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BUILDING IN SCHEDULE CONTINGENCY 111

safety by using the lag function of the software, or by inserting dummy tasks. For
example, we have several items that are needed to support the guardrail work on
our expressway project. These may include the new guardrails, fasteners, hole
diggers, traffic diversion cones, and lane closure signs. We don’t want to purchase
or accumulate these items too early, so we designate them as ALAP tasks. But we
would like to have them scheduled five days ahead of the planned start of the
guardrail work. We can do this in two ways.

One way is to input a finish-to-start lag of 5 days (FS5) between each of these
tasks and the start of the guardrail milestone. The alternate is to insert a dummy
task, called Accumulate Items for Guardrail Work, and assign a five-day duration.

Trap Building a schedule with too much float is as bad as not
having enough float. It will appear to be unrealistic, and will
tend to be ignored. The use of the JIT options allows the de-
velopment of a more practical and believable schedule.

Building In Schedule Contingency

We discuss schedule contingency at length in Chapter 3.2, including the intro-
duction of an entirely different way of dealing with schedule contingency, using
the critical chain method. We attempted to make a case for building contingency
into the schedule, and for using shared contingency concepts, where practical.

For the moment, let’s assume that you are working with traditional CPM tools.
How can we deal with contingency? One option is to use the PERT analysis func-
tion, if it is available in the tool that you are using. You’ll find a discussion of PERT
in Chapter 3.3. Briefly, using the three-duration capability of the PERT mode, and
changing the weighting in favor of the pessimistic value (as can be done with Sci-
tor’s PS8), will allow you to place some contingency into the schedule.

Another way of inserting contingency into the schedule is to account for the
situations that most often result in schedule delays. These situations include:

• Points where a large quantity of predecessors feed into a task. Time is often
lost in communication and confirming that the feeder tasks have been com-
pleted and that the next task can begin.

• Points where there is a change in the location of the next task or in the par-
ties responsible for the next task. As in relay racing, there is often a problem
getting a clean handoff of the baton.

• Points where there is a known or anticipated shortage of resources.