When a municipality seeks to ascertain the overall condition of their pavement network, there are often three primary factors that they consider: Surface Distress Index (SDI, or sometimes referred to as Pavement Condition Index), Roughness Index (RI) and Structural Index (SI). These factors can be combined in order to calculate an Overall Condition Index, or OCI.
While Surface Distress Index is vital and measures the length and severity of surface distresses, Structural Index and Roughness Index are considered enhanced attributes that can improve the reliability of a pavement condition assessment. Structural Index measures the strength of a pavement’s base, but Roughness is focused on something that all travelers will notice; just how bumpy is the street?
In engineering terms, roughness is measured with the International Roughness Index, or IRI. IRI is focused on measuring the change in elevation over a (relatively short) distance, expressed in millimeters/meter. You could also ask, is my road smooth?
When is Roughness Used?
Measuring roughness, often referred to as longitudinal profile, gives municipalities a better understanding of the condition of a particular road, but there are a few places where roughness may not provide the results you are looking for. Roughness that is calculated at extremely low speeds, or over manholes, speed bumps, railroad tracks and the like should be filtered out of a final OCI score. Failure to account for such roadway conditions will result in an inaccurate roughness score that adversely affects an otherwise pristine or newly paved street.
In a semi-automated pavement survey, roughness is measured via a series of gyroscopic sensors. These sensors detect minute changes in elevation over short distances, usually in millimeters per meter. Following a series of calculations that are performed within the pavement management system, a 0 -100 score is recorded. In common terms, a newer street would generally have a Roughness index above 85, while one due for an overlay would be in the range of 40-70. Failed streets typically have roughness values below 40. Some surface distresses such as raveling or rutting can have a large impact on the roughness readings, causing certain surface distresses to have a major impact on the Overall Condition Score once roughness has been included in the calculations.
When roughness is eventually implemented into the final OCI score, it generally accounts for 25-33% of the Overall Condition Score.
To Each Their Own
Though roughness can be a valuable factor in determining the overall condition of a roadway, not all agencies will choose to consider roughness in their final pavement condition score. Some pavement network conditions, such as brick crosswalks, cattle guards, railroad tracks and the like may discourage a municipality from trying to factor in roughness due to the complexities associated with filtering out pavement factors which ultimately crater the final roughness scoring. Additionally some popular pavement management programs, which have been in use by municipalities for years, are not able to factor in IRI readings into a final pavement condition score, leaving a lot of recorded data unused in these cases.
Ultimately roughness can be a very valuable factor to understanding the condition of a pavement network; however, agencies must take care when including roughness and ensure that it is not being used improperly. A meticulous quality control process should be implemented to confirm that roughness factors are not being considered inappropriately and roads are not being punished for their intended design.
For many municipalities around the US the most distressed roadways are likely in need of a full reconstruction. That’s an expensive task. But before you find yourself looking down a multi-million dollar pavement budget hole, take note of a few possible alternatives to reconstructing all of your agency’s failed streets.
Selecting the proper rehabilitation technique for each segment of road and identifying the optimal year to perform this treatment is what pavement management is all about. Factoring in local circumstances such as weather, soil and traffic conditions enables municipalities to determine when a road’s deterioration curve is at its steepest. An experienced pavement management expert will develop a strategy to capture roads before this point, thereby minimizing deferral costs and maximizing limited available funds.
When it comes to pavement management, failed streets that require a full reconstruction have a major difference over all other streets. They will require a full reconstruction no matter how long rehabilitation work is delayed. That means that their cost of deferral is effectively zero (discounting inflation). Compare this to your average local street with a PCI in the low 60s or mid-50s range – this street will gradually increase in repair costs the longer work is delayed. For this reason, municipalities commonly refer to failed streets as “backlog” and frequently allow them to remain in their condition until greater funding is secured.
Let’s take a look at some general rehabilitation rates that will help make this deferral concept clear:
Draw your attention to the colored boxes in the image above. The box that includes “Thin Overlay” (Green) is recommended at a minimum PCI of 60 (marked by the red arrow). The cost associated with this particular rehab activity is approximately $18.00 per square yard.
Directly below the green box is a yellow box; this box identifies “Moderate Overlay” rehabilitation range. The minimum PCI for a moderate overlay is 10 PCI points below the PCI recommended for the thin overlay. Notice the cost difference between the two groups amounts to $3.00 per square yard. This is the cost of deferring a thin overlay candidate for about 5-10 years.
