Pavement Condition Ratings: Don’t stress the distress.
The backbone of any pavement management system is the measurement of the existing pavement conditions. In order to achieve a representative assessment of the current conditions, we need to quickly and efficiently gather information and process the observations into a value that can be used to rate the pavements for evaluation.
This also initiates development of performance curves used for prediction of future performance. We often receive questions regarding the Pavement Condition Index (PCI) values we provide from our field data collection. We believe it may be helpful to answer commonly asked questions about this scoring system. After all, PCI isn’t something to be ignored.
Potential outcome of extreme pavement distress, when PCI is ignored.
What is the Pavement Condition Index (PCI)?
As defined by ASTM-D6433-11, PCI is a parameter commonly used as a scaled measurement of the distresses observed on the pavement surface. A scale from 0 to 100, with the higher values indicating better conditions, represents the pavement’s current state. In order to interpret the PCI values obtained from field observations, we believe it is necessary to first understand how the values are calculated. The PCI score is based on a series of deduct curves representing various distress types with three severity levels for each distress (low, moderate, and high).
Values obtained from these deduct curves depend upon the density and severity of each distress. The variability of deduction values is based on the type of distress, largely by the differential of environmental aging versus structural distresses. The summation of these deducts is basically subtracted from the perfect score of 100, after corrections are made for the number of distress types. It is valuable to understand that not all distresses indicate similar failure or deterioration rates. Deductions for environmental aging distresses may be relatively small while deductions for structural distresses can be four to five times greater.
Pavement distress example imagery.
At what level is the PCI value really used within a pavement management system?
Pavement management can be divided into two operating levels, the network level and the project level. The network level deals with the key administrative decisions of the pavement system and the service level that should be maintained. The question of which street sections need work, how much money is needed, when treatment is scheduled, and which needs should be funded are a few of the elements involved in the network-level.
The PCI value is most often used within the network level to define network conditions and differentiate between management sections that should be chosen for maintenance. Once management sections are chosen for funding within a given year, the project level deals with technical management decisions for more detailed conditions and specific project conditions. Given that a particular section will receive funding for maintenance, the project-level will help find the best alternative treatment to apply.
Pavement project work.
Is the PCI value calculated from all of the distresses within the roadway?
Within each management section of roadway, one or more survey units are inspected and rated to represent the condition of the entire management section. The entire management section is rarely rated completely. Due to cost constraints of rating 100 percent of the roadway, not to mention the time involved, experience has determined that smaller survey areas provide sufficient information to represent the overall pavement condition.
This means that distresses within the roadway that do not occur in the survey area will not be rated, or other distresses may only exist in the survey area but not throughout the entire management section. However, our data collection provides images of all of the lanes driven and can be reviewed at a later time if questions arise concerning distresses outside of the rated survey sections.
PCI road survey results.
Do the surveys cover all of the lanes
The lanes driven during a collection period are chosen to represent the overall condition of the roadway, but may not include all lanes. For example, on a two-lane road, both directions are driven and collected, while on a four-lane roadway, just the outside lanes of each direction are typically driven. For a six-lane roadway, typically the outside and inside lane of each direction are driven.
We generally find that distresses outside of the survey areas are isolated and maintained as such; therefore, it is not imperative that the survey is inclusive of all of the distresses in a management section. Surveying more pavement in a management section, will likely not significantly change the general assessment or decisions made for a particular roadway.
What does PCI really represent?
Scores represent the general conditions, but may not document all distresses that should be repaired within a management section. The percentages of distress observed in the survey area are extrapolated over the entire section to determine maintenance budgets. Detailed project level analysis is required once a particular management section is selected for treatment.
Is the distress evaluation and PCI calculation automated
DTS provides data collection with Mobile Asset Collection (MAC) vehicles, resulting in images of all assets within the right-of-way. The imagery provides GIS information for all assets along with measurable images of the pavement distresses. This portion of the collection is mainly automated as a collection process. However, each pavement distress is identified, evaluated, and measured by engineering technicians viewing these images. These professionals are trained to provide consistency in the rating, yet an amount of subjectivity remains in the process. Each person will view distresses slightly differently, but the descriptions provided in ASTM-D6433-11 help provide uniformity to the process. Having the raters perform their observations in a controlled environment, versus working in the field along busy roadways, reduces the variances within the process.
Two of Data Transfer Solutions, LLC’s state-of-the-art Mobile Asset Collection (MAC) vans.
We hope this discussion has provided some clarity to the pavement evaluation process and answers questions you may have had. If you have additional questions or would like to engage in more detailed discussions, our engineers are available to visit with you and review your data to provide a better understanding of what pavement data collection can tell you.
For more information on how you can obtain your PCI ratings through expert data collection, contact Scot Gordon, PE – Vice President of Asset Management Services: email@example.com