GO OR NO-GO DECISIONS AT THE CONSTRUCTION WORKFACE: UNCERTAINTY, PERCEPTIONS OF READINESS, MAKING READY AND MAKING-DO Ergo Pikas 1 , Rafael Sacks 1 and Vitaliy Priven 1 ABSTRACT Construction work is performed at the end of a chain of decisions made by the individuals involved in planning the work at increasingly detailed levels of resolution. At each step planners make decisions based on their perception of the state of readiness, or maturity, of the work, but there is always, by definition, some residual uncertainty. Therefore, fine-grained planning decisions are often required even after commitments are made in weekly work planning using the Last Planner ® System. These decisions can result in abandoning (or stopping) the planned work or improvisation or ‘making-do’. However, the motivations and context of these decisions are not well understood. Empirical data collected over eleven weeks at a large residential construction project enabled synthesis of a taxonomy of scenarios and proposal of a candidate flow chart of the decision-making process at the operational level. In doing so, we define questions for future research concerning the impact of uncertainty on decision-making in this context. KEYWORDS Last Planner ® System; Make-ready; Making-do; Decision making; Individual behavior and motivation; Task maturity; Uncertainty. INTRODUCTION Much of lean construction research and practice has focused on creating reliable and stable workflows. Koskela’s introduction of the flow view of production in construction, within the Transformation-Flow-Value theory (Koskela 1992; Koskela 2000), together with the work of Howell et al. (Howell, Laufer et al. 1993), paved the way for research of the impact of instability on construction flows. The subsequent work of Tommelein et al. (Tommelein, Riley et al. 1999), Bertelsen et al. (Bertelsen, Henrich et al. 2007; Bertelsen and Sacks 2007), Sacks et al. (Sacks, Esquenazi et al. 2007) and others exposed the direct link between instability in production and measures of throughput, work-in-process and cycle times. The parallels with the theory of production in manufacturing, as set out by Hopp and Spearman (Hopp and Spearman 1996), with special emphasis on Little’s Law, were drawn. The Last Planner ® System (LPS) (Ballard 2000) was devised for the purpose of achieving reliable and stable workflows, and many in the construction industry 1 Virtual Construction Laboratory, National Building Research Institute, Technion – Israel Institute of Technology, Haifa 32000, Israel +972-4-8292245, epikas@tx.technion.ac.il; cvsacks@technion.ac.il; vitaliyp@tx.technion.ac.il