discovered that one of the levels
that was used to obtain measurements did not meet the resolution
requirements for rod-and-level measurements for determining IRI
that are outlined in ASTM Standard E1364-95 (2000).(31)
Measurements obtained from this level produced high IRI values.
The left- and right-wheelpath IRI values computed from the
profiler data collected at 80 km/h (50 mi/h), Dipstick data, and
rod-and-level data are presented in tables 23 and 24, respectively.
The IRI values presented in these tables for the profilers are the
average IRI values computed from the six repeat runs. The Dipstick
IRI values presented in these tables are the average IRI obtained
from the replicate measurements for cases where more than one set
of data were available. For the rod and level, only the IRI values
obtained from the data collected with the level that met the
resolution requirements outlined in ASTM Standard E1364 are
shown.
Table 23. IRI values along the left wheelpath
(1992).
Device |
IRI (m/km) |
Surface Type and Section Number |
Asphalt |
Concrete |
3 |
5 |
6 |
7 |
1 |
2 |
4 |
8 |
North Atlantic Profiler |
1.42 |
1.18 |
0.66 |
1.53 |
1.59 |
2.21 |
4.23 |
1.42 |
North Central Profiler |
1.39 |
1.25 |
0.65 |
1.75 |
1.62 |
2.13 |
4.59 |
1.28 |
Southern Profiler |
1.39 |
1.23 |
0.60 |
1.55 |
1.74 |
2.37 |
4.37 |
1.47 |
Western Profiler |
1.39 |
1.23 |
0.60 |
1.53 |
1.69 |
2.33 |
4.34 |
1.44 |
Dipstick |
1.47 |
1.31 |
0.66 |
1.85 |
1.81 |
2.32 |
4.12 |
1.39 |
Rod and Level |
N/A |
1.45 |
N/A |
N/A |
N/A |
2.13 |
4.15 |
N/A |
N/A = Measurements not obtained. |
1 m/km = 5.28 ft/mi
Table 24. IRI values along the right wheelpath
(1992).
Device |
IRI (m/km) |
Surface Type and Section Number |
Asphalt |
Concrete |
3 |
5 |
6 |
7 |
1 |
2 |
4 |
8 |
North Atlantic Profiler |
1.39 |
0.93 |
0.79 |
3.50 |
2.02 |
1.67 |
5.68 |
1.09 |
North Central Profiler |
1.36 |
0.85 |
0.74 |
3.64 |
1.97 |
1.59 |
5.74 |
1.09 |
Southern Profiler |
1.32 |
0.88 |
0.74 |
3.08 |
1.97 |
1.59 |
5.55 |
1.09 |
Western Profiler |
1.45 |
0.93 |
0.76 |
3.61 |
2.02 |
1.61 |
5.68 |
1.12 |
Dipstick |
1.37 |
0.93 |
0.76 |
3.52 |
2.13 |
1.69 |
5.63 |
1.10 |
Rod and Level |
N/A |
N/A |
0.95 |
N/A |
N/A |
1.66 |
5.57 |
1.20 |
N/A = Measurements not obtained. |
1 m/km = 5.28 ft/mi
The differences between the average profiler IRI and the
Dipstick IRI at the test sections for the left and right wheelpaths
are presented in tables 25 and 26, respectively.
Table 25. Differences between profiler IRI and Dipstick
IRI: Left wheelpath (1992).
Device |
Profiler IRI - Dipstick IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
3 |
5 |
6 |
7 |
1 |
2 |
4 |
8 |
North Atlantic Profiler |
-0.05 |
-0.13 |
0.00 |
-0.32 |
-0.22 |
-0.11 |
0.11 |
0.03 |
North Central Profiler |
-0.08 |
-0.06 |
-0.02 |
-0.09 |
-0.19 |
-0.19 |
0.47 |
-0.11 |
Southern Profiler |
-0.08 |
-0.08 |
-0.06 |
-0.30 |
-0.08 |
0.05 |
0.25 |
0.08 |
Western Profiler |
-0.08 |
-0.08 |
-0.06 |
-0.32 |
-0.13 |
0.02 |
0.22 |
0.05 |
1 m/km = 5.28 ft/mi
Table 26. Differences between profiler IRI and Dipstick
IRI: Right wheelpath (1992).
