J.9_Pavement_Remaining_Service_Interval.pdf

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Pavement Remaining Service Interval (RSI)

Implementation Guidelines PUBLICATION NO. FHWA-RD- May 2012

U.S. Department of Transportation Federal Highway Administration

Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296

DRAFT

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FOREWORD

The FHWA Office of Infrastructure R&D conducts and oversees research and development programs and projects that address critical highway infrastructure needs and priorities of national importance. Studies focus on the design, materials, construction, operation, and preservation of highway pavements, bridges, culverts, tunnels, and other structures. In addition, the Office of Infrastructure R&D provides expert technical assistance to other FHWA offices, other Federal agencies, State and local transportation organizations, industry and academia.

This study addresses the challenging issue of standardizing nomenclature used by highway agencies related to pavement remaining service or structural life.

This document provides guidelines for implementation of the Remaining Service Interval (RSI) concept as a replacement to the current remaining life terminology for pavements. Many issues exist with the current remaining service life terminology and resulting numeric’s which confuse, confound, and complicate proper interpretation, interagency data exchange, and use.

Implementation of the RSI concept is broken down into a series of steps which follow a logical progression. Examples of the concept are presented using pavement engineering methodologies in current use. Suggestions are also provided on communication of the results of the RSI process.

Jorge Pagán-Ortiz

Director, Office of Infrastructure Research and Development

Notice

This document is distributed under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers’ names appear in this report only because they are considered essential to the object of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of the information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvements.

1. Report No.

FHWA-

2. Government Accession No.

3. Recipient’s Catalog No.

4. Title and Subtitle Pavement Remaining Service Interval (RSI) Implementation Guidelines

5. Report Date May 1, 2012

6. Performing Organization Code

7. Author(s) Gary E. Elkins, Gonzalo R. Rada, Jonathan L. Groeger, Beth Visintine

8. Performing Organization Report No.

9. Performing Organization Name and Address AMEC Environment and Infrastructure, Inc.

12000 Indian Creek Court, Suite F Beltsville, MD 20705-1242

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-08-C-00033

12. Sponsoring Agency Name and Address Office of Infrastructure Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, VA 22101-2296

13. Type of Report and Period Covered Implementation Guidelines October 2009 – May 2012

14. Sponsoring Agency Code

15. Supplementary Notes Contracting Officer’s Representative (COR): Nadarajah Sivaneswaran, HRDI-20

16. Abstract The process of providing and managing a pavement network requires a plethora of decisions to be made.

At the heart of those decisions is the prediction of future construction events. However, many issues exist with the current remaining service life (RSL) terminology and resulting numeric’s which confuse, confound, and complicate proper interpretation, interagency data exchange, and use. The major source of uncertainty in the current RSL definitions is the use of the term “life” to represent different points in the construction time-line. In reality, there could be up to four different types of future construction events on which a RSL definition could be based, depending on the condition of the pavement. It is impossible for a single number called RSL to properly describe all of these future construction events.

The recommended path to consistency involves adopting terminology of time remaining until a defined construction treatment is required– RSL is replaced by "Remaining Service Interval" or “RSI.” This terminology has the ability to unify the outcome of different approaches for determining needs by focusing on when and what treatments are needed, and the service interruption created. This document provides step-by-step guidelines for implementation of the RSI terminology. A companion report presents the framework for replacing the current RSL terminology with one based upon more exact construction event terms.

17. Key Words Pavement remaining service life, pavement remaining life, pavement remaining service interval, pavement construction events, pavement construction triggers, pavement threshold limits, pavement performance expectancy curves, pavement data collection, pavement strategy selection, repairable system.

18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized iv

SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km

AREA

in2 square inches 645.2 square millimeters mm2 ft2 square feet 0.093 square meters m2 yd2 square yard 0.836 square meters m2 ac acres 0.405 hectares ha mi2 square miles 2.59 square kilometers km2

VOLUME

fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft3 cubic feet 0.028 cubic meters m3 yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS

oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")

TEMPERATURE (exact degrees) oF Fahrenheit 5 (F-32)/9 Celsius oC or (F-32)/1.8

ILLUMINATION

fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi

AREA

mm2 square millimeters 0.0016 square inches in2 m2 square meters 10.764 square feet ft2 m2 square meters 1.195 square yards yd2 ha hectares 2.47 acres ac km2 square kilometers 0.386 square miles mi2

VOLUME

mL milliliters 0.034 fluid ounces fl oz L liters 0.264 gallons gal m3 cubic meters 35.314 cubic feet ft3 m3 cubic meters 1.307 cubic yards yd3

MASS

g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T

TEMPERATURE (exact degrees) oC Celsius 1.8C+32 Fahrenheit oF

ILLUMINATION

lx lux 0.0929 foot-candles fc cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for th International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. e (Revised March 2003) v

