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APPENDIX E
DESC~PlION OF S~OOTHNES~EASORINC
EgOIP~ENT
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Representative terms from entire chapter:
smoothness measuring
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c)
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APPENDIX E. DESCRIPTION OF
SMOOTHNESS-MEASURING EQUIPMENT
Introduction
Over the last century, a vast array of equipment has been developed to evaluate
the smoothness of pavements. The first of these devices was developed on early
paving projects, while some have been developed In connection with the construction
of test roads. Many of these employed some innovative approaches in the attempt to
quantify and ensure pavement smoothness, and even the early models tended to be
quite sophisticated. In recent years, the growing interest in pavement management
systems has focused on pavement ride as the major factor In evaluating the
serviceability of a road, Hereby creating the need for economically evaluating the
extensive mileage of a highway system. Electronics and space age-technology have
been applied, creating an ever-changing approach to the subject.
This appendix describes the significant types of equipment that have been used
for evaluating the smoothness of pavement surfaces. Those devices that are currently
being used by major highway agencies, as well as those that are believed to provide a
potential contribution in the immediate future, are covered in depth.
Smoothness Measuring Equipment Used in Construction
Currently, there are a variety of types of equipment in use for measuring the
smoothness of newly constructed pavements. Table E-l shows the breakdown of
usage among the 47 States and 3 federal agencies that responded to the agency
questionnaire.
Discussed in this appendix are the pavement smoothness measuring systems
currently used for crucial construction smoothness quality control testing and listed In
table E-~. Several other profile- and smoo~ness-measur~ng systems have been used
for pavement management purposes, including numerous high-speed profile
measuring systems. Certainly, some of these systems also have application in initial
pavement smoothness measurement. New smoothness measurement equipment is
being developed, and these systems are also described in the following sections.
Straightedge / Stringline
Perhaps the most basic method of locating surface longitudinal and transverse
pavement irregularities is win me use of a straightedge or stringline. Straightedge
devices are usually made of wood or metal and can be of any convenient length,
typically in the range of ~ to 16 It (2.4 to 4.9 m). A wire or string stretched tightly
from the ends of a bow-shaped form is also sometimes used. When the straightedge
E-!
Table Eel. Agency use of smoothness-measur~ng equipment.
1
Equipment Type | No. of Agencies Using l
l Californ~a-type Profilograph (generic) | 33 l
Rainhart Profilograph 7
Mays Meter (Vehicle mounted) | 2
Mays Meter (Trailer mounted) | 5 l
| GM Type Profilometer | 4
Rolling Straight Edge 1
| Straight Edge or String line | 33a l
l
a six agencies use this category as Me sole method of smoothness measurement, and me
remaining use it to augment over smoothness testing.
Or stringline is placed on the pavement surface, variations in the pavement surface
from the straightedge can be readily seen and measured. Smoothness is controlled
by allowing no more than a specified deviation from the straightedge when placed on
the pavement surface.
Use of this approach is very labor intensive, because We person doing the
measuring must be very close to the pavement surface, generally in a kneeling
position, to determine if any deviation exists. Continuous longitudinal pavement
surface coverage using straightedges is usually not practical, but Me evaluation of
localized areas can be addressed adequately. Application is limited to identification
Of short wavelength roughness, since measurement accuracy diminishes for
pavement surface wavelengths greater Man about one-half the straightedge length.
Since Me straightedge looks at a pavement surface from a "snapshot" viewpoint,
its output can vary greatly from that determined using a profilograph. For example,
a New York DOT study in 1960 found that straightedge results from measured ramps
noted 25 percent more displacement than a profilograph. However, on mainline
highways the straightedge results contained 50 percent less displacement (Scofield
1993~. This is assumed to be a result of Me tremendous effort required to measure
mainline pavement surfaces and the associated fatigue effects.
Although use of more sophisticated smoothness measuring equipment is the norm
for use on most mainline paving projects, there are some situations in which the
straightedge may be the primary method of measuring smoothness. About two-
~irds of the State agencies polled in 1994 indicate that straightedges are used to
augment other forms of smoothness control.
E-2
Rolling Straightedge
Rolling straightedge equipment, as shown in figure E-1, consists of a rigid
straightedge beam with wheels at each end. At the beam midpoint is a third wheel,
riding on the pavement surface, which is linked to an Indicator showing the deviation
from the straightedge plane. One United States manufacturer, ELK
International-Soiltest supplies a generic rolling straightedge under the name Hi-Low
Detector. It is a precision-made rectangular aluminum beam from 10 to 16 It (3.0 to
4.9 m) long with riding wheels at the ends and a detector wheel at the middle. The
system is pushed lengthwise at walking speed by hand from the rear where the
operator can steer the detector and control the spray marking system. If the deviation
from the straightedge plane is greater than is allowable, the operator can trigger an
inverted spray canister from the steering handle to mark the location of high or low
pavement surface deviations. Calibration can be done by hand on a level surface.
