Kanban: Process Improvement and Bottlenecks Revisited

Bottlenecks constrain flow!

 

We are revisiting one of more popular essays from 2013 and will return to Re-read Saturday next week with Chapter 4 “Creating A Guiding Coalition.”  

Kanban implementation is a powerful tool to focus the continuous improvement efforts of teams and organizations on delivering more value.  Kanban, through the visualization of work in progress, helps to identify constraints (this is an implementation of the Theory of Constraints).  Add to visualization the core principles discussed in the Daily Process Thoughts, Kanban: An Overview and Introduction which include feedback loops and transparency to regulate the process and an impetus to improve as a team and evolve using models and the scientific method and we have a process improvement engine.

Kanban describes units of work that are blocked or stalled as bottlenecks.  Finding and removing bottlenecks increases the flow of work through the process, therefore increasing the delivery of value.

A perfect example of a bottleneck exists in the highway system in Cleveland, Ohio (the closest major city to my home).  A highway (three lanes in each direction) sweeps into town along the shore of Lake Erie.  When it reaches the edge of downtown the highway makes a nearly 90 degree left hand turn.  The turn is known as Dead Man’s Curve.   Instantly cars and trucks must slow down.  Even when there is no accident the traffic can backup for miles during rush hour.  The turn is a constraint that creates a bottleneck.   If the city wanted to improve the flow of traffic, removing the Dean Man’s Curve bottleneck would help substantially.

Here’s an IT example to see how a bottleneck is identified and how a team could attack the bottleneck. We will use a simple Kanban board.   In this example, the team has a backlog similarly sized units of work.  Each step of the process has a WIP limit.  One of the core practices in Kanban is that WIP limits are not to be systematically violated.

Each step can have different WIP limits.

As work is drawn through the process, there will be a bottleneck as soon as the analysis for the first wave of work is completed because development only has the capacity to start work on four items. In our example of an application of Kanban, when a unit of work completes the analysis step it will be pulled into the development step only if capacity exists.  In this case one unit of work is immediately blocked and becomes inventory (shown below as the item marked with the letter “B”.

Unbalanced process flows cause bottlenecks

The team has three basic options.  The first is to continue to pull more items into the analysis step and continue to build inventory until the backlog is empty.  This option creates a backlog of work that is waiting for the feedback, increasing the potential rework as defects are found and new decisions are made.  The second possibility is that team members swarm to the blocked unit and add capacity to a step until the blocked unit is freed.  This solution makes a sense if the reason for the blockage is temporary, like a developer that is out sick.  The third (and preferred) option is to change the process to create a balanced flow of work.  In this example, the goal would be to rearrange people and tools to create a balanced WIP limits.

Process improvement maximizes throughput.

 Visually tracking work is a powerful tool for identifying bottlenecks.  Kanban’s core practices dissuade practitioners from violating WIP because it limits the stress in the process, which leads to technical debt, defects and rework. Other core practices provide a focus on continuous process improvement so that when a bottleneck is identified, the team works to remove it.  Continually improving the flow work through the development process increases an organization’s ability to deliver value to customers.