TABLE OF CONTENTS

EXECUTIVE SUMMARY

CHAPTER 1. INTRODUCTION

BACKGROUND

REFORMULATING RSL TERMINOLOGY

ORGANIZATION OF GUIDELINES

CHAPTER 2. RSI CONCEPT OVERVIEW

CONSTRUCTION NEEDS PROCESS

CONSTRUCTION EVENT TERMINOLOGY

RSI IMPLEMENTATION FRAMEWORK

CHAPTER 3. IMPLEMENTING RSI CONCEPT

STEP 1: SETTING CONSTRUCTION TRIGGERS

STEP 2: SETTING THRESHOLD LIMITS

STEP 3: SELECTING OR DEVELOPING EXPECTANCY PERFORMANCE CURVES 18

STEP 4: IDENTIFYING COLLECTION OF INPUTS

STEP 5: ESTABLISHING STRATEGY SELECTION PROCESS

Network Analysis Project Analysis

STEP 6: PERFORMING PERIODIC ASSESSMENTS AND UPDATES

CHAPTER 4. RSI IMPLEMENTATION EXAMPLES

EXAMPLE 1: HIGHWAY AGENCY USING FHWA’S PHT ANALYSIS TOOL

Background RSI Implementation

EXAMPLE 2: HIGHWAY AGENCY USING 1972 AASHTO DESIGN PROCEDURE .. 33

Background RSI Implementation

EXAMPLE 3: HIGHWAY AGENCY USING MULTIPLE PERFORMANCE

INDICATORS

Background RSI Implementation

LCC CONSIDERATIONS

CHAPTER 5. COMMUNICATING RSI FRAMEWORK RESULTS

APPENDICES

APPENDIX A. GENERIC AGENCY ISSUES

APPENDIX B. BIBLIOGRAPHY

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LIST OF FIGURES

Figure 1. Illustration. Future pavement construction needs process Figure 2. Illustration. Agency RSI implementation flowchart Figure 3. Graph. Conceptual relationship between present worth agency repair costs as a function of pavement condition Figure 4. Graph. General concept of application of corrective pavement treatments as a function of pavement condition Figure 5. Graph. Illustrated service histories of several trial pavement designs incorporating future overlays from the 1986 AASHTO pavement design guide Figure 6. Graph. Hypothetical distress based pavement design approach consisting of pavement roughness and two distress types Figure 7. Photo. Fleet of inertial road profilers used to measure IRI and ride number (RN) and other roughness indices Figure 8. Photo. Falling Weight Deflectometer (FWD) used for structural evaluation Figure 9. Photo. Traffic Speed Deflectometer (TSD) used for structural evaluation Figure 10. Photo. TSD internal pavement response measurement instrumentation Figure 11. Photo. Weigh-In-Motion (WIM) sensor used to record truck axle and gross vehicle weights Figure 12. Photo. Mini site-specific SMP weather station used to record climatic data for pavement research Figure 13. Equation. Reflection cracking model Figure 14. Equation. IRI prediction model Figure 15. Equation. 1972 AASHTO Guide flexible pavement design equation Figure 16. Equation. Structural number equation Figure 17. Illustration. Partial set of construction event combinations and schedule of activities for example 1

LIST OF TABLES

Table 1. Reflection cracking or IRI construction triggers-threshold limits Table 2. Reflective cracking model parameter “d” Table 3. Network level construction triggers-threshold limits Table 4. Project level construction triggers-threshold limits Table 5. RSI based on PSR values and construction treatment Table 6. Construction triggers-threshold limits matrix Table 7. RSI based on construction treatments vii

LIST OF ACRONYMS

Acronym Definition

AASHO – American Association of State Highway Officials AASHTO – American Association of State Highway and Transportation Officials AC – Asphalt Concrete AWS – Automated Weather Station CPR – Concrete pavement restoration CRCP – Continuously Reinforced Concrete Pavement FN – Friction number FWD – Falling Weight Deflectometer GPR – Ground Penetration Radar HERS – Highway Economic Requirements System HMA – Hot-mix asphalt HPMS – Highway Performance Monitoring System HRI – Half-car Roughness Index IRI – International Roughness Index JPCP – Jointed Plain Concrete Pavements LCC – Life cycle costs LTPP – Long Term Pavement Performance MEPDG – Mechanistic-Empirical Pavement Design Guide NAPCOM – National Pavement Cost Model NCHRP – National Cooperative Highway Research Program NCDC – National Climate Data Center PCC – Portland Cement Concrete PCI – Pavement Condition Index PHT – Pavement Health Track PMS – Pavement Management System PSR – Pavement Serviceability Rating RSI – Remaining Service Interval RSL – Remaining Service Life RI – Roughness Index RN – Ride Number RQI – Ride Quality Index RWD – Rolling Wheel Deflectometer SMP – Seasonal Monitoring Program SN – Structural number TSD – Traffic Speed Deflectometer WIM – Weigh-in-motion X-DOT – State X, Department of Transportation Y-SHA – State Y, State Highway Agency