Device |
Profiler IRI - Dipstick IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
3 |
5 |
6 |
7 |
1 |
2 |
4 |
8 |
North Atlantic Profiler |
0.02 |
0.00 |
0.03 |
-0.02 |
-0.11 |
-0.02 |
0.05 |
-0.02 |
North Central Profiler |
-0.02 |
-0.08 |
-0.02 |
0.13 |
-0.16 |
-0.09 |
0.11 |
-0.02 |
Southern Profiler |
-0.05 |
-0.05 |
-0.02 |
-0.44 |
-0.16 |
-0.09 |
-0.08 |
-0.02 |
Western Profiler |
0.08 |
0.00 |
0.00 |
0.09 |
-0.11 |
-0.08 |
0.05 |
0.02 |
1 m/km = 5.28 ft/mi
The standard deviations of the IRI values obtained from testing
performed at 80 km/h (50 mi/h) for the left and right wheelpaths
are presented in tables 27 and 28, respectively.
Table 27. Standard deviations of IRI for 80-km/h (50-mi/h)
runs: Left wheelpath (1992).
Device |
Standard Deviations of IRI (m/km) |
Surface Type and Section
Number |
Asphalt |
Concrete |
3 |
5 |
6 |
7 |
1 |
2 |
4 |
8 |
North Atlantic Profiler |
0.05 |
0.02 |
0.02 |
0.05 |
0.05 |
0.03 |
0.03 |
0.02 |
North Central Profiler |
0.02 |
0.02 |
0.02 |
0.04 |
0.04 |
0.02 |
0.11 |
0.03 |
Southern Profiler |
0.01 |
0.01 |
0.01 |
0.04 |
0.02 |
0.02 |
0.02 |
0.01 |
Western Profiler |
0.02 |
0.01 |
0.01 |
0.04 |
0.04 |
0.02 |
0.03 |
0.03 |
1 m/km = 5.28 ft/mi
Table 28. Standard deviations of IRI for 80-km/h (50-mi/h)
runs: Right wheelpath (1992).
Device |
Standard Deviations of IRI (m/km) |
Surface Type and
Section Number |
Asphalt |
Concrete |
3 |
5 |
6 |
7 |
1 |
2 |
4 |
8 |
North Atlantic Profiler |
0.04 |
0.02 |
0.02 |
0.07 |
0.03 |
0.03 |
0.04 |
0.02 |
North Central Profiler |
0.02 |
0.01 |
0.01 |
0.22 |
0.02 |
0.02 |
0.05 |
0.02 |
Southern Profiler |
0.02 |
0.01 |
0.01 |
0.06 |
0.02 |
0.02 |
0.04 |
0.02 |
Western Profiler |
0.02 |
0.02 |
0.01 |
0.09 |
0.02 |
0.02 |
0.06 |
0.02 |
1 m/km = 5.28 ft/mi
The following are the main findings of this study:
- All profilers showed excellent repeatability in IRI for both
the left and right wheelpaths, except for the right wheelpath of
section 7, which is an AC pavement with high-severity longitudinal
cracking along the right wheelpath. Very high standard deviations
in IRI were observed at this section. It was observed that the
repeatability of the profilers was not affected by the two speeds
of testing or the surface type (AC and PCC).
- Generally, good agreement was found between the IRI computed
from the Dipstick data and the profiler data for all four of the
profilers along both wheelpaths at the majority of the
sections.
- An ANOVA performed separately on the left- and right-wheelpath
IRI values obtained from Dipstick and the four profilers showed
that the device type was not significant.
- An ANOVA performed separately on the left- and right-wheelpath
IRI values obtained from the profilers indicated that the speed of
testing was not significant.
- One of the levels that was used to obtain elevation
measurements did not meet the resolution required for profile
measurements that are specified in ASTM Standard E1364-95
(2000).(31) IRI computed from profiles measured by this level
showed poor agreement with both profiler IRI and Dipstick IRI, with
the rod-and-level IRI being higher.
- IRI obtained from the measurements recorded by the level that
met the ASTM resolution requirements showed good agreement with the
IRI computed from the Dipstick and profiler data for cases where
the IRI was greater than 1.6 m/km (101 inches/mi). However, there
was poor agreement in the IRI for cases where the IRI was less than
1.6 m/km (101 inches/mi). Errors in leveling because of instrument
errors (repeatability errors) and the deviation of the rod from the
vertical will introduce random variations (noise) into the
profiles. An analysis indicated that random variations in a profile
have a much greater effect on the IRI for smooth pavement than for
rough pavement. It was concluded that the effects of random
variations in profiles caused by the previously described factors
caused the rod-and-level IRI to have poor agreement with both the
Dipstick IRI and profiler IRI for wheelpaths that had an IRI of
less than 1.6 m/km (101 inches/mi).
