Scope of This Paper
Initially, the main purpose of the scope of this paper was as an addendum to the estimate of life cycle cost and revenues, to make the owners fully aware of the limitations of the estimate itself.
However, planning and scheduling long-term projects cannot be performed with the usual methods and tools that we normally use for our day-to-day projects. That is to say that deterministic methods are not enough. The inclusion of a proper, higher margin for contingencies, and work variation can help up to a certain point. However, it does not make any more sense if such margins then become a substantial part of an estimated time and cost.
If a project is planned to last 10 years or more, we need to use a fully stochastic planning method that allows the use of probability and constraints. Even these methods will not help in the case of changes in the scope of the works, changes that can be neither foreseen nor kept under control. The project framework can be modified due to owner related events, or to major political events, as well as to causes normally considered as force majeure. In such cases, budgeting becomes highly subject to chance and probability.
It the case relevant to the bridge on the Stretto di Messina, the tender documents included for a calculation of life cycle costs and revenues over a time span of 30 years plus an additional 30 years, for a total time span of 60 years.