EXECUTIVE SUMMARY

The “remaining service life” (RSL) concept has been around for decades and is well entrenched in the pavement community. It is used at all levels of the pavement management decision process to plan for future field construction events. However, there is no single, clear and widely accepted definition of RSL. Moreover, there is a great deal of uncertainty associated with the definition, especially with the use of the term “life” to represent different points in a pavement’s construction history. In addition, when communicated, the meaning of “life” is lost and it is interpreted differently by stakeholders.

To overcome the RSL shortcomings, these guidelines introduce terminology that removes the word "life" from the lexicon since it is the basis for confusion. Instead of “life,” the new terminology introduces the concept of time remaining until a defined construction event is required. Pavements are comprised of interrelated structural parts which can be maintained, preserved, restored, rehabilitated, or reconstructed to serve the intended transportation need.

The Remaining Service Interval (RSI) concept does not provide an alternative to assessing the health of the network or making decisions about where to spend the available funds. It simply provides a clear terminology and a logical process that will move us away from erroneous statements such as "this pavement has only 5 remaining years of life” and moves us toward a consistent construction event-based terminology and understanding -- types of construction events and the timing of those events within the concept of Life Cycle Cost (LCC), risk analyses, and other prioritization approaches based on streams of future construction events and benefits to facility users.

CHAPTER 1. INTRODUCTION

BACKGROUND

The process of providing and managing a pavement network requires a plethora of decisions to be made. At the heart of those decisions is the prediction of future construction events, which is the fundamental basis of engineering design and management of pavement structures. Those future construction events include the do nothing alternative, applications of routine reactive maintenance, application of preventive maintenance and preservation activities, application of alternative rehabilitation treatments, and reconstruction.

A goal of pavement management is to optimize agency resources while providing a maximum level of service to the users. Accomplishing this requires monitoring the condition of the pavement network and forecasting future pavement performance in order to effectively plan future pavement construction events. Clearly, predicting the RSL of the segment units that make-up the pavement network is of paramount importance to pavement management planning.

Knowing or estimating the future condition of pavements sections is the rational basis of informed pavement infrastructure planning decision.

The term remaining service is typically defined as the period over which a pavement section adequately performs its desired function or performs to a desired level of service, and RSL is simply the time from the present to when a pavement reaches an unacceptable condition requiring construction intervention. The central role of RSL in pavement management business decisions is predicting the change in pavement condition as a function of time, traffic loading, and environment. The basic difference in the RSL models used at the project, network and contract administration levels are data requirements related to level of technical detail, extent, quality, precision and accuracy of the model inputs.

While the prediction of time until a construction treatment should be applied is a critical component at all levels of pavement management decisions, many issues exist in the current RSL terminology and resulting numeric’s, which confuse, confound, and complicate proper interpretation, interagency data exchange, and use.

One common RSL definition is the time until the next rehabilitation or reconstruction event, but these are two different events in terms of the condition of the pavement at the time of construction as well as the associated construction costs. Rehabilitation treatments are typically applied before a pavement has suffered extensive structural damage, while reconstruction treatments are generally warranted after a pavement has reached an advanced degree of deterioration. Attempting to interpret combined RSL estimates from mixed rehabilitation and reconstruction "units" provides little information to decision makers. Also, the timing of the next

The central role of RSL in business decisions is to predict the change in pavement condition as a function of time, traffic loads, and environment.

Multiple meanings of the single term RSL confuse, confound, and complicate proper interpretation, interagency data exchange, and use.

rehabilitation or reconstruction will depend on what future lower-level treatments than rehabilitation or reconstructions are applied.

Another common RSL definition is the time until a condition index threshold limit is reached.

This approach shares the same issues as rehabilitation and reconstruction RSL units, but also introduces other service and safety condition indices, which further complicate the meaning of RSL. Setting threshold limits for pavement conditions which are not based on human subjective ratings, such as cracking, can be complicated to justify. Moreover, interpretation of a single RSL number gets even more complicated when it is based upon multiple condition states. For example, if the RSL for roughness is 2 years, RSL for cracking is 5 years, RSL for friction is 7 years, and the RSL for rutting is 20 years, saying the current pavement RSL equals two years can lead to faulty construction decisions since the construction treatment to correct roughness may ignore the more serious cracking issue expected to occur soon after the roughness threshold is reached. Since there are many construction treatments that can be used to correct excessive pavement roughness that can be classified as pavement preservation, this approach adds maintenance type activities to RSL units.

