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WORLD
ANKTECHNICAL
APER
UMBER6
Guidelines
for
Conducting
and
Calibrating
RoadRoughnessMeasurements
Michael
W:Sayers, Thomas
D.
Gillespie,
and WilliamD.
0. Paterson
The
World Bank
Washington,
D.C.,
U.S.A.
7/24/2019 Road Roughness Measurements
4/98
Copyright
(
1986
The
International
Bank
for
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and
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Street,
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1986
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Mfichael
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Department
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Bank.
Library
of
Congress
Cataloging-in-Publication
Data
Sayers,
M. W.
(Michael
W.)
Guidelines
or
conducting
nd
calibrating
oad
roughness
easurements.
(World
Bank
technical
aper,
ISSN
0253-7494
no.
46)
Bibliography:
.
1.
Roads--Riding
ualities--Testing.
.
Road
meters--Calibration.
.
Gillespie,
.
D.
(Thomas
.)
II. Paterson, illiam D. 0. III. Title. IV. Series.
TE251.5.S29
1986
625.8
85-17806
ISBN
0-8213-0590-5
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ABSTRACr
Road roughness s gaining increasing mportance s an indicator f road
condition, oth in terms
of road pavement performance, nd as a major deter-
minant
of road user costs. This need to measure roughness as brought
a
plethora of instruments n the market, covering the range from rather simple
devices to quite complicated
ystems. The
difficulty s the
correlation nd
transferability f measures from various instruments nd the calibration o a
common scale, a situation
hat is exacerbated
hrough a large number
of
factors that cause variations etween readings of similar instruments, nd
even for the same instrument. This need to correlate nd calibrate ed to
the International oad Roughness xperiment (IRRE) in Brazil in 1982, which
is documented n a companion olume in this Series, entitled he International
Road Roughness xperiment: Establishing orrelation nd a Calibration tan-
dard for Measurements (World Bank Technical aper Number 45).
This paper defines roughness easurement ystems hierachically nto four
groups, ranging from profilometric ethods (2 groups) being accurate and
most amenable to detailed analysis through response-type oad roughness
measuring ystems (RTRRMS's) representing he most widely used, practical
and fast instruments to subjective valuation allowing assessments o be
made without use of instruments. The general planning of road roughness
measurement rograms is outlined, s well as the criteria or selection f
measurement ystem to meet the objective. The procedures or carrying out
surveys in the four groups of systems are explained, including nstrument
characteristics, he
need for adequate
checking and verification, nd the
importance
f travelling peed,
as well as the methodology
or data analysis.
The international oughness Index (IRI) is defined, nd the programs for
its calculation re provided. The IRI is
based on simulation
f the rough-
ness response f a car travelling t 80 km/h it is the Reference verage
Rectified lope,
which expresses ratio of the accumulated
uspension otion
of a vehicle, divided by the distance travelled uring the test. The report
explains ow all roughness easurements
an be related to this
scale, also
when travelling t lower speeds than 80 km/h. The IRI therefore merges as a
scale that can be used both for calibration nd for comparative
urposes.
iii
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ACKNOWLEDGEMENTS
These guidelines ave their technical oundations n the published
findingsof two major research rojects:
The international oad Roughness xperiment (IRRE) [1], eld in
Brasilia in 1982, and funded by a number of agencies, ncluding he Brazilian
Transportation lanning Company (GEIPOT), he Brazilian oad Research
Institute (IPR/DNER),
he World Bank (IBRD), he French Bridge
and Pavement
Laboratory LCPC), and the British
Transport nd Road Research aboratory
(TRRL); and
The NCHRP (National ooperative ighway Research rogram) Project 1-18,
documented y NCHRP Report No. 228 [2].
Per Fossberg (IBRD) nd Cesar Queiroz (IPR/DNER) re acknowledged or
their contributions n the development f these guidelines. Also, grateful
acknowledgement s extended to Clell Harral (IBRD), ho conceived he idea of
the IRRE and arranged for the participation f the various agencies nd the
subsequent reparation
f these guidelines.
iv
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TABLE
OF CONTENTS
CHAPTER 1: SCOPE ....................................
.
I..*.........**.
CHAPTER 2: PLANNING A ROUGHNESS
MEASUREMENT PROJECT......................
3
2.1 Overview of the IRI
Road Roughness Scale
........................
3
2.2 Roughness Measurement Methods....
............
.... 6
2.2.1 Class 1:
Precision profiles................................
6
2.2.2 Class 2: Other profilometric
methods.......................
7
2.2.3
Class
3: IRI
estimates from correlation
equations..........
8
2.2.4 Class 4: Subjective
ratings and
uncalibrated measures......
9
2.3 Factors
Affecting
ALccuracy o............................e..............e.
2.3.1 Repeatability error........................................1l
2.3.2 Calibration error..........................................l2
2.3.3 Reproducibilty error.......................................13
2.4 Planning
the Measurement Project
..................
........ 14
2.4.1 Long-term network monitoring
..............................
14
2.4.2 Short-term project
monitoring.
........................ .. ... 15
2.4.3 Precise
monitoring
for
research............................17
CHAPTER
3: MEASUREMENT OR IRI USING PROFILOMETRIC
METHODS (CLASSES 1 &
2).19
3.1 Description
of Method ...........................................
9
3.2 Accuracy Requirement ..
...........................................
l19
3.3
Measurement of
Profile.o......s
........o.........
......2
3.3.1
Rod and Level Survey.......................................22
3.3.2
TRRL Beam Static Profilometer...o...............
.........
.26
3.3.3
APL Inertial Profilometer.
. .... ................. 27
3.3.4 K.
J. Law Inertial Profilometers............................29
3.3.5 Other profilometers .......................................
1
3.4 Computation
of IRI
....................
3.4.1
Equations
................... .............................
1
3.4.2
Example
program for computing
IRI ....
3.4.3 Tables
of coefficients
for
the IRI equations
..............35
3.4.4 Program for computing
coefficients
for the IRI equations...35
3.4.5 Test
input for
checking computation.........................40
v
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CHAPTER 4: ESTIMATION OF IRI USING A CALIBRATED RTRRMS (CLASS 3) .......... 5
4.1 Selection nd Maintenance f a RTRRMS ............................5
4.1.1 The
ramtr...................................4
4.1.2
The vehicle ............
4
4.1.3 Installation f the roadmeter n the vehicle..............o.47
4.1.4 Operating
peed.............................................47
4.1.5 Shock
absorber selection ... e...
..
. .. ............ e.. .48
4ol.6 Vehiclelodn.........................
4.1.7 Tire pressureo.....o............ e o
o.o @ *.o**.*
..... **49
4.1.8
Mechanical inkages n the roadmeter........................49
4.1.9 Tire
imbalance nd
out-of-roundness
..... o................
9
4.1.10 Temperature
ffects..........................................49
4.1.11 Water and moisture
effects
..................................
50
4.2 Calibration f a RTRRMS.............................................50
4.2.1 Calibration
method-.o.oo ...
.*o....oooo
.. .....
.
. .
.51
4.2.2
Calibration equation.. ....................... .............
53
4.2.3 Selection f calibration ites.... ..... o..o.... .o......53
4.2.4 Determining RI
of calibration ites.........................58
4.2.5
Compensation
for non-standard
speed.............o.........o.58
4.3 Operating nd Control est Procedures.............................60
4.3.1 Vehicle and roadmeter peration .......... e................0
4.3.2 Data processing .............................................2
4.3.3 Temperature ensitivity est
..............................
