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.
Identifying the problem
The first step in reducing the concern of vehicle skidding is to identify areas of your pavement network where distresses related to vehicle traction are present. The most accurate and cost effective means of doing this is through a pavement network survey. The survey should collect data on asphalt streets with excessive bleeding and raveling while focusing on scaling and excessive polished aggregate on concrete streets.
Asphalts streets with excessive bleeding or raveling will suffer from reduced tire traction. Luckily these distresses are easily fixed in most cases.
Asphalt bleeding is caused when asphalt is improperly mixed and the excess asphalt binder rises to the pavement surface. If the bleeding is light it can be soaked up through a light application of coarse sand, while heavier bleeding should be shaved away using a motor grader.
Raveling is usually an effect that stems from another pavement distress, such as an improperly sealed crack or a poorly maintained patch. Asphalt streets that receive heavy snowfall may also see raveling as the result of studded tire or snowplow traffic. Usually minor raveling can be simply swept aside through a standard street cleaning processes, but if it is more severe or there are other distresses present on the road it may be more effective to rehab the entire segment with an overlay rather than continually sweep up loose asphalt material from the crumbling pavement.
Compared to the porous nature of asphalt, concrete is impermeable. This causes water to sit on the surface until it evaporates, all the while increasing the danger of skidding on the slick concrete. This is especially apparent in damp environments where sitting water is slower to evaporate from the surface. To address this aspect of concrete pavement, construction companies apply a process known as tining. This is where a metal rake creates grooves in the pavement designed to increase friction. It is important to note that time, weather and traffic will have a wearing effect on concrete tining and slowly grind down on the pavement grooves. In this case it is often most cost effective to wait until further distresses like cracks and scaling trigger a panel replacement to rehab these areas.
If replacing the concrete panel is not an immediate option, it is possible to apply a post-construction texturing to the pavement surface through the process of diamond grinding. This process requires specialized equipment with rotating diamond bladed saws and it may not be appropriate for all sections of concrete pavement.
Improving Public Safety
If your city has seen frequent snow or rainfall, or has aging pavement infrastructure, it may be pertinent to develop a strategy towards skid resistance roadways. Utilize a pavement surface survey and determine where drivers in your city may be at risk. Pavement texturing treatments are a great way to increase public safety without breaking the bank. Every life lost in a car accident is a tragic loss for our whole society. If your city takes active measures to reduce vehicle skidding, you WILL save lives.
Want to learn more about setting up a pavement management program in your city? Check out "Designing and Implementing a Pavement Management System" - An IMS Whitepaper
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:
1.Conduct a Sidewalk Condition Survey at 5-10 year Intervals
The first and most important step to managing a sidewalk network is to collect and maintain a database of sidewalk condition data. With this database public works managers can track the condition of sidewalks throughout the network. This should be done every 5 to 10 years to ensure accurate and up-to-date information. Don’t wait for a lawsuit to discover a problem with your sidewalks, take an active approach to management and fix problems before they are liabilities. IMS conducts regular sidewalk surveys in cities throughout North America.
2.Fix Obstructions First
Fixing obstructions first is very important for a variety of reasons. Obstructions on a sidewalk are not only an ADA compliance violation; they also prevent survey vehicles from measuring the condition of the pavement. This often results in a sidewalk database entry that does not accurately reflect the surface condition of that pavement. Additionally, removing obstructions is often the cheapest way to improve the walkways for pedestrians. Trimming a bush or moving lose materials that may be obstructing the sidewalk is far less expensive than panel replacements.
3.Maintain a Database of all ADA Accessible Ramps
In addition to an inventory of sidewalk pavement assets, it often behooves a municipality to maintain a database of ADA accessible ramps. This accomplishes two things. First, it allows city managers to locate, review and plan rehabilitations or upgrades to any ramp in the city. Second, it demonstrates a good-faith effort to comply with ADA regulations, something any municipality can be proud of.