Another intriguing aspect of RSL based upon threshold limits is negative RSL. When a pavement condition index limit is reached, from a numerical standpoint, the years it remains in service after this time could be considered a negative service life - which is counterintuitive. One approach is to set negative values to zero; thus, not allowing a negative RSL value to be provided by the process. Another approach is to consider negative RSL as overdue needs, in which case the number of years overdue can be considered as information content to decision makers, if they know the basis of the condition in need of attention.

Yet another approach to RSL is based upon agency management rules on the time between applications of corrective pavement construction treatments. For example, a state agency might establish a policy that every eight years a resurfacing, rehabilitation, or reconstruction treatment is applied to each construction segment unit on their system. Some agencies consider this a proactive approach to keeping their highest level functional class pavements in the best condition. The RSL becomes the difference in time between the policy construction frequency and how long it has been since the last treatment was applied. While this approach can work for agencies with sufficient budget to satisfy all pavement repair needs within its system, it typically does not provide for optimal distribution under a limited funds constraint scenario of budget planning.

Moreover, an unintentional consequence of using current RSL terminology is that it tends to promote "worst-first" approaches to correcting pavement deficiencies. By expressing pavement condition in terms of RSL, laymen and politicians expect that pavements in the worst condition get treated first. Construction treatments on pavements in the worst condition tend to cost the most. Applying a "life" extending corrective rehabilitation treatment before the pavement condition gets too bad, tends to cost less than reconstruction treatments. Optimum allocation of annual pavement resurfacing, rehabilitation and reconstruction budgets will be a mixture of pavements with differing remaining lives and not based solely on a worst first approach.

REFORMULATING RSL TERMINOLOGY

The objective of these guidelines is to provide a definition of and process for determining pavement remaining service life that will promote consistency in the use of the terminology. As noted earlier, a great variety of RSL definitions are currently used to describe different events in the construction history of a pavement. Construction related history best describes the use of RSL models at all levels of the pavement management decision process because the primary purpose for predicting remaining pavement service life, or “life” within the context of pavement management, is to plan for future field construction event(s), whether it be the application of maintenance, preservation, rehabilitation, reconstruction, or other treatments to correct some attribute of the pavement structure. Regardless of name given to different treatments, these are all field construction events that cost the highway agency to provide and impact facility users.

Ideally, the definition of RSL should be independent of business decisions.

The major source of uncertainty in the current definitions is the use of the term “life” to represent different points in the construction history. When communicated, the meaning of “life” is also lost and it is interpreted differently by different stakeholders. In the pavement design context, "life" is used to represent the time until the “as-designed” pavement structure reaches an unacceptable condition, since the pavement designer must make assumptions on pavement properties. In the pavement management context, after construction of the pavement structure, the "as-constructed" properties become more important in pavement life expectations than the assumed inputs into the original design process. A pavement structure can be thought of as a system whose components include subgrade treatments, subsurface drainage features, base layers, shoulders, bound structural load bearing layers, and surface layers. As a “repairable system”, the life of the system is not defined by correctable component failures.

The proposed solution to the problem is to remove the word "life" from the lexicon since it is the basis for confusion. Instead of using remaining service life, the recommended path to consistency involves adopting terminology of time remaining until a defined construction treatment is required to replace the generic ill-defined RSL term. This terminology has the ability to unify the outcome of different approaches to determining needs by focusing on when and what treatments are needed, and the service interruption created – "Remaining Service Life" is replaced by "Remaining Service Interval" or “RSI.”

Moreover, adoption of a definition related to construction treatments opens up the vocabulary to treatments related to other factors besides pavement condition. For example, if a construction cycle is defined in terms of time until the next construction event requiring lane closures, then capacity improvements, shoulder widening, utility construction, and realignment construction activities can be included in the construction event. In turn, this provides for broadening the application of the definition in the future. In some situations, for example, capacity issues can

Pavements are repairable systems;

correctable component failures do not define system life.

The path to consistency is adopting terminology of time remaining until a defined construction treatment is required – RSL is replaced by Remaining Service Interval or RSI.

have more of an effect on the service provided by a pavement structure than condition of the pavement surface. Or the pavement has reached a level that the next utility cuts and resulting repairs can be performed within a defined time window. This shifts the emphasis on the life remaining in a pavement structure to the time remaining until the next planned construction lane closure is required or future type of defined construction treatment is needed.

ORGANIZATION OF GUIDELINES

The guidelines presented in this document are intended to provide a common definition and process that may be referred to by anyone attempting to evaluate the remaining service interval -or RSI - of a pavement segment or network. More specifically, a more refined construction activity needs analysis terminology and approach is provided in these guidelines to reduce potential confusion over the use of the remaining service life nomenclature. To accomplish this, the guidelines have been organized into the following five chapters:

1. Introduction – provides background information on the RSL concept and establishes the need to reformulate this concept.

