The impetus for originally developing the critical path method was as a way to plan a project’s duration that minimises the project’s overall cost (and the cost for all other feasible durations).
The steps and trade-off calculations required to solve this inherent time-cost problem, despite being of primary importance to the project and a topic of ongoing academic interest, are yet to become widespread. This unfortunate situation means that in project planning practice, the time-cost problem is ignored and unsolved, allowing this gap to be filled by subjective and isolated answers to questions of project duration and cost.
It is proposed that by revisiting this previously established workflow, planners can relearn how to setup a project plan as a solvable time-cost problem, thereby fulfilling CPM’s original promise.
IN THIS PRESENTATION we shall describe how CPM software's scheduling engine that produces the familiar bar chart can be modified to also enable the solution to a project's time-cost problem, by compressing the bar chart. The end result is a graphical solution showing the duration and cost for all the feasible schedules between the 'all-normal' schedule and the 'fully-crashed' schedule. This provides a quantified reference for the selection of a baseline schedule.
The key steps to achieve this are:
- develop a valid network model, using the typical bar chart, but checked for validity using the activity-on-arrow chart format.
- inputting 'utility data' that describes the normal means for carrying-out any given activity, as well as the alternatives available that MAY accelerate that activity's completion at extra direct cost.
- estimating the time-related project indirect cost.
- compressing the network model to plot the time-cost curve.