4.Prepare an Actionable Repair Plan and Dedicated Sidewalk Budget
Once a city has prepared a database of their sidewalk assets and determined the rehabilitation needs of the network, city managers can prepare an actionable plan with a dedicated budget. Once again, the development of this plan can demonstrate a good-faith effort to repair the sidewalks in the city. This can be of enormous value in the case of a civil or DOJ legal filing against the city for a sidewalk related injury or ADA compliance violation. The development of a budget plan for improving the sidewalks in a city is also a visible and positive way to win the support of residents within a community.
5.Encourage Healthy Walking Habits
In 2012 National Geographic published a 17-nation study that covered a variety of national statistics; among them were use of public transit and walking activity. The United States of America came in dead last in both of these categories. Only 34% of Americans reported that they occasionally walk to destinations such as jobs, shopping, school, etc. What is more, poor conditions for walking affect low-income Americans more than others. This is because low-income households commonly spend up to 42% of their income on transportation related costs. Infrastructure policy decisions that encourage low-income communities to walk or bike can have a positive impact on the economic conditions of individuals in a particular community. By improving the sidewalk infrastructure, a city can encourage residents to create healthy walking habits, reduce transportation costs, reduce traffic, and save money.
Improving the sidewalks in your city can result in meaningful improvements to public safety, ADA compliance, economic opportunity, and even the overall appraised value of a community. Not all municipalities have the resources, technical or human assets needed to manage their sidewalk network, but don’t wait for a lawsuit or resident complaints to do something about it. Conduct a sidewalk asset survey and discover how easily you can begin improving the walking conditions for pedestrians in your city.
To learn more about sidewalks, take a look at "Does Your City Have a Sidewalk Problem?"
- an IMS Whitepaper.
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.
Streets with a low PCI score of 0-25 are generally considered to be in very poor condition, where as a street with an 85-100 PCI will be considered excellent. A very poor street will require reconstruction to return it to full service, while an excellent street does not yet require any rehabilitation effort. Streets that score slightly above poor, usually in the 40-50 (marginal) range are generally the streets that need the most urgent attention. The reason for this is that these streets usually present the last opportunity for surface-based repairs. In general, the service life of these streets is such that if deferred for too long, they will require costly reconstruction. Streets rated as marginal are typically selected first for rehabilitation as they provide the greatest cost/benefit to the City by providing the greatest increase in service life per rehabilitation dollar spent.
Deterioration and Performance Curves
A successful pavement management program develops a confidently accurate performance model of a roadway, and then identifies the optimal timing and rehabilitation strategy for its needs. The benefits of this exercise are long term cost savings and an increase in pavement quality over time. The key is to develop policies and practices that delay the inevitable total reconstruction for as long as practical yet still remaining within the target zone for cost effective rehabilitation. That is, as each roadway approaches the steepest part of its deterioration curve, apply a remedy that extends the pavement life, at a minimum cost, thereby avoiding costly heavy overlays and reconstruction.
In this graph the different color lines represent various conditions that may affect the overall deterioration rate of a road. This can include heavy traffic growth, poor foundation materials, intense weather conditions and more.
A pavement information management software can track the deterioration of your entire network and recommend the proper rehabilitation activities as a road approaches its “need year”. Without a fully implemented pavement information management system, the process of identifying and tracking the need year of every segment of road in an entire pavement network is borderline impossible. The need year refers to the last possible year where a particular rehab treatment will be effective. If a street in its need year is deferred, a more costly treatment will be required to return the street to full service.
Avoid the Management Pothole
A trap that municipalities often fall into revolves around the worst-first rehab philosophy. The idea behind this management strategy is very straight forward; repair the most distressed streets first. This is a poor management strategy for a number of reasons. A cost comparison of rehabilitation techniques makes this concept much clearer: (Unit rates may vary slightly by location)
In the chart above, notice the increase in cost between Rehab Code 56 and Rehab Code 70, and again between 26 and 30. In this particular example the cost doubles from surface based overlays to base reconstructions, and quadruples from surface treatments to overlays. For the cost of a single mile of reconstruction, a municipality could instead extend the life of 5 miles of other roads in need of thick overlays. Keep in mind that the segments in need of Thick Overlays (Rehab 56) will soon become full reconstruction candidates, increasing their rehab cost 2 fold (500K becomes 1M). A pavement segment that requires reconstruction will not increase in cost through deferral; it will simply remain a reconstruction candidate until it receives proper treatment. Proper rehab planning could be the difference between $1,000,000 for a single mile of reconstruction or $100,000 for a single mile of surface based repairs.