- Results from a study at one section indicated that the IRI for
a concrete pavement could be affected considerably by slab curling.
At that section, the morning and afternoon IRI values obtained by
the same profiler for the left wheelpath were 2.40 and 2.11 m/km
(152 and 134 inches/mi), respectively, while the corresponding
values for the right wheelpath were 1.85 and 1.59 m/km (117 and 101
inches/mi), respectively.
1998 COMPARISON: URBANA, IL TX
The four LTPP T-6600 profilers participated in this comparison.
This profiler comparison was the first-ever comparison of the four
T-6600 profilers since profile data for the LTPP program was first
collected in late 1996. The information presented in this section
was obtained from a document written about this
comparison.(13)
Four test sections were used in this study. Two of the sections
were asphalt-surfaced, while the other two were PCC sections. When
selecting the test sections, the goal was to select for each
surface type one section with an IRI of less than 1.6 m/km (101
inches/mi) and one section with an IRI greater than 2.2 m/km (139
inches/mi). Dipstick measurements were obtained along both
wheelpaths at all of the sections. Profile testing was conducted at
a speed of 80 km/h (50 mi/h). Each profiler conducted five
error-free profile runs on a test section.
The left- and right-wheelpath IRI values computed from the
profiler data and the Dipstick data are presented in tables 29 and
30, respectively. The IRI values presented in these tables for the
profilers are the average IRI values computed from the IRI for the
five repeat runs.
The differences between the average profiler IRI and the
Dipstick IRI at the test sections for the left and right wheelpaths
are presented in tables 31 and 32, respectively.
The standard deviations of the IRI values for the profilers for
the left and right wheelpaths are presented in tables 33 and 34,
respectively.
The following are the main findings of this study:
- The precision of a profiler along each wheelpath was evaluated
by computing the standard deviation of the IRI for that wheelpath
using the IRI values obtained from the five repeat runs. A profiler
was considered to have failed the precision criterion if the
standard deviation of the IRI for a wheelpath exceeded 0.04 m/km
(2.5 inches/mi). All of the profilers met the precision criterion
along both wheelpaths at all of the sites.
- The IRI bias of a profiler along each wheelpath at a section
was evaluated by computing the difference between the profiler IRI
(average IRI from five runs) along that wheelpath and the IRI
obtained by Dipstick. A profiler was considered to have satisfied
the bias criterion if this difference in IRI was within ±0.16 m/km
(±10 inches/mi). The North Atlantic, Southern, and Western
profilers passed the bias criterion for both wheelpaths at all of
the test sections. The North Central profiler passed the bias
criterion for all of the cases, except for the right wheelpath of
the rough AC section (section 2). The variability in the IRI values
obtained by the North Central profiler for the repeat runs is
considered to be the cause of the profiler failing the bias
criterion at this section.
Atlantic, Southern, and Western profilers passed the bias
criterion for both wheelpaths at all of the test sections. The
North Central profiler passed the bias criterion for all of the
cases, except for the right wheelpath of the rough AC section
(section 2). The variability in the IRI values obtained by the
North Central profiler for the repeat runs is considered to be the
cause of the profiler failing the bias criterion at this
section.
Table 29. IRI values along the left wheelpath
(1998).
Device |
IRI (m/km)) |
Surface Type and
Section Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
North Atlantic Profiler |
1.02 |
2.49 |
1.30 |
2.77 |
North Central Profiler |
1.04 |
2.55 |
1.28 |
2.90 |
Southern Profiler |
1.02 |
2.56 |
1.27 |
2.83 |
Western Profiler |
1.02 |
2.59 |
1.28 |
2.90 |
Dipstick |
0.95 |
2.52 |
1.17 |
2.87 |
1 m/km = 5.28 ft/mi
Table 30. IRI values along the right wheelpath
(1998).
Device |
IRI (m/km) |
Surface Type and Section Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
North Atlantic Profiler |
1.08 |
2.38 |
1.26 |
3.09 |
North Central Profiler |
1.05 |
2.62 |
1.24 |
3.17 |
Southern Profiler |
1.04 |
2.39 |
1.24 |
3.05 |
Western Profiler |
1.04 |
2.50 |
1.22 |
3.20 |
Dipstick |
0.96 |
2.46 |
1.13 |
3.17 |
1 m/km = 5.28 ft/mi
Table 31. Differences between the profiler IRI and
Dipstick IRI: Left wheelpath (1998).