3
4.3.4 Control tests for RTRRMS time stability.....................63
CHAPTER 5: ESTIMIATIONF IRI BY SUBJECTIVE VALUATION CLASS 4) ...........1
5.1 Descriptive
valuation ethod
........ ............................
1
5.1.1 Method......................................................71
5.1.2 Description f the IRI Scale................................71
5.1.3 Personnel ...............o....o...o...oo.........oo.......o.o...o....75
5.1.4
Calibration o...oo .............
.o..o.............
o.o.-
......o....5
5.1. Survey eoo ooooogso*eoo.....o.....................oo....o.........o
5.1.6 Data Processingo...
........................................
76
5.2 Panel Rating of Ride Quality.
... . . . ...... . . .. . . .. . . . . . . .o.. . . . . .. o..76
GLOSSARY
.*.oo oooo.oo.e.go.o.o....oo...o......................
.o79
REFERENCES
....... ....................................
vi
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CHAPTER 1
SCOPE
This documentpresents guidelines or use by personnel
n highway
organizations esponsible or setting up or operating oad roughness
monitoring rograms.
It provides guidance on:
* Choosing a method for measuring road roughness;
*
Calibrating he measurement quipment to a standard oughness
scale;
* Using procedures hat ensure reliable easurements n routine
daily
use.
The suggestions nd procedures resented ere are intended to
guide the practitioner n acquiring oad roughness ata from which to
build a roughness
ata base for a road network. Adherence to these
guidelines ill help ensure:
* That the roughness ata indicate road condition s it affects
using vehicles
in terms of ride quality,
user cost, and safety;
* That data acquiredin routine measurement
perations ill
be
related to a standard roughness cale, and that erroneous ata can
be identified rior to entry into the data base;
*
That
the roughness ata
can be compared directly
to data acquired
by other highway organizations lso following he guidelines; nd
* That the roughness easures have the same meaning on all types of
roads used by highway trucks and passenger ars, including
asphalt, oncrete, urface treatment,
ravel, and earth
surfaces.
The procedures resented n this document are primarily pplicable
to roughness easurements f two types:
*
Direct measurement f roughness n the standard cale, derived
from the longitudinal
rofile of the road
* Estimation of the standard roughness easure, using calibrated
response-type oad roughness
easurement ystems
(RTRRMSs)
1
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CHAPTER 2
PLANNINGA ROUGHNESSMEASUREMENT
ROJECT
The
design
of a project for
surveying
he roughness f
a road
network should start with a clear
understanding f
the objectives o
be
achieved from
the measurement ffort.
A substantial nvestment f
manpower
and money
can be consumed
n a typical roject,
thus it
is
desirable o design the program carefully. The design itself is a
synthesis
rocess taking into
account the project
goals, the resources
available,
nd the environment
f the project. Perhaps
the most
critical element in
the design is the
selection f a roughness
measurement
ethod that is
practicable, et suitably ccurate or
the
purposes
of the project.
This section reviewsthe various measurement
methods available,
lassified ccording
o how directly
they measure
roughness
n a standard cale (Generally, he
more direct methods
are
also the most
accurate). In addition,
t explains
the types of errors
to
be anticipated, nd their importance o
various kinds of measurement
projects.
2.1 Overview f the IRI
Road Roughness
cale
In order
to address
specifics
f roughness easurement,
r issues
of accuracy,
t is first necessary o define
the roughness cale.
In
the interest
f encouraging
se of a common
roughness easurein all
significant
rojects throughout
he world, an International
oughness
Index (IRI)
has been selected.
The IRI is so-named ecause
it was a
product of
the International oad
Roughness xperiment
IRRE),
conducted
by research
eams from Brazil,England, rance,
the United
States, and
Belgium for the purpose of identifying
uch an index. The
IRRE was held
in Brasilia, razilin 1982 [11 and involved the controlled easurement
of
road roughness or
a number of roads under
a variety of conditions
and by
a variety of instruments nd
methods. The roughness
cale
selected
s the IRI was the
one that
best satisfied
he criteriaof
being time-stable, ransportable,
nd relevant, hile
also being readily
measurable y all practitioners
The IRI is a standardized
oughness easurement
elatedto those
obtained
y response-type
oad roughness easurement
ystems(RTRRMS),
with recommended
nits: meters
per kilometer
(m/km)
=
millimeters er
meter (mm/m)=
slope x 1000.
The measure
obtained
from a RTRRMS
is
called either
by its technical
ame of average
rectified
lope (ARS), or
more commonly,
y the units used
(mm/km,
in/mi, etc.).
The ARS measure
is a
ratio of
the accumulated
uspension otion
of a vehicle
(in,
mm,
etc.), dividedby the
distance travelled
y the vehicle
during the
test
(mi, km,
etc.). The reference
TRRMS
used for
the IRI is a mathematical
model,
rather
than a mechanical
ystem,
and exists
as a computation
3
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IRI (m/km =
mm/mr)
NUSEAL
A
.~~~~~S
16 EROSION ULLEYS
AND
DEEP
DEPRESSIONS
14
_ :^^^
..
. 50
km/h
12
-
FREQUENTHALLOW
DEPRESSIONS,
OME _
. 60 km/h
10
DEEP.
.
ROUGH
S
:.*^UNPAVED
....
8 FREOUENTUNAE
ROADS
~80 km/h
MINOR
DEPRESSIONS
.
6
rDAMAGED
SURFACE.
PAENT
o _
OLDERAVEMENTS)
0= ABSOLUTE
I NEWPAVEMENTS)
4 ERFECTION AIRO W
USSUPERHIGHWAYSJ
Fig.
1. The
IRI roughness
cale.
5
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*
overall
ride
quality
*
dynamic
wheel
loads
(damage
to
the
road rom
heavy
trucks;
braking
and
cornering
afety
limits
available
to
passenger
cars)
*
overall
surface
condition
The
IRI
is
also recommended
henever
the measurements
ill
be
obtained
using a RTRRMS at highway speeds (50 100 km/h), regardless f the use
made of
the
data.
However,
hen
profilometric
ethods
are
used
to
measure
wheeltrack
roughness,
hen
other
measures
may
serve
as
better
indicators
or
some
qualities
f
pavement
condition,
r
for
specific
components
f
vehicle
response
encompassed
y
the
IRI. These
guidelines
ddress
only
the
measurement
nd
estimation
f
the IRI.
2.2 Roughness
Measurement
Methods
The many approaches or measuringroad roughness n use throughout
the
world can
be
grouped
into
four
generic
classes
on
the basis
of how
directly
their
measures
pertain
to
the
IRI,
which
in turn
affects
the
calibration
equirements
nd
the
accuracy
associated
ith
their
use.
2.2.1
Class
1:
Precision
rofiles.
This
class
represents
he
highest
standards
f accuracy
for measurement
f IRI.
A
Class
1 method
requires
that
the longitudinal
rofile
of
a
wheeltrack
e
measured
(as
a
series
of
accurate
elevation
oints
closely-spaced
long
the
travelled
wheelpath)
as a
basis
for calculating
he
IRI
value.
For
static
profilometric
ethods,
the
distance
between
samples
should
be no
greater
than
250
mm (4
measures/meter)
nd
the
precision
n
the
elevation
measures ust be
0.5 mm
for
very
smooth
pavements.
