6.2.1 Types of Performance-Based Data to Monitor

Differences in Performance and Condition

The terms ‘performance’ and ‘condition’ are often used interchangeably, although they have different meanings in a performance-based environment. The performance of an asset relates to its ‘ability to provide the required level of service to customers3’ while condition is generally considered to mean the observed physical state of an asset, whether or not it impacts its performance. For example, a bridge with scour may continue to perform adequately in the short-term even though it may receive a low National Bridge Inventory (NBI) rating because of the deterioration.

Inventory Information

An asset inventory provides information other than performance data important for estimating the amount of work needed, identifying the location of work in the field and determining characteristics capable of influencing the type of work to be performed. The RCM approach introduced in Chapter 4 can be used to help an agency determine what information is needed to support the management of each type of asset. The asset inventory requirements for those assets managed based on a specified interval for repair, such as pavement markings, is very different than those required for an asset managed using a condition-based approach, such as pavements or bridges. Regardless of how detailed the asset inventory is, it is important an agency establish processes to ensure data quality and keep the inventory current over time.

There are several basic data attributes essential to effectively managing transportation assets, including asset type, quantity and location. Additional information that is important is to differentiate between the types of work to be performed, which may also be added to the inventory, the type of material used to construct the asset, the last time work was performed and factors influencing the use of the asset (e.g. traffic levels, highway functional classification or climatic conditions).

As discussed in Chapter 7, managing asset inventory information using an integrated approach to data management helps promote consistency in asset data across an agency and provides access to help ensure the data is used by decision makers at all levels of the organization. An out-of-date inventory makes it difficult for an agency to estimate work quantities accurately for budgeting purposes.

Condition Information

Asset condition information is used to determine how assets are performing and how performance changes over time. The lack of condition information may lead to premature or unexpected failures with the potential to be very costly, negatively impacting system performance and increasing agency risks. Methods of collecting asset condition information are discussed further in Chapter 7. To ensure that condition information remains current, it is important that the information is updated on a regular basis.

Asset Condition

There are several approaches for assessing asset conditions, each of which is influenced by the type of asset and the resources available to support the process. Typically, an assessment of asset condition involves a method of evaluating the presence of deficiencies and/or deterioration at the time of inspection. The results are used to assign a rating or LOS used to determine the need for maintenance, rehabilitation or replacement now or in the future. Asset condition ratings may also be used to establish rates of deterioration, allowing an agency to forecast future conditions for planning purposes.

Examples of commonly used types of asset condition ratings are listed below.

• A pavement condition index based on the type, amount and severity of distress present, which could be on a 0 to 100 scale, with 100 representing an excellent pavement.
• The National Bridge Inventory (NBI), which assigns a rating between 1 and 9 based on the deterioration present in each element (deck, superstructure, substructure and culvert).
• A LOS rating of A to F for maintenance assets, such as the percent blockage in a culvert or the percent of guardrail not functioning as intended.

Maintaining asset condition information is important for evaluating performance to determine whether improvements are needed to achieve the agency’s strategic objectives. The lack of current condition information, or a lack of confidence in the condition information, makes it difficult to present investment needs to stakeholders with any degree of confidence.

Asset Performance

The results of condition surveys or inspections are used to evaluate the performance of each asset in terms generally understood by stakeholders, such as Good, Fair or Poor.

It is common for transportation agencies to report the percent of the network in Good or Fair condition or the percent of drivers traveling on roads in Good and Fair condition. Asset performance can also be reported in terms of a health index, such as the Remaining Service Life (RSL) used by some state DOTs to indicate the amount of serviceable life left in the asset. In the maintenance community, some state DOTs have developed a Maintenance Health Index or overall LOS grade to represent the performance of the entire Maintenance Division rather than report the grades of each category of assets separately.

Asset performance also influences overall system performance, as demonstrated by the impact on system reliability associated with unplanned road or bridge closures due to flooding or an on-going lack of maintenance. Performance data related to delay, unplanned closure frequency, GHG emissions, and crash locations may all be impacted by asset conditions and affect an agency’s ability to achieve its broader, strategic performance objectives such as system reliability, congestion reduction, environmental sustainability, and freight and economic vitality. For example, it is important to monitor performance characteristics such as travel time reliability to determine whether capital improvements are needed to add additional lanes or whether ITS assets could improve traffic flow during peak periods.