Maintenance and Preservation
This page features information on maintaining and preserving assets. Whether you are defining condition and performance measures or monitoring the state of your assets, you will find what you need here.
Legislation and Regulations
The federal government recognizes the importance of asset management practice and requires states to develop transportation asset management plans. Many state governments also have implemented laws related to asset management.
The transportation authorization legislation Moving Ahead for Progress in the 21st Century (MAP-21) signed into law in 2012 includes a number of provisions related to asset management and performance management for both highway and transit modes. The requirements established in MAP-21 were continued in the subsequent legislation Fixing America First Act (FAST) signed into law in 2015. For the highway mode MAP-21 defines asset management in the context of transportation and requires that State DOTs develop risk-based transportation asset management plans (TAMPs) for assets on the National Highway System (NHS). The law also includes a number of requirements related to performance management. Regarding transit MAP-21 requires that U.S. transit agencies develop TAMPs that detail asset conditions and include a prioritized list of state of good repair (SGR) investments.
Following passage of MAP-21 and FAST the Federal Highway Administration (FHWA) and Federal Transit Administration (FTA) developed rules detailing the TAM requirements for highways and transit, respectively. In 2016 FHWA finalized § 23 Code of Federal Regulations (CFR) Part 515 – Asset Management Plans. FHWA’s requirements specify that a TAMP should detail asset inventory, current conditions, and predicted future conditions over a 10-year period, using performance measures detailed in FHWA’s performance management regulations. The TAMP should include the following elements:
- Asset Management Objectives
- Asset Management Measures and Targets
- Inventory and Conditions
- Performance Gap Identification
- Life-Cycle Planning
- Risk Management Analysis
- Financial Plan
- Investment Strategies
In 2016, the FTA finalized asset management requirements U.S. transit agencies must follow. These requirements are detailed in §49 CFR Parts 625 and 630. The FTA requirements detail that transit agencies must prepare TAMPs covering a four-year period and including their revenue vehicles, infrastructure, facilities, and equipment (including service vehicles). Agencies must use a decision support tool to help analyze SGR investment needs and develop a prioritized list of needs. Larger agencies (with rail systems and/or 100 or more vehicles in peak revenue service) must include additional materials in their TAMP, such as a TAM/SGR policy, TAM implementation strategy, evaluation plan, and identification of resources required to implement the plan.
The Basic TAMP
A TAMP describes an agency’s goals and objectives for maintaining its assets over time. It describes an agency’s most critical assets, and their current condition. It also describes the agency’s strategy for preserving its assets, predict future conditions given the agency’s planned investments, formulate and deliver an investment plan, and discuss how the agency manages risks to its assets.
This section discusses the requirements for a TAMP that is consistent with TAM leading practice. A TAMP includes:
- TAM Policies, Goals and Objectives
- Asset Inventory and Condition
- Life Cycle Planning Approach
- Predicted Asset Conditions
- Investment Plan
- Risk Management
Note there are additional specific requirements for a TAMP that is prepared to comply with Federal requirements. State DOTs are required to prepare a TAMP with a 10-year horizon that includes, at a minimum, NHS pavements and bridges. Transit agencies that receive Federal funds are required to prepare a TAMP with a four-year horizon that includes their revenue vehicles, facilities, infrastructure, and equipment (including service vehicles). FHWA provides a checklist of elements of TAMPs compliant with Federal requirements: https://www.fhwa.dot.gov/asset/guidance/certification.pdf. A similar FTA document is available at: https://www.transit.dot.gov/sites/fta.dot.gov/files/docs/regulations-and-guidance/asset-management/55371/compliancechecklistfy2018_0.pdf.
TAM Policies, Goals and Objectives
A TAMP summarizes an agency’s policies, goals, and objectives and describes how its approach to TAM helps support these. For instance, the document might discuss how maintaining assets in good repair supports the organization's broader goals for strengthening mobility and supporting economic development. It may also describe how the organization defines the desired state of repair of its assets, or criteria for evaluating whether or not an asset is in good repair. A clear linkage between TAM objectives and the achievement of wider agency goals should be directly illustrated within the TAMP.
Asset Inventory and Condition
In preparing the TAMP, the agency must decide which asset classes to include in the document, and the level of detail in which the assets are described. For a highway plan, critical assets include pavements and bridges. A TAMP that is prepared to comply with Federal requirements must include these assets on the National Highway System at a minimum. Other assets addressed in a highway TAMP may include, but are not limited to: drainage assets such as culverts; traffic and safety assets such as signs, signals, and lighting; maintenance facilities; and Intelligent Transportation System (ITS) devices. For a transit plan, critical assets include revenue vehicles, facilities, infrastructure (for agencies that operate fixed guideway) and additional equipment, such as service vehicles.
