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.
When the time comes to plan a pavement condition survey for your city, there are a lot of factors to keep in mind. Which software do you use? What functional classes will you survey? Do you want to include structural condition data? At IMS, one of the most common questions we are asked is how conducting a deflection test will affect the overall analysis results, and how that might impact budgeting decisions. Let’s examine that question farther, using a real world example.
First, understand that the purpose of a deflection test is to measure the structural strength underneath the pavement. The condition data gained from this new information can dramatically affect the overall assessment of a street, leading to much more accurate deterioration predictions and more optimized budget allocations throughout the network.
In order to recommend an appropriate rehabilitation treatment, a street’s condition is summarized by a number referred to as a PCI (Pavement Condition Index) score. This number takes into consideration surface distress measurements, Roughness Index score, and occasionally structural condition data from a deflection test. The simplest way to see how much of an impact deflection data has on treatment recommendations is to calculate a street segments PCI score with and without deflection data.
Here is a real example of a town that used structural condition data to save hundreds of thousands of dollars:
Lynnwood is a beautiful, small town located in Snohomish County, Washington just north of Seattle. When the town decided to conduct a pavement survey back in 2016, town officials sought after the most reliable pavement condition data possible. Officials in Lynnwood elected to perform deflection tests on all their arterial and collector roadways. IMS considers deflection testing on arterial and collector streets to be, “best practice” as these streets see a majority of the traffic and are more vulnerable to base failure from compounding load associated distresses.
The most common trend that emerges from reviewing the analysis of Lynnwood is the increase in PCI resulting from the implementation of deflection data. On most roadway segments, PCI is higher when it includes the structural condition data. This simply means that the streets of Lynnwood are built on a strong base, but suffer from surface distresses. From a pavement management prospective this is very good news for Lynnwood, because surface treatments are far cheaper than reconstruction jobs. Let’s take a look at one of the most common situations in the Lynnwood analysis.
On one street designated by Lynnwood as a Minor Arterial the initial PCI score was calculated to be a 58. From this score an Edge Mill + Moderate Overlay was suggested at $29.00/yd2 .
The analysis was then calculated to include the structural condition data from Lynwood’s deflection tests.
With the structural data included the PCI was calculated to be a 66 with the recommended rehabilitation to be an Edge Mill + Thin Overlay at $20.00/yd2 .
With the structural data implemented the newly recommended treatment results in $9.00/yd2 cost reduction. To put this is perspective; this results in Lynnwood saving approximately $306,000 per mile on this road without compromising the quality and longevity of their repairs.
In this small town network, this is just 1 of 170 similar rehab adjustments analysts identified as a result of deflection testing.
If deflection testing saved the small town of Lynnwood, Washington over $300,000 per mile, can you imagine the impact it would have in your home town?
What happens when the base of a road fails? You can expect to see cracks spreading rapidly, for one. These cracks will often compound into a variety of other distresses, resulting in severe raveling and the formation of potholes. Soon the roadway conditions become undrivable and even dangerous. Expensive reconstruction is the only option.
Deflection testing is the process by which the structural strength of a road’s base is measured. By understanding the strength of a pavement base, a municipality can have a better idea of the future rate of deterioration on that street. This leads to better condition and budget projections as well as more accurate rehabilitation plans.
The surface of a street can often tell you a lot about the condition of its base; as well. Poor drainage and alligator cracking may represent structural failings that stem from flaws beneath the surface, while sporadic transverse cracking, bleeding or raveling may not provide any information on a street’s underlying weaknesses. Surface based analysis on pavement is very reliable, so why do so many cities also go through the process of conducting structural testing with Dynaflect or Falling Weight Detectors (FWD)?
Through the use of oscillating or falling weights the unit applies a nondestructive 1,000lb load to the pavement and measures the load’s deflection through a series of sensors. The data is typically collected every 300-500 feet along the outside lanes of a roadway. A structural analysis is then performed using the data collected from the sensors and expressed as a 0-100 score. A score greater than 75 indicates a structurally adequate roadway, while a score in the 50-75 range reflects a pavement that requires additional surface thickness. A score below 50 typically means that a road segment will require reconstruction as well as an increase in surface thickness.
There are many instances where a deflection test is precisely what the city needs to accurately determine their pavement condition. Here are a few all-too-common scenarios:
Saving Time and Money
Preforming a deflection test before investing huge amounts of money in rehabilitation efforts often saves municipality’s money as well as time. Any roadwork done to the surface of a pavement segment with a structural score less than 50 will need to be completely redone in the near future. For example:
A rural community has seen rapid growth and is now contending with an Average Daily Traffic (ADT) far greater than their streets were originally designed to support. In this case, it is common for the city to make the mistake of simply widening the road, without reconstructing the full base. As traffic persists the base will weaken until the entire road, including the newly widened areas, need to be completely reconstructed. A deflection test would have revealed this outcome, saving the community time, and potentially millions of dollars.