(Less
precise
measurements
re acceptable
or
rougher
surfaces,
s
specified
n
Section
3.2.)
High-speed
rofilometers
ffer
a potential
eans
for
measuring
IRI
quickly;
owever,
the profilometer
ust
be
validated
t
some
time
against
an established
rocedure
uch
as
rod and
level
to
prove
its
accuracy.
At
the
present
time,
only
rod and
level
(Section
3.3.1)
and
the
TRRL
Beam
(Section
.3.2)
methods
have
been demonstrated
to be
valid
Class
1
methods
for
determining
RI
over
a broad
range
of
roughness
evels
and
road
types
for the
320 m site
length
used
in
the
IRRE.
Methods in this class are thosethat producemeasuresof such high
quality
that
reproducibility
f
the
IRI
numeric
could
not
be
improved.
While
this
definition
ight
at
first
appear
to
imply
an unreachable
ideal,
there
is usually
a practical
imit
to the
repeatability
hat
can
be obtained
in measuring
road
roughness,
ven
with
a "perfect"
ethod
and/or
instrument.
The
practical
imit
results
from
the inability
o
6
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measure
roughness epeatedly
n
exactly
the same wheeltrack.
Therefore,
a method qualifies
s
Class 1 if measurement
rror
is negligible
n
comparison
ith
the uncertainty
ssociated
ith
trying to locate
exactly
the
same
wheeltrack
wice.
In
the IRRE
the methods found to
qualify
as Class
1 had negligible
measurement
rror
for sites 320 m
long, when
the wheeltracks
ere marked
with
painted
reference pots
spaced at
about 20
m intervals. The
repeatability nder these conditions s about 0.3 m/km IRI on paved
roads, and about
0.5 m/km
for all other road
types.
For wheelpaths
marked
even more
precisely, ethods
described
n these
guidelines s
Class
1 could
perhaps not
qualify
as Class 1 (although
t is
uncommonto
have an application
here
such a
high levelof accuracy
is
needed).
On
the
other hand,
less
stringent pecifications
ight
be suitableif
longer test
sites were
used,
or if the wheeltracks
ere not
marked
at
all.
In many
cases, a
method that
yields this level
of accuracy
ill
have an
associated
isadvantage f
requiring
great
deal of effort to
make the roughness easurement for example, y the rod and level
method).
The accuracyobtained
sing
a Class 1
method by definition
matches
or exceedsthe
requirements
f a
given application,
nd thus
the
Class
1 method
is viewed
as having primary
utility
for validating
ther
methods,
or
when special high-accuracy
ata are required.
2.2.2 Class
2: Other
profilometric
ethods.
This
class
includes
all other
methods in which profile
is
measured as the basis
for direct
computation f
the IRI,
but which
are not capable
of the
accuracy
required
for
a Class 1 measurement.
Though
the hardware
and methods
used for
profile
measurement re functionally
erified
by an independent
calibration rocess,
they
are
limited to accuracy
r bandwidth
less
than
that needed to qualify as a Class 1 method. Consequently, he IRI value
computedfrom a
Class 2 profile
measurement
ay not
be accurate
to
the
practical imit
due to
random
or bias errors
over some
range
of
conditions.
This
class presently
ncludes
IRI values
computedfrom
profiles easured
with
high-speed
rofilometers
nd with
static
methods
that
do not satisfy
the
precision nd/or
measurement
nterval
requirements
pecified
n
Section 3.2.
At the present
time,
the APL Trailer
(Section .3.3)
is
the only
dynamic
profilometer
hat
has been experimentally
alidated
ver the
range
of roughness overed
in
the IRRE. The
GMR-type
Inertial
Profilometer ith follower heels has been validated or roadswith
roughness
evels
less than an IRI
value
of about 3 m/km
[2], above
which
errors
are introduced
ue to bounce
of
the follower heels.
This
type
of
design is no longer
commercially
vailable n
the United
States,
however,
as the
follower heels
have
been replaced
ith non-contacting
sensorsto eliminate
the
bounce problem.
Two high-speed
profilometers
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are
presently
old by K.J. Law,
Inc. (Section
.3.4),
and both are
designed
to provide
the
IRI roughness
uring
measurement.
Both are
considered s
Class
2 systems
at this time,
although
their accuracy
and
range
of operation
ave
not been
verified against
rod and level yet.
Tests with these and
other profilometers
ave been performed,
ut
the
analysesof
the data
have not
yet been completed
ufficiently
o
quantify
their ability
to measure
IRI
High-speed rofilometers
ave
the disadvantage
f being
the
most
expensive
nd complex
instrumentation
ystems
used
to measure road
roughness,
nd
generally require
operators
ith engineering
raining.
Yet, they
offer
a great
advantage n
being able
to obtain
high-quality
measurements
apidly,
ithout
requiring
hat great
effort
be spent
in
maintaining
alibration.
Detailed
procedures
or operating
profilometer
o
measure
IRI are highly
specific
to the design
of the
profilometer;
ence, the manufacturer
hould
be consulted.
Sections
3.3.3
and 3.3.4
briefly
describe several
of
the high-speed
rofilometers
that have
been used
to measureIRI.
2.2.3Class 3: IRI
estimates
rom correlation
quations. By far,
the majorityof
road roughness
ata that is collected
hroughout
he
world
today
is obtained
with RTRRMSs.
The RTRRMS
measure
depends
on the
dynamics
of
a vehicle
to scale
the measurements
o
yield
roughness
properties
omparable
o the
IRI.
The dynamicproperties
re
uniquefor
each
vehicle,
however,
and change
with
time,
Thus, the "raw"
measures
of
ARS obtained
from
the RTRRMSmust
be corrected
o the IRI
scale using
a calibration
quation
that
is obtained
experimentally
or
that specific
RTRRMS. Because
the dynamics
of
a vehicle change
easily, very
rigorous
maintenance nd operating
rocedures ust be
employed
for the
vehicles
used,
and control
testingmust
be
made
a routine
part
of normal
operations.
When changes
occur, there
is no simple
correction
hat can
be applied;
instead,
the entire
roadmeter-vehicle
ystem
must be
re-
calibrated.
This
class
also includes
other roughness
easuring
instruments
capable of
generating
roughness
umeric reasonably
orrelated
o the
IRI
(e.g., a rolling straightedge).
The measures
obtainedcan
be used
to estimate
IRI throughregression
quations
if a correlation
xperiment
is performed.
This approach
is
usually
more troublethan
it's
worth
In 1984 a Road Profilometer eetingwas held in Ann Arbor, Michigan,
to determine
the performance
haracteristics
f
a number of
profilometers,
ncluding
oth of
the currentnon-contacting
ystems
from
K.J.Law,
Inc. (USA), the
Swedish
VTI laser system,
the
APL Trailer,
and
several
non-commercial
ystems.
The
study,which was
funded
by the U.S.
Federal
Highway
Administration
FHWA)
and conducted
y UMTRI,
is still
underway
31.
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(better easures
can be
obtained
ith less effort),
nless there
is a
need to convert
a large
amount
of past data to
the IRI
scale.
A method for measuring
roughness
ualifies
s Class 3
if it uses
the "calibration
y
correlation"
pproach described
n Section
4.2,
regardless f
what type
of instrumentation
r vehicle
is
used to
obtain
the
uncorrected oughness
easure.