A TAMP should provide a listing, typically in summary form, of the assets the agency has identified for inclusion. For each asset class the document should describe the physical extent of the asset, and current asset conditions. Chapter 3 of this document describes approaches for measuring asset condition and performance. Note that FHWA and FTA have developed specific requirements for reporting asset conditions for highway and transit assets, respectively. However, agencies are not limited to these measures, and may include multiple measures of condition in their TAMP to help provide a complete description of asset conditions.
Often it is helpful to place the data on an agency’s asset portfolio's current condition into some context. For instance, the TAMP may include photographs of representative asset condition to help illustrate what is meant by a given value for a performance measure. Also, a TAMP may include historic data on asset conditions to help illustrate condition trends.
Life Cycle Planning Approach
A critical component of a TAMP is a discussion of how an agency maintains its assets over their life cycle. Ideally the agency’s approach to life cycle planning should help maintain assets at a target level of service over their life cycle in the most efficient manner possible, while supporting agency goals and objectives. This section of the TAMP should describe the treatments the agency typically performs on its assets, and detail the analytical approaches it uses to assess investment needs, prioritize work, and predict future asset conditions. If the agency has implemented specific management systems for one or more of its asset classes, such as pavement, bridge or enterprise asset management systems, this section should describe those systems and how they are used to support decision making. Chapter 4 of this document provides further detail on life cycle planning.
Predicted Asset Condition
This section of the TAMP should describe how an agency’s assets are predicted to perform in the future. The horizon of the predictions should be commensurate with the horizon in the investment plan described in the next section. Typically the planning horizon is at least four years, but may be up to 20 years.
This sections should show what conditions are predicted given expected funding, as well as any gaps between predicted performance and the agency’s goals for its assets. This section may include results for multiple funding scenarios, particularly if there is uncertainty concerning future funding, or if including results for multiple scenarios helps document the process used to prioritize funding. For instance, the document might show predicted asset conditions over time given the current funding level, predicted future funding, and scenarios with more or less funding than the predicted level.
The TAMP should detail planned investments given expected funding. Depending upon the agency size and assets included in the plan, the document might include specific investments the agency plans to make or projected funding levels by asset class and type of work. This section may provide additional details on sources of funding, and the agency’s specific strategy for investing in its assets considering available resources.
Managing transportation assets also entails managing risk. Considering risk is important in developing a TAMP, for the simple reason that there are various risks that, if they occur, may impact an agency’s ability to follow its TAMP. For instance, the occurrence of a natural hazard may require an agency to spend significant resources in response, to address or mitigate damage. Employing risk management strengthens asset management programs by explicitly recognizing that any objective faces uncertainty, and identifying strategies to reduce that uncertainty and its effects. This section of the TAMP should describe the agency’s approach to risk management. It should identify major TAM-related risks and describe the agency’s approach to addressing these.
To ensure alignment with the requirements of MAP-21, Colorado DOT developed a requirements checklist that provides a quick reference/summary of the legislation requirements. The checklist is based on FHWA guidance (Transportation Asset Management Plan Annual Consistency Determination Final Guidance) that was issued in February, 2018. Its content was provided to help DOTs ensure their TAMPs are compliant and consistent with statute and regulatory requirements.
Source: FHWA. Transportation Asset Management Plan Annual Consistency Determination Final Guidance. https://www.fhwa.dot.gov/asset/guidance/consistency.pdf
Beyond the Basic TAMP
This section contains suggestions for developing a TAMP that goes beyond the basic elements of a TAMP described in the previous section. An agency can expand the scope of the TAMP to include additional asset types and systems. An agency may further tailor their TAMP to address specific needs.
A highway agency focused on complying with Federal requirements will typically focus on including its NHS pavements and bridges in its TAMP. While these assets make up the greatest portion of a typical state highway agency, an agency may wish to include additional assets in its TAMP. Also, the agency may wish to extend the network scope of the TAMP. In updating a TAMP with NHS pavement and bridges, an agency may include other assets, such as drainage assets, traffic and safety features, or the agency may wish to include all of the assets it owns.
For transit TAMPs, the initial focus is on revenue vehicles, facilities and infrastructure, as these are the assets that require the greatest investment. An agency may wish to expand its TAMP to include additional assets that are important to the systems, albeit less costly, such as bus shelters and signage.
TAM Implementation Plan
As described in Section 2.3, it is often helpful to prepare an implementation plan describing a set of planned business process improvements that an agency intends to undertake to strengthen its approach to TAM. There are many examples of TAMPs that focus specifically on an agency’s TAM approach and how it plans to improve its approach. Ideally a TAMP should both describe an agency’s assets and planned investments, and detail how it intends to improve its TAM approach. Where an agency has developed both a TAMP and TAM implementation plan, the implementation plan can be incorporated as a section of the TAMP.
