Virtually all transportation infrastructure assets are designed to have long service lives, lasting years or even decades. This means life cycle management must include long-term predictions that come with inherent uncertainty. Further complicating matters, the condition or performance of some assets may be difficult, expensive, or impossible to discern. This is most common with geotechnical assets or hidden elements on complex structures. Addressing this uncertainty requires integration with the agency’s risk management practices, and consultation with technical experts, such as hydraulics and geotechnical engineers. Risk management practices are discussed in more detail in Chapter 5. This section highlights how uncertainty should be considered when selecting a management strategy to maximize service life and address risk.

Condition-Based Management

A condition-based management approach is the life cycle management approach that is the most commonly associated with asset management at U.S. transportation agencies. In condition-based management the condition of an asset is measured, and used to forecast and identify the onset of failure. Maintenance and preservation activities are identified to address the failure and restore or extend service life. While the objective of asset management is to support the reliable performance of the asset, the performance measures most commonly used for physical assets are condition-based. Agencies that are very advanced in their asset management practices may be able to apply the condition-based management approach to other aspects of asset performance.

Condition-based management relies on the collection and analysis of asset condition and defect data. This data is then used to understand the current state of individual assets and when aggregated is used to predict the future condition state of similar asset types. When linked with intervention data and condition threshold information, the future impact of potential actions can be assessed, all with the view of optimizing an asset’s service life cost-effectively. Accordingly, a condition-based management approach combines condition monitoring with performance predictions and knowledge of preventive or restorative actions, to establish a cost-effective life cycle plan. The condition-based management approach can be applied to simple and complex assets, groups of single assets or a whole network. In a network perspective, components could be individual assets such as pavement segments and bridges and at a project level, components could be elements of individual assets.

Interval-Based Management (Age Based)

Interval-based Management is most commonly applied to operations assets (striping, signs, guardrail), where just an inventory is maintained. Condition assessments may not be financially feasible or practical. Additionally, these assets are often related to compliance, meaning their condition state either meets a specific standard, or does not. With interval-based management, asset performance data or manufacturer’s suggested life estimates are used to establish a time interval representative of the service life beyond which the cost of asset failure outweighs the cost of replacement. The service life being the average life that all assets or components of a type are expected to last. Cyclically applied interventions can also be classed as interval-based management strategies, as there is fixed period between a set of predefined actions that have to be taken. An interval-based approach is most commonly applied to manufactured assets with highly uniform performance levels. It is less applicable to assets constructed on site or long-lived complex assets where there is a greater level of uncertainty surrounding the expected life of the asset. Examples of the types of assets that are often maintained on an interval-based approach are signals, ITS equipment, and other mechanical and electrical related items.

Reactive Management

Reactive management unlike condition or interval maintenance does not use forecasting to understand the likely timing of an intervention. Accordingly, reactive management excludes all or most actions to address asset condition or performance, until the asset reaches an unacceptable condition state. The condition state may be influenced by accumulated deterioration or a specific event, like a crash or intense storm. Reactive-management is commonly applied to low-value or less critical assets, redundant assets, or assets for which failure represents an acceptable risk. To create a reactive-based management strategy, minimum acceptable condition thresholds, must be defined. Reactive management strategies often require an agency to have a mechanism to deliver required work within a specified time frame, to avoid unacceptable levels of risk. This may include properly staffed and equipped in-house maintenance forces or “stand-by” contracts, so work can be dispatched and delivered quickly. Examples of assets managed using a reactive-based approach include fences, brush, lighting, raised pavement markers, impact attenuators, and rockfall.

Factors for Comparing Life Cycle Management Approaches

Failing to achieve a service level target requires an intervention, or reassessment of the reasonableness of the target. If improvement is required, selecting a management strategy is a function of where performance is insufficient. Safety improvements can reduce crash rates, additional lane capacity can improve travel time reliability, operational enhancements can improve emergency response rates and road availability during inclement weather. Where condition is below target, at a network or corridor level, interventions may be required in multiple areas.

Selecting interventions to achieve condition targets for an asset class or subclass is a data-driven, risk-based process. It evaluates what circumstances lead to asset failure, the subsequent consequences of failure, the options available to avoid failure and their costs. Costs should include the cost to monitor/analyze/ manage an asset in addition to the cost to repair. Based on an understanding of these factors, an agency can determine what strategy will be the most appropriate. The three management strategies introduced in the previous section are incorporated into Table 4.2 along with summaries of the various factors used to compare the approaches.

Reliability Centered Maintenance

Several of the principles described in this section are based on a Reliability Centered Maintenance (RCM) approach, a technique that is sometimes used by an agency to identify the most appropriate management method. Looking at an asset or asset class from an RCM perspective helps to select a management approach based on safety, operational and economic criteria. RCM is commonly applied to complicated assets that may require a range of management approaches for different components of the asset.

