4.2 Common Approaches to Managing Transportation Assets

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.