The rolling straightedge is slow and incapable of measuring "true" pavement
surface profile. No record of the equipment output is provided by this system except
for the paint markings on the pavements surface, but it is useful for bridge decks and
small projects. Costs for the 10- to 16-ft (3.0- to 4.9-m) systems in 1995 range from
$3,300 to $4,300.
Figure E-~. Rolling straightedge. (Source: ELK)
E-3
Profilograph Equipment
The term profilograph refers to a rigid frame device carried by a system of
support wheels that provides a dawn from which pavement surface deviation
measurements can be made. A profile wheel, which rests on the pavement surface at
the center of the unit, is linked to a mechanical strip chart recorder or computer, and
variations In vertical movement of the profile wheel with respect to the established
datum are recorded. For the mecharucal models, Me strip chart is then evaluated
manually or electronically. Computerized models are programmed to produce a strip
chart and a tabulation of pertinent smoothness information automatically. All of the
devices in this category are operated In the range of 2 to 3 mi/hr (3.2 to 4.S km/hr).
Two basic types of profiIograph have evolved, differing In We support wheel
configuration. Support wheels on Me California-type profilograph have varied in
number from four to twelve, with systems in many States using twelve wheels.
These wheels are attached to the ends of a 25 It (7.6 m) truss and mounted on a
mulliple-axie carriage Cat includes four wheels 17 in (432 mm) from Me truss
centerline and two wheels 17 In (432 mm) on the opposite side of the truss centerline.
The support wheels are commonly spaced at 2.7 it (0.82 m) intervals and positioned
near the ends of the tmss, resulting In an overall profilograph span of about 33 It
(10.0 m). The twelve support wheels for Me Rainhart-type profilograph are evenly
spaced along its 24.75 it (7.5 m) span at offsets up to 22 in (559 mm) such that no
wheel follows the same path. On bow systems, the front support wheels can be
steered by the operator.
The following sections will provide a short history of the profilograph systems
and discuss several of the different models within the profilograph group. These
include the Cox, McCracken, Ames, SSI, Paveset, Soiltest, and Rainhart systems.
California ProfiIograph Background
The development of the California profilograph followed many avenues in Me
period from the 1930s to Me 1950s. Units win a beam length ranging from 10 ft to
30 ft (3.] m to 9.3 m) were used and the model that ultimately became popular has a
length of 25 It (7.6 m). This type has come to be known generically as Me California
profilograph, developed under Me direction of F. N. Hveem, former Materials and
Research Engineer with Me California Division of Highways, and is described In a
classic report from Mat era (Hveem 1960~.
The basic 25-ft (7.~m) long California profilograph, as developed In the late 1950s,
is typically supported be a carriage of six wheels at each end, arranged In an
articulated manner and provided win steering capability. (Current models in use by
the State of California consist of a single axle and two wheels at each end of the 25 It
[7.6 m] beam.) A profile wheel is located at Me beam midpoint and is linked to a
recorder Mat provides a paper strip chart showing changes in Me distance between
the pavement at Me point of the profile wheel and the datum established by the
E-4
carrying wheels. The strip chart produces the deviations on a true vertical scale and
on a 1:300 (25 ft/in [0.3 m/mm]) horizontal scale.
Overall pavement smoothness is expressed by this equipment in terms of its
"profile index" (Pl) and a tolerance for individual bumps. Pi is expressed in inches
per mile (mm per km) and represents the total accumulated excursion of the strip
chart trace beyond a tolerance zone. That tolerance zone typically ranges from 0.2 in
(0.5 mm) to less than 0.001 in (0.025 ~run). For individual bumps the tolerance limit is
expressed as some height, usually 0.3 in (7.6 mm) over a 25 ft (7.6 m) base length as
read on Me strip chart. Some agencies use 0.4 in (10.2 mm) or 0.5 in (12.7 mm)
tolerance levels. When the specifications are exceeded, it is necessary to identify the
individual bumps on the pavement surface so that grinding can be completed to
remove the bumps.