Device |
Profiler IRI -Dipstick IRI (m/km) |
Surface Type and
Section Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
North Atlantic Profiler |
0.07 |
-0.03 |
0.13 |
-0.10 |
North Central Profiler |
0.09 |
0.03 |
0.11 |
0.03 |
Southern Profiler |
0.07 |
0.04 |
0.10 |
-0.04 |
Western Profiler |
0.07 |
0.07 |
0.11 |
0.03 |
1 m/km = 5.28 ft/mi
Table 32. Differences between the profiler IRI and
Dipstick IRI: Right wheelpath (1998).
Device |
Profiler IRI-Dipstick IRI (m/km) |
Surface Type and
Section Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
North Atlantic Profiler |
0.12 |
-0.08 |
0.13 |
-0.08 |
North Central Profiler |
0.09 |
0.16 |
0.11 |
0.00 |
Southern Profiler |
0.08 |
-0.07 |
0.11 |
-0.12 |
Western Profiler |
0.08 |
0.04 |
0.09 |
0.03 |
1 m/km = 5.28 ft/mi
Table 33. Standard deviations of IRI: Left wheelpath
(1998).
Device |
Standard Deviations of IRI (m/km) |
Surface Type and Section Number |
Asphalt |
Concrete |
North Atlantic Profiler |
0.02 |
0.02 |
0.02 |
0.02 |
North Central Profiler |
0.01 |
0.03 |
0.01 |
0.01 |
Southern Profiler |
0.01 |
0.03 |
0.01 |
0.01 |
Western Profiler |
0.01 |
0.02 |
0.03 |
0.01 |
1 m/km = 5.28 ft/mi
Table 34. Standard deviations of IRI: Right wheelpath
(1998).
Device |
Standard Deviations of IRI (m/km) |
Surface Type and
Section Number |
Asphalt |
Concrete |
1 |
2 |
3 |
4 |
North Atlantic Profiler |
0.01 |
0.02 |
0.02 |
0.02 |
North Central Profiler |
0.01 |
0.04 |
0.02 |
0.00 |
Southern Profiler |
0.01 |
0.02 |
0.01 |
0.01 |
Western Profiler |
0.01 |
0.02 |
0.01 |
0.03 |
1 m/km = 5.28 ft/mi
- The evaluation of the bias and precision values showed no
distinct trend for a profiler that would indicate that it was
different from the other profilers.
- An ANOVA that was carried out separately for the left- and
right-wheelpath IRI values for the four profilers indicated that
there were no differences in IRI values obtained for the four
profilers in both the left and right wheelpaths.
- A visual review of the profile data plots indicated excellent
repeatability of the profiles for the North Atlantic, North
Central, and Western profilers for the following wavebands: (1) 1
to 30 m (3 to 100 ft), (2) less than 10 m (33 ft), (3) 10 to 20 m
(33 to 66 ft), and (4) 20 to 30 m (66 to 100 ft). The Southern
profiler also exhibited similar results, except for the rough PCC
site. At this site, the Southern profiler showed poor repeatability
for wavebands between 10 and 20 m (33 and 66 ft), and 20 and 30 m
(66 and 100 ft), with the repeatability being poorer for the latter
waveband. This may be caused by the condition of the connection
between the profiler bar and the vehicle. After completion of the
comparison test, the connections between the profiler bar and the
profiler vehicle in the Southern profiler were inspected and
tightened. Subsequent testing indicated that this profiler was able
to collect repeatable profile data on rough sections.
2000 COMPARISON: COLLEGE STATION, TX
The four LTPP T-6600 profilers participated in this comparison.
The information presented in this section was obtained from a
document written about this comparison.(13)
Five pavement sections were used for profile testing: (1) a
smooth AC site, (2) a medium-rough AC site, (3) a chip-seal
section, (4) a smooth PCC site, and (5) a rough PCC site. The
smooth AC and the medium-rough AC sections were located within the
Riverside Campus of Texas A&M University and are used as
calibration sections to certify the Texas Department of
Transportation (TxDOT) profilers. The IRI values computed from
measurements made with an ARRB walking profiler were available for
these two sections. However, the walking profiler data for these
two sections were not made available by TxDOT because these sites
are used for certifying profilers. Measurements made with a
reference device (e.g., Dipstick or a walking profiler) were not
performed at the other three test sections. Profile testing was
conducted at a speed of 80 km/h (50 mi/h). Each profiler was
required to obtain five error-free profile runs on a test
section.