The RCM process has its roots in the aviation industry related to the mechanical components of aircrafts, but has been adopted across multiple industries for mechanical, electrical and infrastructure assets. Within the highways industry RCM has been considered for ITS assets. More information on the use of RCM for ITS assets has been published by Austroads (2016): Reliability-centered Maintenance Strategy and Framework for Management of Intelligent Transport System Assets.

RCM considers seven fundamental questions to select the most appropriate management approach for a set or type of assets (SAE International 2009). These questions can be applied to the selection of life cycle management approach. Based on the responses to these questions, an agency can determine what maintenance approach, for which parts of the asset, will maximize the likelihood of an asset performing its desired function for the lowest practicable cost. These questions are as follows:

• What is the item supposed to do and what are its associated performance standards?
• In what way can the asset fail to provide the required functions?
• What are the events that cause each failure?
• What happens when each failure occurs?
• In what way does each failure matter?
• What systematic task can be performed proactively to prevent or diminish to a satisfactory degree the consequences of the failure?
• What must be done if a suitable preventive task cannot be found?

RCM can be presented in a decision tree to aid agencies in selecting the best management approach. Agencies can also customize the questions and decision tree to meet their specific need. Figure 4.6 represents a portion of a decision tree customized to select the appropriate management approach for ancillary highway assets. By applying these questions to an asset class, an agency can prioritize asset classes for monitoring and active management. An agency can also determine which assets present limited risks to system performance and can be managed through less expensive means.

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.

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

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.

Probabilistic Modeling

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 4.7. 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.

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
• Earthquakes
• 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.

When to Use Approaches Other than Condition-Based Management

Condition-based management requires a commitment to reliable asset condition information. The necessary level of effort is not likely to be appropriate for some assets. Some assets do not lend themselves to management using a traditional condition-based management approach. The four most common reasons assets do not fit a condition-based approach are as follows:

• The assets do not have a typical life cycle – This group of asset classes includes rock slopes or other perpetual features that do not have predictable deterioration patterns.
• The assessment of condition or performance may not be feasible – The most common type of assets in this second group are geotechnical or utility assets for which many elements may be buried or otherwise inaccessible. The absence of a rating methodology may also drive the management of assets using something other than a condition-based approach.
• The life cycle is driven by factors other than condition – There are many assets that are replaced when they are worn out or obsolete. Technology assets, which are susceptible to obsolescence at a frequency similar to their functional service lives, are examples of assets that fall into this category.
• The assets have long service lives and the failure of individual assets presents limited risks to safety or system performance – Examples of these asset classes include guardrail, gravity retaining walls, or highway lighting.
• The performance expectations require the asset to remain in near-new condition. For safety-critical assets, replacement may be necessary before signs of deterioration are evident. This is most common in risk-averse industries such as aviation. However, contractual arrangements, such as in public-private partnerships (P3), may require condition or performance targets that warrant a life cycle management approach other than condition-based.

As discussed earlier, assets that fall in these categories are typically managed using an interval-based approach or a reactive approach. Some agencies also use a risk-based approach for certain types of assets, such as rockfall management. These three different approaches are briefly explained, and examples are provided for each approach.

Alternative Life Cycle Management Approaches

Three alternative life cycle management approaches are discussed in this section. These are interval- or age-based strategies, reactive strategies, and risk-based strategies.

Interval- or Age-Based Management

Interval- or age-based strategies can be utilized for failure-critical assets, assets subject to obsolescence or assets with no or limited maintenance actions. Age-based strategies replace assets after a given time in service without regard to the asset’s condition at that time. This approach can also be used for very short-lived assets, such as paint markings. Advantages include proactive minimization of failure and reduction of uncertainty in funding needs. An agency that replaces signs on a 7-year cycle or replaces pavement lane markings annually is using an interval- or age-based approach to manage its assets.

Interval-based strategies are also useful for assets that do not show physical wear, but are safety- or operations-critical.

Reactive Management

Reactive strategies can be used for assets that have long service lives and limited maintenance options. Reactive strategies can be based on the results of an on-going monitoring program or on event reporting. Examples of assets that may be monitored periodically to check that they are working as intended includes retaining walls and overhead sign structures. Assets that may be more likely to be maintained based on a report that the asset is damaged or no longer working include light bulbs and guardrail.

Risk-Based Management

While all management strategies are risk-based, there are times when risk assessments are used directly as the measure to establish objectives, set targets, drive decision making, or assess progress. This approach is used when the condition of the asset does not directly represent the level of asset performance, and the potential impact of an asset’s condition on system performance must be considered. This approach is commonly used for managing slopes and other geotechnical assets.