TAM-Related Business Processes
An agency may wish to include a discussion of one or more of the business processes related to TAM in its TAMP. Alternatively, there may be other agency documents that provide more detail on these issues that can be referenced in the TAMP. These areas include:
- Performance Targets. As described in Chapter 5, setting performance targets can help guide the resource allocation process. However, agencies often have broader efforts to establish and track performance beyond the scope of TAM.
- Financial Planning. While developing a TAM investment plan is central to developing a TAMP, often the revenue forecast used to support developing the investment plan is developed separately and used for other purposes beyond the scope of TAM. It may be valuable to document the agency’s approach to forecasting future revenues for TAM and other applications. Chapter 5 describes provides additional detail on this topic.
- Work Planning and Delivery. As described in Chapters 4 and 5, work delivery approaches can impact how assets are maintained over their life cycle, and how resource allocation decisions are made. Some agencies have adopted formalized approaches for evaluating and selecting different work delivery approaches.
- Data Management. Chapter 7 discusses the importance of implementing an approach to data management and governance. Some TAMPs include additional information on this topic given its relationship to TAM.
AASHTO TAMP Builder
The AASHTO TAMP Builder website (available at https://www.tamptemplate.org/) hosts annotated plan outlines to assist agencies in preparing TAMPs. The site also provides resources to customize an outline in order to meet agency-specific objectives and requirements. The website integrates a database of TAMPs, dating from 2005, that support the functionality of the outlines created using the site.
Defining Life Cycle Management
Through life cycle management, agencies employ data on asset condition, treatment options, costs, deterioration rates, replacement cycles, and other factors to determine the most cost-effective, long-term strategies for managing assets throughout their lives.
All transportation infrastructure assets have a life cycle, which includes several stages from initial construction to removal or replacement (see figure 4.1). Life cycle management is an investment approach that considers maintenance, renewal, replacement, or repair options through an asset’s service life with the intent to maximize the benefit provided by the asset at the minimum practicable cost. It employs data on asset condition, treatment options, costs, deterioration rates, replacement cycles, and other factors to evaluate trade-offs between possible investment strategies and treatment timings. Effective life cycle management requires knowledge of the agency’s strategic priorities and an understanding of the performance criteria driving investment decisions, so the right management strategy can be identified and implemented for each asset class. Aligning asset management measures with agency priorities ensures the investments made to extend asset service life provide the maximum impact to the agency’s long-term goals.
Figure 4.1 illustrates a variety of interventions that occur over an asset life cycle. The larger circles represented in the figure are service life altering, and represent a capital investment in infrastructure. Capital investments provide significant life extension, and may alter or enhance the operational nature of the asset, e.g. expand capacity, without fully replacing the asset. Maintenance (reactive, interval based and routine) activities are required throughout the life cycle to ensure the asset achieves its service life.Preservation treatments restore condition or performance to achieve service life, and may extend service life as well, but do not significantly alter the operational nature of the asset. Some agencies may capitalize investment in these preservation activities; however, regardless of the timing and character of the selected interventions, all of them are part of the life cycle management process. More (lower cost) maintenance interventions can offset the number and cost of the larger (and more costly) interventions. Balancing the right intervention, at the right time, can greatly reduce the overall investment needed for infrastructure to be reliably available for providing service.
Life cycle management can be used at both network level and at project level. At network-level, life cycle management considers the needs of an entire asset class, as well as the available funding, to determine the most appropriate life-cycle strategies. For example, analysis can establish the optimal proportions of overall investment that should be allocated to different types of interventions over the network, to minimize investment to achieve performance targets or an average condition level. At a project level, life cycle management is commonly used to develop asset-specific strategies. Project level life cycle plans provide input into the network level life cycle plans. Large bridges or other distinct network components are often planned and managed in this manner.
Life Cycle Cost Analysis (LCCA) is an engineering-economics approach that can be used to quantify the differential costs of alternative design approaches. Network level life cycle management, while a more wholistic process that manages every stage of an asset’s life, may employ LCCA or other forms of analysis to inform management decision-making. Figure 4.2 highlights some of the major differences between life cycle management and life cycle cost analysis. At the network level, LCCA can be used to understand how to best manage the network as it ages. At a project level, it is used to understand what are the most effective actions to be taken on the assets within the project scope at the time of project delivery. Both network level and project level analyses contain many aspects of engineering economic analysis, such as consideration of user benefits, user costs, and the time-value of money to identify alternatives that represent the lowest practicable life cycle cost over the analysis period to achieve the desired objectives.
Figure 4.2 Attributes of network level life cycle management and project level life cycle cost analysis
- High level.
- One asset class or subclass.
- Multiple locations.
- Looks at impacts of varied treatment timing.
- Considers future cost changes.
- Multiple asset classes.
- Single location.
- Treatment timing fixed for all options.
- Uses discount rate.
