Flexible strategies for long-term sustainability under uncertainty

Assessing the economic and environmental life cycle impacts of long-lasting construction projects presents numerous methodological challenges. Three advances over established methods are presented for the life cycle evaluation of construction projects. First, future uncertainty during the project life or study period is explicitly accounted for. This involves moving from a deterministic approach requiring precise data to a probabilistic approach where uncertain variables are defined by ranges. The outcome of life cycle evaluation is then given by probability distributions, generated by Monte Carlo simulation. Second, flexible strategies are considered that allow for adaptation to changing conditions during the project life. Flexible strategies (also modelled by Monte Carlo simulation) incorporate specified life cycle options which are exercised if it is advantageous to do so, otherwise they remain unexercised. Third, cost-based life cycle costing (LCC) and environmental life cycle assessment (LCA) are linked in a single LCC+A evaluation tool. There are still differences between cost and environmental evaluation, but the use of a shared framework enables the two aspects to be compared systematically. The two-dimensional ecoportfolio diagram presents one way of analysing results. The innovations are demonstrated in a case study that assesses both economic and environmental impacts while accounting for future uncertainties.