Pavement managers are constantly wrestling with lengthy lists of rehab needs. In order to precisely manage a limited budget while dealing with these needs, it is important to adopt pavement management software that can organize the network streets. By actively rehabilitating roads in their need year and utilizing proper rehab deferment techniques, pavement managers can optimize taxpayer budgets and provide better services to the community.
Want to learn more about setting up a pavement management program in your city? Check out "Designing and Implementing a Pavement Management System" - An IMS Whitepaper
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?
Origins of ASTM Standards
The origins of ASTM standards can be traced back to the late 1800s and The Pennsylvania Railroad Corporation. During this time a Yale Ph.D. recipient by the name of Charles Dudley was promoting a new standard in material specifications for steel rails. In his first major report “The Chemical Composition and Physical Properties of Steel Rails,” Dudley analyzed the durability of various types of steel rails and recommended an improved formula for manufacturing steel rails to be used by Pennsylvania.
Though Dudley’s first major manufacturing standard did not catch on right away due to disagreements between suppliers and manufacturers, this experience would lead to the creation of the first technical committee for material standards in the railroad industry. This technical committee produced the first manufacturing standard with the ASTM label and became the basis for the ASTM organization that we have today.
Using ASTM for Pavement Management
ASTM D6433 outlines various standards that are used to identify pavement distresses and measure their impact on the overall condition of the pavement. The concept of PCI (Pavement Condition Index) actually comes from the ASTM standards. To read more about PCI please see our article “Understanding PCI and what it means for Your Roads”.
There is an immeasurable value in an objective, scientifically-based standard through which pavement condition can be quantified. Through the use of measurement tools included in the PCI standards from ASTM D6433, each distress that is recorded during a pavement survey can be assigned a numerical value and factored into an overall assessment of the pavement quality. This is used to determine everything from proper rehabilitation techniques to accurate pavement deterioration curves, which in turn help to form the groundwork for budget models.
The ASTM standard defines pavement distresses, alerting survey crews and analysts of the degree in which severity and frequency of a distress impacts the overall PCI score. In addition to outlining how a distress should be calculated, it also outlines how it should be measured. For example:
ASTM standards have an enormous value in science and engineering, forming the bedrock through which industries can perform objective measurements and build models based on proven techniques. In pavement management, it is no different. ASTM D6433 outlines the basis through which pavement distresses are measured and factored into the overall condition of a pavement segment. By basing the processes of pavement management on sound logic and proven techniques, municipalities all over America can accurately and objectively plan for the future.
Want to learn more about spotting a failing pavement surface? Check out "A Guide to Key Indicators of Failing Pavement" - An IMS Whitepaper
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.
Setting up the System
There is a variety of pavement management software applications (i.e., Lucity, ESA, Micropaver) that a municipality can use to manage their pavement assets. Regardless of the software that your network uses, it must be properly linked with GIS and frequently updated with the current pavement condition.
The best way to collect the data your city needs is through a semi-automated pavement condition survey. A pavement condition survey will collect and organize distress data on pavement segments throughout the network. The system will automatically age streets with their distress data in mind, and recommend rehabilitation methods based on need and cost effectiveness.
At this stage it should be the goal of pavement managers to set up “need-year” rehabilitation plans. This method refers to a process of deferring work on a segment until the last possible year in which a rehabilitation technique can be effective. If these segments are deferred any longer, a more expensive rehab activity will be needed to return the street to full service. By prioritizing repairs based on need-year, a municipality can optimize their annual budget and prolong the life of as many roads as possible. To learn more about prioritizing rehab work, take a look at “Common Mistakes in Pavement Management that Could Cost Your City Millions”.