The IRI values computed from the profiler data and the walking
profiler data for the left and right wheelpaths on the tests
sections are presented in tables 35 and 36, respectively. The IRI
values presented in these tables for the profilers are the average
IRI values computed from the IRI for the five repeat runs.
The differences between the average profiler IRI and the Walking
Profiler IRI at the test sections are presented in table 37.
The standard deviations for the IRI values for the profilers for
the left and right wheelpaths are presented in tables 38 and 39,
respectively.
Table 35. IRI values along the left wheelpath
(2000).
Device |
IRI (m/km) |
Test Section |
Smooth AC |
Medium AC |
Chip Seal |
Smooth PCC |
Rough PCC |
North Atlantic Profiler |
1.13 |
1.93 |
3.00 |
1.54 |
2.94 |
North Central Profiler |
0.98 |
1.81 |
2.72 |
1.52 |
2.68 |
Southern Profiler |
1.01 |
1.85 |
3.31 |
1.48 |
2.78 |
Western Profiler |
1.04 |
1.94 |
3.33 |
1.56 |
2.90 |
Walking Profiler |
1.01 |
1.85 |
N/A |
N/A |
N/A |
N/A = Measurements not performed. |
1 m/km = 5.28 ft/mi
Table 36. IRI values along the right wheelpath
(2000).
Device |
IRI (m/km) |
Test Section |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic Profiler |
0.72 |
1.77 |
2.02 |
1. |
2.95 |
North Central Profiler |
0.79 |
1.75 |
2.77 |
1.68 |
2.92 |
Southern Profiler |
0.73 |
1.81 |
1.98 |
1.63 |
2.96 |
Western Profiler |
0.66 |
1.72 |
2.11 |
1.63 |
2.88 |
Walking Profiler |
0.67 |
1.75 |
N/A |
N/A |
N/A |
N/A = Measurements not performed. |
1 m/km = 5.28 ft/mi
Table 37. Differences between the profiler IRI and the
walking profiler IRI (2000).
Section |
WheelPath |
Average Profiler IRI - Reference IRI (m/km) |
Profiler |
North Atlantic |
North Central |
Southern |
Western |
Smooth Asphalt |
Left |
0.12 |
-0.03 |
0 |
0.03 |
Smooth Asphalt |
Left |
0.08 |
-0.04 |
0 |
0.09 |
Medium Asphalt |
Right |
0.05 |
0.12 |
0.06 |
-0.01 |
Medium Asphalt |
Right |
0.02 |
0 |
0.06 |
-0.03 |
1 m/km = 5.28 ft/mi
Table 38. Standard deviations of IRI: Left wheelpath
(2000).
Profiler |
Standard Deviations of IRI (m/km) |
Test Section |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic |
0.03 |
0.02 |
0.10 |
0.01 |
0.01 |
North Central |
0.05 |
0.03 |
0.06 |
0.01 |
0.03 |
Southern |
0.01 |
0.02 |
0.07 |
0.02 |
0.03 |
Western |
0.01 |
0.02 |
0.08 |
0.01 |
0.01 |
1 m/km = 5.28 ft/mi
Table 39. Standard deviations of IRI: Right wheelpath
(2000).
Profiler |
Standard Deviations of IRI (m/km) |
Test Section |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic |
0.01 |
0.02 |
0.02 |
0.01 |
0.03 |
North Central |
0.06 |
0.02 |
0.06 |
0.01 |
0.03 |
Southern |
0.02 |
0.02 |
0.09 |
0.02 |
0.03 |
0.00 |
0.01 |
0.01 |
0.01 |
0.01 |
0.01 |
1 m/km = 5.28 ft/mi
The following are the main findings of this study:
- At both the smooth AC and medium AC sections, the difference
between the profiler IRI and the walking profiler IRI was within
the LTPP-specified bias criterion of ±0.16 m/km (±10 inches/mi) for
all of the profilers for both wheelpaths. With the exception of the
left wheelpath on the smooth AC section for the North Atlantic
profiler and the right wheelpath on the smooth AC section for the
North Central profiler, the difference between the profiler IRI and
the walking profiler IRI was less than 0.1 m/km (6 inches/mi).
