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When to Crash or Compress a Schedule

written by: Rupen Sharma, PMP • edited by: Michele McDonough • updated: 4/20/2013

You're midway through a project and realize that the project will miss a key milestone. To deliver on-time, you’ll need to play with the schedule and look for resources. Crashing or compressing the schedule may be your only feasible option to deliver on-time.

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    The Schedule's the Thing

    Delivering a project on-time will always be challenging for project managers. Sometimes through intricate planning and a bit of luck, your project will meet the deadline without any turbulence. However, more often than not, turbulence is a part of any project. It is how you cope with this turbulence that determines whether you will deliver on-time. Crashing and Compressing are scheduling techniques that you may want to implement when the project is behind schedule. As we'll see at the end of this article, both of these techniques come with their own challenges and risks.

    To apply either of these techniques, you need to have a firm understanding of precedence diagrams and critical path methods.

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    Crashing a Schedule

    Crashing a schedule involves allocating more resources so that an activity can be completed on time or before time, assuming that by deploying more resources the activity can be completed earlier. When you crash a schedule, you do not need to crash all activities. The activities that impact the schedule are those with a float of zero, i.e. activities on the critical path.

    For example, consider the following Precedence Diagram. (Click the image for a larger view.)PrecedenceDiagram Critical Path In this project, if you allocate more resources to the Purchase Wood activity and complete the activity ahead of schedule, the Project End date will not change. That is because the Purchase Wood activity is not on the Critical Path. However, if you allocate more resources to the Dig Foundation activity, then the project will be completed earlier than expected.

    Caution: Not all activities can be completed earlier by allocating more resources. For example, the completion of the Harden Cement Foundation activity is also dependent on the natural rate of cement hardening, which has nothing to do with resource allocation.

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    Compressing a Schedule

    Compressing a schedule means that you will be conducting project activities in parallel. Take a look at the precedence diagram displayed in the Crashing section: You could implement the Select Design activity at the same time as the Purchase Plot activity. By doing this, the critical path is reduced by two days.

    Similar to Crashing, Compressing is not applicable to all project activities. For example, you can’t implement the Hire Workers and Dig Foundation activities in parallel because to dig a foundation you need to have someone to do the digging!

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    Associated Risks

    The risks associated with Crashing are:

    • Budget: Since you allocated more resources, you will not deliver the project on-budget.
    • Demoralization: Existing resources may get demoralized by the increase in people to complete activities that were originally assigned to them.
    • Coordination: More resources translates to an increase in communication challenges.

    Coordination is the main risk associated with Schedule Compression.

    Best Practice: Given a choice between crashing and compressing, always attempt compressing first. It is less risky.

    Whichever technique you use, ensure that the top three risk management rules are followed--managing, analyzing, and tracking risks.