2. RSI Concept Overview – discusses the basic process for determining future pavement construction needs, introduces construction event terminology, covers the framework associated with the RSI concept, and introduces the RSI implementation steps.

3. Implementing RSI Concept – provides a step-by-step description of the process required to establish the RSI concept by highway agencies, including construction triggers, threshold limits, expectancy curves, collection of inputs, strategy selection, and assessments and updates.

4. RSI Implementation Examples – presents hypothetical examples to illustrate the RSI implementation process described in the previous chapter.

5. Communicating RSI Framework Results – discusses key issues surrounding the communication of results generated within the context of the RSI framework.

Appendix A addresses generic issues associated with the implementation of the RSI concept within an agency; these issues are not part of the actual RSI implementation process, but they are critical to the success of an agency’s migration to the RSI concept. Appendix B contains the bibliography of RSL references used in the development of the RSI concept, which could be of benefit to potential users of the guidelines.

These guidelines have been developed based on the results of the effort carried out under FHWA Contract No. DTFH61-08-C-00033 titled “Definition and Determination of Remaining Service and Structural Life.” These results have been documented in FHWA Report No. XXXXX titled “Reformulated Pavement Remaining Service Life (RSL) Framework,” dated April 2012. Users of these guidelines are encouraged to read this document prior to implementation of the RSI concept, as it provides the foundations for the concept along with other valuable information such as basic pavement design and management concepts, RSL models and the results of the literature review performed as part of the project.

CHAPTER 2. RSI CONCEPT OVERVIEW

CONSTRUCTION NEEDS PROCESS

The basic process to determine future pavement construction needs is illustrated in figure 1.

Most pavement construction activity planning is based on an annual fiscal time cycle used by the agency. The steps in this figure are cyclical and depend on the time cycle appropriate to the type of pavement asset. In this figure, the process starts with input data. Input data are fed into the expectancy models which produce prediction of future change in the construction trigger models.

The outputs from the predictions are used to select the most appropriate construction strategy, which is used to develop construction plans and specifications. The feedback cycle starts with documentation of the actual condition observed over time as well as the actual construction activities performed. Monitoring measurements are performed to provide updated inputs for the next planning cycle and also to refine expectancy models.

Figure 1. Illustration. Future pavement construction needs process.

Within the context of the process illustrated in figure 1, the fundamental elements required to replace the existing RSL terminology with the new RSI terminology include:

1. A "controlled" vocabulary to define pavement construction events.

2. A common basis for "when" the future construction event is needed.

3. "How" future needs are determined (differentiation between different levels of business decisions).

4. "Where" defines the location and extent of the needed treatment.

The logic of this structure is based upon separating the definitions of what future construction event is needed from how the need is determined.

CONSTRUCTION EVENT TERMINOLOGY

The objective of the construction event terminology or vocabulary is to uniquely define the "what" in the type of predicted future construction event need. This vocabulary is needed to describe the construction treatments in order to promote database integration and increasing level of aggregation at local, district, state, and national levels. Moreover, the terminology in question requires identification of three attributes – time when a treatment is needed, type of construction treatment, and reason for the construction treatment.

Time is being specified since this is the basis of budgeting decision making. This is meant to replace prediction models based upon traffic applications. Traffic application rates used in the modeling process need to be converted to a time basis. Conversion of traffic application rates to a time basis is a complex process based upon consideration of the “design lane” which receives the most truck loadings, on multilane facilities, “damaged lane” which is the lane in worst condition since it is not always the design lane, and other local factors which influence pavement damage from vehicle and environmental effects.

The following are example definitions of construction events based on the expanded paradigm of common pavement improvements included in many pavement management systems:

• Crack sealing – application of sealants in surface cracks.

• Joint sealing – application of sealants in preformed joints.

• Surface treatment – application of a layer of material of intended uniform thickness less than 12 mm (0.5 in.) thick.

• Thin overlays – application of a layer of material layer of intended uniform thickness greater than 12 mm (0.5 in.) and less than 50 mm (2 in.) in thickness or which does not increase the thickness of the bound material layers by more than 25 percent.

• Thick overlays – application of a material layer of intended uniform thickness greater than 50 mm (2 in.) in thickness and increases thickness of bound pavement layers by more than 25 percent.

• Concrete pavement restoration – application of full or partial depth joint repairs, slab replacement, dowel bar retrofit, or other restoration treatment not covered in another definition.

• Grinding – removal of portions of the surface layer of a pavement without placement of a new material layer.

• Grooving – cutting of grooves in the surface of a pavement without application of a new material layer.

• Milling – removal of bound portions of a pavement that is associated with placement of a new material surface layer.