This section focuses on the aspects of implementation that are most directly related to using life cycle management results to maximize the service lives of infrastructure assets as cost-effectively as possible. It highlights the need to evaluate agency policy, data issues, and work processes to support life cycle management.

Linking Life Cycle Strategies to Asset Management Policy

Agency policies influence the types of decisions that are made within an agency and the priority with which activities are funded. The life cycle management approach selected for each asset class will impact the type of policies, procedures, and data required to support investment decisions to ensure alignment between planned and actual work activities.

Aligning the organization to support the implementation of life cycle management strategies involves many of the same types of organizational change processes discussed in Chapter 2. As part of this alignment, an agency must ensure that it has in place the processes and resources needed to deliver the work activities required for executing the selected life cycle strategies.

Chapter 2 introduced the importance of establishing Asset Management policies to help integrate asset management at all level of an organization. An Asset Management policy can support life cycle management by establishing processes for setting realistic performance objectives and treatment strategies that focus on a commitment to sound, long-term investments. The following examples demonstrate how agencies can select a life cycle approach that supports the agency’s higher-level policies.

Data Required for Implementation

All life cycle management approaches need inventory and performance information, but the extent, detail, accuracy, and precision of the required information varies greatly given the chosen approach.

Assets that are managed using a condition-based approach rely on detailed inventory and performance information so that current and future conditions can be estimated, and the benefits and costs associated with each viable strategy can be evaluated. Interval-, time-based, and reactive approaches can be performed with less detailed information about the assets. Agencies using these approaches may estimate the size and age of the inventory at early levels of maturity. Over time, the type of information available and the level of detail associated with it may improve, allowing the agency to mature in terms of its analysis capabilities.

Table 4.3 provides examples of typical management strategies for common highway asset classes and the types of information used to support each one. The information in table 4.3 reflects general trends in transportation agencies. In practice, each agency must identify the specific elements and data requirements needed to support their needs within resource constraints. Chapter 7 addresses methods of collecting information efficiently (see table 7-3) and Chapter 6 stresses the importance of keeping inventory and performance data current. Establishing data governance structures to manage asset data is also an important consideration, as discussed in Chapter 7.

Table 4.3 - Typical Maintenance Strategies and Supporting Data

Incorporating Life Cycle Management into Work Planning and Delivery

Life cycle management approaches and corresponding life cycle strategies are the means by which agencies identify the work necessary to meet their asset management goals within funding constraints. However, for those asset management goals to be met, the necessary work must actually be delivered. This requires the recommendations from life cycle analyses to be incorporated into the business processes by which the agency identifies, prioritizes, programs, designs, and delivers work. In most agencies this includes multiple business processes and funding streams. The following subsections describe how life cycle management can be incorporated into common processes within transportation agencies.

Planning and Programming

The planning process seeks to identify the set of investments that will effectively and efficiently achieve an agency’s goals and objectives. As an agency alters its approach to managing assets, this may change assumptions previously influencing the planning process. Significant changes in an agency’s approach to managing its assets can require updates to long-range or strategic plans. Similarly, changes in long-term objectives or plans can prompt a change in life cycle strategy or approach.

Coordination is needed between long range transportation planning, performance-based plans such as the TAMP, and programs of work, such as TIPS and STIPs (see chapter 2). In particular there is a need for alignment between the financial planning procedures and documentation between these different efforts and products. Although programs tend to be relatively short term, often 1 to 4 years in length, agencies must identify investment needs several years in advance to ensure projects can be delivered when required. Complex reconstruction or modernization projects can take 10 years or more to deliver from scoping to construction. Thus, it is important to keep planners informed of changes in selected life cycle strategies. Changing new life cycle strategies may lead to significant differences in the projects selected.

Project Engineering

Life cycle management is a framework for identifying the appropriate treatments throughout an asset’s service life to maximize performance. Project engineering includes the processes for packaging work into contracts for delivery. Thus, project engineering is responsible for ensuring the right treatment is delivered at the right time and within the anticipated cost. Additional details on work packaging to support asset management are provided in chapter 5.

Maintaining strong internal controls ties project decisions to their impacts on anticipated asset performance. Project schedule changes may cause inappropriate treatments to be applied to assets, resulting in unnecessarily high costs or poor performance. Scope changes often lead to cost changes, and while cost changes may be addressed for a specific project, the funds added to that project would not be available to address other system needs.

Use of Agency Maintenance Forces

Effective delivery requires adequate labor capacity with appropriate training, proper equipment, and necessary materials. Changes in an agency’s management approach can alter the requirements for any of these aspects of maintenance management. The necessary treatments cannot be delivered if a properly sized and equipped crew cannot be assembled. Maintenance staff cannot administer treatments for which they are not properly trained or correctly supplied. Therefore, it may be important to have maintenance management staff actively engaged in the process of identifying preferred life cycle management approaches.