The potential applicability of the Life-Quality Index to maintenance optimisation problems

The Life-Quality Index (LQI) is a tool for the assessment of risk reduction initiatives that would enhance safety and quality of life. The paper evaluates the impact of road maintenance programs on the quality of life in the Netherlands using the LQI method. The LQI is calibrated using the specific economic and demographic data for the Netherlands. A preliminary cost-benefit analysis shows that the current road maintenance program is beneficial to the Dutch society. The paper also concludes that the LQI can be promising in supporting decisions for structure and infrastructure maintenance. 2 INFRASTRUCTURE MAINTENANCE IN THE NETHERLANDS To optimise the maintenance of structures and infrastructures, the Netherlands Ministry of Transport, Public Works, and Water Management (Rijkswaterstaat) has defined the so-called Basic Maintenance Level (BML) that should be satisfied against lowest life-cycle costs. 2.1 Basic Maintenance Level (BML) Usually, maintenance is defined as a combination of actions carried out to restore a structure to a specified condition in which the structure can perform its required functions. Rijkswaterstaat refers to this specified condition as the basic maintenance level (BML) for structures (Klatter, 2003). In defining the BML, Rijkswaterstaat identifies the following five functions (see also Klatter et al., 2006): 1. Mobility (structural reliability, availability, maintainability); 2. Traffic safety (probability of no harm – injury or death – to human beings); 3. Life quality (personnel safety, human health, well-being, environment, noise nuisance, sustainability); 4. User comfort (road surface, risk perception); 5. Aesthetics (design and colours of a structure, absence of graffiti). In civil engineering, a failure is often condition failure (disability of a structure to perform its required functions within constraints of legal safety margins), whereas in mechanical engineering failure is often physical failure (breakdown). In structural engineering, condition failure generally means that the probability of a collapse is unacceptable high. Rijkswaterstaat is currently investigating the risks of a structure’s disability to satisfy the BML during a pre-specified reference period. In maintaining the BML against the lowest possible costs, the total costs should ideally be considered over the whole life of a structure or infrastructure. Generally, the following lifecycle phases can be identified: design, construction, use, and demolition. All costs should be considered, regardless of the funding source. Therefore, life-cycle costs should not only include the direct costs of construction, maintenance, and demolition, but also the indirect costs to the society and environment. In defining and maintaining the BML, the user benefits should be taken into account as well. Therefore, effective maintenance should also consider possible user benefits with respect to mobility, traffic safety, life quality, user comfort, and aesthetics. Unfortunately, as pointed out by Besseling et al. (2004) and Ruijgrok et al. (2004), the contribution of maintenance measures to the user benefits is largely unknown, because these costs are very hard to quantify. In the opinion of the authors, the Life-Quality Index has great potential to quantify the impact of life-quality related benefits of a maintenance program. 2.2 Costs and benefits of the infrastructure users In general, the longer the maintenance is postponed, the lower the BML and the higher the user costs. In this respect, the following user costs are important to consider (Besseling et al., 2004): mobility (the lower the BML, the higher the unavailability and the more restrictions on vehicle weights and speeds), traffic safety (the lower the BML, the larger the probability of a traffic accident), life quality (the lower the BML, the rougher the road surface and the more fuel consumption, tire wear, and noise nuisance), user comfort (the lower the BML, the less comfortable the driving and the higher the risk perception), and aesthetics (the lower the BML, the higher the risk perception). On the other hand, maintenance can increase user costs in itself. Major road maintenance works can cause traffic jams and increased risk of fatal accidents. They concern both traffic safety and personnel safety. The current BML in the Netherlands is relatively high. The Dutch roads are among the safest among the European Union and are becoming safer, despite the increased car traffic. Furthermore, restrictions on vehicle weight and speed (in addition to legal limits) due to a backlog of maintenance are exceptions. In 2002, the number of traffic fatalities was 1,066, which decreased by almost 30 percent since 1996 (Rijkswaterstaat, 2004). On the other hand, the number of emergency repairs increased from 400 in the year 2000 to 750 in the year 2002 (Besseling et al., 2004). Unfortunately, a quantitative relation between the state of maintenance and the traffic safety cannot be derived using available data. 3 LIFE-QUALITY INDEX To avoid failure, preventive maintenance is performed. In order to determine an appropriate maintenance strategy, we need to balance the costs of maintenance and failure. The consequences of failure can be subdivided into monetary and non-monetary losses (Maes et al., 2003). Monetary losses deal with direct and indirect economic losses, such as damage, repair, loss of assets, production losses, loss of appearance, loss of service, user delay or inconvenience, and impact on growth and employment. The costs associated with such consequences are relatively easy to value. Non-monetary losses represent losses suffered by individuals or groups of individuals. They include death, maiming, injury, loss of long-term income, emotional distress, loss of valuables, social disruptions, and environmental damages. The “costs” associated with these consequences are much harder to estimate. Non-monetary cost can be dealt with using the Life-Quality Index. If maintenance improves the life quality, it must be quantifiable in terms of money or life years and it can be included in the LQI. On the other hand, if the improvement is purely abstract (“feel better kind of thing”), then the LQI or any other measure is of no help. An advantage of the LQI is that a direct estimation of the value of human life is avoided. Instead, the LQI focuses on wealth, long life in good health, and leisure.