Methods for analysis if the strip chart profiIogram include manual and
computerized techniques. Manual evaluation of the strip chart is done using two
clear plastic templates. The profile index is determined for each 0.! mi (0.16 km) of
pavement using a plastic template 21.12 In (536.45 mm) long (21.12 in x 25 ft/in = 528
It [161 mid. The template is scribed in 0.1 in (2.5 mm) vertical increments to allow
the vertical excursion to be counted. A smoothness tolerance represented by a
blanking band runs the length of Me template. The blanking band is typically 0.2-in
,_ ~ ~ .. . . ~ ~ ~ ~ . `~ _ ~ . ~ ~ ~ ~
to.l-mm) wine; however, some agencies nave used a U.1-ln t;~.~-mm) wine nancl and
some have used a 0.0-in blanking band. The blanking band, when used, is placed on
the profile to cover as much of Me trace as possible. The accumulated distances of
the trace above and below Me blanking band are used to determine the profile index.
Individual bumps are manually identified using a second clear plastic template
with a ~ in (25 mm) scribed base length and a parallel I-in (25-mm) long slot
separated by Me bump tolerance limit, typically 0.3 in (7.6 mm).
Computerized recording and analysis of profiIogram traces is completed by the
manufacturer's software, once the appropriate parameters have been defined. Prior
to completing the measurement pass, the critical bump height and blanking band
width defined by the applicable specification must be defined. In addition, the
computer filter setting, which essentially defines the baseline trace, is selected. The
Cox and McCracken manufacturers have developed data filters in an effort to match
the electronic data profiIogram to Me trace Mat would be measured by a manual
profiIograph. Cox produces a baseline trace and accompanying null band by filtering
a copy of the profiIogram to remove short-wavelength chaNer and produce a smooth
trace that matches the profile trend. The McCracken profiIograph software
reportedly breaks Me section into shorter intervals and analyzes the short intervals by
the standard manual methodology (Scofield 1993~.
The 25-ft (7.6-m) long frame for the profiIograph is comprised of five segments for
ease of transportation and storage. All of the frame segments and the wheel
assemblies, steering mechanism, and recorder can be carried in a pickup or van and
assembled at the job site. Propulsion can be manual or by the use of a small
E-5
motorized unit that is attached alongside the profilograph.
carries the operator as well as propelling the equipment.
The propulsion unit
California implemented a profiIograph specification for concrete pavements
.
beginning In IV58 All of the California ~01~ prohlographs have been constructed ~
the machine shop of the Materials and Research Department, and the fleet eventually
grew to about 20 units. They were built with various materials over the years. Early
frames were constructed using plywood boxes, and later devices were built with
rectangular aluminum tubing. Different recorder designs have been used and the
wheel assembly was redesigned in 1983 to consist of a total of four wheels rather
than We twelve Cat were used: earlier.
As other agencies adopted the California profiIograph, obtaining the device was
somewhat difficult. Some States constructed them in Weir own shops or In a local
machine shop using plans obtained from CALTRANS. As Me demand grew, Me
units were made available commercially. At the present time, Me California
profilograph is being marketed by five firms: Cox and Sons, McCracken Division of
International Pipe Machinery Corp, Ames Corporation, ELK International-Soillest,
and Surface Systems and Instruments-~LC. A dual-lane testing system was also
recently Introduced by Paveset America. The accuracy, repeatability, and ease of use
reportedly varies between these systems.
Numerous State Agencies have developed detailed descriptions for operating
profilographs and for evaluating the profilogram traces. The American Society for
Testing and Materials has developed a standard method for profilograph testing-
ASTM E 1274, "Standard Test Method for Measuring Pavement Roughness Using a
Profilograph." In 1978, Me California DOT prepared their latest revision of California
Test 526 "Operation of the California Profilograph and Evaluation of Profiles."
The increased use of Me California-type profilograph over Me past 35 years
suggests that it has filled a definite need in the area of construction smoothness
control. However, there is growing concern about certain lunitations of this
instrument, including the following (Scofield 1992; Scofield, Kalevela and Anderson
1992):
· Speed The slow operating speed of 2 to 3 mi/hr (3.2 to 4.8 km/hr) is
becoming less tolerable. Agencies need a faster way to obtain profile
v
information.
Precision- Recent studies have focused on the precision of Me instrument and
trace evaluation methods operating under Me current state of the art. It is
questionable whether the profile index can be obtained win adequate
precision to justify its use in specifications that have incentive/dis~ncentive
payments based on ~ in/ml (0.02 m/k~rl) increments. For example, a 1992
study by the Arizona DOT found that Me average standard deviation was 1.9
n/mi for four trace reduction operators on new pavements win average PI
ratings from 2.6 to 4.S ~n/mi (Scofield 1992~. On four rougher sections, with
an average PI of 8.6 ~n/mi (136 mm/km), Me average standard deviation was
E-6
.
.
