### Lean Construction Management and the Last Planner(r) System  
The term lean construction management (LCM) is derived from lean principles being applied in the production industry and refers to the original concepts of the Toyota Production System (TPS). One of the core elements of lean management, in general, is the aim for maximization of value from the customer's perspective by eliminating waste. Waste in the construction industry can e.g., be referred to as rework or waiting time [35].  
The Last Planner(r) System has been developed for the construction industry as a production planning and controlling system. It aims at both increasing schedule reliability and smootheningflow of work [36], and is been considered as one of the most import lean methods in construction execution [10]. The LPS strives for the achievement of its purposes through collaboration, transparency, continuous improvement as well as reliable commitments from the responsible persons for actual work completion, the Last Planners [37].  
According to [PERSON] [36], every possibly occurring task, needed for the completion of a construction project, can be technically categorized into four groups during its execution phase: (1) SHOULD-tasks include in principal all tasks needed for achieving global milestones defined by an existing master schedule or client's requirements. (2) CAN-tasks for a preliminarily defined project look-ahead window consist out of SHOULD-tasks, which are free of constraints and thus ready for immediate execution. (3) WILL-tasks are considered as CAN-tasks whose execution by a defined due date has been assured by consensus of all involved and explicitly by the responsible last planner. (4) DID-tasks in turn, are all accordingly completed WILL-tasks of the preventient LPS-cycle. The latter ratio in LPS applications can be expressed as a percent planned complete value (PPC).  
The SHOULD-CAN-WILL-DID (SCWD) logic is supposed to be applied in five consecutive steps which are characterized by corresponding plan phases with increasing level of detail: (1) master scheduling, (2) phase scheduling, (3) make-ready-planning, (4) commitment-planning and (5) learning and control [38]. This procedure is shown in Figure 2.  
The least mentioned step learning and control accounts for the analysis of completed tasks with respect to their commitment. Crucial at this point is a profound analysis of reasons for non-completion (RNC) of tasks that have not been completed as committed in terms of both quality and due date in order to avoid those mistakes to re-occur, as part of a continuous improvement process (CIP) [39].  
Of equal importance is the social process going along with the implementation and application of the LPS in construction projects. These interpersonal matters are especially characterized by open and transparent discussions between involved trades represented by their last planners, increasing trust among them as well as collectively emerging learning cycle effects. The latter can be seen as an inherent consequence of the analysis of RNC [40; 41].  
According to [PERSON] [36], the main advantages of the LPS include the following points:  
* Stabilization of project-based production systems
* Making control proactive  
Figure 2: Last Planner® System (LPS), adapted from [PERSON] and [PERSON] (2010).  
* Reduction of waiting times and project durations
* Decentralization of decision-making processes
* Early communication of insufficient project status  
As with many lean-based process changes, the necessary commitment of all those involved and thus resistance to change can be stated as disadvantages. At the process level, it should be noted that the LPS does not offer any functionalities with regard to cost control and is therefore not sufficient as the sole method for holistic project management with regard to the optimization of the three target variables quality, time and budget.