• Undersealing – injection of cementitious material underneath bound pavement layers.

• Reconstruction - removal and replacement of all bound layers of an existing pavement.

• Addition of lanes – construction of additional lanes to the facility designed to permit greater traffic capacity.

• Addition of tied shoulders – removal and construction of PCC shoulders tied to adjacent PCC pavement structures.

• Shoulder widening – extending the width of the existing shoulder with use of similar materials.

The above definitions only describe what type of construction treatment is being applied to the pavement. An indication of the reason(s) why a future construction event is predicted is also needed to complete the definition since pavement improvements are based on different needs.

The following are examples of controlled vocabulary that can be used to explain the basis of predicted time to a threshold event:

• Roughness exceeds y. The y value is the generally accepted limiting value for pavement roughness in terms of International Roughness Index (IRI).

• Cracking exceeds limit requiring major rehabilitation.

• Cracking exceeds limit requiring reconstruction.

• Rut depth correction requires major rehabilitation.

• Rut depth correction requires reconstruction.

• Skid resistance reaches safety limit.

• Pavement Condition Index reaches threshold x. For systems based on a PCI based index, x represents the various thresholds between rehabilitation and reconstruction.

• Pavement Serviceability Rating reaches x. For systems still using the PSR/PSI concept, x is the terminal serviceability value considered by the agency appropriate for the route.

Typically, an agency will develop a decision matrix to use as part of their pavement management. This matrix will relate reason(s) for construction with types of construction events. For example, if the roughness exceeds the IRI threshold, then one typical approach would be placement of an overlay to correct the roughness.

RSI IMPLEMENTATION FRAMEWORK

The framework for implementing the new RSI terminology is illustrated in figure 2. As shown in the flowchart, the key components of the framework that must be addressed by highway agencies to develop, implement, maintain, and update a construction needs analysis methodology include generic agency and RSI implementation issues.

These components should be tailored to the individual agency requirements related to budgeting process, types of pavements in use, common types of pavement deficiencies requiring correction, construction contract instruments, and other considerations.

The generic agency issues address the establishment of the agency’s RSI protocol, the identification of a RSI coordinator and the dissemination of the RSI concept within the agency.

These issues only need to be addressed once, with periodic monitoring and revision to ensure they are still appropriate; however, they are vital to the success of an agency’s RSI program.

These generic-agency issues are discussed in more detailed in appendix A.

Figure 2. Illustration. Agency RSI implementation flowchart.

The RSI implementation issues, on the other hand, focus on the step-by-step approach necessary for successfully establishing the RSI concept within the agency. They include:

1. Setting construction triggers.

2. Setting threshold limits.

3. Selecting or developing expectancy performance curves.

4. Identifying collection of inputs.

5. Establishing strategy selection process.

6. Performing periodic assessments and updates.

These RSI implementation steps are discussed and illustrated in the ensuing two chapters of the guidelines, respectively.

1. Construction triggers,

2. Threshold limits,

3. Expectancy curves,

4. Collection of inputs,

5. Strategy selection, and

6. Assessments and updates

1. RSI Protocol

2. RSI Coordinator

3. RSI Dissemination

Generic Agency Issues

RSI Implementation

CHAPTER 3. IMPLEMENTING RSI CONCEPT

The first step in implementing the RSI concept is the decision that a change is needed in how an agency presents pavement construction needs to different departments within the agency, to decision makers, and an appreciation of the benefits that can accrue from interagency information exchange. The RSI concept is based upon the technical aspects of when, what and why the next and future construction treatments will be required, whereas the RSL concept pretends to be an overall measure of the system life status based on hidden factors not properly expressed in a single number called life. The RSI concept creates the rational basis for application of modern risk based models, which address the variability inherent in current condition measurements, future condition predictions, and resulting economic impacts of pavement management decisions. This allows creation of multi-faceted pavement performance measurements tools which are based on more than simple pavement condition indices.

It is recommended that highway agency personnel responsible for the implementation of the RSI concept undertake the following prior to the actual start of the implementation activities:

• Review FHWA Report No. XXXXX “Reformulated Pavement Remaining Service Life (RSL) Framework,”

• Review the guidelines contained in this document, and

• Hold a brainstorming meeting to discuss the various RSI elements, issues and implementation steps.

Once done with the above, and with an overall defined purpose, highway agency personnel should be able to proceed with the six implementation steps in a more clear and efficient manner.

This chapter addresses the six steps to the successful implementation of the RSI concept by a highway agency, including alternative options within each step where applicable. The steps are presented in a logical sequence, but this does not imply that they are independent of each other.

Setting construction triggers in step 1 or setting threshold limits in step 2, for example, cannot be done independently from selecting the expectancy performance curves in step 3.