Beneath the yellow box is an orange box which represents “Thick Overlay”. In this grouping the cost per PCI point has jumped from $21 to $32. This $11 per square yard difference represents the cost of deferral associated with going from a moderate to a thick overlay.
Finally, notice the surface and base reconstruction candidates in the bottom red box. The red arrow points to a minimum PCI range of 25 for a surface reconstruction. This rehab activity is recommended only 15 PCI points lower than the thick overlay, and yet, the cost of deferral has inflated to nearly $26.00 at a total of $58 per square yard. This area is the steepest part of a roads deterioration curve and if deferred any longer will ultimately result in a full base reconstruction totaling a whopping $70.50 per square yard.
The rehabilitation activity needed for a road becomes progressively more expensive the longer repairs are deferred; however once it reaches a PCI under 40, surface or full base reconstruction becomes the only viable method to restoring a road to full-service. At this stage, cost effective overlays are no longer a workable rehabilitation option. Further deterioration of a base-reconstruction candidate will not change its rehabilitation prescription; therefore the cost of deferral will not increase beyond this point.
Financially Savvy Deferrals
As shown in the above example, an optimal pavement rehabilitation plan is built around a strategy that minimizes the cost of deferral. Let’s consult the colored chart one more time and see if we can determine the most cost effective way to prioritize our planned work.
If we were to prioritize work solely based on cost of deferral it would look something like this:
However, budget constraints, level of service goals, and even the political environment in a municipality often impact these priorities. For example: when considering budget constraints, one of the more frequent questions that we field on our analysis relates to "fall through year" rehabs. These are streets identified as a need in an analysis year that funding won't cover. Most clients assume that they are prioritized in the next year, but many times they are not. The reason is that, often, these streets drop into the next rehab category. They now have more time in the new rehab category before becoming a "critical" roadway that is within 2-3 points of dropping into the next rehabilitation band. It's all about time left in the current rehabilitation category and which road segments are in their “need year”.
If a particular segment of road is designated for a surface treatment, but the street’s deterioration curve forecasts that it will still be in the rehab category of surface treatment for another 4 years, it should not be prioritized over the moderate overlay candidate that is set to fall into the thick overlay category in the next year. This “Need Year” methodology prioritizes rehabs on a case by case basis, and only selects a road for treatment when it is on the verge of dropping into the next, more expensive, rehab category. This allows municipalities to perform maintenance work on only the segments of road that are an immediate risk of a cost of deferral increase.
The street segments that each municipality selects for rehabilitation can be seen as an entirely unique and case by case process. Each municipality faces its own set of budget constraints, level of service goals, and other local factors that must be considered in this process. It is for that reason that there is no generic “one size fits all” solution. There are, however, some basic considerations that every municipality should think about when it comes to the cost of deferral and rehab selection. By organizing maintenance work along these principles, municipalities can take tremendous steps toward optimizing pavement management funds, and providing the best service possible to taxpayers and residents of their community.
For more tips on managing your pavement budget, check out "Managing a Pavement Budget" HERE.
You probably never imagined how many lives could be saved by simple pavement renewal efforts. In October, 2014 the Federal Highways Administration and U.S Department of Transportation released the results of a 10-year study on fatal car crashing in the United States. A gut wrenching 371,104 fatal crashes occurred in the U.S from 2000-2009. (FHWA, 2014) The report identifies 12.6% of these fatal accidents occurred on wet pavement. The FHWA then asserts a shocking recognition; 70% of these fatal accidents could have been prevented or minimized by simply improving pavement surface friction. That’s 32,730 lives that could have been saved by inexpensive and easily identifiable pavement rehabilitation efforts.
The most commonly deferred roads are those that display only surface distresses, such as raveling (loose pavement material on the surface) or bleeding (excess asphalt binder on the pavement surface). Although these distresses do not reflect an imminent failure of the pavement base, they do reduce tire traction and increase the possibility of a vehicle skidding.
Thankfully there are some easily implemented solutions that can alleviate these concerns and make your roads a safer place to drive.