Source: Applied Pavement Technology, Inc. 2017
Decision Making Context
Life cycle management is driven by the need for owners to provide consistent service to those that use the transportation system with the resources available. Infrastructure decision making can take place at several levels within an organization, and in each case, considers different but often interrelated factors. These are illustrated in table 4.1.
Figure 4.3 Analysis of KYTC Future Costs Under Two Strategies
Source: Kentucky Transportation Cabinet Transportation Asset Management Plan, 2018.
Table 4.1 - TAM Decision-Making Contexts
Key Questions and Connections to Other Chapters
|Key Decisions||Setting goals and objectives.||Capital investment prioritization and scoping and Integration of maintenance and renewal strategies||Delivery of the capital program, routine maintenance, and highway-operations activities.|
|Decision Makers||Directors and managers who are asset stewards.||District and field mangers, supervisors, and staff.|
|Other Factors||Decisions and outcomes of these strategic questions help focus investment. They add value to overall performance of the transportation system by setting priorities, values, and help prioritization of investment at lower levels. Creating new assets and disposing of existing ones are strongly influenced by decisions and priorities defined at this level.|
Chapter 2 discusses these considerations in more detail, and the level of service section in this chapter discusses linking these strategic priorities
to decision-making at lower levels. Performance and target setting in Chapter 6 also discusses this linkage and how targets can be set to achieve these strategic goals.
|This Chapter focuses on these questions and on the analysis that informs their corresponding answers and decisions. Life cycle management and analysis focuses on the existing transportation system and evaluates how:||Delivering a program work, ranging from maintenance activities to capital improvements, requires a coordinated management of a large workforce. It requires processes that minimize input of resources to get the output required for desired system performance. Work management systems, efficiency
and improvement techniques and performance management focus on improving decisions at this level. These concepts are discussed in Chapter 5, 6 and 7.
Kentucky Transportation Cabinet (KYTC)
In the early 2000s, KYTC found that the cost of hot-mix asphalt (HMA) was increasing faster than its budget to maintain pavement conditions. In response, KYTC evaluated the feasibility of strategies that relied heavily on preventive maintenance overlays such as thin HMA overlays (< 1 inch), chip seals, cape seals, and slurry seals. KYTC found that while the costs of these treatments were substantially less than a traditional HMA overlay, their service lives were only marginally shorter. As a result, the agency began increasing the use of these treatments on its secondary system. As part of developing its risk-based TAMP in 2018, KYTC evaluated life cycle strategies, as shown in Figure 4.3 Analysis of KYTC Future Costs Under Two Strategies that expanded the use of preventive maintenance overlays to its parkway and interstate pavements. The analysis results led the agency to select a life cycle management strategy that maximizes the use of preventive maintenance overlays on secondary roads and parkways and increases their use on interstate pavements over time. As shown in Figure 4.3, this new life cycle strategy achieved conditions over the 10-year TAMP analysis period that would have cost an additional $644 million if they had continued to rely on traditional 1- to 2-inch HMA overlays. By implementing these improved strategies, KYTC has significantly reduced the risk that the infrastructure will reach an unsustainable cost to maintain in the future.
Source: KYTC Transportation Asset Management Plan, 2018. http://www.tamptemplate.org/wp-content/uploads/tamps/048_kentuckytc.pdf
Defining Asset Service and Performance Levels
Before asset performance can be managed, an agency must first define what it is seeking to achieve. In TAM, asset performance is most commonly defined in terms of asset condition or maintenance level of service. Performance may also be evaluated in terms of safety, availability, reliability, resiliency and other service attributes. Regardless of the method used to monitor performance, it should be used to inform analysis that supports decisions to help ensure that investments enable an agency to achieve its goals cost-effectively.
Establishing Desired Levels of Service
Before a whole-life strategy can be developed and implemented, an agency must determine what they seek to achieve. In many transportation agencies, the desired level of service (or asset management organizational objectives, in ISO 55000 terminology) provides the linkage between what the goals of an agency are, and what investments and interventions should take priority when managing assets. High level goals should directly influence investment choices when resource allocation decisions are made. Service levels help establish when gaps need closing to achieve a goal, and merits investment. Chapter 2 discusses ways to create linkages between goals and investment decision making.
When managing the life cycle of existing assets, performance targets are commonly established as a way to manage service levels for the transportation network. How to determine the expected level of performance may vary depending on the type of asset being managed. Level of service targets that are part of performance framework typically are a mixture of both customer focused performance measures, and technical service measures that help those responsible for the asset assess what types of interventions might be required and when. Customer focused service measures are important to road users and other stakeholders that require mobility. Travel time reliability, safety, load capacity and clearances, and lane availability are all examples of service targets that are customer focused. Condition, strength, regulatory compliance and examples of technical service attributes are commonly of greater interest to asset stewards than asset users. Both types are service level targets that are important to evaluate the efficacy, effectiveness and efficiency of a transportation system.
