The Project Schedule Part 6: The Critical Path

Planning

With tasks, resource assignments, durations/effort and dependencies defined, your project scheduling software will create a schedule. The path of dependent tasks that in aggregate take the longest amount of time is called “The Critical Path”. This is because if any one of these tasks is completed later than originally scheduled, your project end date will move.

When you are in the “Execution and Monitoring” Phase of your project, regular examination of the state of your critical path tasks is a top priority. It is important to routinely check in with the assigned resources to determine if the “days to completion” is still valid. If you wait until the task is late, it will be too late to do anything about it. Your only choice would be to examine the other tasks on the critical path to see if any task times can be reigned in to make up for the lost time. We will examine techniques you can use for this in the next post.

A technique you can use to make your critical path less volatile is to estimate your individual tasks more aggressively and aggregate the extra time you would have assigned to individual tasks into one “critical path buffer”. If critical path tasks come in early, you can add the time saved to the buffer. If critical path tasks come in late, you subtract time from the buffer. Using this technique, your schedule will not move with any one late task and it will encourage team members to work faster and ignore distractions. Also, the health of the buffer would be the key metric instead of the health of each individual task.

You can measure the health of the critical path buffer with two metrics:

  1. % or original buffer remaining
  2. Divide the “% of elapsed project time” into “% of buffer used”. If this is a number less than one you are tracking well. If it is greater than one it is an early warning sign to take action

For example: Your project has used 30% of it’s original buffer but you are only 10 weeks into a 50 week project (only 20% of the project schedule has elapsed), You divide 30%/20% and this equals 1.5 (greater than one) meaning you need to take remedial action.

If your project only used 15% of your original buffer, 15%/20% = 0.75, which is less than one indicating a healthy schedule.

When using this technique, it is very important to regularly update the “days to complete” for each critical path task so you can have confidence in the status of your buffer.

Whatever technique you use, constant monitoring of the health of the critical path is one of the most important tasks for the Project Manager.

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