“Queues lie at the root of a large number of product development problems. They increase variability, risk, and cycle time. They decrease efficiency, quality, and motivation.”
“Large queues form when processes with variability are operated at high levels of capacity utilization. In reality, the misguided pursuit of efficiency creates enormous costs in the unmeasured invisible portion of the product development process, its queues.”
“Since high capacity utilization simultaneously raises efficiency and increases the cost of delay, we need to look at the combined impact of these two factors.”
“We have already pointed out that companies do not manage product development queues. What do they manage? Timelines...In contrast, when we emphasize flow, we focus on queues rather than timelines. Queues are a far better control variable than cycle time because, as you shall see, queues are leading indicators of future cycle-time problems. By controlling queue size, we automatically achieve control over timelines.”
- Don Reinertsen, 2009 – The Principle of Product Development Flow: Second Generation Lean Product Development
If you’re new to or rusty on CFDs, it would be helpful to review “Basics of Reading Cumulative Flow Diagrams” first. This earlier post covers basic definitions and the mechanics of reading WIP (work-in-progress), lead-time, and an average completion rate (throughput) from a CFD. It also includes links to external sources, one showing a basic example of how to create a CFD using MS-Excel, and another providing a quick overview of their use in the kanban method context. From this foundation I’d like to shift here toward a visual analysis perspective, exploring a few contexts where a bottleneck in our workflow is more or less present and see how it might appear on a CFD.
To be clear, I don’t think CFDs are the only way or “a best way” for spotting a bottleneck in your workflow. If you’re adequately visualizing your workflow on a board and diligently measuring and managing work items as they flow through your process, you’re well on the way to being able to identify where any bottleneck might be occurring. (Note: see my Kanban Board Design Primer under Resources/Nuggets here). That said, don’t under-estimate the value of using the CFD as well for learning about what happened, is happening, or will happen in your workflow. It can be a very effective tool for creating an easily accessible visual historical record and a trending perspective of a workflow in your context.
What is a Bottleneck?
Let us get a shared understanding of the term “bottleneck” by first looking at these selected Wikipedia definitions:
- Metaphorically a bottleneck is a section of a route with a carrying capacity substantially below that characterizing other sections of the same route. This is often a narrow part of a road, perhaps also with a smaller number of lanes, or a reduction of the number of tracks of a railway line.
- In engineering, a bottleneck is a phenomenon by which the performance or capacity of an entire system is severely limited by a single component.
- A bottleneck in project management is one process in a chain of processes, such that its limited capacity reduces the capacity of the whole chain.
As we continue our discussion, a key point from these definitions to keep in mind is the “singular” characteristic. Additionally, I’ll infer a “stationary” characteristic as well for the bottleneck throughout the time reflected by the example CFDs that follow. (continue reading…)