The process of developing cost estimates on the Big Dig was necessarily evolutionary. It is not possible at the beginning of such a large, lengthy, and complex project to anticipate, with precision, all final design and program decisions that will be made by the state and other interested parties, as well as the extent and nature of unanticipated conditions that impact cost and Key Facts 6 schedule. Nor is it possible to predict, with accuracy, the fluctuating bid climate and related market conditions that may exist throughout the life of a long project. As decisions were made and conditions evolved on the Big Dig, however, B/PB factored them into its cost assessments and kept the client fully informed, even in the face of strong political pressures