4.2.1 Life Cycle Management Approaches

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.