critical chain

The Critical Chain/Buffer Management (CC/BM) approach uses project and feeding buffers to add safety time to the project baseline schedule and to guarantee the timely completion of the project with a high probability. Buffers are sized according to the properties of the path or chain feeding those buffers, such as the length of the path, its total variance or the number of activities it contains. This article describes the Root Squared Error Method (RSEM) to determine the size of the project and feeding buffers and is based on the predefined uncertainty of the activity durations of the chain merging in the buffer. 

The Critical Chain/Buffer Management (CC/BM) approach uses project and feeding buffers to add safety time to the project baseline schedule and to guarantee the timely completion of the project with a high probability. Buffers are sized according to the properties of the path or chain feeding those buffers, such as the length of the path, its total variance or the number of activities it contains. This article describes the cut and paste method, which is probably the simplest method to determine the size of the project and feeding buffers and is solely based on the activity duration of the chain merging in the buffer.

The Critical Chain/Buffer Management (CC/BM) approach uses project and feeding buffers to add safety time to the project baseline schedule and to guarantee the timely completion of the project with a high probability. Buffers are sized according to the properties of the path or chain feeding those buffers, such as the length of the path, its total variance, its average resource use or the number of activities it contains. In this article, a non-exhaustive overview of buffer sizing methods is given. Moreover, an example project is given in figure 1 which is based on other CC/BM articles and which will be used to illustrate the different buffer sizing methods in detail in other articles.

Inserting buffers in a resource feasible project schedule is one of the last steps in the Critical Chain/Buffer Management (CC/BM) approach. Although the insertion of the buffers in the baseline schedule looks like a straightforward task, this insertion mechanism is often a cumbersome task which leads to problems that harm the general philosophy of critical chain/buffer management. Inserting buffers often leads to resource conflicts in which some of the resources are overallocated (see “The critical path or the critical chain?: The difference caused by resources”). In this article, three simple techniques are described to cope with these resource conflicts  in a CC/BM buffered schedule, as follows:

The Critical Chain/Buffer Management (CC/BM) approach uses project and feeding buffers to add safety time to the project baseline schedule and to guarantee the timely completion of the project with a high probability. Inserting buffers into the project schedule creates a buffered project baseline schedule that can act as a tool to measure performance and provides dashboards (i.e. the buffers) that need to be monitored to trigger corrective actions. In this article, the insertion of buffers is discussed and potential problems caused by activity shifts due to the time buffers are highlighted.

The Critical Chain/Buffer Management (CC/BM) approach aims at the construction of latest start schedules where the project activities use aggressive time estimates and puts a clear focus on the determination of a realistic project deadline. In order to keep the probability high that the project deadline will be met, the CC/BM approach protects the project duration and the critical chain of the project using various buffers. This buffered scheduling approach is the topic of this article and is discussed along the following dimensions:

During the construction of a project baseline schedule in the Critical Chain/Buffer Management (CC/BM) approach, activities are scheduled as-late-as-possible towards the predefined project deadline. In this article, the contrast between the traditional resource-constrained project scheduling approach and the CC/BM scheduling approach is discussed along the following dimensions:

Estimates for activity duration in the Critical Chain/Buffer Management (CC/BM) approach are assumed to be aggressive estimates and refer to the distinction between the average estimate and the low-risk estimate of an activity duration. It is a reaction to the commonly made assumption of adding safety time in the activity time estimates as is usually done in practice which might lead to quite unrealistic project deadlines.

The Critical Chain/Buffer Management (CC/BM) approach originally introduced by E. Goldratt in his novel “Critical Chain”, written in 1997 as an application of the “Theory of Constraints”, is a project management technique that introduces some novel ideas on top of the well-known and generally accepted resource-constrained project scheduling principles. It introduces the idea of buffering projects, rather than individual activities, in a clever way in order to guarantee that the project deadline is met, and can therefore be considered as a new approach to assure better project control through project and feeding buffer management.