While
most Class
3 methods
will
employa roadmeter
hat
accumulates
uspension
otion
to measure
ARS as
describedin Section4.1, other systemsare in use that employ
accelerometers
r other
types
of instrumentation.
However,
the
roadmeter-based
TRRMS that measures
ARS
most closelymatches
the IRI
concept,
and these
guidelines oncentrate
n
the calibrated
TRRMS as
the
principle lass
3 method.
Unless a
RTRRMS
is calibrated
y correlation,
t does not
qualify
as
a Class 3
method. Without the
calibration,
here
is no verifiable
link
between
the measuresobtained
ith any
two RTRRMSs, or
to the IRI
scale.
The reproducibility
ssociated
ith a calibrated TRRMS is about
0.5 m/km (14%)
for paved
roads for
sections 20 m long,
and about
1.0
m/km (18%)
for unpaved surfaces
f
that length.These
accuracy
figures
are only
approximate verages,
s the
errors generally
ary both with
roughness
nd surface
type.
Better accuracy
is possible
by using
longer
test sections.
2.2.4 Class
4:
Subjective
atingsand
uncalibrated
easures.
There are situations
n which
a roughness
ata base
is needed,
but high
accuracy
is not
essential,
r cannot
be afforded.
Still,it is
desirable
o relate
the
measuresto
the IRI
scale.
In those
cases,
a
subjective
valuation nvolving
ither
a ride experience
n the
road or
a visualinspection ould be used. Another possibility s to use the
measurements
rom
an uncalibrated
nstrument. Conversion
f these
observations
o the IRI scale
is
limited
to an approximate
quivalence,
which
can
best
be established
y comparison
o verbal
and/or
pictorial
descriptions
f roads
identified
ith
their associated
RI
values,as
described
n Section
5.0.
Essentially,
he estimates
f equivalence
re
the
calibration, owever
approximate,
nd they may
be considered
o be
"calibration
y description."
When these
subjective
stimates
f roughness
re
converted
o the
IRI scale
the resolution
s limitedto about
six
levelsof roughness
with accuracy
ranging
from 2
-
6 m/km
(about
35%) on the IRI scale.
(Roughness
ccuracy, xpressed
ither
in absolute nits
of m/km
or as a
percentage,
ill
generally
ary with
roughness
evel and surface
type.)
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Note that
unless
a
valid calibration
y
correlation
s used
with
a
RTRRMS,
thereis no way
to
link the
measureto
the
standard
scale.
Thus,
an uncalibrated
TRRMS
falls within
Class
4.
2.3
Factors
Affecting ccuracy
Roughness ata
are
normally
utilized
in applications
epresenting
two extremes:(1) statistical nalysesinvolving oughness easurements
on
major segments
f
a road
network,
and (2)
individual
tudies
related
to
roughness
t specific
road
sites.
The
roughness ata
will
necessarily
nclude
some
errors
arising from
random
and systematic
effects.
The
significance
f these
errors depends
on the
nature of
the
application
or
which the
data
are intended.
An
example
of
the first type
of
application
s a
road-user
ost
study,
in which
the data
base
of operating
osts
for a fleet
of
vehicles
is regressed
gainst
the data
base
of roughness
or
the roads
on
which
those
vehicles
were
operated.
In that
case,
the
need is to
determine
levelsof roughness or comparison ith trends of costs,using
regression
ethods.
Random
errors in
individual
oughness easurements,
caused
by poor precision
r a
peculiarroad
characteristic,
ill tend
to
average
out
if the study
includes
a large
number
of
road sites.
Thus,
random
error is not
of great
concern
for this
type
of study.
On the
other
hand,
systematic
rrors
will
bias the cost
relationships
btained.
Therefore,
teps should
be taken to
keep the
systematic
rrors
to
minimal
levels.
The results
of the study
will not
be transportable
unless a standard
roughness
cale
is used,
and
steps are taken
to
ensure
that
the roughness
ata more
or less
adhere
to that scale.
Studies
that
involvemonitoring
oadway
deterioration
r
the
effects of maintenance re examples of the secondtype of application.
In
these
cases, it
is of
interest
to maintain
a continuing
ecord
of
small
changes
in the roughness
ondition
t specific
road
sites.
Random
errors
in measurement
ill
reduce
the certainty
ith which
the trends
of
interest
can
be discerned.
A
constant
ias in
the
data can
be
determined
nd corrected
n
order
to compare roads
or
apply economic
criteria,
ut it is perhaps
even more critical
to ensure
that the
bias
does
not
change
with time.
Thus,
for
measurements
o be
used
for these
applications,
he practitioner
hould
employ
procedures
hat will
minimize
randomerrors
while
also maximizing
ime-stability.
This
normally
translates
nto using the
same
equipment
nd personnel
or
regularmonitoring f a road site, utilizing epeat tests to improve
repeatability,
nd
carefully
aintaining
he calibration
f
the
equipment.
The
end use
of the roughness
ata in applications
uch as these
has a direct
impact
on
the accuracy
that
will be
necessary
n the
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as would
be
obtained
on
a
320
m test
site
after
five
repeats
(5
x 320
m
= 1.6
km).
As a
rule
of
thumb,
a
total
length
of 1.6
km
(1.0
mile)
or
longer
is
recommended
o minimize
repeatability
rror
for
instruments
used
at
highway
speeds.
Another
means
for
increasing
he
averaging
or
a RTRRMS
instrument
is
to
use a
lower
speed
for
a
given
length
of test
site;however,
this
approach
is
not
recommended,
ecause
changing
the
speed
also changes
the
meaningof the roughness easure for the RTRRMS and increases ther
errors.
2.3.2
Calibration
rror.
Systematic
rrors
exist
in
instruments.
These
cause
the
measurements
f
one
to be
consistently
ifferent
from
those
of
another,
or
cause
one instrument
o
vary
with time.
This
can
be corrected
y calibration,
o that
the roughness
easurements
re
rescaled
to cancel
systematic
ifferences
ringing
the
measures
to a
common
scale.
However,
if
the calibration
oes
not
cover
all
of
the
variables
that
affect
the
measurement,
hen
the
rescaling
ay
not be
correct,
and
a calibration
rror
remains.
Profilonetric
ethods
(Classes
1 and
2):
Calibration
rror
is
minimal
when
direct
profile
measurements
re
used
to
obtain
the IRI.
The
instruments
hat
measure
the profile
are
calibrated
t the
factory,
and
do not
change
much
when
given reasonable
are.
Nonetheless,
systematic
rrors
can
appear
in
profile-based
easures
when
(1)
the
profile
elevation
easures
contain
errors
(usually
aking
the
profile
seem
rougher
than
it
is), (2)
when
profile
measures
are
spaced
too
far
apart
such
that
some
of
the roughness
eatures
are
missed
(making
the
profile
seem
smoother),
nd
(3)
when
profile
measures
are
subjected
o a
smoothing
r a waveband
limitation
s
occurs
with
a dynamic
profilometer
(making
the
profile
seem
smoother).
The
specifications
nd
procedures
recommended n Sections3.2 and 3.3 were designed to hold theseeffects
to
negligible
levels.
RTRRMSs
(Class
3): Calibration
y
correlation
ith
a reference
(Section
.2)
is required
or
a RTRRMS
for
many
reasons,
including
hese
important
hree:
1) The
overall
dynamic
response
f
any particular
TRRMS
vehicle
will
differ
to some
degree
from
that of
the
reference.