1.6 in/ml (25.3 mm/km). For mechanical and computerized profilographs, the
range of test results for the same pavement with the same operator and trace
reducer was between 3.5 and 7.0 in/ml (55.3 and 110.6 mm/km) for a smooth
section and between 7.0 and 11.0 (~10.6 and 173.S mm/km) for a rougher
wheelpa~. This is clearly more variability than can be considered acceptable
for Implementing ~ncentive/disincentive specifications. The combination of
variability from trace reduction, test path location, equipment properties, and
computer filter settings makes obtaining precise smoothness statistics with the
profilograph difficult.
Smoothness Index With the growing Interest in pavement management
systems and the Increased sophistication that is being applied to this activity,
there is interest in moving away from Me profile index standard and adopting
some other sublunary statistic such as the International Roughness Index (IRI)
or Root Mean Square Vertical Acceleration (RMSVA), neither of which can be
obtained using a profiIograph. This would allow a given index to be used for
new construction and throughout the life of the pavement.
Relation to User Response Because Me profilogram is known to amplify and
attenuate Me true pavement surface profile, there is some concern about how
well the profilograph output relates to the wavelengths of a pavement profile
that are felt by highway users. Several cases have been documented in which
new pavements that received low PI ratings, and in some cases incentive
payments, were found by the roadway users to be uncomfortably rough. This
calls into question the suitability of using profilograph data for construction
control and suggests the need for refinement in evaluation procedures (Parcells
1992; Scofield 1992~.
California ProfiIograph-Cox Models
James Cox and Sons, Inc. of Colfax, California, began manufacturing profilographs
in 1973. The basic parameters of the California type were adhered to, but Cox
developed numerous innovations in design and construction. In the mid-19SOs, Cox
developed a computerized version, shown in figure E-2, that is currently marketed as
Model CS 8200 at a 1995 price of approximately $24,000. The CS 8200 is a
microcomputer-based profile measuring device designed to measure roadway profiles
and to reduce profile data in accordance with test method Califorrua 526 (1978~. The
CS 8200 reduces Me measured profile data and generates graphic reports containing
the measured profile annotated win stationing, excursion information, and
documentation points. Profilograms may be reduced to obtain profile index or high
points or may do bow sunultaneously. Cox no longer markets a manual
profilograph.
California ProfiIograph-McCracken
The McCracken Division of International Pipe Machinery Corp. of Sioux City,
Iowa, has marketed mechanical profilographs since 1984 and a computerized mode]
since 1990. They are priced (1995) at approximately $16,000 and $26,000, respectively.
E-7
Figure E-2. James Cox & Sons, Inc. computerized profilograph. (Source: Cox & Sons)
The computerized version, illustrated in figure E-3, is fully capable of automatically
providing Me full analysis of profile information in a manner similar to that
performed by the Cox machine. The manufacturer indicates that PI repeatability with
one unit and one operator is about 7 percent (0.5 in/ml [7.9 mm/km] for 7 in/ml
[~10.6 mm/km] pavement).
California ProfiIograph Ames
The Ames Unit is manufactured by Ames ProfiIograph of Ames, Iowa was
developed In 1986. Bow a manual and a computerized version are available, priced
at approximately $10,000 and $22,000, respectively (1995~. The manual unit is
referred to simply as the Ames ProfiIograph and the computerized unit is known as
Computerized ProfiIograph Mode! 4000.
The Ames units are designed to produce the same profile trace as the other
California type units that have been mentioned, but it is considerably different In
basic design, as shown in figure E-4. The wheel assemblies are similar to those of
over models in that an articulated system consisting of a total of six wheels is used
to support each enct of the device.
E-8
Figure E-3. IPMC McCracken computerized profilograph. (Source: IPMC)
.~....
Figure E-4. Ames computerized profilograph. (Source: Ames Profilograph)
E-9
ICC MDR Profiling System
The South Dakota profiling system is now manufactured commercially by
International Cybernetics Corporation (ICC) of Clearwater, Florida. This company
has a family of road profiler equipment in its "Mobile Data Recorder" (MDR) product
line, each mounted in a small- to mid-sized cargo van. These include the following:
MDR 4084 Profile/Roughness System featuring Profile/IR] in one wheelpath;
average rut depth in two wheelpaths to center of lane; one inertial reference
accelerometer; three height sensors; one linear distance sensor, and a m~rumum
recording interval of 3 in (76 mm).
MDR 4085 Enhanced Profile/Rut depth/Roughness System featuring
profile/IRI in two wheelpaths; average or half-car simulation {RI; average rut
depth in two wheelpaths to center of lane; two inertial reference
accelerometers; three height sensors; one linear distance sensor, and a 3 in (76
mm) minimum recording interval.