Sticking to a Plan
Once a network has a functioning pavement management system the task of identifying a budget must begin. The primary components that should be considered when determining the budget are:
Average Pavement Condition – IMS considers networks with a PCI score from 60-65 to fall within the national average for the US. If the network average is not yet 60, that should be a primary consideration before a budget is determined.
Percentage of Backlog Roads – The next important consideration should be the percentage of the pavement network that contains reconstruction candidates. These are roads with a PCI score from 1-40 and represent the most expensive repairs in the network. These roads are very expensive to return to full service and can eat up large portions of an annual budget, thus the percentage of roads in this category is recommended to stay below 15%, the lower the better.
Percentage of Excellent Roads – Excellent roads have a PCI from 85-100 and represent the areas of a network that require little to no investment to maintain. These are usually recently paved streets and the percentage of excellent roads can often indicate how money has been spent over the past 5-10 years. Since the percentage of these streets represents the percentage of the network that does not require any investment, the higher this number the better. IMS recommends at least 15% of a network’s roads fall within the excellent category.
Once these factors are considered, a pavement management software can generate a financially optimal pavement rehabilitation budget given the goals of the network and the ideal repairs based on need year.
Since every city is different, it is always a great idea to reach out to a pavement management consultant to best determine how these considerations should fit into your pavement plan.
Interested in setting up a pavement management program in your city? Check out "Pavement Management: A Professional's Guide" - An IMS Whitepaper
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.
Managing Pavement Equity
In a perfect world, a city would fix every defect in their entire pavement network. This is an unattainable goal, but it is important to understand the cost of achieving this goal in order to calculate the equity removal. This cost is known as a “Fix All Budget”. Using the Fix All budget, pavement management software is able to calculate the cost per PCI (Pavement Condition Index) point. Pavement managers use a PCI number system to rate the overall condition of a road.
When a pavement manager knows the cost per PCI point they can calculate an accurate estimate of how much value is lost or gained from the pavement network given a particular budget scenario. These budgets are then compared to something called the “Steady State PCI” budget. A Steady State PCI budget is the funding necessary to maintain the city’s current average PCI score.
The condition of a roadway network may be equated to equity in a depreciating asset. Regular payments to that asset must be made in order to maintain the equity at a constant level. Should those payments fall short, the equity must eventually be replaced through a large influx of capital in order to make the investment whole again. Roadway networks are no different. Long term underfunding of rehabilitation and maintenance is the direct equivalent of removing equity from an asset – eventually it must be repaid through total reconstruction.
The following table compares the real cost of the various budgets against the Do Nothing and Steady State options for an example municipality:
As you can see from the table, the Do Nothing budget after 5 years results in an additional $24 million need to recover the average PCI to the starting level of 63. Try telling a group of taxpayers that improper pavement maintenance and funding cost them $24 million in just 5 years. I’ll just watch from a safe distance…
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?
Right-of-Way Asset Database
In order to execute on their responsibility as a steward of a city’s assets, municipalities must determine where the assets are, and how many assets they maintain. The first step to organizing this information is performing a right-of-way asset survey. This can be done a variety of ways, but the end result is similar; an organized database of signs, signals, markings and more is compiled together. The assets should then be organized using GIS information and plotted to a map of the city.
With a GIS integrated asset database the city can track everything they are required to maintain, and properly document repairs as they are completed. When a call is received regarding a failing traffic light, or missing stop sign, the information can be entered into the records and proper measures can be taken to fix the issue before it results in an injury. Demonstrating the ability to track asset repairs may also be important for avoiding potential legal concerns associated with the upkeep of city owned assets.
The goal of maintaining a right-of-way asset database is threefold: Convenience, Accountability and Public Safety.
Convenience – The process of managing thousands of assets can be daunting, but organization is key. When a city has a properly organized asset database it becomes a trivial task to notate complaints and issue repairs in a timely manner. This simplifies the tasks of city employees that are responsible for this type of documentation, eliminating waste and errors associated with disorganization.