The Pavement Management Prophet
Another value of deflection testing is that it enables the city to make more accurate predictions for pavement condition and required budgets. For example:
A busy metropolitan district performs their own pavement condition assessment. They create a rehabilitation plan based on the findings of a manual survey of their network, and petition the city council for a budget. Five years down the road they begin to see a rapid decline in many of the areas that had recently been given overlays and other surface based rehabs.
When the city hires a contractor to perform a deflection test it is revealed that the base of many of the city streets are failing rapidly, and several require a full reconstruction. Their projections and budget analysis were totally off, because they were unable to detect how many streets had begun to experience structural failure. Instead of preemptive rehabilitations, the city must now focus their budget on digging themselves out of a hole. This situation can often lead to Major Pavement Backlog Problems within the community.
Short Term Savings, Long Term Benefits
Sometimes the pavement is in better condition than it looks. Performing a structural test may allow a city to defer some pavements that were otherwise scheduled to receive treatment. This can open up more funds for rehabilitation on segments that are in more desperate need of repair. For example:
An older city is facing budget shortcomings and looking to save as much money as possible by deferring a lot of their pavement rehabilitation needs. By conducting a deflection test on many of their higher traffic collector and arterial streets, they can make more accurate predictions about the deterioration rates of these streets. The city discovers that many of the roads with previously planned rehabs could be deferred several more years before they need repairs. This saves the city money and allows them to focus repairs on streets in more desperate need of work.
Each of the examples above is a common representation of a municipality that benefits through the added information that can only be gained through deflection testing. In practice, nearly every pavement network could save money and time through the more accurate pavement condition data provided by deflection testing. If your city is planning a pavement survey, be sure to consider performing a deflection test on your high-traffic streets. The benefits will continue to show for years to come.
Take a look at our Pavement Assessment Page to learn more about performing a Pavement Condition Assessment in your area.
With billions of tax dollars being spent around the country on maintaining pavement infrastructure it is important to know how to spot a road in need of repair, before those repairs become critical and expensive. Some road rehabilitations are far cheaper than others and can help prolong a pavement segment’s lifespan while sensibly optimizing a city’s budget.
The most important things to recognize when doing a visual survey of a street are the types and quantities of pavement distresses that are present. The distresses measured can reflect the rehabilitation method that is best suited for each road segment. They can also provide a glimpse into the future condition of a roadway if it does not receive any rehab treatment. So, what are the different types of pavement distresses and how do they impact the overall lifespan and cost of rehabilitating a road?
For the purposes of pavement analysis certain types of distresses may have a more drastic effect on the overall pavement quality score.
Types of Pavement Distresses
There are several different pavement distresses that are identified by the ASTM (American Society for Testing and Materials). These are separated into two categories, Load Associated Distresses (LAD) and Non-Load Associated Distresses (NLAD).
Below is a collection of the eight most common distresses that may be present on asphalt streets:
Raveling – Raveling is the loss of fine aggregate materials on the pavement surface measured by the severity and number of square feet affected. This is an NLAD caused primarily by normal weathering. This distress is also commonly found in areas where there is heavy traffic around a turning area and the friction of tires can cause the surface materials of the road to come loose. Raveling reduces the friction of tires and increases roughness on the pavement surface. Raveling can spread very quickly.
Bleeding – Bleeding is the presence of free asphalt binder on the roadway surface caused by too much asphalt in the pavement or insufficient mixing of the aggregate materials. The result is a pavement surface with low skid resistance, especially when wet, and is measured by the amount and severity of the area. This is an NLAD that is commonly found in wheel paths.
Alligator Cracking – Alligator cracking or fatigue cracking is quantified by the severity of the failure and number of square feet. Even at low extents, this can have a large impact on the condition score as this distress represents a failure of the underlying base materials. It is one of the most common types of LAD and can spread rapidly if left unchecked.
Edge Cracking – Though edge cracking only appears on streets with unpaved shoulders, it can also be a sign of severe weakening of the pavement base. Edge cracking commonly occurs on rural roads without sufficient drainage. This allows water to seep under the surface of the street and begin eroding away at the base. Edge cracks may start forming from just outside the wheel path along the shoulder, but may spread very rapidly to the center of the street where much more damage will result in the form of alligator cracks and potholes. Drainage should be properly established so water cannot seep under the surface of the pavement.