For pavements and bridges, and other assets managed using a condition-based approach, asset condition is commonly used to establish expected technical levels of performance, but also is relevant to customers. For example, condition is employed as a proxy in this way for pavements because it is objectively measurable, deterioration has some predictability. It is a valuable service attribute because often, user experience is also directly connected to condition as well. Potholes, rutting and roughness all reduce quality of service from a pavement. Performance measures, such as those discussed in Chapter 6, are used to establish the desired long-term performance and to set short-term targets that can be used to track progress towards the long-term objectives. For other highway assets, including those managed using interval- or time-based maintenance approaches, performance may be linked to the expected service life, the ability of the asset to fulfill its intended function, and/or other operational factors. For these other highway assets, performance targets are often established as part of a Maintenance Quality Assurance (MQA) program in terms of desired maintenance levels of service (MLOS) and integrated with operational service targets that may also be customer focused.
Risk can also be used as a measure of performance. As described in chapter 2, risk considers both the potential impact and consequence of failure. This can be particularly useful when the potential consequences of failure impact other assets or facilities. An example of how Colorado uses risk to manage rockfalls is included in section 4.3 of this chapter. Additional details on how to track risk-based performance measures is included in Chapter 6.
Establishing a desired level of performance is typically a collaborative process that considers existing conditions, available funding, expected demands on the system, policy goals and guidance, and stakeholder priorities. The desired level of performance is typically established once baseline data is available, so performance trends can be evaluated. The desired level of performance may be adjusted over time to reflect changes in agency performance, changes in asset condition, capacity, safety, resiliency and other factors.
Three types of service expectations are often used in combination to manage asset performance:
- Performance target – the level of performance beyond which additional performance gains are not desired or worth the additional cost. When performance is measured based on condition, the desired performance may describe the desired state of good repair. There may be an expected specific time frame to achieve this desires performance target.
- Current Performance – an intermediate level of performance achieved by the organization and is usually reported relative to the desired target. Target setting is described in more detail in Chapter 5.
- Minimum acceptable performance – the lowest level of performance allowed for the asset or asset class to still function as designed.
Performance expectations may be set for the road network, a road corridor, for individual assets or for a group of assets. Commonly, performance expectations are set using a combination of asset class or subclass or sub network, such as:
- Key network corridors.
- Bridges on the National Highway System.
- Interstate pavements.
- Culverts larger than 10 feet in diameter.
- Traffic signals serving more than 10,000 vehicles per day.
The nature of performance expectations can be either strategic or tactical or operational. Strategic expectations support freight movement; for example, the long-term goal of providing unrestricted flow of legal loads is supported by a performance expectation of no load-posted or restricted bridges on interstate highways. This expectation cannot be accomplished without the tactical delivery of work to address factors contributing to the physical condition of bridges. Thus, an agency may include tactical expectations to perform maintenance and repair on structural members on a routine basis or as conditions warrant. These enhancements can be also integrated with renewal and other rehabilitation interventions to help improve both tactical performance metrics, as well as achieve higher level goals and objectives. Operational improvements such as more responsive snow clearance, and better signage are all integrated treatment options to achieve the strategic objective.
Life cycle management analysis, and the decisions it supports, require service levels, performance targets and other objectives to be able to determine the optimal choices for agencies to select during resource allocation. Over an asset life cycle, a range of interventions are possible, from reactive, routine and preventative maintenance, to large investment associated with renewal, replacement, or removal. Having targets helps select the right interventions and investment option while balancing risk, service and cost.
Connecting performance measures to higher level strategic goals also supports an agency’s ability to communicate how technical measures relate to system performance as experienced by highway users and other external stakeholders, thus tying asset management outcomes to system performance. Asset management measures are often very technical. Performance indicators like bridge ratings, pavement distress measurements, and risk ratings are not commonly understood by those outside transportation agencies. However, agencies can use these technical measures to support the performance indicators that are more commonly understood and prioritized by system users and external stakeholders. Communicating system performance and the status of the road network is discussed in Chapter 2, and is illustrated in several examples below. Customer service level targets are often established for this purpose, and give users an ability to understand the quality of service they should expect on the transportation system.
Each year, the Colorado DOT must report to its legislature on the statewide highway infrastructure and the agency’s ability to meet those needs with available resources. This requirement is met through the Annual Infrastructure Deficit Report, which addresses pavements, bridges, and annual maintenance. The agency supports the annual maintenance portion of this report with its Maintenance Level of Service Measure, which rates the delivery of services in nine program areas in terms of a letter grade from A to D and F. The agency has used historic data to develop deterioration rates for each service area that estimate the resources needed to improve the maintenance level of service by a given amount over a specific time period. These estimates are summarized in the Report, which is in turn used by the Legislature and the DOT to establish the annual maintenance budget. The figure provides an example of information on MLOS in the 2016 Report. Once the targeted MLOS is established, maintenance funding can be allocated to ensure that agency priorities are met.