RSI implementation steps:

1. Setting construction triggers

2. Setting threshold limits

3. Selecting or developing expectancy performance curves

4. Identifying collection of inputs

5. Establishing strategy selection process

6. Performing periodic assessments and updates

STEP 1: SETTING CONSTRUCTION TRIGGERS

Construction triggers are measureable aspects or other aspects of a pavement’s condition that can be used to indicate the need for application of a corrective treatment. The selection of construction triggers is the basis for development of field data collection programs to measure the condition state of each pavement segment. Some of the considerations in the selection of construction triggers include:

• Historical practice.

• Related agency practice.

• Extent of the pavement network being managed.

• Data collection budget.

• Types of pavements, or family of pavements managed by the agency.

• Required measurement accuracy, precision, and detail.

• Functional class of pavements in the network.

• Common distress manifestations.

• FHWA Highway Performance Monitoring System (HPMS) reporting requirements.

Construction triggers that may be considered by an individual highway agency based on their current or planned pavement practices include the following:

• Level of service – these triggers are primarily based upon human factor ratings of the pavement serviceability and measurement of pavement roughness. The use of pavement roughness as a primary indicator of level of service is originally based on the AASHO Road Test conducted in the late 1950s, but the pavement industry has evolved to where pavement roughness, expressed in terms of the IRI is the most common measure of pavement level of service.

• Pavement surface distress – while national standards exist for more than 15 possible types of pavement distress attributes for each type of pavement, they are not all typically required for pavement construction decisions. Reducing the number of distresses to a small number of core distresses can reduce field data collection costs.

Methods that can be used to create construction triggers based on pavement distress measurements include:

+ Survey of the predominant types of distresses common to an area or region which deteriorate the quickest requiring construction intervention to correct.

+ Use of the predicted distress types from the pavement design method.

+ Creation or use of existing numerical index based on assigned deduct values for the type, extent and severity of a selected range of distresses.

Options:

• Level of service

• Pavement surface distress

• Structural considerations

• Safety aspects

• Agency time based rules

• Traffic capacity

+ Development of a correlation between distresses and level of service indicators.

+ Association of distress types with corrective treatments; e.g., potholes can be corrected with patches and severe fatigue cracking usually requires pavement reconstruction.

• Structural considerations – these considerations are typically based upon certain types of distress and non-destructive pavement deflection testing. Common distresses associated with pavement structural integrity include cracking in the wheel path (fatigue cracking), corner cracks on jointed PCC pavements, faulting on jointed PCC pavements, punch outs on CRCP, and rutting associated with subgrade and base instability. On the other hand, deflection measurements can be used as a diagnostic tool to look below the pavement surface to get an indication of subsurface damage. Pavement structural information from deflection measurements include:

+ Modulus (stiffness) of the pavement foundation layer (subgrade).

+ Indicators of the relative stiffness of the surface and base layers.

+ Load transfer across joints and transverse cracks in PCC pavements.

+ Stiffness characterization of distinct pavement layers.

+ Effective structural capacity of pavement based upon the 1993 AASHTO Pavement Design Guide or other methodology.

• Safety aspects – pavement condition safety aspects are primarily related to friction and hydroplane potential. Pavement friction characteristics are most often characterized using a skid number parameter. Hydroplane potential is related to ponding of water on the pavement surface due to the ability of pavement ruts to hold water or drainage defects in the surface profile. The nominal depth of water can be associated with hydroplane potential based on the speed limit. Another pavement condition related to safety concerns is excessive pavement roughness relative to the speed limit. It is possible for localized bumps, dips, faults, and holes in the pavements to reach a level that negatively influences vehicle control.

• Agency time based rules – one of the simplest construction need triggers is the time since the last construction treatment. Some agencies have implemented rules on the maximum time between construction events. The time based rules are intended to reduce field measurement costs and provide a proactive pavement management approach to keep pavements in good condition.

• Traffic capacity – in changing the definition for remaining service life to one that is related to assessing future construction needs, it is important to identify when a roadway width will need to be expanded to add new lanes due to traffic growth. These types of rules are generally outside the realm of pavement management, but are a required consideration when developing an estimate of future budget needs.

STEP 2: SETTING THRESHOLD LIMITS

Threshold limits are used to indicate when a construction trigger reaches a condition and a corrective or preventive construction treatment is needed.