- At the chip-seal section, the North Central profiler had an IRI
value that was 0.74 m/km (47 inches/mi) higher than the average IRI
for the other three profilers in the right wheelpath, while for the
left wheelpath, it had an IRI value that was 0.49 m/km (31
inches/mi) lower than the average IRI for the other three
profilers. After testing was completed, the North Central profiler
operator indicated that the sensor covers might not have been taken
off when this section was profiled. Under such conditions, only the
accelerometer data are used for computing the profile. This can
explain why the IRI from the North Central profiler was different
from the IRI values obtained by the other three profilers at this
site.
- All profilers showed excellent repeatability of IRI values at
the smooth AC, medium AC, smooth PCC, and medium PCC sites. At
these four sites, the precision criterion for IRI that is used in
the LTPP comparison studies (a precision of less than 0.04 m/km
(2.5 inches/mi)) was satisfied by all four profilers along both
wheelpaths, except by the North Central profiler at the smooth AC
site. At this site, the North Central profiler had IRI precision
values of 0.05 and 0.06 m/km (3.2 and 3.8 inches/mi) along the left
and right wheelpaths, respectively. The IRI precision at the
chip-seal section that had significant cracking was variable, with
precision values for a wheelpath for the four profilers ranging
from 0.01 to 0.10 m/km (0.6 to 6 inches/mi).
- An evaluation of the point-to-point profile repeatability
values for the left, right, and center paths for the profilers did
not show any trends that would suggest that a specific profiler was
different when compared to the other profilers.
- It was noted that at the smooth AC and medium AC sites, the
left sensor of the Western profiler was noisy when compared to the
other three profilers. This noise was not influencing the IRI
values computed from these profiles; however, it may influence the
ride indices that weigh shorter wavelengths more heavily.
- The wheelpaths on the smooth AC and medium AC sections were
marked with white paint dots. These marked wheelpaths had a spacing
that was slightly greater than the LTPP profiler sensor spacing.
Therefore, when profiling the sites, LTPP’s profilers profiled a
path that was slightly inside the marked path. Small spikes were
noted on some of the profiles collected at this site, and these
appear to have been caused when the sensor traversed over the
wheelpath markings. However, these spikes did not influence the
computed IRI values.
- A visual examination of the profile data plots showed good
agreement in profiles collected by all of the profilers along the
left, center, and right wheelpaths, except for two cases: The two
cases involved data collected by the North Central profiler along
the left and right wheelpaths at the chip-seal section. At this
section, the data collected by the North Central profiler along
both wheelpaths were different from the data collected by the other
profilers. (Note: It is believed that the profiler had the sensor
covers on when the profile data were collected at this site.) At
the two PCC sites, the North Central profiler had some
inconsistencies in the data collected with the center sensor. The
North Central region indicated that they were aware of this problem
with this sensor and were in the process of correcting it with the
help of K.J. Law Engineers.
2003 COMPARISON: MN/ROAD, ALBERTVILLE, MN
The four LTPP ICC profilers were used in this comparison, which
was conducted at the Mn/ROAD facility in Albertville, MN. This was
the first comparison of four of LTPP's ICC profilers after they
began collecting data for the LTPP program in August 2002. One of
LTPP’s T-6600 profilers that was used to collect profile data for
the LTPP program was still operational, and this profiler was also
used in the comparison. The information presented in this section
was obtained from a document written about this comparison
Five test sections were used for profile testing: (1) a smooth
AC section, (2) a rough AC section, (3) a smooth PCC section, (4) a
medium-rough PCC section, and (5) a chip-seal section. Dipstick
measurements were obtained along both wheelpaths at all of the test
sections. Profile testing was conducted at a speed of 80 km/h (50
mi/h). Each profiler was required to obtain five error-free profile
runs on a test section.
The left- and right-wheelpath IRI values computed from the
profiler data and the Dipstick data are presented in tables 40 and
41, respectively. The IRI values presented in these tables for the
profilers are the average IRI values computed from the IRI for the
five repeat runs.
Table 40. IRI values along the left wheelpath
(2003).
Device |
IRI (m/km) |
Section 1 |
Section 2 |
Section 3 |
Section 4 |
Section 5 |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic:ICC |
1.27 |
2.76 |
0.92 |
1.45 |
2.25 |
North Central: ICC |
1.26 |
2.75 |
0.93 |
1.57 |
2.15 |
Southern: ICC |
1.29 |
2.78 |
0.93 |
1.45 |
2.15 |
Western: ICC |
1.28 |
2.75 |
0.91 |
1.43 |
2.20 |
K.J. Law Engineers |
1.31 |
2.75 |
0.94 |
1.47 |
2.25 |
Dipstick |
1.17 |
2.80 |
0.88 |
1.32 |
2.24 |
1 m/km = 5.28 ft/mi
Table 41. IRI values along the right wheelpath
(2003).
