Applying Other Life Cycle Management Approaches
Assets that are managed using an interval-based or reactive management strategy require different approaches for planning and optimizing work than assets managed using condition. The life-cycle plans for these assets range in terms of sophistication depending on the available data.
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 five 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 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.
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.
Nevada DOT recognized that the level of investment in ITS equipment (e.g., closed-circuit cameras, dynamic message signs, flow detectors, highway advisory radios, environmental sensor stations, and ramp meters) was increasing significantly and the importance of this equipment to network operations was growing. As a result, the DOT chose to establish a method of managing its ITS assets that would minimize the risk of failure and provide information to support budgeting activities. However, since the DOT had limited data on its ITS components, a process was developed that relied on the following factors to establish maintenance cycles:
- Historical performance
- The typical timeframe before the software became outdated
- Manufacturer recommended service life
- To determine the condition of ITS traffic cameras, Nevada DOT developed a transition probability matrix with four condition criteria based on the device manufacturers’ recommended service life as follows:
- Good – device age is less than 80 percent of the manufacturer’s recommended service life
- Low risk – device age is between 80 to 100 percent of the manufacturer’s recommended service life
- Medium risk – device age is between 100 to 125 percent of the manufacturer’s recommended service life
- High risk – device age is greater than 125 percent of the manufacturer’s recommended service life
The transition probability matrix was used to model ITS asset deterioration and program maintenance actions over a 10-year analysis period via the use of a simple spreadsheet tool. The results of this analysis showed an interval-based approach to managing ITS assets would result in an estimated savings of $1.1 million over a 20-year period.
Source: Nevada DOT TAMP (2018)
Colorado DOT responds to between 50 and 70 geotechnical emergencies a year. The traditional approach to managing rockfalls was based on the size and frequency of rockfalls. This approach did not consider the criticality of the facilities that could be impacted by a geohazard event. Since 2013, the Colorado DOT has used a risk-based approach to evaluate and prioritize geohazard mitigation activities based on the size of the geohazard areas and the frequency of falls. Colorado DOT’s approach includes a measure of Risk Exposure (RE), which is based on three components:
- Average Annual Daily Traffic (AADT).
- Likelihood of a Vehicle Being Affected by a Geohazard Event. This metric considers site-distance, the number of previous rock-fall accidents, and a measure of how frequently a vehicle is below the hazard on a daily basis.
- Reduction Factor. This considers the effectiveness of prior mitigation actions, to reduce the RE score.
Colorado DOT’s geohazards program uses the RE to allocate an annual budget of about $10 million to manage geohazards. Due to the inherent uncertainty of geohazard management, in addition to the geohazard management program, maintenance staff regularly patrol highways known to have geohazards. If a hazard requiring immediate action is identified, maintenance crews respond promptly. Using the RE for prioritization allows Colorado DOT to focus its efforts on reducing the impact of geohazards on users of the highway system.