Arrow Network Diagram Technique

A technique that I have found that really assists project managers in sequencing project activities, identifying gaps, and identifying possible dependency relationships is the arrow network diagram technique. In many cases, a project manager literally cannot see the forest for the trees; problems start arising later on the project when he or she realizes that there are, in fact, dependencies that had not been recognized, and the sequence was done incorrectly. Therefore, it is important to have a simple technique to reflect dependencies in graphic form. However, there are some rules to this graphing technique.

The network diagram is always drawn from left to right. It is not drawn to scale.

An arrow represents an activity, with the tail indicating the start and the arrowhead its completion.

Arrows must follow the sequence of the work to be done. The length of the arrow is not important. The start and end points of an activity are called events and are represented by circles.

The events are usually labeled with a number (1, 2, etc.). Broken-line arrows represent dummy activities and show where one activity depends on another.

Using these rules, the activity network is built to allow for some adjustments and refinement of the network where needed (see Figure 5.6). It may be the case that activities are either to be deleted or reassessed. The network is built in the following way.

List all activities. Separate the project into a list of activities, depending upon the size of the project and desired depth. Use the WBS as a reference tool.

Sequence the activities. Start sequencing all the activities in their correct order and include the applicable activity dependencies that apply to them. Remember to look at those activities that must be completed before the next activity can begin as well as those activities that can start at the same time.

Figure 5.6: Arrow network diagram Project Critical Path

In essence, the critical path is a technique for calculating the total duration of a project based on a specified start date and on the individual duration of activities and their dependencies upon one another. Remember that if there is an activity on this critical path that gets delayed, then the project is delayed—pushing the project status into red, and that is not where anyone wants to be. For all those activities that are not on the critical path, it means that the project manager is okay and can be more flexible with those specific tasks. Understanding exactly how one gets to a critical path is somewhat tricky. First, the project manager needs to create a well-documented network diagram. There are a host of software packages that can be used to do this, and some create it very quickly. Once the project manager has the network diagram, he or she simply adds each parallel path's activities together; the path that requires the longest time to run through the project is the critical path. This means that it is the shortest time in which the project can be completed.

Once the project manager has determined the critical path, it is very important to monitor this path and understand that, if the activities start slipping on the critical path, it is highly likely that the overall project may start failing. To reduce the project time, the project manager should allocate more resources to those activities on the critical path.


Predicting the outcome of any project is difficult because there are numerous methods for estimating what a project would cost. Projects that are similar and have historical data are easier for the project manager to estimate, compared to projects that are unique in nature and have never been attempted before. While there is no such thing as a reliable estimate, there are realistic ones. An accurate estimate reduces the risk of project overruns, thus sharply curtailing negative affects on business. Estimating is a skill that improves over time, and project managers should not initially attempt to do any estimation work without guidance from experienced project estimators or cost accountants. Without accurate estimates, the following scenario will occur:

Figure 5.6: Arrow network diagram Project Critical Path

Your project will be behind schedule—thus late. Your project will be over budget—thus have cost overruns. You will likely lose your client—because you can't meet client expectations.

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