There are a number of basic concepts that are relevant to the scheduling of each step in large municipal construction projects.
When I was a purchasing manager we approached a project in a way that may be visualized as a series of events or tasks.
An event is something that needs to occur, but does not involve the performance of an assignment or other carrying out of work, such as time required for concrete to harden. A task is something that needs to be done that will require time to complete. A milestone is a significant point in the progress of the project.
In my view, once these events and tasks have been identified, it is possible to determine which of them are dependent and which are independent. A task or event is dependent when it cannot begin before a previous task finishes or a previous event occurs. Dependency need not involve physical impossibility, provided that in a rational sequencing, the first step would be completed prior to the second.
To illustrate the concept of lead time it exists where a subsequent task or event cannot commence until some other prior task or event has also begun, but where it is not necessary for that task or event to be completed before the subsequent task or event begins. It is therefore possible for the prior and subsequent events or tasks to overlap to at least some degree.
For instance, the final work on design can often occur while the site is being prepared for construction. Thus, the lead time is the extent of overlap between tasks or events that have dependency.
For example, if a subsequent task can start before the prior task is half finished, there is a lead time of 50 per cent for the prior task. It should be noted that the project management use of the term differs from normal usage of that term — i.e. the time required to bring an idea, scheme or proposal into operation.
In contrast, lag time is the minimum amount of time that must pass between the finish of one task or event and the start of a succeeding task or event. Simply put, lag time is a delay between tasks that have dependency. One of the most obvious examples are appeal periods following the making of some sort of court, administrative or other order. If no step can be taken to enforce an order for 30 days after it is made, there is a lag time of 30 days.
Most people relate the critical path of a project as the series of tasks from beginning until its completion that takes the longest time. It defines the shortest time in which all tasks in the project can be completed, since no task on the critical path can have any slack time. In other words, no task on the critical path can be delayed or extended without affecting the finished date of the project.
To be clear, determining a project schedule requires technical knowledge of the steps required to carry out the project. Much of this knowledge is outside the training and experience of the purchasing department and quite possibility the user department as well.
The construction of a new municipal building, such as any hypothetical project you want to describe, will require input from the facilities management department. The best result possible is when all departments work together with the consultants to one single purpose. It is a good starting point to understand that target date for completion will dictate in large measure the resources required to get the project completed on time and on budget.
Sadly, the average person feels that government projects at all levels have consistently performed with overrun budgets and also fail to be executed within the project timetable.
Stephen Bauld is a government procurement expert and can be reached at swbauld@purchasingci.com.
Some of his columns may contain excerpts from The Municipal Procurement Handbook published by Butterworths.
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