This
effect
can
cause
the "raw"
ARS
measure
from
the
RTRRMS
to be
higher
or lower
than
corresponding
RI values,
depending
n
whether
the
RTRRMS
is
more
or
less
responsive
han
the
reference.
2)
The roadmeter
n the
RTRRMS
generally
as freeplay
and
other
forms
of
hysteresis
that
cause
it to
miss
counts,
resulting
n
lower
roughness
easures.
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Reproducibility s
not improved by repeating easures
on the same
site, since the effect is systematic or that site.
2.4
Planning the Measurement roject
The execution
f a high-quality
oad-:oughness easuring
rogram
is critically ependent n establishing ell-thought-out rocedures that
are adhered to in a strict and consistent ashionthroughout he
project. This section outlines the
planning needs for
the three main
kinds of roughness easurement
rojects, o aid the planner in
appreciating he logistics hat are involved.
2.4.1 Long-term
etwork
sonitoring. Long-term oughness
monitoring rograms are an integral part of network condition valuation
surveys and pavement anagement systems.
Typical objectives nclude:
1) Summary of
network condition n a regular
basis for
evaluation f
policy effectiveness
2)
Input into a network-level conomic
analysis of
pavement design
standards, aintenance olicy, and transportation osts
3) Quantifying roject condition or prioritizing aintenance nd
rehabilitation
rograms.
To meet these objectives, he measurements ill usually be continuous
over
links of the network and the total length will exceed 1000
km (or
even 10,000 m). It is essential that measures made in different reas
of the network be directly comparable,
nd that the measures be
consistent ver
time. However, the accuracy requirements or individual
roughness easurements ill generally ot be as demanding s for other
types of projects, ecause data averaging ill reduce
the effects of
random errors. Of the three sources of error
described n Section 2.3,
the calibration rror is the most critical to control.
When planning a long-term onitoring program, ne should consider:
a)
Type of roughness easuring nstruments: The rapid collection
and automatic rocessing f data are paramount onsiderations o
facilitate torage in a data bank, and streamline nalysis. Only
instruments hat can be operated at the higher speeds should be
considered. (The instrument hould operate at least at a speed of 50
km/h, and preferably t 80 km/h or faster.) Any type of RTRRMS is
suitable. A high-speed rofilometer s also suitable and can provide
useful descriptive umerics in addition
to IRI.
b)
Number of instruments:
When
the network is very large or
spread-out, ore than one instrument
ay be required. If this is the
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case, a fleet of RTRRMSs might be more affordable han a fleet of
profilometers. The vehicles sed for RTRRMSs preferably hould
be of
the
same make for the sake of interchangeability,
lthough this is not
essential hen
sound calibration rocedures re followed.
c) Calibration ections (for RTRRMSs only ): A series of eight to
twenty calibration
ections ill be needed at a central location
nd
possibly t distant
regional ocations o permit full calibration f the
test vehicles
at regular intervals Section .2).
d) Control sections:
A small number of control sections three to
five) will be needed in every region here the instruments ill operate
to permit control checks on a daily or weekly basis (Section
.3.4).
e) Measurement peed (for RTRRMSs only3): This
may be a
compromise f conflicting onsiderations. The standard speed of 80 km/h
is likely to be applicable n the majority f situations. Severe road
geometry or
congestion ill dictate a lower speed of 50 or 32 km/h on
some links, but this should not influence he choice for the majority f
the survey. The simultaneous ollection f other data during the survey
may influence he choice.
f)
Data
processing nd reporting: Data collection ust include
location
nd other event markers
for reconciliation ith other pavement
management ata. Computerization t the earliest possible tage and use
of standard
oding forms where necessary hould be considered o
facilitate ata entry. Measurements hould be recorded t intervals f
no more than 1 km. Reporting ill usually comprise ean values either
by link or homogeneous ection of 10 km or longer, with summary
histograms f roughness
istribution y road length. These reporting
units should coincide ith at least the major changes in traffic volumes
to facilitate stimates f vehicle operating osts. For efficiency, he
data can be
managed so as to permit
separating he more
detailed
reporting equirements f
simultaneous roject evaluation nd
prioritization
tudies.
2.4.2 Short-term roject monitoring.
Evaluation f specific
rehabilitationr betterment
rojects nvolves ither
short-term
observations ver periods
up to 3 years
or one-shot oughness
measurements.
Typically, he sites
will range from 5 to 50 km in length
and will not necessarily
e contiguous.
Careful consideration hould
be
given to the detail
and accuracy required,
s accuracy
requirements an
sometimes
e more stringent han for long-term
etwork monitoring
2
Profilometers re calibrated t the factory r in a laboratory.
3
Speed requirements or profilometers re specific o the profilometer
design.
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(Section
2.4.1).
On the other hand,
if only
approximate
oughness
measures
are
needed, considerable
conomy
can be achieved.
If a history
of surface
roughness s
desired,
then the instrument
should
be capable
of providing
repeatable
easures over
a period
of
time, and it
will be important
o
maintain calibration
rror
to small
levels. Also,
if high accuracy
is desired, repeated
easurements
an be
averaged
to reduce the repeatability
rror that might
otherwise
ask
small changesin roughness. In general,efficiency n data acquisition
is not critical for
short-term
rojects, nd therefore
mphasis
should
be placed
on obtaining
ata with quality
as high
as possible
from the
instrumentation.
In some cases,
transportability
f the
data (obtained
y using
the
standard
IRI scale)
may
not be as critical
as maintaining
high
standard
of
internal
consistency. In
practice,
owever,
the careful
controls eeded to
maintain
internal consistency
ill often
result
in
adherence o the
IRI
scale anyway
(particularly
or RTRRMSs).
a)
Profilometric ethods
(Classes
1 and 2):
Profilometric
methods
are suitable
and
can optionally rovide
useful
descriptive
numerics
in addition to
IRI, which
can be used to
diagnose
the nature
and
probable
sources
of distress. (For
example,
the APL
72 system
normally
provides
three waveband roughness
ndices.
The predominantly
long
wavelength
roughness
ndicates ubgrade
r
foundation
nstability,
whereas
shortwavelength
oughness
ndicates
ase or surfacing
distress.)
If
a profilometer
s available,
t can
probably
be appliedwith
little
modification
n procedure,
requiring
nly a
more detailed
reporting ormat
and possibly
ore
carefulmarking
of test
sites. If
no
roughness easuringinstrumentations available, profilometer ight
be imported
temporarily
ith
less overallcost
than the
purchaseof less
sophisticated
ystems
that require
extensive
alibration
ffort.
b)
Calibrated
TRRMS
(Class
3):
These methods
need to be under
rigorous
control
to be satisfactory
hen high
accuracy is desired.
If
possible,
singleinstrument
hould
be used
to performall of
the
measurements
n order to
minimizereproducibility
rror.
The
complete
calibration see Section
4.2)
may need
to be repeated ore
frequently
than
for other applications,
s even
small
changes in the response
properties
f the
RTRRMS may
mask the desired
roughness
nformation.
If a fully equipped TRRMS is available(froma long-term
project),
t
can possibly e applied
with
little
modification n
procedure,
equiring nly
more detailed
measurement
nd reporting
formats.