MDR 4087 Enhanced Profile/Rut depth/Roughness System, shown in figure E-
9, featuring profile/IRI in two wheelpaths; average or half-car simulation IRI;
average rut depth In each wheelpath; two inertial reference accelerometers; five
or more height sensors one linear distance sensor, and a minimum recording
interval of 3 in (76 mm).
~ _
_
~ __
Figure E-9. ICC MDR 4087 profiler. (Source: ICC)
International Cybernetics Corporation offers ultrasonic or laser sensors on all
current MAR systems. The lasers are more expensive than the ultrasonic sensors but
offer several advantages. First, the lasers can be used when roads are wet as long as
there is no standing water to alter the readings. Second, more data points can be
sampled with the laser so that a better average height can be obtained, allowing
better repeatability. Also, the laser is less sensitive to temperature changes, which
may occur quickly in hilly or changing terrain. Finally, the accuracy of ultrasonic
sensors is affected by macrotexture on asphalt pavements, according to a national
study (Perera 1994~.
Reported accuracy of the distance measuring system is 0.02 percent. The standard
deviation of two laser-based {CC MDR 4087-L systems tested in 1993 on eight
sections at four sites was 4 for AC pavements and 2 for PCC pavements. IRI at the
sites ranged from 55 in/ml (869 mm/km) to more than 300 in/ml (4,740 mm/km)
(Perera 1994~. Setup effort, including equipment warm up, calibration, and system
initialization, for this type of system is minimal, requiring 15 to 30 minutes. Data can
be collected at highway speeds, and is stored and processed by computer. Costs of
these systems range from $80,000 to $110,000 in 1995 dollars. A single wheelpath
portable laser profiler is also available for $45,000.
Dynatest Profiling System
In 1995, Dynatest introduced a fully-automated roughness measurement test
system called the Model 5051 RSP (Road Surface Profiler) to meet the FHWA Long
Term Pavement Performance monitoring specifications. The base system, mounted
on Me front of a mid-s~zed van, generates response-type output using a single
accelerometer. The system is shown in figure E-IO.
Up to eleven lasers can be added to the response-type system, using the in-place
accelerometer, to provide longitudinal and transverse pavement surface profile and
rutting information ~ real tune at speeds up to 100 km/hr (62 mi/hr). The lasers and
accelerometers can be mounted in single boxes, S.5-ft (2.~m) rut bars, and In fold-out
extensions to measure up to Il.5 ft (3.5 m) of road width.
The software is capable of automated data recording and post-process~ng, or real-
t~me data processing of longitudinal or transverse profile and the TR] statistic.
Longitudinal profile recording Intervals down to ~ in (25.4 mm) are available.
Transverse profile measurement can be measured on the same frequency. With a
single accelerometer, the software is capable of providing a response-type roughness
index developed at the University of Texas (Walker 1991~. Using a combination of
accelerometers and laser sensors, the Dynatest 5051 RSP system can provide real-time
~ values for each wheelpath and maximum "stringl~ne memos" rut values using
the roadway cross section. Precise, high quality distance measurement
Instrumentation is also provided.
E-22
Figure E-10. Dynatest 5051 Road Surface Profiler (Source: Dynatest Consulting, Inc.)
FHWA PRORUT
The PRORUT device was developed through an FHWA contract with the
University of Michigan Transportation Research Institute (UMTRI) in 1983 (Gillespie
and Sayers 1987~. PRORUT is an inertial profiling system that can be used to
measure and record various roadway characteristics, including longitudinal pavement
profiles, rutting, and roughness levels of the bow wheel tracks. The system is
mounted In a van and uses commercially available components.
Laser sensors and accelerometers are used to obtain the profile measurement in
each wheel track. A centrally mounted laser sensor is also included for measuring
the crown between Me wheel tracks and determining an average rut depth. The
electronics and software system provide for two additional sensors so that Me rut
depth in each wheel track can be measured, if desired.
An IBM-compatible personal computer controls system operation and processes
the data. The menu-driven software leads the operator through system calibration,
component checks, and data collection. Data can Men be analyzed and presented
graphically and numerically. The graphic records are useful in detailing the road
profiles, and Me tabular output is preferable for listing Me International Roughness
Index (IRI) and the mean rut depth averaged over selectable lengths of the test
sections (Brown 1990~.
E-23
IMS Laser RST Propter Swedish
The IMS Laser RST Profiler is a road surveying system developed by the Swedish
National Road Adm~rustration. It can be used to measure longitudinal pavement
profile, rut depth, megatexture, and macrotexture at a recording interval of ~ in (25.4
mm) or more. An accelerometer is used to establish an inertial reference plane, and
roughness is measured continuously at speeds up to 55 mi/hr (90 km/hr). The
roughness measurement output is IRI, although over roughness indices can be
computed. A modification of this system has been used for ~ree-dimensional profile
mapping. Figure E-~1 shows a version of the Laser RST system.