Accountability – Cities must remain accountable to their asset stewardship responsibilities. Whether the goal is avoiding a lawsuit, or satisfying the requests of city board members, a properly maintained asset database is a strong indicator of a responsibly run local public works administration.
Public Safety – This is arguably the most important responsibility of a local government. When a stop sign has been damaged or vandalized, it is only a matter of time before an accident ensues. Maintaining an organized database of this type of right-of-way asset allows an administration to act quickly when reports of damaged or missing assets come in. Timely repairs may save lives.
If you are part of a team tasked with managing thousands of right-of-way assets the value of an organized asset database is not lost on you. Take the leap towards improving public safety and accountability in your city by preparing a GIS integrated database of all right-of-way assets. Just as drivers look to the street signs, city managers can look to the asset database to ensure they are headed in the right direction.
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.
Surface Condition Survey
A pavement condition survey is a complete overview of your pavement network assets. This data is arranged into categories depending on a street segment’s rehabilitation needs. The information is not only required to hold up to accountability standards, such as GASB 34, but it is also important for allocating dollars for pavement rehabilitation treatments.
When a city understands the rehab needs of a road, they can apply the proper treatment to get optimal value per dollar from the investment. This is helpful for budgeting as proper pavement repairs will cost the city fewer dollars in the long term, and “more-than-needed” repairs will be less frequent. This enables pavement managers to redirect budgets to segments that are a wiser investment for the city and its citizens.
A surface condition survey covers the basics for a city looking to optimize its pavement management budget. For those that are really looking to save money, however, structural testing is an extremely valuable addition. Through the structural testing process, pavement managers can make much more accurate assessments to the need, cost, and remaining lifespan of street segments.
Structural testing immediately saves a municipality money in wasted repairs. If a structural analysis reveals that a road’s base is failing, the city can often defer surface maintenance until reconstruction dollars are secured. This prevents pavement managers from having to repeat work on failing streets.
Conversely, this more accurate testing may also allow pavement managers to save money by utilizing lighter surface repairs to roads that maintain a stronger base. This helps the city succeed with lighter and less expensive repairs on certain pavement segments where it is appropriate, without causing long-term harm to the overall value of the network.
The budget and rehabilitation projections following a pavement survey are of enormous value to a municipality concerned with optimizing its pavement budget. These projections take into account various annual budget levels, the condition analysis, and price of optimal rehabilitation efforts for segments in distinct condition ranges.
Using this type of analysis, a pavement manager can create an accurate model of the pavement rehabilitation plan over the next 5 to 10 years. This can be automatically adjusted using pavement management software to reflect changes or improvements made by the city.
It is a matter of neglect for a municipality to allocate taxpayer dollars towards pavement management without first seeking out the only reliable way to optimize those dollars. By conducting a properly objective pavement condition survey (with or without structural testing) a municipality gains the ability to utilize taxpayer funds in a data-driven, appropriate and equitable manner.
A variety of factors go into determining the deterioration rate of a street. When managing a network of roads, an important step is identifying which of these factors influence the deterioration rates on your roads.
The deterioration rate of a road is an average rate at which a pavement condition is projected to decay. This is instrumental to developing a pavement management plan that optimizes rehabilitation activities in conjunction with the network’s budget requirements. Among the factors that should be considered are impacts from surface distresses, drainage, ADT & ESAL (Average Daily Traffic and Equivalent Single Axis Load), and the conditions of the pavement base.
Let’s examine each of these factors individually:
The extent and severity of surface distresses along a pavement segment can reveal a lot about the future deterioration of the road. In some cases, a surface distress such as alligator cracking may even reveal failures in the pavement base. Certain pavement distresses may spread quickly if untreated, and some can appear as symptoms of other problems along the roadway (i.e. edge cracking spreads quickly as a result of poor drainage).
Tracking surface based distresses of a pavement network is vitally important for municipalities that seek to optimize their budget. This is because the distresses are often the most heavily-weighted component in determining the best rehabilitation strategy for a road. Experts recommend that pavement condition surveys are scheduled on a regular 1-3 year basis to track surface distresses and ensure that public works departments get the most out of their pavement budget.