However,
if the accuracy
requirements
re significantly
ore
stringent han
for the other
project,
then the procedures
ill need
to
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often been used for this application, ut generally ack adequate
precision nd give rise to uncertainty n the trend data. It should be
noted that profile
measures can also be processed to yield a variety of
surface
condition ndicators ther than the IRI, whereas RTRRMSs are
capable of only the single type of measurement.
A trade-off n the frequency f measurement
s possible: Class 1
or 2 measures need be made only annually and in conjunction ith major
maintenance ctivities, ecause of their higher accuracy. However,
Class 3 RTRRMS measures should be made at least two to three times per
year, in order to ensure confidence n the data trends. Portability f
the system is important: Class 3 methods require the
establishment f
supporting ontrol sections in distant regions, hereas Class 1 or 2
systems do not.
Data processing nd analytical ethods will usuallybe project-
specific; hus, these
topics are not addressed ere. Reporting
hould
include computation f the IRI
for the purposes of transferability, ven
if other numerics are used more directly in the research.
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TABLE 1. Accuracy
requirements
for Class
1 and
2 prof lometric
measurement
of IRI
Maximum
convenient
sample
interval
between points
Precision
of elevation
Roughness
range
(mm)l/
measures (mm)
2
/
IRI (m/km)
Class
1 Class 2
Class
1 Class 2
1.0
-
3.0
250
500
0.5
1.0
3.0 - 5.0
250
500
1.0 1.5
5.0
- 7.0
250 500
1.5 2.5
7.0 -
10.
250
500
2.0
4.0
10 - 20 250 500 3.0 6.0
1/
For tapes marked
in
foot units,
the maximum
convenient
intervals
are
respectively
Class 1:
1 ft.
Class 2: 2 ft.
2/
Precision Class
1 yields
less
than 1.5% bias
in IRI.
Precision Class
2 yields
less
than 5% bias
in IRI.
Note:
Precision
Class
2 is adequate
for the
calibration
of response-type
systems (RTRPMS's).
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applications
ut
not
for others.
Thus,
accuracy
requirements
etermined
for
other
applications
re not
necessarily
alid
for
measurement
f
IRI.
3.3 Measurement
f Profile
3.3.1
Rod
and Level
Survey.
The most
well-known
ay
to measure
profile
is
with conventional
urveying
quipment.
The equipment
consistsof a precision od marked in convenient nits of elevation
(typically
ajor
divisions
re cm or ft),
a
level that is
used
to
establish
a horizontal
atum
line,
and
a tape used
to
mark the
longitudinal
istance
along
the
wheelpath.
This
equipment
s widely
available,
nd can
usually
be
rentedor
purchased
t
a cost that
compares ery
favorably
ith
other
roughness
easuring
quipment.
However,
the method
requires
great deal
of
labor,
and is generally
best to
use when
only a
few profiles
re to be
measured.
Detailed
instructions
or
using a rod
and
level
are beyond
the scope
of these
guidelines;
owever,
the measurement
f
a road
profile
is not
a routine
application
f these
instruments,
nd
therefore n
overview
f the
procedure s providedbelow along with guidance
specific
for this
application.
a) Equipment.
In order
to measure
relativeelevation
ith the
required
recision
or paved
roads,
it
is necessary
o obtain
precision
instrumentation
sed
in construction,
s the
rod and
level equipment
used
for routine
land surveying
ork
cannot
provide
the
required
accuracy.
With
the precision
instrumentation,
n
which the rod
and
level
are calibrated
together,
he
level
usually includes
a built-in
micrometerto
interpolate
etween
marks on the
rod.
Note
that
the
accuracy
requirements
n
Table
1
are straightforward
with regard to rod and level:the elevation precision s generally
equivalent
o
the resolution
ith
which
the rod
can be
read through
the
level,
while the
sample
interval
is the distance
(marked
on the tape)
between
adjacent
elevation
easures.
When
a
tape is marked
in
meters,
an
interval
f 0.25
m
is convenient
or
Class
1 measures,
and
an
interval
f 0.50 m
is convenient
or Class
2 measures.
When
the
tape
is
marked in
feet,
an interval
f 2
ft (610
mm) can be
used
for Class
2
measures,
hile
the
largest
convenient
ncrement
or Class
1 measures
is
0.5 ft
(152.4 m).
b)
Field measurements.
The exact
methodology
dopted to
measure
and record
the
elevation
oints
is not
critical,
nd can
be matched
to
the
local
situation
egarding
vailable
ime,
equipment,
nd manpow4er.
Recent
improvements
n
procedure
eveloped
y
Queiroz
and
others
in
Brazil
in
obtaining
rod
and
level profiles
for the
explicit
purpose
of
measuring
roughness
ave proven
helpful,
and are
suggested
ere.
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bl.25
M1
M
61.
Q 74
Qe
36.5
99
otom.
61
75
74.25
86.75
99.25
Z
s
~~62
74.5
9
87
99.5
:
of
JOiM
62.25
74.75
87.25
9975
(400-500)
62.5 75 87.5 100
Site Desc
2 L2.
Date
I Stort:
0=
OLD
-7*O4
_
top
o
V599
AS
of
form
.25
75
25.25
37.75
(500-600)
75
1 .2
I
__
13.5 ff
6
so 38.s
_
1.25
t[1
13.75:r
26.25
23
1.5
1
4
Ill
26.5
S
1 7 5
1425
-79
26
7
a) Pre-printed field forms for recording
rod
readings.
-.
profile
Tape
Rod
Eleu.
8o0
497.5
7047
6939
497.75
7044
6942
498
7039
6947
498.25
7045
6941
Ele.u
498.5
7044
6942
498.75
7046
6940
499
7044
6942
499.5
7041
6945
499.75
7044
6942
400
Tape
Position
600
500
7044
6942
500.25 7591 6948
r
' ontrol 26.2
500.75
7586
6953
10000
0
100
Tape
Int
|
500.7
7586
6953
12616
100.25
175
pen..5
501
75R.
6953
11378
175.25
200
Tape
=
501.25
501
.251
75
12545
200.25
300
501.5
13224
300.25
400
new
digits
= 2
501.75
13986
400.25
500
502
14539
500.25
end
Total
length
501
502.25
GL
used
502.
tI
used
502.75
lT used
b) Display
of the
microcomputer
screen
when typing
date into
the
computer
from
the field
form.
Fig.
2.
Example
of field
forms
and
special
computer
program
used to
record
and
enter
data
from
rod
and
level.
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readings
o elevation alues should be deferred.
Instead, hese
tasks
can all be performed
y the computer fter the rod readings
re entered.
If possible,
he computer program
should present
a display to the
person entering ata
that approximately atches the field form, to allow
the quick
detection f any
typing errors. To
help detect errors,the
computer an be programmed o check
for differences
n adjacent
elevation
alues exceeding level that would indicate rroneous
ata.
An even better check is to plot the elevation rofileat a scale that
will reveal any obviously rroneous ata values. Figure
2b shows the
display
of a data entry program that was used together ith the
field
form shown
in Figure 2a [31. This is, in fact,
an exact replica
of the
screen of the Apple Macintosh icrocomputer
hen running this particular
program, hen the typist has finished ntering
the rod reading at tape
position 501 and is about to enter the reading
for 501.25. The screen
is shown to indicate
ow the data entry task has been been streamlined
in one project.