Danish Road Institute ProfiIograph
The Danish Road Institute (DRI) ProfiIograph was developed in 1990 and is quite
similar to the Swedish device mentioned above, except Cat it is mounted in a car
rather than in a small van. As shown in figure E-12, it has a vertical accelerometer,
three aclditional accelerometers, two gyroscopes and one odometer, so that all six
degrees (three translatoric and three rotoric) are evaluated. Road surface elevation is
measured by up to 17 laser sensors mounted on a beam attached to the front of the
vehicle. Lasers are also mounted at an angle on We extendable support bar to
measure surface profile for the entire travel lane width.
Because of the large number of accurate sensors and positioning instruments, this
system can provide a large amount of Information. This includes lon~tud~nal and
transverse surface profile, ruding, side slope, surface macrotexture (influencing fire
noise), surface microtexture (influencing friction characteristics), and many profile-
and response-related pavement smoothness indices. In 1994 the Danish Road
Institute ProfiIograph Incorporated GPS technology using We GPS satellite navigation
system to identify the vehicle's position within a few centimeters.
clinometer-Based Profiling Systems
Three manually propelled profiling systems have been developed using highly
sensitive inclinometer sensors. The Face Dipstick was developed for smoothness
measurement on ultra-smooth warehouse floors and later has been used for
calibration of high-speed road profile systems. On the over hand, We CSC Profilair
was intended as a replacement for rod-and-level profile measurement of airfield
runways. The ARRB Walking Profiler was developed and manufactured by We
Australian Road Research Board and is marketed In the United States by Trigg
Industries International, Inc. for pavements, building slabs, and game courts as a
World Bank Class ~ profile measuring device. These systems are discussed below.
E-24
Figure E-ll. Infrastructure Management Services Laser RST profiler. (Source: IMS)
Figure E-12. DRI Profilograph system. (Source: Darrish Road Institute)
E-25
E.W. Face Dipstick
The Dipstick (DIP = Digital Incremental Profiler) is a precision smoothness
measuring device, operated by hand. Its shape is somewhat similar to a walking
cane with a I-ft (0.3 m) long base, as shown In figure E-13. In the base is a vertical
displacement measuring device that provides slope information to a small attached
computer.
By rotating the base end to end, an operator can move along a highway at 3-, 6-,
9-, or 12-in (7~, 152-, 229-, or 305-mm) Increments, determining Me surface profile,
with a resolution of 0.001 in (0.025 mm). About 900 measurements can be made In
an hour at 1-ft (0.3-m) increments.
The computer and available software can produce a record of the profile
measurements and also calculate an TRT, RMSVA, Mays Output, PSI, PRI,
instantaneous vertical and angular acceleration, F-numbers (floor smoothness ratings),
and cumulative deviation from a selected straightedge. Surface contours can be
plotted, overlay thicknesses can be determined, and cumulative and running IR! can
be computed and displayed.
cot
Begs
It hands
MEOW
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Gem
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Ale
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feel
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filet
Cat
-Cat
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Exam* ~
Figure E-13. Dipstick Auto-Read Profiler. (Source: Face Construction Technologies)
E-26
A 1991 study by the Center for Transportation concluded that "the manual-read
version of the dipstick is an effective Class ~ profiling instrument, as long as
operational techniques, including loop closing and repeat runs are followed. It is
many times faster than the rod-and-level surveying method, and has a resolution 12
times better, making it an extremely accurate device" (Bertrand, Harrison, and
Hudson 1991~. Class ~ profiling instruments are assumed to provide absolute
elevation relative to true horizontal profile with less than I.5 percent bias.
In highway applications, the Face Dipstick is used primarily to calibrate other
types of smoothness measuring equipment and is also used to evaluate the
smoothness of warehouse floors when smoothness is a critical factor In automated
storage/retrieval operations. Because of its accuracy, the Dipstick has been used
recently by the FHWA to provide a baseline profile for verification of high-speed
profile system accuracy.
CSC Profilair
Developed in 1992 by Civil Structural Consultants (CSC) of North Vancouver, B.C.
and commercially available in 1994, He CSC Profilair was originally designed to
replace rod-and-level profile measurement of airport runways. The system, shown in
figure E-14, is a gravity referenced device using an inclinometer for measuring the
vertical angular deviation between adjacent elevation points. The elevation difference
is then computed and added algebraically to He value of the previous elevation.
