Last Planner System (LPS) is known as one of the most popular Lean Construction (LC) tools, which focuses on improving the workflow of the project’s activities. This is applied through the emphasis on identifying then eliminating – or reducing – the potential time wastes that could happen during the construction phase  . Two main ingredients are essential under LPS: stakeholders’ collaboration for detecting potential time wastes and Percentage Plan Complete (PPC) parameter for tracking activities’ progress based on the estimated duration. Tracking activities progress is definitely important and it is what distinguishes LPS, but what about productivity progress? Is there a way to include it?
To answer these questions, let’s begin by delving deeper into the main steps of LPS to understand where each of these ingredients comes in.
How is the Last Planner Applied?
There are five main steps under the LPS: Master Plan, Collaborative Programming, Look-Ahead Planning, Make Ready Process and Weekly Work Planning. As the name suggests, in the Master Plan step the project’s milestones are determined. Collaborative Programming is the second step where our first main ingredient – stakeholders’ collaboration – is emphasized and most essential to identify the main tasks.
Once this happens, it becomes time for Look-Ahead Planning, which takes place 3~6 weeks before activities execution begin, to determine the projects activities, focusing on activities that are time wasting and can be eliminated. This takes us to Make Ready process where the determined time-wasting activities are eliminated usually one week before the activities execution. Now the activities execution is up and running which calls for the fifth step, the Weekly Work Planning, where our second main ingredient – PPC parameter – comes in; the PPC value is calculated on a weekly basis for the activities accomplished the week before  .
So, stakeholders collaboration means involving the different parties continuously and consistently to avoid potential time wastes through identifying the necessary tasks and activities, but what exactly does PPC tell us about the project activities flow?
How Do We Calculate PPC?
As previously mentioned, PPC values are calculated weekly to track and determine the progress of the project’s activities – completion wise, as shown in Equation 1. The PPC value is calculated by dividing the weekly number of finished activities over the estimated number of activities planned to be accomplished in the same week.
So, what PPC does tell us is how many activities were completed as planned in a given week, but what it does not tell us, as a result of excluding the time factor, is how far this result reflects progress, productivity wise.
A New PPC Parameter
As reflected in Equation 1, calculating the PPC value depends on the number of the finished activities, showing an assumption that the activities are equal in cost and duration. For example, the reinforcement steel for the second slab in the project is considered as one activity, as well as the painting of a small room which is regarded as another activity in the same project. As demonstrated in the example, one activity could be five times longer in duration than another. To have an estimate of productivity progress, the quantity to time ratio should be considered and this is possible to include here. So, a question here is: how do we distinguish between the project’s activities and integrate the productivity factor into the PPC parameter?
Integrating Productivity into PPC
To integrate productivity into the PPC parameter, a new equation is proposed. The value of PPC – in which productivity is integrated - in the new equation can be obtained by dividing the actual productivity of each activity over its expected productivity based on the estimated duration, as shown in Equation 2 . It is important to keep in mind that the productivity is material quantity over the duration of the actual finished – or the expected to be finished – activity.
But why add productivity to obtain the PPC value?
As demonstrated in Equation 2, the value of PPC does not only reflect whether or not the activity is completed; it rather depends on the weekly productivity of each activity. In the second equation, the time factor is added in the calculation of PPC values, resulting in a PPC parameter that tracks productivity progress. So, back to the example of the reinforcement steel for the second slab; if the estimated time for this activity to be completed is two weeks, the new PPC parameter would reflect the productivity progress of this activity in the first week, allowing more enhanced tracking of progress. This allows for an early view of potential delays in order to avoid them.
So, responding to the very first question we raised, YES there is a way to include productivity progress tracking in LPS.
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