In this example,
he tape
distance s shown in the
left-most.
column on the computer screen. The numbers match those of the field
forms, allowing the typist to easily see
the correspondence
etween the
position n the computer
screen and the field form. As each rod reading
is entered,
t is shown in the second
column on the left. The elevation
is computed nd shown
in the third column. At the same time, the
elevation s added to the plot shown in the upper-right
and corner of
the screen. Any erroneous ata points
can be seen as "glitches"
n the
plot,
so errors are easily
detected nd.corrected. (The two
boxes in
the
lower right corner were
used to store the changes in the levelling
instrument eight
and to control the flow of the program.)
Using microcomputers
ith "user-friendly" rograms ritten
specifically or entering rod and level data, a typist an enter about
1000 measures per hour (including hecking or
errors).
f) Computer
selection.
The computer elected
to process the
rod
and level data should
ideally have the ability to store the
profile data
permanently
n tape or disk, the ability to plot
profile, nd the
ability to
transmit iles to other
computers. An often
overlooked
consideration
hat should receive high priority
is the availability
f
the computer for
the project. A $500 "home" computer
hat is available
100% of the time
can be much more usefulthan a $100,000 ain-frame
computer shared by a large group that
is neither readily
available or
easily programmed.
3.3.2 TRRL Beam
Static Profilometer.
An automated eam
profilometer
uch as the TRRL
Beam can reducethe survey effort required
for profile
measurement
onsiderably. A two-mancrew can measure
elevations t 100 mm intervals n
two wheeltracks 20
m long in
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wavelengths s long as 100 m when towed at 150 km/h, or as short as
0.3 m when towed at 21.6 km/h.
The APL Trailer
is the only high-speed rofilometer
hat has been
proven to measure IRI over a full range of roughness, ncluding ough
unpaved roads.
Although the APL Trailer can be used to measure IRI, it was
developed or other purposes y LCPC, and is routinely sed in Europe
for other applications. It is normally packaged ith special
instrumentation n one of two configurations: PL 72 for routine survey
work; and APL 25 for precision ork involving uality control and
acceptance, roject evaluation, nd research.
a) APL 72. The APL 72 system employs a powerful odern station
wagon as towing vehicle (sustaining 00,000 km per year for testing and
transfers) [4]. Single-wheeltrack ystems are the norm, although ual-
track systems (two APL Trailers, ne towed in each of the travelled
wheelpaths) ave been used. In normal survey usage in Europe the wheel
travels between the wheeltracks. The profile signal from the trailer,
the speed, distance travelled, nd manually entered event comments are
all recorded n magnetic tape in the towing vehicle. Data processing s
performed ater in the laboratory. Traditional rocessing ethods
classify the roughness n a ten-point cale of signal energy in three
wavelength ranges, i.e., 1
-
3.3 m/cycle, 3.3
-
13 m/cycle, and 13
-
40
m/cycle.
Site lengths need to
be selected in multiples
of 100 m, generally
with a minimum of 200 m and normal length for APL 72 of 1000 m.
Adequate allowance f approach length is necessary or the faster test
speed.
The APL 72 system
can be easily adapted to measure IRI, by
processing the recorded ata differently n the laboratory. The
manufacturer's nstructions hould be followed for details of test
operation. In the laboratory, he analog signals stored on the tape
recorder should be digitized sing standard microcomputer ardware (also
available s part of the APL 72 system, or available n different forms
from various commercial ources). Once the profile signal is digitized
and stored on a microcomputer, t can then be processed s any other
profile data, as described in Section 3.4. When this is done, the
APL 72 can be considered o be a Class 2 method for measuring IRI.
b)
APL
25. The APL 25 system consists of a towing vehicle and
only one trailer, and is used at a slower speed of 21.6 km/h [5]. A
different nstrumentation ystem is used. It digitizes he profile
signal and stores the numerical alues on digital cassette tape along
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with
a single summary roughness ndex called
CAPL 25, calculated or
every 25 m of wheeltrack hat is covered.
Because
of the relatively ow towing speed
used with the APL
25,
it does not sense the longer wavelengths o which to the IRI numeric is
sensitive. Thus, the APL 25 cannot be used to directly easure IRI
without introducing ias. It can, however, e used to estimate
IRI
through the use of experimentally
erived regression
quations hat
relate IRI to other numerics that can be measured by the APL 25. This
approach ould qualify as a Class 3
method. It should not be expected
to be as accurate s the direct measurement hat can be made with the
APL 72 or with other systems sing the APL Trailer at higher speeds,
however.
Therefore, he APL 25 data collection
ystem is not the system
of choice
for measuring RI with the APL Trailer.
3.3.4 K.
J. Law Inertial rofiloseters.
These profilometers,
manufactured
y K. J. Law Engineers, nc. in the United States,
are
modern versions of the original GMR-type nertial rofilometer,
developed
n the 1960's [6]. The profilometer
s an instrumented an
that measures profile in both wheeltracks s it is driven along the
road. Vertical accelerometers rovide the inertial eference. The
distance to the road surface is sensed, riginally y mechanical
follower heels, but more recently ith non-contacting ensors (optical
or acoustic, epending n the model). The accelerometer ignals re
double-integrated
o determine he position f the profilometer ody.
When this position is added to
the road-follower osition ignal, the
profile is obtained.
The original profilometers sed analog electronics o perform the
double-integration nd other processing,
nd the operator as required
to maintain constant travel speed during easurement.
In the late
1970's, the design was upgradedto replace
the analog processing
ith
digital
methods.
With the conversion o digital
methods, new
computation rocedure as
developed o make
the profile
measurement
independent f speed. This allows
the profilometer
o be operated ith
greater ease in traffic.
In addition to measuring he road
profile, these profilometers
routinely
alculate ummary
statistics ssociated ith
quarter-car
simulations. Originally,
he BPR Roughometer
imulation
as used. In
1979, the QCS
model used for the IRI was added
to these profilometers,
and has been in use since that time. Thus, both
models have the IRI
measuring apability
uilt in and automated, nd can be considered s
Class 2 methodsat this time. Neither model has been validated gainst
rod and level yet, although
alidation or a wide
variety of paved road
types is underway [3].
Two versions of a profilometer re currently vailable:
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a)
Model 69ODNC Road Profiloneter.
This version is the more
expensive nd offers the greater capability. It includes van, the
full instrumentation eeded to measure profiles in both wheeltracks, n
on-board minicomputer, 9-track digital tape system, and various
software ptions for computing umerous profile numerics (including
IRI). The road-following eight is detected by a noncontacting ensor
using a visible light beam, replacing he mechanical ollower wheels
used in earlier versions.
The software that calculates he IRI type of roughness as
developed uring the NCHRP 1-18 project [2], and is called the Maysmeter
simulation. It differs from the IRI in that it is computed from both
wheeltracks emulating passenger car with an installed roadmeter)
rather than the single-track RI. Some of these profilometers an
measure the roughness f the wheeltracks eparately s required for the
IRI; if not, the software can be enhanced readily by the manufacturer.
When obtained from the Maysmeter simulation, he IRI is reported ith
units of inches/mile, ather than
m/km (1 m/km = 63.36 in/mi).