Sensitivity of the angular measurement is based on a + 14.5 degree range digitized
into + 4,096 units of angle, providing a static resolution of 0.001 in (0.025 mm).
The 3-wheeled device is comprised of a metal structure that moves by rolling on
solid balloon-type natural rubber tires. It can be divided into three 70-Ib (32 kg), or
less, sections for airline or vehicle transportation. Immediately behind He steering
wheel is a fourth wheel for recording He surface elevation. Data from the
inclinometer attacher! to Cat wheel is stored on a 3.5 in (89 mm) floppy disk. The
interval for testing is ~ ft (0.3 m), and the recommended rate of data collection is
5,000 ff/hr (0.42 m/s). Power for He inclinometer data collection system is supplied
by a 12-voll bakery for up to ~ hours of operation, and power for forward movement
is provided by the operator.
At the conclusion of data collection, the disk can be removed and installed in a
portable computer for computation of He profile and roughness Indices IRI and
RMSVA. Bump criteria for selected baselength can be input before processing with
the result that locations of out-of-tolerance bumps are marked on the profile and
listed In a separate table. The software makes corrections for temperature and state
of motion variations. To unprove accuracy, a reverse run is generally necessary, and
the software is designed to adjust for these closed-loop profiles.
E-27
-
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l
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111 1 ~:
~ ~-
~ ~ s.- ~ ~
or ~ ~_
~ 1 _
f ~ ~-
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AL. _ ~ _
.:. - :' - - a
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4:.~ - ~w
I: x ~ ~
i: ~I --
~ i:
1 ,:
~ :: ::
~: ::: ~
~ :::: ::::: i: :::: : : ~ ::: : : :::
:: : :: :::::: : : : ::: :::: :: ::
~::::~: ::::: :: ~: ~ :~ ::
: ~ : : ::: ::: ~ ~ ~ ~ ~ :
: :, ::~ id: ~:: ::::::::::: ::~-:
. ~a
: ~::: ~- :: -
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Figure E-14. CSC Profilair. (Source: CSC Profilair)
ARRB TR Lld. Walking Profiler
The Walking Profiler, developed and manufactured by the Australian Road
Research Board, is a multi-wheeled incI~nometer-based device that is pushed by the
Operator at walking speed (1 km/hr [3,280 ft/hr]~. It continuously records the
relative height of successive points at intervals of 241 mm (9.5 in), storing the vertical
and horizontal deviation from the starting position in an onboard laptop computer.
Software is available to compute and graph surface profiles and determine IRI.
Accuracy reported by the manufacturer is +2 mm (0.0787 in) per 100 m (328 It) of
horizontal distance.
Other Profile and Smoothness Measuring Systems
In addition to the above described pavement smoothness measuring devices,
several other devices have been used for smoothness evaluations. These Include the
ChIoe slope variance measuring system, Me Siometer accelerometer-based system, the
Transportation Road Research Laboratory (TRRL) ProfiIometer, and the
multifunctional ARAN pavement evaluation system.
CHLOE Profits
Developed at the AASHO Road Test during the late 1950s by Carey, Huckins,
Leathers, and other engineers, Me ChIoe Profiler provides a "slope variance" (SV)
statistic as a measure of pavement roughness, which in turn was intended to be used
as an element of serviceability (Carey et al. 19621. Me Chioe Profiler is a relatively
simple electrical-mechanical device. It is a trailered unit 25.5 it (7.8 m) long that
measures the difference in angles between the 20-ft (6.! m) long trailer tongue and a
small beam with two wheels, 9 in (229 mm) apart, recording the measured pavement
slope at 6-~n (305-mm) increments. When in operation, the device is limited to a
E-28
speed of less than 5 mi/hr (8.0 km/hr) (Gillespie, Sayers, and Segal 1980; Carey et al.
1962).
The gain from the CHLOE system is near 1.0 for wave numbers between 0.02 and
30 cycles/ft (0.006 and 98 cycles/m), and is less than 1.0 for higher wave numbers.
A gain of 1.0 indicates prefect representation of the "true" pavement profile. This
trueness to the actual slope profile is a positive advantage of the CHLOE system;
however, the SV statistic is derived from an band of profile wave numbers much
broader than is significant to an automotive vehicle, and as a result introduces a
random error that degrades the agreement between RTRRM system output and SV
(Gillespie, Sayers, and Segal 1980~.
Walker Siomeler
The Siometer accelerometer response device was developed at We University of
Texas in the 1980s (Walker and Phung 1987~. Within the Texas SDHPT, the primary
application of the Siometer is for evaluation of ride quality. The device became
known as Me Siometer because its primary OUtDUt iS Me sewiceabili~ index (SI) for a
particular pavement section. Currently, Me system consist of a sensor, a main control
module, and a laptop computer for storing results. Included In the sensor system are
an accelerometer, housed in a small case mounted vertically inside the trunk of a
vehicle, and a distance measuring signal. The sensor unit and Me main control
module cost $20,000 (1995~.