Colorado DOT Example of Funding Needed to Support Maintenance Levels of Service
Source: Colorado DOT. 2016. https://leg.colorado.gov/sites/default/files/cdot_smart_2017_presentation.1.pdf
Washington State DOT
When seeking to establish the connection between investments and performance across a wide range of assets or roadway attributes such as litter, vegetation height, drainage, or functionality it is helpful to relate all of the various measures of performance to a common rating scale. Washington State DOT has developed its Maintenance Accountability Process to establish the relationship between maintenance level of effort and the resulting level of service. The process rates conditions and services in seven areas using a common letter-grade system, or MLOS.
- Roadway Maintenance & Operations.
- Drainage Maintenance & Slope Repair.
- Roadside and Vegetation Management.
- Bridge & Urban Tunnel Maintenance and Operations.
- Snow & Ice Control Operations.
- Traffic Control Maintenance & Operations.
- Rest Area Operations.
Each group of services or conditions includes several performance measures, which are translated to the MLOS grades of “A” (highest performance), “B”, “C” (adequate performance), “D” or “F” (unacceptable performance). Applying the MLOS grades allows for a consistent means of rating performance across services and geographic regions. Letter grades can also be represented in photographs of facilities that meet the criteria for each condition state to support communications with stakeholder groups. The MLOS are outcome-based measures that allow the agency to predict the expected level of service that can be achieved based on anticipated budget and work planning decisions. By tracking maintenance expenditures and MLOS results annually, Washington State DOT is able to adjust its maintenance priorities and budgets to address system needs and stakeholder wants.
New Zealand Local Government Act legally requires councils to consult with their communities on their long-term plans. The consultation plan provides an effective basis for public participation in infrastructure decision-making associated with the long-term plan. It includes a fair representation of overall objectives, and how tax levels, debt, and levels of service might be affected by the intended plan and can be readily understood by interested or affected people. The Auditor General recently reviewed plans produced by communities across the country. Key findings highlighted aspects that help define good practice:
- Consultation documents present their information in a concise, readable and understandable way.
- Clear and unambiguous explanations on why proposed taxation and debt increases and significant changes in plans or intentions were considered “affordable” or “equitable” make consultation documents more effective.
- Some communities used a road-trip analogy throughout the document. The analogy makes technical subjects relatable without over-simplifying the issues.
- Some used a personalized approach that connected with people. For example, one uses two primary school children, Maia and Xander, who are pitched as the “champions of the Long Term Plan 2018-2038.”
By focusing on the inclusion of transportation customers, New Zealand municipalities are better able to address customer needs, inform customers of the actions they are taking, and refine work planning practices to address concerns critical to infrastructure operations and customer expectations.
Managing Assets Using Condition Based Management
The condition-based management is the most complex of the approaches introduced in Section 4.2 and requires a commitment to the collection of reliable inventory and condition information over an extended period and the of condition models to predict future deterioration to evaluate the type and timing of various treatment actions in terms of risk and performance.
Using Computerized Management Systems to Optimize Life Cycle Management
For condition-based analysis, computerized management systems are valuable tools for evaluating life cycle strategies. Computerized systems support the larger life cycle management process by providing relevant, reliable information and analysis results to decision makers at the right time.
Condition-based management is common for pavement and bridge assets. Often pavement and bridge decision making is supported by a computerized system that is used to support optimized life cycle management. The results from this analysis provide insights into optimal life cycle strategies for all network assets or for a specific group of assets. These models can be configured to include the effects, maintenance, preservation, rehabilitation, and reconstruction actions. Depending on the type of condition-based modeling approach, uncertainty can also be included.
Various life cycle scenarios can be generated by modifying one or more variables in the analysis. By running multiple network-level scenarios and comparing the results, pavement and bridge management systems can identify viable life cycle strategies and help an agency select the strategy that best achieves the stated objectives.
More information on the use of pavement and bridge management systems is available in the FHWA document, Using a Life Cycle Planning Process to Support Asset Management: A Handbook on Putting the Federal Guidance into Practice. Life cycle planning is a required component of risk-based TAMPs developed by state DOTs (23 CFR 515), that uses computerized asset management systems to establish long-term life cycle strategies for pavements, bridges and other highway assets. NCHRP Report 866, Return on Investment in Transportation Asset Management Systems and Practices, provides an assessment of how state DOTs have implemented asset management systems, including practice examples. The end of this section includes a how-to guide for using a pavement management system for life cycle planning, a requirement for risk-based TAMPs developed by state DOT’s for pavements and bridges on the National Highway System (23 CFR 515).
These computerized systems are designed to develop network-level scenarios for analyzing the impacts of different program variables over long periods of time. Typical pavement management scenarios will cover 10 to 40 years, while bridge management scenarios may need to cover 100 years or more to ensure inclusion of multiple life cycles within the scenario.
