Based on measurements of roughness, surface distress, skid resistance and
deflection, pavements can be assigned a score that reflects their overall
condition. This score, sometimes called a pavement condition rating, quantifies a pavement's
overall performance and can be used to help manage pavement networks. By
carefully choosing the rating scale (called the condition index), pavement
condition scores can be used to (Deighton, 1998):
Trigger treatment. For instance, once a pavement's condition
rating reaches a certain level, it can be scheduled for maintenance or
rehabilitation.
Determine the extent and cost of repair. A pavement condition
score is a numerical representation of a pavement's overall condition and can
thus be used to estimate the extent of repair work and the likely cost.
Determine a network condition index. By combining pavement
condition scores for an entire road network, a single score can be obtained that
gives a general idea of the network condition as a whole.
Allow equal comparison of different pavements. Since a
pavement condition score accounts for all types of pavement performance
measures it can be used to compare two or more pavements with different
problems on an equal footing.
A pavement condition index is simply the scale, or series of numbers, used to
describe a pavement condition. Typical pavement condition indices may be
based on a scale of 0 to 5 or perhaps 0 to 100. The proper pavement
condition index depends upon the objectives of whatever system is used to manage
a particular pavement network (called a Pavement Management System or PMS).
This section will present two example pavement condition indices.
The Present Serviceability Index (PSI) is a 0 to 5 scale that was originally
based on a panel of raters who, between 1958 and
1960, rated various roads in the states of Illinois, Minnesota, and Indiana.
PSI ranges from 5 (excellent) to 0 (essentially impassable), and is still used
today throughout the country. It is often a good choice for a smaller,
less sophisticated pavement rating system.
WSDOT uses a more sophisticated pavement rating system for its
Pavement
Management System (PMS). This system uses three different rating scales:
Pavement Structural Condition (PSC). A measure of pavement
distress such as cracking and other distress measures and ranges from 100 (no
distress or very good condition) to zero (extensive distress or very poor
condition).
Pavement rutting condition (PRC). A measurement of rut depth
in inches. The scale ranges from 100 (no rutting) to 0 (0.70 inches of
rutting).
Pavement profile condition (PPC). A measure of roughness
using IRI.
Generally, as a pavement gets older and more worn its PSC and PRC decrease,
while PPC increases.
Figure 1: An Example of the WSDOT
Pavement Condition Rating System