Condition Rating Systems

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 1997):

  • 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.

Present Serviceability Index (PSI)

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’s Pavement Rating System

WSDOT uses a more sophisticated pavement rating system for its Pavement Management System (PMS).  This system uses three different rating scales:
  1. 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).
  2. 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).
  3. 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.