The inputs for lifecycle planning are as follows:
Asset inventory:This is the number, size, and/or dimensions of the asset that is to be analyzed. For a pavement maintenance project, this will be the length and width of the treatment area.
Analysis period: This is the duration over which the maintenance costs are to be evaluated. It should extend over at least one full lifecycle of the asset/treatment under consideration. Once an analysis period has been selected, it must be consistently applied across all maintenance options that are under consideration. Failure to do so will prevent meaningful comparisons between the lifecycle plans.
Treatment options: A treatment option needs to be selected for the lifecycle plan and can be prescribed for each maintenance strategy. Options could range from small-scale superficial works to wholesale replacement or reconstruction. A range of materials options or specification types should be considered. For a pavement maintenance project, treatment options will likely include a range of treatment depths.
Service life: The service life of an asset or treatment will determine the timing of future maintenance interventions. The use of realistic, achievable service lives is of primary importance in lifecycle planning. Service lives should be determined locally and be based on a number of factors, including performance history, material type, specification (including construction practices and workmanship), local environment, and demand (such as traffic levels and energy consumption, not necessarily applicable to all assets). These factors are based on practical experience, but they could be amended to suit local practices or performance histories.
Unit rates: This is the cost per unit measure (number/length/area/volume) to maintain an asset or part of an asset. It could, for example, be the price per square meter to apply a particular resurfacing treatment to a carriageway or the cost to replace a single lighting column. It is important that the engineer appreciates what is included in a particular rate and is aware of any assumptions that were used in deriving its value. This is considered to be essential to arrive at an accurate works cost.
Works costs: This is the direct cost of undertaking planned maintenance activities on site. Unit rates are used to estimate the works cost. The cost of site establishment, traffic management, and preliminaries should be included.
Routine maintenance costs: These are the (direct) ongoing costs of maintaining an asset in a safe and serviceable condition. These costs exclude cyclic activities such as sweeping and cleaning (because these are normally constant factors that will not vary according to treatment strategies or types). Routine maintenance costs need to be factored into the lifecycle plans if competing maintenance strategies are likely to result in significantly different ongoing costs.
Discount rates: Discounting is a technique used to compare costs (and benefits) that occur at different times throughout the analysis period. It works by adjusting these future costs (and benefits) to their present-day values. This practice enables competing maintenance options to be compared on a common basis, in that once a discount rate has been selected, it must be consistently applied across all maintenance options that are under consideration. Failure to do so will prevent meaningful comparisons between the whole-life costing results.
The outputs from the lifecycle process are as follows:
Investment strategy: The maintenance strategies, timing, and (direct and indirect) costs determined above will enable the production of a profile showing future investment in each year of the analysis period. By analyzing cost profiles across a program of works, it is possible to identify instances in the future where major works on several projects may coincide in a single year. These instances may pose future funding issues (and create network management and workload issues). Alternative maintenance strategies can then be considered to alleviate peak demands.
Discounted works cost: This is the present-day cost of all future maintenance requirements. It provides a basis for comparing alternative maintenance options and indicates the level of investment that will be required to meet future expenditure.
Once the need for maintenance has been identified, the input parameters above can be used to undertake a lifecycle analysis by considering the maintenance strategy to be adopted:
Do Nothing: Under this strategy, the organization would undertake reactive repairs for safety defects only. These repairs are likely to be superficial and would possibly be temporary in nature. The repairs would not arrest the decline of the asset, and frequent revisits are likely to be required. In the short term, routine maintenance costs are likely to be high due to the ongoing liability.
Do Minimum: Under this approach, the organization seeks to do the minimal amount of routine maintenance work to keep the asset safe and serviceable. Works will normally be restricted to the repair of safety defects; repairs will normally be permanent in nature, although they will add no value to the asset. In the context of a pavement project, this approach might be limited to the permanent repair of potholes only. These repairs would be undertaken on an isolated basis or may extend to small patches.
Do Something: This approach is likely to involve capital expenditure by an organization rather than routine expenditure. It may include the wholesale replacement or major repair of an asset to a level that will enhance its long-term durability and minimize future routine maintenance. A proactive approach may also be adopted, which means that repair takes place before the condition intervention level is reached. In the context of a pavement project, this approach could see the treatment of a section of pavement classified as being in need of maintenance.
It is recommended that more than one Do Something strategy is evaluated for each maintenance strategy in order to explore the range of available treatment types. For the Do Something strategies, the required timing of the initial maintenance intervention requires consideration. Options may include
If the latter (deferred) option is selected, then the additional routine maintenance costs need to be included in the lifecycle plan. In the context of a pavement project, the above factors could be realized. For example, a pavement nearing the end of its serviceable life may exhibit surface defects, such as potholes. If the initial treatment is deferred, then there will be an ongoing (possibly increasing) requirement to revisit the site during the period of deferment to carry out repairs to these defects. The costs of these repairs need to be included in the lifecycle plan. If the initial treatment is deferred, then more deterioration may occur to the pavement structure. This may result in a more extensive treatment eventually being required compared to the treatment that would otherwise have been implemented if the site were repaired earlier. By considering a range of treatment strategies and permutations on the type and timing of the initial intervention, an optimal maintenance strategy can be determined.
The maintenance strategy with the lowest net present value (NPV) is generally regarded as the most economically beneficial option (see Error: Reference source not found.4). However, whole-life costing is only one factor when selecting a preferred maintenance option. Other factors, such as engineering judgement, network operations, buildability, affordability, and risk management, also require consideration.
An organization may implement the above process according to its skills and capabilities, including data availability and performance models, as follows:
Where insufficient data are available, a more basic approach to lifecycle planning may be sufficient to meet the requirements of the organization. However, even standard approaches require data on asset hierarchy, inventory, and service life (estimated life of the treatment option). This approach may require assumptions to be made based on the experience and local/technical knowledge of the staff involved in the process. This experience and knowledge may include quantum as well as the current and predicted future performance of the asset. Any assumptions need to be documented and any significant risks set out.
A more advanced approach is likely to require higher quality data for performance or deterioration modelling in order to determine the service life of the proposed treatments (as described above). Subsequently, additional investment in data collection and asset management tools may be required in order to analyze and interrogate these data. Where this is the case, the argument should be made for any additional investment based on the benefits and efficiencies that can be obtained through adopting a more advanced approach.