Device |
IRI (m/km) |
Section 1 |
Section 2 |
Section 3 |
Section 4 |
Section 5 |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic: ICC |
1.68 |
2.81 |
0.98 |
1.70 |
2.54 |
North Central: ICC |
1.73 |
3.01 |
1.02 |
1.72 |
2.54 |
Southern: ICC |
1.69 |
2.62 |
0.96 |
1.67 |
2.54 |
Western: ICC |
1.66 |
2.54 |
0.97 |
1.71 |
2.50 |
K.J. Law Engineers |
1.64 |
2.46 |
0.96 |
1.70 |
2.44 |
Dipstick |
1.81 |
2.79 |
0.99 |
1.64 |
2.63 |
1 m/km = 5.28 ft/mi
Table 42. Differences between the profiler IRI and
Dipstick IRI: Left wheelpath (2003).
Profiler |
Average Profiler IRI - Dipstick IRI (m/km) |
Section 1 |
Section 2 |
Section 3 |
Section 4 |
Section 5 |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic: ICC |
0.10 |
-0.03 |
0.04 |
0.13 |
0.01 |
North Central: ICC |
0.09 |
-0.04 |
0.05 |
0.25 |
-0.09 |
Southern: ICC |
0.12 |
-0.02 |
0.05 |
0.13 |
-0.09 |
Western: ICC |
0.11 |
-0.05 |
0.03 |
0.11 |
-0.03 |
K.J. Law Engineers |
0.14 |
-0.05 |
0.06 |
0.15 |
0.01 |
1 m/km = 5.28 ft/mi
Table 43. Differences between the profiler IRI and
Dipstick IRI: Right wheelpath (2003).
Profiler |
Average Profiler IRI - Dipstick IRI
(m/km) |
Section 1 |
Section 2 |
Section 3 |
Section 4 |
Section 5 |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic: ICC |
-0.13 |
0.02 |
-0.01 |
0.05 |
-0.09 |
North Central: ICC |
-0.08 |
0.22 |
0.03 |
0.08 |
-0.09 |
Southern: ICC |
-0.12 |
-0.18 |
-0.03 |
0.03 |
-0.08 |
Western: ICC |
-0.15 |
-0.25 |
-0.02 |
0.07 |
-0.13 |
K.J. Law Engineers |
-0.18 |
-0.33 |
-0.03 |
0.05 |
-0.19 |
1 m/km = 5.28 ft/mi
The standard deviations of the IRI from the profilers for the
left and right wheelpaths are presented in tables 44 and 45,
respectively.
Table 44. Standard deviations of IRI: Left wheelpath
(2003).
Profiler |
Standard Deviations of IRI (m/km) |
Section 1 |
Section 2 |
Section 3 |
Section 4 |
Section 5 |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic: ICC |
0.02 |
0.03 |
0.01 |
0.03 |
0.02 |
North Central: ICC |
0.01 |
0.04 |
0.01 |
0.04 |
0.02 |
Southern: ICC |
0.02 |
0.02 |
0.01 |
0.03 |
0.03 |
Western: ICC |
0.01 |
0.04 |
0.01 |
0.01 |
0.04 |
K.J. Law Engineers |
0.02 |
0.03 |
0.01 |
0.01 |
0.06 |
1 m/km = 5.28 ft/mi
Table 45. Standard deviations of IRI: Right wheelpath
(2003).