Wheel Path Rutting – Starting at a minimum depth of ¼ inch, wheel path ruts are quantified by their depth and the number of square feet encountered. Like alligator cracking, low densities of rutting can have a large impact on the final condition score. This is a LAD that is caused by vehicle movement shifting the underlying pavement materials and is considered a pavement distortion.
Potholes – These are commonly seen in areas with lower structural standards and poor drainage where an already present distress, such as alligator cracking, have filled up with water enough that the soil beneath the pavement has begun to erode. Combine this erosion with continued pressure from street traffic and the surface asphalt is forced out of place. This creates a hole in the pavement where the asphalt surface is completely missing. Potholes are measured in severity from low at less than 25mm to high at over 50mm. Potholes can grow and become very dangerous if left unattended to. They can severely damage tires and vehicle suspensions, and even cause serious accidents. Potholes themselves are a NLAD but they are also usually a symptom of a much greater problem with the pavement base.
When assessing the overall condition of a roadway, taking notice of these common pavement distresses is key. Not only can these distresses help you to ascertain the remaining life in a roadway’s base, but they also reveal the types of rehabilitation treatment that may best suit a particular segment.
Here is a short list of the above distresses and their recommended rehabilitation treatments:
If you are interested in pavement management, check out our article on the Advantages of a Well-Maintained Pavement Infrastructure. Learn a few of the social, economic and quality-of-life benefits that come with good quality roads.
Nationwide, billions of dollars are invested in roadway networks by municipal, state and federal governments. It is not uncommon for the smallest municipalities to spend upwards of 1 million dollars per mile of roadway. This means that even very small municipal districts could be sitting on a 100 million dollar infrastructure asset that needs to be maintained. A roadway network that is taken care of properly will provide many economic and social advantages to a city, as well as its people.
Roadway networks form the economic backbone of a community. They provide means for goods to be exchanged, commerce to flourish and commercial enterprises to generate revenue. Higher pavement network quality is strongly correlated with increased household incomes, and provides a valuable incentive to attract new businesses and other outside investments.
On top of the economic boons, the social benefits of a well-maintained pavement network cannot be overstated. Increased social integration promotes diversity, a greater sense of community, and reduced income inequality throughout a city.
Roadways Drive Investments
The quality of the roadway is likely among the first things a visitor will notice upon touring a city. First impressions are important, and each and every visitor should be seen as a potential investor in the community. Pavement segments that have an aesthetic appeal are likely to draw increased investments such as high income residential neighborhoods and more high-end shopping districts. Likewise, a well maintained industrial network will attract large investments in factories and other major job creators. Balancing the maintenance of these networks with limited budgets is a major challenge that all municipalities face.
Impacts of a Degrading Network
The devastating impacts of a deteriorating and improperly maintained pavement network are anything but subtle, and can actually take quite a toll. Poor road conditions increase fuel and tire consumption while shortening intervals between vehicle repair and maintenance. In turn, these roads result in delayed or more expensive deliveries for businesses and consumers. This can lead to rapid divestment from industry and residents in your city; the consequence of which is difficult to quantify and may take decades to completely recover from.
Neglect of a pavement network could also put your city in the crosshairs of multiple civil lawsuits from personal injury or even a failure to comply with ADA standards. When cutting transportation budgets, local governments should be aware of the adverse consequences that may bring about important and unanticipated welfare effects on a community, damaging the social fabric of a city through the mismanagement of pavement.
Letting your pavement infrastructure funding slide can send you down a slippery slope of greater investment requirements over time and reduced service to the public. As a segment of pavement ages, aesthetic defects begin to give way to load associated distresses. Load associated distresses, such as alligator cracking or wheel path rutting, are directly related to traffic loading and structural capacity. The appearance of these pavement distresses indicates that the base structure of a road is beginning to fail, and much more expensive rehabilitation activities will be needed to restore the road to good condition and prolong its lifespan.
Doing it Right (for) the First Time
A well-managed pavement network brings a high level or service and pride to a city. This in turn attracts investments in business and industry, as well as fosters a healthy, diverse and prosperous community. Conversely, a poorly maintained pavement network suffers from an increasingly unmanageable deteriorating asset, poor service to a community and divestment from local businesses and industry.
Governments at all levels must wake up to the importance of a proactive maintenance approach when dealing with their pavement network. A city’s pavement network is akin to a circulatory system through which your community lives and breathes. The impacts of choking that system should not be taken lightly.
If learning about the advantages of well-maintained pavement got your blood flowing, check out our article, "How to Spot a Failing Asphalt Street". Learn how you can recognize a street that is in serious need of repairs.