Friday, January 18, 2008

Project Activity Duration Reserve Time

You've probably heard of the Army Reserves. The Reserves are made up of citizens who are trained as soldiers and who can be called upon in situations that demand extra resources.

Similarly, reserve time is added to project activity durations to provide the extra time that may be needed based on identified risks. Risks can affect the project schedule and cause delays. Reserve time helps offset such delays.

Reserve time should be documented along with other data and assumptions relating to the project. Reserve time, like other assumptions, is contingent on project results and subject to change as the project progresses. Two methods you can use to determine reserve time are discussed below.

1. As a percentage of activity duration
Reserve time is normally calculated as a percentage of the estimated activity duration. Using this method, reserve time can be calculated by simply adding an extra percentage to each activity duration estimate.

Reserve time can be reduced or eliminated as specific project information becomes available. Its use is at the discretion of the project team and is normally guided by expert judgment or historical information.

Consider this example. You are managing a road construction project and you have estimated that it will take you 50 days to build an overpass. After consulting with one of your lead engineers, an expert on highway construction, you decide to add an additional 20 percent to the duration estimate as reserve time.

To calculate the reserve time as a percentage of the estimated activity duration, you simply multiply your duration of 50 days by 20 percent. The reserve time for this activity is 10 days.

2. As a fixed number of work periods
Another approach to creating reserve time involves simply tacking on an additional fixed number of work periods to the current estimates for each activity. Work periods are often measured in days, but may vary by project.

Let's say you're managing a similar road construction project and you have estimated once again that it will take you 50 days to build an overpass. This time, though, after reviewing historical information on similar projects, you decide to calculate the reserve time by adding five additional work periods, or days, to your estimate.

If you take into account your reserve time of five work periods, your adjusted activity duration estimate for building the overpass would be 55 days.

Whether you decide to determine reserve time as a percentage of the estimated activity duration or as a fixed number of work periods, make sure you consult with a team member who is familiar with the given activity. This will help ensure that the reserve time you decide upon is as accurate as possible.

When performing activity duration estimates for your project, remember to allow for reserve time to accommodate circumstances that could interrupt or delay the progress of your project activities.

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