Critical Path Method (CPM) is a widely used project scheduling technique. It’s useful in other settings as well: cooking a roast dinner means the potatoes are on the critical path if we want everything to be ready at the same time!
The basic idea of CPM is to work out and visualize the longest sequence of tasks. In other words, you’re looking for the path through the work that represents the minimum duration of the project. ‘Longest sequence’ and ‘minimum duration’ are often the phrases that confuse people because you normally ‘minimum’ is interpreted to mean shortest! We’ll explain all in this article.
What is a critical path?
The critical path is the longest sequence of dependent tasks that must be completed for a project to be finished on time. In other words, if there is a delay on any of the critical path tasks, the overall project timeline pushes out. It’s the journey through the project where there is no slack or flexibility.
To work out the critical path, you need to know the tasks, dependencies between tasks and the duration of each activity…and that’s where CPM comes in.
Creating a schedule
Before you can see the critical path, you need to have a fully completed project schedule. Break down the work into tasks, estimate the durations of the tasks with input from the subject matter experts, and then make sure that the tasks are sequenced properly.
Identifying the critical path
Fortunately for us, modern project managers don’t have to work out the critical path by hand. Enterprise project management scheduling tools such as Primavera P6, will flag the critical path with a couple of clicks, so you can easily identify the tasks that will impact your project end date should they slip.
You’ll see the critical path highlighted on the Gantt chart. When you know what tasks are critical, you can make sure that resources and time are put towards making sure those stay on track.
Tasks that are not on the critical path have float or slack. That means they can move forwards or backwards a bit, within the parameters of the schedule, and not have an impact on the overall delivery date. Knowing which tasks have wiggle room is useful because these are the tasks you can flex to free up resource or get ahead – and that will help you avoid delays.
Common challenges with managing the critical path
Here are some common pitfalls for managing the critical path:
- Incorrect dependencies: One common mistake is failing to accurately identify task dependencies. If you miss a dependency, that can have implications for the whole of the rest of the critical path.
- Inaccurate estimates: Estimating is hard, but put enough effort into making sure that you’ve got robust estimates. When critical path tasks are identified, go back and check those estimates specifically, as any problems here will push out your end dates.
- Resource constraints: CPM only takes tasks into account and assumes you have access to unlimited resources. Meanwhile, back in the real world, you’ll know that you have to adjust timing to fit with the people available. Use resource management reports to uncover bottlenecks and smooth or level your resources to get the best allocations for your schedule.
Tracking progress
Now you’ve got your critical path identified and flagged in your software, you have to monitor and track the project to ensure work continues to progress as expected. Earned Value Management is a good way to do this, or you can use Schedule Performance Index (SPI) to track how the work is going compared to the original expectations.
You can also use scenario planning to work through ‘what if’ analysis which will help you understand the impact of situations that may arise. For example, you can plug in different dependencies and see what impact these would have on the overall schedule. That data can give you useful insights for contingency planning or proactive risk management.
Dealing with delays
Let’s say that despite all your best efforts, your tracking shows that one of the critical path tasks has slipped and is now running late. That’s going to give you an overall delay on the project. When that happens (because it is quite likely that you’ll hit a challenge during a project), there are a few things you can try.
Look at mitigating the delay by re-ordering tasks. You could crash the schedule or fast-track activities. Some could be run in parallel if you are prepared to accept the risk that they might then require rework. You could add additional resources. Or you could simply talk to the project sponsor and explain the delay and present a couple of options, having them choose the best route forward at this point.
The critical path may also be impacted by new work, new dependencies or changes, so over the life of a project it’s likely it will be adjusted and you’ll have to keep stakeholders updated.
CPM is useful for project managers because it helps identify the priority tasks that must stay on track if the project is to deliver on time. And that ensures the team focuses on the right work at the right time, making sure people are available for activities that will drive delivery.
The good news is that identifying the critical path is easy with modern project management tools, and when you have that information, everything else can follow. It’s worth having a play around with the features in your software to see how you can highlight the critical tasks. Or why not come along to one of our training sessions and find out how to do it in the most efficient way?