Various life cycle scenarios can be generated by modifying one or more variables in the analysis. By running multiple network-level scenarios and comparing results, pavement and bridge management systems can identify viable life cycle strategies and help an agency select a strategy that best achieves the stated objectives.
As required under MAP-21, Ohio DOT conducted a risk assessment to identify the most significant threats and opportunities to its pavements and bridges. The analysis revealed that anticipated flat revenues, combined with the annual increases in cost to pave roads and replace bridges, would lead to significant reduction in conditions without changes to existing practice. The potential deterioration in pavement and bridge conditions were expected to significantly increase future investment needs due to the increase in substantial repairs that would be required.
Following the risk assessment, a life cycle analysis was conducted. The analysis found that by focusing on the increased use of chip seals and other preventive maintenance treatments on portions of the pavement network, the annual cost of maintaining the network could be reduced. A life cycle analysis for bridges showed similar results. The bridge analysis found that with just 5 percent of the NHS bridges receiving a preservation treatment annually, the DOT could reallocate $50 million each year to other priorities. The investment strategies outlined in the TAMP and the changes made to the DOT’s existing business processes enabled the agency to offset the potential negative impact of the anticipated flattened revenue projections.
The differences in the adopted life cycle strategies are compared to the past strategies in the Figure. Although the total number of treatments applied over the analysis period increases, the annual life cycle cost decreases because of the reduction in the number of rehabilitation strategies needed.
Ohio DOT’s Pavement Preservation Strategy Comparisons
Source: Ohio DOT Transportation Asset Management Plan. 2018. http://www.dot.state.oh.us/AssetManagement/Documents/ODOT_TAMP.pdf
Predicting Asset Performance
A life cycle strategy is enhanced by the availability of models and analysis tools that facilitate the evaluation of different combinations of treatment type and timing across the asset class. For this analysis a model that predicts future asset deterioration and response to treatments is required.
For condition-based approaches to managing assets, historical performance is typically used as a baseline for developing models to predict future performance. The predicted conditions are used to determine the type of treatments that may be needed over an asset’s service life, so the ability to accurately predict asset conditions in the future, with and without treatment, is an essential component of asset management. Models are developed by comparing performance, typically measured as asset condition, over time with actions or treatments performed on specific assets. This means that performance is associated to the last action or treatment that impacted performance in a positive way. However, assets may also receive treatments that delay the onset or advancement of distress. As a result, most models assume assets receive some level of preventive or routine maintenance between more significant treatments. If agency practices change to delay or cease maintenance activities, assets may not perform as models predict.
Several methods can be used to estimate future asset performance, the two most
common of which, deterministic and probabilistic, are described below. Additional information has been published by NCHRP (Report 713, 2012 ): Estimating Life Expectancies of Highway Assets. This report also contains guidance on selecting the most appropriate modeling approach for various highway asset classes.
Deterministic modeling is a common and relatively simple approach for using historic data to predict future asset performance. Deterministic models apply regression analysis to one or more independent variables, typically condition over time, and develop a “best-fit” equation to determine the rate at which asset conditions change. The independent variables are used to predict a single dependent variable, most commonly represented as the predicted condition at some point in time in asset management applications. Developing deterministic models is relatively easy but relies on quality data collected consistently over several years to produce dependable results. Deterministic models are more easily implemented as they are more readily paired with linear program solving. They also provide consistent outputs. The downside of deterministic models is the limited insight that they provide into the cost uncertainty surrounding a strategy.
Unlike deterministic models, which provide a single repeatable outcome, probabilistic models provide a distribution of possible strategies that provides insight into the cost uncertainty of plans. Probabilistic models can also more readily accept uncertainty in other variables, as represented by the shading in Figure 4.8. Given that condition changes are probabilistic, no two strategies that the model will provide are the same. This means that multiple iterations of the model with the same inputs can provide different results. Accordingly, probabilistic models are useful for setting funding limit expectations, while deterministic models help to provide insights into which projects are best to apply to specific assets.
Common approaches to developing probabilistic models are the Markov, Semi-Markov and Weibull models. Markov modeling works well for assets with condition ratings based on regular inspections. There are several ways of establishing a Markov model, but the simplest is to calculate the proportion of assets that change from one condition state to the next in any given year. These proportions are then used to develop what is known as the transition matrix. At the start of the model run, an asset “knows” its condition state. Once this is known there is then a probability it will change from its current condition state to the next in any given year. While these types of Markov approaches have been widely used, they do not necessarily model deterioration effectively, as the rate of change of condition increases with time. To address this, Semi-Markov models are used. Like Markov, Semi-Markov models have a condition transition matrix, but this is also augmented with a time selection matrix. In these models the probability of a condition jump is calculated, then the length of time an asset will remain in that condition state is also selected. Using more advanced mathematical techniques, the Semi-Markov approach can be expressed similarly to the Markov approach, but for Semi-Markov, the transition matrix changes with time. This reflects the increasing likelihood the asset will transition (deteriorate faster as its ages). Such models are typically used on long-lived assets.