The performance f the Model 69ODNC has not yet been validated
against
a static method for measurement f the IRI. The earlier designs
with mechanical follower heels were validated p to roughness evels of
about 3 m/km on the IRI scale in NCHRP Report 228 [2]. With the
noncontacting ensors, peration to higher roughness evels should be
possible. Three Model 69ODNC systems participated n the 1984 Road
Profilometer eeting in Ann Arbor, and validation f the profilometer
will be provided from that study [31. The Model 69ODNC has not been
tested on unpaved roads, and is not likely to be tested soon, since
there is little interest in measuring the roughness f unpaved roads at
the present time in the United States.
b) Model 8300 Roughness urveyor.
The Model 8300 is a single-
track profilometric nstrument esigned specifically o measure IRI. In
order to minimize its cost,
the instrumentation s used to provide
an
internal profile signal only as input to the IRI calculations, hereby
eliminating he need for many of the expensive omputer nd recording
components ncluded in the Model 69ODNC. Although the system provides
IRI roughness s the default, other roughness ndices can be obtained s
options
from the manufacturer.
The Model 8300 utilizes a bumper-mounted nstrumentation ackage
containing
n ultrasonic oad-follower
ystem and a vertical
accelerometer. The system can be mounted on most passenger ars. It
has not
yet been validated or measurement
f the IRI, but did
participate n the 1984 Road Profilometer eeting; hence, information n
its validity (on paved roads) is expected from that study [3].
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V=
(Y -Y) /
dx = slope input (8)
and
Zj'=
Z from previous osition,
=1,4
(9)
and sij and p are coefficients hat are fixed for a given sample
interval, x. Thus, Equations - 7 are solved for each position long
the wheeltrack. After they are solved for one position, qn. 9 is used
to reset the values of Z1 , Z
2
, Z
3
1
, and Z
4
' for the next position.
Also for each position, he rectified
lope
(RS)
f the filtered rofile
is computed s:
RSi = IZ3 Zli (10)
The IRI statistic s the average of the RS variable over the length of
the site. Thus after the above equations ave been solved for all
profile points, the IRI is calculated s:
IRI 1 t RSi
(11)
The above procedure s valid
for any sample interval
etween
dx-.25 m and dx=.61 m (2.0 ft). For shorter sample intervals, he
additional tep of smoothing he profile ith an average value is
recommended o better represent he way in which the tire of a vehicle
envelops the ground. The baselength or averaging s 0.25 m long. The
IRI can then be calculated n either of two ways:
1) The elevation oints falling ithin each .25 m of length ay be
averaged o obtain an equivalent rofile point for the .25 m
interval. Then the IRI is calculated rom the above equations
based on a .25 m interval sing the coefficients or the .25 m
interval.
2) A "moving average" s obtained s the average of all points
falling ithin a .25 m interval entered n the profile elevation
point. Then the IRI is calculated y solving the equations or
each averaged oint using coefficients n the equations
appropriate or the smaller interval.
The algorithm sed in the example computer rogram listed in
Figure
3 in Section 3.4.2 is validfor any baselength ver the
range 10
- 610 mm. When dx is less then 0.25 m, it applies the proper moving
average to the input.
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Lines
1260
1360 computethe
slope
input from
the entered
elevation oints.
The
Y array is a buffer
used
for temporary
torage
of
up
to 26 profile
points. Only
the first
K elements
are ever used,
however.
Thus, when DX is
0.25 m or
greater, hich will
be the
case for
most
applications
here profile
is
measured manually,
=2
and only the
first
two elementsin
the Y array
are needed. For
very short
sample
intervals,
owever,the
Y buffer
is needed
for the moving
average.
When
DX
=
.01 m, then
all 26
elementsin
the Y
buffer
are used.
Lines
1380
-
1490
are straightforward
translations
of Eqs. 4
-
10.
A major
change
that is
recommended o
make
the programmore
practical
s to provide
for reading the
measured
profile
from disk or
tape. Since
file
structures re specific
to different
achines,
he
example program
does
not do
this, but instead requires
hat
the user
enter
each
profile elevation
n sequence.
Lines
1160, 1170, 1280,
and
1290
can be replaced
ith equivalents
hat read
data
from stored
files.
Details concerning
the characteristics
f the
reference
nd this
particular
omputation ethod are readilyavailable [1, 2].
3.4.3 Tables of
coefficients
or the
IBI equations.
The
coefficients
o
be used in Eqns.
4 -
7 and in the example
IRI
computation
rogram depend
on
the interval t
which
the elevation
measurements
re
obtained.
Table 2
provides
the coefficient
alues
for
the commonly-used
ntervals hat are
convenient
or manual
measurement
of profile. When
an interval
is
used that is not
covered
in the table,
then
the coefficients
an be computed
sing
the algorithm
isted in
Figure
4 in Section
3.4.4.
3.4.4 Program
for computing
oefficients
or the IRI equations.
Coefficients or use in Eqns. 4
-
7 can be determined or any profile
interval
by using the computer
program
listed in
Figure 4.
The language
is BASIC,which
was discussed
in Section3.4.2.
The details
of the
vehicle
simulation
re coveredelsewhere
[1],
so only
the actual
equations
sed
in the programare included
ere.
The coefficients
sed in
Eqs. 4 -
7 are derived from
the dynamic
properties
f the reference
ehicle
model.
These dynamic
properties
re
described
y four
differential
quations,
hich
have the matrix
form:
dz(t)/dt
=
A
* z(t)
+
B
*
y(t)
(12)
where z is a vector containingthe four Z variables f Eqs.
I - 7;
A is
a 4 x 4 matrix
that
describes
the dynamics
of the model;
B
is a 4 x 1
vector
that describes ow
the profile
interacts
ith the
vehicle;
and
y(t) is
the profile
input,
as perceived
y a
moving vehicle.
These
matrices
are defined as:
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Table 2.
Coefficients for the IRI Equations.
dx=
50 n, dt= 00225
sec
.9998452
2.235208E-03
1.062545E-04 1.476399E-05
4.858894E-05
ST
= -.1352583
.9870245
7.098568E-02
1.292695E-02 PR
6.427258E-02
1.030173E-03 9.842664E-05
.9882941
2.143501E-03 1.067582E-02
.8983268 8.617964E-02
-10.2297
.9031446
9.331372
dx = 100 mm, dt= .0045 sec
.9994014 4.442351E-03 2.188854E-04 5.72179E-05 3.793992E-04
ST = -. 2570548
.975036
7.966216E-03
2.458427E-02 PR
.2490886
3.960378E-03
3.814527E-04
.9548048
4.055587E-03
4.123478E-02
1.687312
.1638951
-19.34264
.7948701
17.65532
dx = 152.4 mm 0.50 ft), dt = .006858 sec
.9986576
6.727609E-03 3.30789E-05
1.281116E-04
1 309621E-03
ST = -. 3717946
.9634164
-. 1859178
3.527427E-02
PR
=
5577123
8.791381E-03 8.540772E-04
.8992078
5.787373E-03
9.200091E-02
2.388208
.2351618 -27.58257
.6728373
25.19436
dx =
166.7 mm,
dt = .0075015 sec
.9984089 7.346592E-03
-1.096989E-04
1.516632E-04
1.70055E-03
ST = -.4010374
.9603959
-.2592032 3.790333E-02 PR
= .6602406
1.038282E-02
1.011088E-03
.8808076 6.209313E-03
.1088096
2.556328 .2526888 -29.58754 .6385015 27.03121
dx = 200 mm, dt
= .009 sec
.9977588 8.780606E-03
-6.436089E-04
2.127641E-04
2.885245E-03
ST =
-.4660258
Recommended