Project Scheduling
This chapter discusses making the transition from project planning to project scheduling by introducing two techniques, push scheduling, also known as the CPM method, and pull scheduling, also known as agile scheduling. Both have distinct advantages and disadvantages.
The Critical Path in Living Order
In any undertaking, keeping track of the sequence of activities that must be completed to ensure that a project is concluded on time is essential. Indeed, in some situations, identifying and monitoring the critical path using CPM is a contractual obligation. This is most common in governmental work, especially in construction projects for departments of transportation.
But in highly fluid, living order situations, it's important to ask exactly how much time and effort you should spend keeping track of the critical path. CPM advocates would argue your primary job as a project manager is to monitor the critical path. But some experts experienced in managing large, highly complex projects argue that focusing too much on the critical path can be counterproductive.
In their insightful paper, "The Marriage of CPM and Lean Construction," two experienced Boldt company executives – Bob Huber, scheduling manager, and Paul Reiser, vice president of production and process innovation – look at the scheduling process through the lens of Lean. True to their experience in Lean construction techniques pioneered by the Boldt company, they start by asking the essential question of any Lean enterprise: what value does it provide? Their analysis shows that a schedule provides different value to different stakeholders. For the owner, the "value received from the schedule is the ability to communicate project duration and financing needs to upstream and downstream interested parties". The value provided to other stakeholders include "project duration, impacts to adjacent facilities, expectations for the timing of engineering deliverables, crew flow map, just-in-time delivery opportunities".
For stakeholders primarily interested in project duration, the critical path is a special focus. But not everyone involved in a project requires minute details on the status of activities on the critical path. Huber and Reiser argue that, on a construction site, providing constant schedule updates using the complicated software available to manage CPM schedules wastes one of the most important resources available on any project: the attention of project stakeholders.
The explosive growth in the capability and sophistication of computer-based project management software over the last few decades has not been closely matched by a parallel interest in or need for the data and analysis that they provide. This is especially true of the interests and needs of the front-line production manager on a construction site. The planning effort, as it demands time and energy from the front-line managers, has to compete with day-to-day project requirements for safety and environmental considerations, scope management, financial management, labor relations, owner relations, procurement, payroll, and documentation. In this competitive environment, the competition being that for the attention of the front-line production manager, the CPM schedule must necessarily deliver its value quickly and efficiently or it faces the distinct possibility of losing out to other persistent demands on the manager's time and attention. Just because we can create an extremely detailed WBS-based resource loaded and leveled schedule and just because we can report its content in a mind-numbing array of diagrams, charts, and graphs doesn't mean we should. In fact, practiced as an interactive discussion of crew flow and site coordination needs, with data captured and analyzed for alignment with project needs in real time, the CPM scheduling process can fulfill its assigned functions very efficiently. The test should always be whether the CPM schedule is delivering value and being readily consumed by the site production controllers.
John Nelson, adjunct professor of Engineering at the UW-Madison, and a veteran of many years in the construction industry, argues that an excessive focus on the critical path can derail a project's chance of success: "Most critical path projects don't meet their milestones. Most living order projects which ignore critical path do meet their milestones. An excessive focus on the critical path uses up too much energy; everyone is working on updating the critical path without actually getting anything done".
Still, he explains, all forms of scheduling have their benefits. "Instead of just focusing on one way of thinking about a schedule, you should take advantage of all the scheduling techniques available: critical path, push, pull, and so on. If you use all these techniques to stress-test your conceptual understanding of the project, then you're going to have a higher probability of success. And always keep in mind that a schedule conceived in one situation may have to be thrown out if externalities intervene. That's the nature of living order. This is a special concern with CPM. If you try to manage to a critical path that was conceived under different circumstances, you have a lower probability of meeting your goals".