If you are planning a pavement survey or just curious about the process, the PCI score is one of the most important figures to understand. PCI is an abbreviation for Pavement Condition Index. Created by the Army Corp of Engineers, PCI is a number on a scale from 1-100 that is used to summarize the overall condition of a roadway segment.
The PCI score of a road segment can be used to recommend potentially viable rehabilitation methods, costs of repairs, and even to make predictions on the future condition of pavement infrastructure. This makes the task of calculating an accurate PCI score of considerable importance. But how is PCI calculated?
PCI can take into account several factors when determining an ultimate score:
When these three calculations are completed they are then added together to complete an overall PCI for a segment of roadway. This calculation is commonly done as follows:
Structural Testing – PCI = 25% Roughness + 25% Structural + 50% Surface Distress
Without Structural Testing – PCI = 33% Roughness + 67% Surface Distress
Surface Distress Index – The surface distress condition is based on both the extent and severity of distresses encountered along the length of a roadway. Following ASTM D6433 protocols for asphalt and concrete pavements, distresses such as cracking, potholes, raveling and the like are considered by the traveling public to be the most important aspect in assessing the overall pavement condition. For an in depth understanding of each pavement distress, take a look at, “How to spot a Failing Asphalt Street”.
Presented on a 0 to 100 scale, the Surface Distress Index (SDI) is an aggregation of the observed pavement defects. Within the SDI, not all distresses are weighted equally. Certain load associated distresses (caused by traffic loading), such as rutting or alligator cracking on asphalt streets, or divided slab on concrete streets, have a much higher impact on the surface distress index than non-load associated distresses such as raveling or patching. Even at low extents and moderate severity – less than 10% of the total area – load associated distresses can drop the SDI considerably. ASTM D6433 also has algorithms within it to correct for multiple or overlapping distresses within a segment.
Roughness Index - Roughness is measured following the industry standard “International Roughness Index” (IRI), an open-ended score that measures the number of bumps per mile and reports the value as millimeters/meter. The IRI value is converted to a 0 to 100 score and calculated to the Roughness Index (RI)
The results of the RI calculation presents a newer street with a Roughness Index above 85, while one due for an overlay would be in the range 40 to 70. Failing streets typically have roughness values below 40.
Structural Index – Structural adequacy can be measured using a Dynaflect or FWD (Falling Weight Deflectometer) device. The field data from these devices is then compared to the expected load on a particular segment of road to evaluate if the base materials and pavement structure are working as a single unit.
The final result is a single 0 to 100 index value. Scores above a 75 indicate the pavement is structurally adequate, between a 45 and 75 indicate additional structure is required, and those below a 45 generally require replacement. On streets where no deflection testing is completed, the relationship between the final pavement condition score and amount of load associated distresses is used to estimate a structural index.
The graph below demonstrates the typical lifespan of an asphalt roadway as it corresponds to various PCI levels and common descriptive terms. The highest PCI scores are defined as “Excellent” and generally fall in the 85-100 range. The lowest scores in the 0-25 range are referred to as “Very Poor”.
Notice that the PCI range of a particular segment corresponds with a suggested rehabilitation technique. By knowing the price range of a particular rehab technique and the amount of roads within each of the PCI ranges, pavement managers can make very astute budget recommendations for a network.
Prediction and Recommendation
Through the use of a PCI figure, pavement managers can make predictions as to the future condition of a full network. As shown in the graph above, most PCI categories can be given a lifespan of approximately 5 years. By taking into account the deterioration rate of various street segments and the recommended rehabilitation technique for each category, accurate estimates may be made as to the budget requirements of maintaining a particular network. Most municipality budgets exceed 1 million dollars per year. In accordance with the responsibly of managing such a large budget, the more accurate information one has, the better.
In summary, the PCI is a figure that summarizes the results of a pavement survey. PCI includes: Surface Distress Index, Roughness Index and sometimes Structural Index. PCI can be used to understand the current and future state of a pavement network, but can also be the basis for budget recommendations for the city.
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