What never moves and has no feet, but frequently wears shoes, sandals and boots? Sidewalks are one of the most utilized city assets, and yet, simultaneously they remain one of the most neglected. In our 30 years of surveying infrastructure assets in cities across North America, we can say with confidence that the majority of municipalities are struggling with sidewalk compliance and repair backlogs that remain largely underfunded.
Sidewalks can increase public safety, encourage healthy outdoor activity, and even promote economic well-being in low-income communities. On the other hand, when improperly managed, sidewalks can be a tremendous financial drain on a city’s budget. Pedestrians seldom hesitate to file personal injury lawsuits against cities that fail to maintain their sidewalks. There is also the issue of ADA compliance looming over every sidewalk construction project. In addition to managing a backlog of repair projects, settling lawsuits can undermine a municipality’s budget. With this in mind, here are 5 useful tips that will ensure you maintain a happy and healthy pedestrian community:
Some distressed roads need to be fixed right away, some don’t. If you are in charge of a municipality’s pavement management decisions then you have probably been faced with the difficult decision about how to optimize the spending of a limited budget. To navigate those situations with expertise you must be aware of the deferment cost.
In pavement management, road segments are assigned a score depending on their overall quality; this is known as a PCI, or Pavement Condition Index. Depending on the PCI score of a street, pavement management software will recommend a suggested rehab treatment and factor in the average cost. There are a variety of rehab categories to be aware of, all varying in cost depending on the functional classification of the roads in question.
Over 12,000 ASTM (American Society for Testing and Materials) standards are used around the globe, standardizing work in engineering, manufacturing and many other fields. The standards created by ASTM cover everything from construction standards and sustainable design to chemical research and environmental safety. ASTM standard use is ubiquitous across a wide variety of industries, but where do these standards come from?
Preservation of existing roads and street systems has become a major activity for all levels of government. Because municipalities must consistently optimize the spending of their budgets, funds that have been designated for pavement need to be used as effectively as possible. The best method to obtain the maximum value of available funds is through the use of a pavement management system.
A pavement management system is a computerized database that is linked to GIS and contains every individual pavement segment throughout a network. Since it is cost-prohibitive to completely repair every road in a network in one year, a pavement management system should be configured to adequately age particular segments in accordance with their condition analysis (i.e., roads with a weak base deteriorate quicker). A pavement management system is highly recommended to organize ongoing rehabilitation activities because it is common for a network to contain thousands of road segments.
All around the country municipalities are faced with a difficult question.
“How can we provide the best possible service to our community with the limited budget we have?”
When it comes to the pavement network of your city, it should be seen as the most valuable visible asset that the city maintains. Because these assets are constantly under heavy use, municipalities must always be coming up with new strategies and methods for maintaining them. In some cases, street maintenance can be deferred without significantly increasing the future costs associated with needed repairs. In other cases, deferring a street can result in a tremendous increase to the cost of repairs. In pavement management, this concept is referred to as, “equity removal”. Without a sufficient grasp of this important concept, cities risk losing millions of dollars in value from their pavement network.
Traffic signals, street markings, and right-of-way signage dictate the flow of traffic for millions of people. It is easy to take these traffic guides for granted, forgetting that every sign, every traffic signal and every pavement marking must be maintained by the city. There are thousands of these right-of-way assets scattered throughout a city, and keeping track of them can be a challenge.
Government accountability standards such as GASB 34 require municipalities to act as good stewards in maintaining public assets. This includes any right-of-way asset owned by the city. As a matter of fact, the FHWA suggests that a missing or damaged regulatory sign, such as a stop or one way sign, should be replaced or repaired within hours of discovery. The date and time of the notification, as well as the date and time of the repair activity should also be properly documented. So, how do city’s organize and track this type of vital reporting information?
The pavement network is the most valuable visible asset that the city maintains. Even smaller networks are usually valued at close to $100 million. If you are tasked with maintaining such a valuable asset on a dwindling budget, you better make the most out of your investments.
When a municipality is creating a budget plan to allocate millions of dollars to the pavement network, it is considered proper due diligence to base this plan on the most accurate, objective assessment of the network’s condition and need. Reporting of this assessment also falls under statement 34 of The Government Accounting Standards Board (GASB).
Acknowledging that completing a pavement survey is necessary, and recognizing the ways in which it will save your city money are different things, however. Below are three ways in which a pavement survey will help your city instantly save money.