A Weibull model offers another approach for modeling asset deterioration. A Weibull distribution predicts the likelihood of asset failure or deterioration as a function of age. Weibull models are particularly useful for addressing assets rated on a pass/fail basis during inspection. The Weibull model provides an additional factor meant to address the increasing or decreasing likelihood of an asset moving from an acceptable to an unacceptable state between inspection cycles. Reliability is the inverse of the probability of failure (i.e. 1 -p(f)). Reliability, like Weibull can thus be used to assess the likelihood an asset will provide the required service. The relationship between time and reliability is assessed by analyzing asset behavior to understand potential modes of failure. This analysis is a core aspect of reliability-centered maintenance, and is more typically used on short lived assets.
Figure 4.8 Example of a Probabilistic Model
Source: Adapted from Transportation Research Board. 2012. Estimating Life Expectancies of Highway Assets, Volume 1: Guidebook. https://doi.org/10.17226/22782.
Accounting for Uncertainty in Asset Performance
Performance modeling uses historic data to estimate future performance; however, not all future events are predictable nor is past performance necessarily a predictor of future performance. This section considers the how uncertainty can be introduced into the analysis.
The unpredictability of future events introduces uncertainty into prediction models. Additionally, the amount of uncertainty tends to increase with time so their affects are compounded. As outlined in the previous section, probabilistic modeling is one approach that can be used for accounting for uncertainty, but what level of uncertainty is acceptable?
To minimize uncertainty, an agency must first understand the source of the uncertainty. A common type of uncertainty related to asset management is the behavior of the assets themselves. Due to the advancement of technology and knowledge and differences in materials and construction practices, there can be significant differences in performance between otherwise similar assets. The change in behavior can be positive, such as the introduction of epoxy-coated reinforced steel in bridge decks to delay the onset of corrosion from road salt intrusion or the introduction of Superpave and performance graded asphalt binders to reduce pavement cracking and rutting. Other changes in behavior are less easy to predict, such as the impact of salt intrusion on prestressed, post-tensioned concrete box-beam bridges. Other sources of uncertainty include:
- Weather events, e.g. flooding, drought, or freeze-thaw
- Climate change
- Traffic accidents
- Data inaccuracies
- Inaccurate models
- Poor assumptions
Uncertainty caused by variability in the data can often be addressed through the development of quality assurance plans that describe the actions an agency has established to ensure data quality, whether the data is collected in-house or by a contractor. Common quality assurance techniques include documented policies and procedures to establish data quality tolerance limits, independent reviews of collected data, and training of data collection crews. Data management strategies are discussed in more detail in Chapter 7.
To evaluate the accuracy of models and assumptions, agencies can include multiple scenarios in their life cycle planning analysis to test the impact of different decisions. This type of sensitivity analysis can be helpful in identifying areas in need of further research or developing contingency plans if the initial assumptions turn out to be inaccurate.
To understand whether time and effort should be invested in minimizing uncertainty, a risk-based approach can be used. Assuming the consequence arising from a defined issue or event remains the same, the cost in terms of data collection of reducing uncertainty can be investigated. As an example, the condition state of an asset, as determined using a visual approach, may not provide the required level of insight, which results in poor or unknowable treatment decisions. To minimize the uncertainty, extra testing can be carried out. The level of testing would be defined by the risk-cost reduction ratio. Similarly, with climate change, how much would have to be invested in studies to understand the effects on asset longevity? Thus, through risk management, an agency determines which risks are tolerable and which must be actively managed through investigations, studies other research. The risks are identified, prioritized, and tracked using a risk register (see Chapter 2). For those risks that should be managed, plans are developed to outline actions that will be taken to mitigate threats or take advantage of opportunities, as discussed in Chapter 6.
Halifax Regional Water Commission
Halifax Regional Water Commission (Halifax Water) has employed a deterministic modelling approach to create a plan for their storm water assets. The management system was used for long-term planning their culvert portfolio (approximately 1744 cross culverts on 3700 lane km of regional roads). The software uses deterioration curves, a temporal model periodic simulation model and has integrated Geographic Information System (GIS) capabilities.
Initially the analytical objective of the model was to maximize the average condition of all the culverts and minimize the investment. Several constraints were embedded within the initial model analysis including:
- Non-Increasing percentage of culverts in critical condition
- Replace all culverts that exceed expected useful life
- Budget not to exceed scenario
The scenario analysis allowed Halifax Water to establish a minimum investment level required to bring the portfolio to an acceptable average condition state, have a reliable forecast of future condition trends, and quantify an estimate of accepted risk of failures. The figure below shows the agency’s forecasted risk of failure over time based on the selected strategy and projected funding.