Project Managers Need to Understand Queuing Theory

I was at the store the other day to pick up a few items. I found what I wanted and walked to the front checkout counters. There I found a long line of people waiting to be checked out. I had spent a year with a personal coach working on patience so I didn’t let this bother me. Instead I drifted into thoughts of queuing theory. If you don’t understand queuing theory I am sure you can find thousands of articles and white papers on the topic. But it might be easier for you to grab one of your portable lawn chairs and go sit at the checkout counters of most any retail store. If you don’t get thrown out as a vagrant you can watch what happens throughout the course of the day.

You will notice there will be times where there are few or no people in line. People will arrive randomly and there will not be much wait time for any customer. Then there will be other times when many people arrive at the checkout counters at nearly the same time. At this point those random people that were arriving earlier continue to arrive and the lines get longer. (It seems that this is always the time that I arrive but I am patient thanks to my coach, Carly.) Finally these customers find their way out the door and you don’t see another customer for 15 minutes or longer. Why does all this happen? Queuing theory.

I thought about this in terms of projects. There are days when I find myself busier than a one armed wall paper hanger. Then there are days when I can actually make a choice as to what I want to do to better understand my project and move it forward. While some of this is unavoidable we might be able to help prevent most of this through good planning.

I heard a saying once that goes, “if it wasn’t for time, everything would happen at once.” There are times when queuing theory certainly makes us feel like everything is happening at once. I suggest that you may want to take a close look at your project plan. Project plans are often designed so that everything happens at once. This has less to do with queuing theory but more to do with poor planning. If there are five sets of activities required to complete a deliverable, the plan often shows all of these activities completing at the same time. Could it be that all five sets of activities take the exact same amount of time? Not likely. More likely, it is your project team playing a game of chicken.  Once the longest task commits to a date all the others fall in line to meet that date. Once this plan is approved everything is now on the critical path and any blip on the project causes a delay. Worse yet, when you reach the point of delivery you feel like a one armed wall paper hanger.

Good project management practice says that you should create a realistic timeline for all project activities, milestones and deliverables. This means that you should plan each piece of the project independently from the others rather than planning toward a fixed end date. Planning in this way will now circum to queuing theory and some activities will all bunch up together. But rather than bunching up at the very end of the project they will bunch up throughout the project at various times. This is where a little resource leveling comes into play. With

resource leveling we can spread out some of the bunched up activities and fill the gaps when we are less busy.

So you see that queuing theory is a natural phenomenon in our universe but good project management practice you can certainly lessen the impact to your project. While this may not impact your personal day to day workload it will make your project run a lot smoother and more efficiently.