-A - c,
In 1995, the Siometer technology was incorporated into the Dvnatest Mode] 5051
RSP, described in an earlier section. This system provides a small van, a sensing
accelerometer, hardware, and software for determining Me vehicle response-type
roughness statistic. Including the test van, the 5051 RSP-R0.1 version is currently
sold for about $41,000.
- 1 - ~
. · . ..
-
TRRL ProfiIometer
Developed by the United Kingdom TRRL, the TRRL ProfiIometer originally
consisted of a 2-wheeled trailer coupled to a lowing vehicle Jordan and Porter 1983~.
The current system consists of a single vehicle into which is incorporated a beam
encapsulated in foam and 15.4 ft (5 m) long, upon which four noncontact laser
displacement transducers are mounted. Each transducer measures the vertical
distance of pavement surface below the beam. The foam encapsulation inhibits the
development of vertical temperature gradients in the beam, which would otherwise
cause the beam to bend. Through a series of aigoriduns, He pavement surface
profile is measured without He use of accelerometers or gyroscopes.
· . ~ ~ ~ ~ ~ ~ . ·~ ~ ~ . ~
Reported capabilities of the equipment include measurement of longitudinal
profile in either wheelpath, measurement of average rut depth, surface macrotexture
measurement, and measurement of gradient, cross-fall, and radius of curvature.
Windshield-mounted video cameras are also available. As reporter} by the
manufacturer, the system is capable of accurately measuring pavement surface
E-29
wavelengths between 8 In (200 mm) and 493 it (150 m).
accuracy is 0.5 percent.
Distance measuring
The equipment has been used to measure longitudinal profile on asphalt and
concrete roads and airfields In bow the OK and continental Europe. It can operate at
speeds from 3 to 62 mi/hr (5 to 100 km/hr).
ARAN Profiler
The Automatic Road Analyzer (ARAN) is a multi-function road quality surveying
instrument. It is equipped with the following subsystems: (a) pavement surface
roughness measurement, ebb rut clepth and transverse profile measurement, (c) gyro,
(~) right-of-way video logging, (e) pavement condition video logging, and (f)
pavement rating. System hardware Includes axle and body accelerometers, analog
signal amplifiers, analog low-pass fillers, and a 12-bit analog to digital (A/D)
converter. The software includes digital band-pass filters Passing wavelengths of 1 It
~_ ~ ~- ~ e e ~e ~bed ~
1 ~ (A
tO ;5tJU ~ (Ue;, m tO Yle4 m), alglta1 nlgn-pass nlters passing wavelengths of 2 It (Oe61
m) or less, and statistical models generating the reported roughness statistics RMSVA
(roof mean square vertical acceleration), MAS (mean absolute sIope) and TEXTURE
(surface texture) (Lu et al. 1994~. The current ARAN Laser SDP mode] provides
surface profile, IRI, Serviceability Index (SI), and Ride Number output. The software
is also capable of identifying must-grind locations, using algorithms developed by
States. Accelerometers and laser-based distance measuring sensors are included In
this self-calibrat~ng system mounted in a full-sized van.
Smoothness Measuring Equipment of the Future
What will be in Me future for pavement smoothness measuring equipment?
Given Me rapid advances In technology, it would be hazardous to predict Me future.
However, Improvements In accelerometers and gyroscopes advanced by Me space
industry should make it possible to more accurately measure long wavelength
(greater than 300 It [91.4 m]) surface deviations.
Faster data collection systems, unproved data storage hardware, higher-speed
computing capabilities, and better height sensing mechanisms should make it more
possible to measure and evaluate megatexture (noise source) and microtexture
(friction source) using noncontact profiling systems. Global positioning may be used
to pinpoint areas of pavement roughness on maps that are linked to databases
contouring construction, as well as maintenance and performance data for an entire
States pavement inventory.
As the capabilities of new equipment to measure pavement profiles Improve, the
highway community will be unpolled to define the question, "How accurate is
accurate enough?", especially in the area of new construction smoothness control. If
drivers and vehicles do not respond negatively to very long or very short pavement
surface wavelengths, it is not necessary for Crucial construction equipment to
E-30
accurately measure these wavelengths. Of course, other uses can be made of the new
information made available by technological advances, including friction and noise
evaluations, and highway agencies will use these advances to maintain high quality
pavements In an era of shrinking budgets.
E-31