There are two general types of threshold limits – one related to road users and the other one based on agency economics. For example, ride quality, rutting, and skid resistance are related to road users, while cracking and faulting (although it impacts ride quality) are related to agency economics and should ideally be based on life cycle costs (LCC). The specific methods and procedures that can be used to establish the various types of threshold limits include:

• Subjective – these threshold limits are based upon ratings from a panel(s) of judges comprised of laymen facility users, pavement "experts," or a combination. The basic process is to create a formal rating scale to be used by the judges, and then use statistical methods to interpret the ratings and establish limits. Subjective ratings can be used to define an absolute acceptable limit or degrees of acceptability for a measured condition attribute. The following are some acceptance scales that can be used to capture subjective panel ratings:

+ A binary or two-level acceptable/not acceptable or pass/fail rating scale, which limits the range of response to two in order to identify the acceptance threshold, but also limits analysis of the results.

+ A 5-level Likert scale, which provides a measure of the range in acceptance criteria to be considered; e.g., 5 – definitely acceptable, 4 – less acceptable, 3 – not sure, 2

– not acceptable, and 1– definitely not acceptable.

+ A 4-level Likert scale, which removes the neutral middle rating to force raters to provide either an acceptable or unacceptable rating; e.g., 4 – definitely acceptable, 3 – less acceptable, 2 – not acceptable, and 1– definitely not acceptable.

+ The degree of acceptability can also be based on a Likert scale by altering definitions of the ratings; e.g., 5 – very poor, 4 – poor, 3 – fair, 2 – good, and 1 – excellent. In this example, to improve the repeatability of the results, it is useful to provide the raters with a more refined definition of each category that is related to the attribute of interest.

• Engineering – considerations used to establish these threshold limits are based upon pavement performance mechanistic concepts or pavement-vehicle interaction factors.

Some examples include:

+ Cracks extend completely through bound pavement layers.

+ Potential depth of water held in ruts.

+ Depth of top-down cracks on AC pavements.

Options:

1. Subjective

2. Engineering

3. Empirical

4. Economic analysis

5. Combinations

+ Increase in applied dynamic truck loads caused by pavement roughness.

+ Pavement structural capacity diminished to the point where stress and strain level of applied traffic loads accelerates pavement damage.

• Empirical – this approach to setting threshold limits is based upon observations of events. A critical aspect to this approach is that it is most applicable to the inference space of the observations from which they were developed. Technology advancements or other changes that are outside of the inference space of the original observations can limit the applicability of existing empirical models to future events. Examples of empirical approaches to setting threshold limits include:

+ Analysis of friction data and associated accident rates or field experiment to set a safe level of friction.

+ Statistical analysis of the pavement condition when construction treatments have been applied and their effectiveness (as a function of condition) when it was applied.

The advantage of this approach is that it does not require a thorough understanding of the mechanism being modeled. For example, it may be postulated that the accident rate on a section of roadway is related to the level of friction offered by the pavement surface. It may also be recognized that the accident rate on this same section of roadway is related to the speed of the vehicles traveling that roadway. With an empirical approach, it is not necessary to fully understand all of the mechanisms associated with the accident rate; rather, the correlation of the friction with the accident rate can assist in identifying an unacceptable level of friction on the roadway.

• Economic analysis – construction limit thresholds can be developed from an economic analysis of construction time-series costs over a long term period. This analysis depends on knowing or estimating how long alternative construction treatments will last based upon the predicted condition of the pavement at the time of the treatment, and the cost of the construction treatment. A critical factor in pavement construction time-series economic analysis are the rules concerning deterioration rate of the pavement, what type of repair treatments are considered, the effect pavement condition has on the resulting performance for each repair treatment, and costs included in the analysis. To avoid manipulation of the results from pavement life-cycle cost analysis due to the assumptions of the person performing the analysis, highway agencies need to create a set of rules to be used in this type of analysis. To the extent possible, these rules – pavement deterioration rates, repair treatment types considered, effect of pavement condition on performance of repair treatments, and costs included in analysis – should be based upon observations from pavements under agency jurisdiction. However, the use of engineering judgment based upon available data may be the best an agency can do to create the rules. Establishment of a preliminary set of rules provides a basis to evaluate and update the rule set based upon experience. Part of the rules should be standard estimates of error and error distribution forms for use in stochastic/risk-based analysis. Figure 3 illustrates the expected outcome of an economic analysis on the most cost-effective repair strategies as a function of pavement condition for an individual pavement.

Figure 3. Graph. Conceptual relationship between present worth agency repair costs as a function of pavement condition.

• Combinations – under this scenario, the development of threshold limits is done through a combination of the approaches previously described. The recommended approach to setting threshold limits on need for corrective construction intervention is by use of a combined engineering economic approach. The objective should be to determine condition states where maintenance or preservation treatments, rehabilitation treatments, and reconstructive treatments are most cost-effective. Considerations to determine appropriate pavement state thresholds for application of maintenance or preservation treatments include:

+ Preservation maintenance treatments should be applied while a pavement is still in relatively good condition. When possible, the upper limit should be based upon specific pavement defects which can be corrected to "good-as-new" condition without need for structural restoration treatments.