Profiler |
Standard Deviations of IRI (m/km) |
Section 1 |
Section 2 |
Section 3 |
Section 4 |
Section 5 |
Smooth AC |
Rough AC |
Smooth PCC |
Medium PCC |
Chip Seal |
North Atlantic: ICC |
0.07 |
0.11 |
0.02 |
0.02 |
0.02 |
North Central: ICC |
0.01 |
0.13 |
0.01 |
0.01 |
0.03 |
Southern: ICC |
0.07 |
0.08 |
0.02 |
0.03 |
0.04 |
Western: ICC |
0.08 |
0.09 |
0.01 |
0.01 |
0.03 |
K.J. Law Engineers |
0.04 |
0.08 |
0.02 |
0.02 |
0.03 |
1 m/km = 5.28 ft/mi
The main findings of this study are:
- Overall, all of the profilers appear to be obtaining repeatable
IRI values. These data did not indicate that a particular profiler
was behaving differently than the other profilers as far as IRI
repeatability is concerned. The precision criterion for IRI that is
used in the LTPP comparison studies is that the IRI standard
deviations from multiple runs on a section should be less than 0.04
m/km (2.5 inches/mi). However, sometimes this criterion cannot be
met if distresses are present along the wheelpath, because even a
slight shift in the path profiled can have a significant impact on
IRI. The IRI precision criterion was met for all of the cases,
except for the following: (1) all profilers, except for the North
Central profiler along the right wheelpath of the smooth AC section
(section 1); (2) all of the profilers along the right wheelpath of
the rough AC section (section 2); (3) left wheelpath of the rough
AC section (section 2) and medium-rough PCC section (section 4) for
the North Central profiler; and (4) left wheelpath of the chip-seal
section (section 5) for the K.J. Law Engineers profiler. Distresses
were present along the right wheelpath on the smooth AC section
(section 1) and along both wheelpaths on the rough AC section
(section 2), and variability on the paths profiled by the profilers
was the most likely cause of the failure of the profilers to meet
the specified criterion at these two sites.
- Good agreement between profiler IRI and Dipstick IRI was
obtained for the majority of the cases. The LTPP criterion used for
the comparison studies is that the difference between the Dipstick
IRI and the profiler IRI should be within ±0.16 m/km (±10
inches/mi). This criterion was met for all of the cases, except for
the following: (1) right wheelpath of the smooth AC section
(section 1) and the chip-seal section (section 5) by the K.J. Law
Engineers profiler, (2) left wheelpath of the medium-rough PCC
section (section 4) by the North Central profiler, and (3) right
wheelpath of the rough AC section (section 2) by all profilers,
except for the North Atlantic profiler. Extensive distresses were
present on the rough AC section (section 2), and the failure of the
profilers to meet the specified criterion at this site may be
caused by the differences in the way downward features in the
pavement are measured by Dipstick and the profilers.
- An evaluation of the profile data collected by the North
Central, North Atlantic, and Western ICC profilers indicated that
the profile data collected by these profilers generally have
similar repeatability. The K.J. Law Engineers and Southern ICC
profilers showed much higher variability in the profile data for
repeat runs along both wheelpaths when compared to the other three
ICC profilers. A comparison of the profiles obtained by the four
ICC profilers on the five test sections indicated that all four of
the profilers are capturing similar profile features. A profile
feature that appeared in any ICC profiler was also present on the
profiles collected by the other ICC profilers. After the profiler
comparison, another evaluation was performed to investigate the
repeatability of the profile data collected by the Southern
profiler. This investigation indicated that the Southern profiler
was obtaining repeatable profile data that was comparable to the
data obtained by the other three ICC profilers on the Mn/ROAD test
sections. The poor profile repeatability obtained by the Southern
profiler on the Mn/ROAD test sections may have been caused by
problems with the operational procedures that were followed by the
profiler operator (e.g., insufficient lead-in, not maintaining a
constant speed, etc.).
- Collection of profile data at speeds of 35, 50, 65, 80, 95, and
110 km/h (22, 38, 41, 50, 59, and 69 mi/h) was performed by the
K.J. Law Engineers and Southern ICC profilers on one section. The
analysis of the data indicated that the IRI value did not appear to
be influenced by the speed of testing.
- There were differences in IRI values computed for the Dipstick
data using ProQual and RoadRuf. RoadRuf is a software program
developed by UMTRI. However, a comparison of IRI values obtained by
ProQual and RoadRuf for profiler data showed that the IRI values
were similar. For the Dipstick data collected along 10 wheelpaths
(from 5 sections), the differences in the IRI values from ProQual
and RoadRuf ranged from 0.004 to 0.079 m/km (0.25 to 5 inches/mi),
with the IRI values from ProQual being higher than those obtained
by RoadRuf for all of the cases. When ProQual computes the IRI from
the Dipstick data, it first applies a filter that has an
upper-wavelength cutoff of 100 m (328 ft), then it uses the
filtered data to compute the IRI value. When RoadRuf computes the
IRI from the Dipstick data, the software uses the Dipstick
elevation profile to compute the IRI without any prefiltering of
the data. The filtering of the Dipstick data performed by ProQual
may be the cause of the differences in the Dipstick IRI values
between RoadRuf and ProQual.