Another important factor to consider when assessing the deterioration rate of a pavement surface is the condition of the drainage systems along the roadway. The drainage along the side of a roadway significantly impacts the deterioration of the base, as well as the surface conditions. When a roadway has inadequate drainage, water may tend to pool along the edge or in the cracks of pavement. This is particularly worrisome in colder climates where the freeze/thaw cycle of water can accelerate the rate of surface and base deterioration.
On a roadway with poor drainage, pavement distresses such as edge cracking tend to spread much more quickly. More severe distresses, like alligator cracks, may fill with water and quickly end up becoming potholes. These failures accelerate the deterioration rate of a roadway segment, but are usually easily addressed through the addition of drainage ditches and proper curb sides.
ADT/ESAL and Traffic Loads
If you have experience in pavement management than you will certainly be familiar with these two terms. Average Daily Traffic, or ADT, is an obvious general indicator of the lifespan of a road. In most cases, however, Equivalent Single Axle Load, or ESAL, is a much more reliable indicator. The reason mostly boils down to the impact of heavy vehicles on the pavement surface.
If you are examining a quickly deteriorating pavement segment with a low overall ADT, it may be practical to take a look at the ESAL. Heavy truck traffic by garbage, recycling, and semi-trucks have approximately 1000x the impact on a pavement surface than their smaller, lighter counterparts – personal vehicles.
“The ESAL statistic represents a mix of different axle loads and axle configurations predicted over the design or analysis period and then converted into an equivalent number of 18,000-lb. single axle loads summed over that period.” (Texas DOT)
Since the measurement references 18,000-lb increments, heavier traffic contributes much more significantly into the final results. This is not calculated in the standard ADT figures and means that ESAL is a much more reliable measurement for the rate of deterioration on a road.
The final, and most telling, component that forecasts the deterioration rate of a pavement segment is the condition of the pavement base. Though surface based distresses can often provide fair insight into the base conditions, it is often best practice to perform a deflection test on roads from which the base condition is an important consideration.
Structural testing is performed using a device such as a Dynaflect or Falling Weight Deflectometer. The purpose of the structural testing is to identify the relationships and interactions between pavement quality, life expectancy and rehabilitation planning. The structural analysis facilitates a much more in-depth understanding of the City’s transportation corridors. Structural analysis also assist in rehabilitation selection by constraining inadequate pavement sections from receiving too light of a rehabilitation and conversely, identifying segments suitable for lighter weight treatment.
The overall deterioration rate of a roadway segment considers a variety of factors. ADT/ESAL, Base Conditions, Drainage, and Surface Distresses all play a valuable role to pavement managers that are peering into the tea leaves to determine the deterioration rate of their roads. Luckily all of these factors are measurable through a pavement condition survey and deflection test. Forward thinking public works departments should consider the benefits of conducting a survey in their home town. It could save the city millions.
Looking to learn more about pavement management? Check out "A Guide to Key Indicators of a Failing Pavement" - An IMS Whitepaper
You may not realize it if you have not been involved in public works for very long, but the pavement network that runs throughout your city is the most valuable visible asset that your city owns and maintains. Because the utility of this asset is so great and it is constantly deteriorating from use, it is very important to understand proper pavement management processes.
The pavement assets managed by your city require constant upkeep. In order to assess the need in your network, a dedicated pavement management process is necessary. This requires pavement management software, GIS integration, high tech survey equipment, and dedicated personnel. Most municipalities will hire a pavement management consultant with expertise unique to the city’s needs.
Here are some of the most common mistakes cities and counties make that end up misusing millions in tax payer dollars:
In pavement management the term backlog refers to streets that cannot be rehabilitated without partial or complete reconstruction. Because reconstructing a street is much more expensive than placing a seal or an overlay on the surface, pavement segments that fall into the backlog category are often deferred until the funds are available to dedicate towards such projects. The constant deferral of these projects can lead to a build-up of a network’s backlog streets until it reaches an unmanageable state. The figure below illustrates how a proper pavement life cycle should look.
