Ziwei Yang

Ziwei Yang
TTE 5837 Pavement Management Systems
Department of Civil and Coastal
Engineering
Dec 7, 2012

Introduction
PSI (Present Serviceability Index)
IRI (International Roughness Index)
Correlations Between PSI and IRI
Measurement Techniques

Rideability
Maintenance costs
Vehicle delay costs
Fuel consumption
Roughness!

Serviceability is the ability of a specific
section of pavement to serve high-speed,
high-volume, mixed traffic in its existing
condition.
Road quality
and condition
PSI
IRI

PSI is the foundation of pavement maintenance
decision and road economic analysis. It is used
to judge the condition of the road whether
meet the traffic requirement.
PSI (based on AASHO Road Test) is a
mathematical combination of values obtained
from certain physical measurements so
formulated as to predict the PSR for those
pavements within prescribed limits.

Flexible pavement PSI can be obtained
by the equation (1):
Rigid pavement PSI can be obtained
by the equation (2):

1. Since PSI is based on the AASHO Test data
about 50 years ago, and the vehicles, road
characteristics and traffic speeds have been
improved a lot, the applicability is
questionable.
2. PSI includes not only the rideability but also
the surface defects. For the management of
pavement inventory, it would be better to have
separate measures of ride quality and surface
defects.
3. People use more advanced instruments to
measure roughness, but the PSI equations are
based on the profilometer which is no longer
used today, thus, there must be some errors
using PSI equations.

IRI is used to define a characteristic of the
longitudinal profile of a traveled wheeltrack
and constitutes a standardized roughness
measurement. (m/km; mm/m)
Rougness Experiment was held in Brasilia,
Brazil, in 1982
Sponsored by the World Bank

IRI Roughness Scale

60 inches
RARS80 :
reference average rectified slope @ 80 km/hr
It is the ratio of the accumulated suspension
motion of a Quarter-Car divided by the distance
it traveled with a speed of 80 km/hr during the
test.
1 mile

Disadvantage:
Measurement of IRI has the deviation to asphalt
pavement and against concrete. This is because of
the fact that most concrete pavements have sawed
joints at regular intervals, and given a “rough”
surface.
Advantages:
Better repeatability:
Repeatability refers to the ability of one machine to
get the same result on the same stretch of roadway
in two different passes.
Better reproducibility:
Reproducibility refers to the ability of two machines
to get the same result on the same stretch of
roadway.

Reported by Paterson in 1986
PSI = 5×e (-0.18×IRI)
Al-Omari and Darter in 1992
PSR = 5×e (-0.0026×IRI)
Hall and Munoz in 1999
PSI = 5-0.2397x 4 +1.771x 3 -1.4045x 2 -1.5803x
x = log(1+SV)
SV = 2.2704(IRI) 2
However, since Holman’s equations database is much
smaller, Al-Omari and Darter’s equation is more widely
used.

Profile Dipstick
A handle is mounted on
the frame for walking
A microcomputer is
fixed on the dipstick to
record the data and
computer the slope of
the road
An inclinometer
enclosed in a case which
is supported by two legs
separated by 12 in

MERLIN Instrument: simple and low cost
(Machine for Evaluating Roughness using Low-cost
Instrumentation)
It is a 1.8m long metal
structure, with a wheel
in front, a fixed base at
the rear and an
oscillating central
support. The latter
measures the elevation
of a point with respect
to the grade line
defined by the other
two points.
200 measurements (one record for each revolution of the
instrument’s wheel) have to be made at regular intervals
to determine roughness.

Profilographs:
Widely used for rigid pavement construction inspection,
quality control and acceptance
These devices consist of bogie wheel sets at the front and
rear, a recording wheel at the center and a strip chart
recorder for capturing the movement of the recording
wheel relative to the bogie wheels.
Roughness is recorded by the strip chart
The most common
profilograph is the
truss-type California
profilograph. The
profilograph is pushed
along the pavement,
and 3 to 5 kilometers
of the pavement can
be measured in 1 hour

Profilograph Output
Advantages:
1) The initial cost is low.
2)The operation of profilograph is simple.
3) It has good repeatability.
Disadvantages:
1) The speed of operating a profilograph is low.
2) It is unable to measure roughness at
wavelengths equal to integer multiples of the
wheel base.

Inertial Profilometers
The principal components: the height sensor(s),
accelerometer(s), a distance measuring system,
and computer software and hardware.
Most common height sensors: Laser sensors