A network is treading into precarious territory when the backlog exceeds 15% of the total pavement network. Once a network's backlog exceeds 15%, the cost of reconstruction projects begins to eat up large portions of the budget that would otherwise be used for preventative care. This spirals into a situation where pavement segments fall into the reconstruction category faster than the city can repair them. This situation can be devastating to a city’s budget and can ultimately bankrupt a public works department.
Many public works departments that have little experience in pavement management will make the mistake of always scheduling rehabs through a worst-first methodology. Municipalities that have a “worst-first” pavement management philosophy often spend far too much of their limited budget on reconstructing segments of roadway. This is where the pavement management lifecycle curves seen below is important to understand.
The figure below illustrates how pavement that has degraded to “poor and very poor” categories is much more expensive to rehabilitate than the preventative maintenance on streets in the “good and very good” category.
Municipalities should focus the majority of their budget on less expensive preventative maintenance. This will prolong the lifespan of these roads and prevent them from falling into the more expensive rehabilitation categories. Notice the quick decay in pavement quality when preventative maintenance methods are not followed.
This is similar to the notion of applying oil to a vehicle, rather than waiting until the engine needs to be replaced. The oil need is more frequent, but the cost savings over an engine rebuild is dramatic.
Need Year Rehabs:
The need-year is a segment’s last possible year that it can benefit from a particular type of rehabilitation. Understanding the concept of need-year is very important for optimizing your pavement management budget. This process is almost impossible to track without dedicated pavement management software that can select the ideal year for a rehab to take place. The rationale of embracing the need-year concept is that a municipality can know when deferring a rehabilitation project is appropriate and will not result in a dramatic increase in cost.
The ideal is to defer rehabilitation on a street as long as possible without increasing the cost of the maintenance on that segment. This allows the municipality to focus repairs on streets that will become more expensive to rehabilitate if put off for any longer, thereby optimizing limited annual funds.
Ignoring Signs of Pavement Base Failure:
Often times, streets that require more expensive rehabilitation efforts are in areas where a portion of the road’s base is failing. When the base of a street begins to fail there are often some clear signs that come in the form of load associated distresses. A load associated distress is a type of crack or other pavement distress that reflects on the overall structural integrity of a pavement segment. Read more about Load Associated Distresses HERE.
The most reliable way to measure the structural strength of a pavements base is to do what is known as a deflection test. A deflection test is done with specialized equipment that applies moderate weighted stress to a pavement section and measures the amount of feedback. This can be used to calculate a structural integrity score for a road and determine the type of rehabilitation technique needed to return it to complete service. Pavement engineers can also use this type of data to make more accurate predictions about the future quality of a street.
It is important and extremely cost effective for municipalities to routinely conduct structural testing on their high-traffic roads to avoid the exaggerated cost associated with a sub-optimal rehabilitation plan.
Misjudging Rehab selection (over/under-repair):
A street that is paved over without regard to the strength of its base is likely to receive a sub-optimal treatment that does not utilize a city’s limited budget in the most efficient way. Even worse, a street that receives too light of a rehabilitation may see a rapid decline in pavement quality leading to greater rehabilitation needs in the near future. Such is the importance of a pavement management system that identifies the proper rehabilitation techniques using the most accurate possible data.
The only way to get that data is through a laser road survey and a proper pavement management system. The collection and organization of this data is the primary reason why municipalities hire pavement management companies like IMS.
(Bonus) Under Budgeting:
Under budgeting pavement infrastructure is a nearly ubiquitous problem for municipalities throughout the country. From public works departments that continually kick the can down the road, to politicians that divert pavement management funds for other purposes; chronic pavement infrastructure under-funding has led many municipalities down a tragic path of financial destitution.
Our paved road systems are the one of the most utilized and valuable components of our nation’s infrastructure. If we cannot recognize the need to invest in such assets, perhaps it is time again to invest in the rearing of horses for our future transportation needs.
Interested in setting up a pavement management program in your city? Check out "Pavement Management: A Professional's Guide" -An IMS Whitepaper