Advantages and Disadvantages of the Critical Path Method

For project managers, thecritical pathis the longest sequence of dependent tasks in a project. By identifying the critical path, project managers can more easily prioritize tasks, build realistic schedules, keep projects within budget, and reduce or offset delays.

Project managers can determine the total duration of the project by calculating the time between the start of the first task and the end of the last item on the critical path. Any tasks that are independent or that belong to a shorter chain of dependent tasks do not add to the total project duration and are therefore not on the critical path. The critical path is the core concept of thecritical path method(CPM), a scheduling and project management technique that was first developed in the 1950s. While the critical path method is still most commonly used for managingconstruction, aerospace, and defense systems projects, its core principles are applicable to any sector.

When project managers anticipate delays using the critical path, they are more likely to keep projects within budget. Whether you incur penalties for late delivery, need to expedite shipping, or suddenly require additional staff, unexpected delays are almost always costly. By reviewing the critical path, project managers can find ways to compensate for delays and anticipate additional resource needs that should be factored into the budget.

Tasks on the critical path follow four kinds of dependencies: finish to start, finish to finish, start to start, and start to finish. In the case of finish to start, a team cannot begin work on one task until the previous task is completed. For example, when constructing a building, workers must pour the foundation before they can begin framing, so foundation pouring and framing are two dependent tasks on the critical path. Taken together, these tasks create a chain of interdependent activities that must occur in a certain order to achieve the project objective.

Project managers refer to and update the critical path schedule frequently when a project is underway. Critical path network diagrams andcritical path templateshelp project managers create clear visual representations of project timelines, so teams can quickly access and understand important information. Critical path timelines often appear asGantt charts, which are useful visual tools for communicating dependencies, concurrent work, progress, and milestones. To learn more abouthow CPM and Gantt charts work together, see this comprehensive guide.

Lastly, identifying your critical path is important if and when legal disputes arise. When contractors and owners do not agree on who is responsible for delays, or whether a delay or cost overrun triggers contract penalty clauses, clear critical path documentation can serve as important evidence and protect you and your company from liability.

The critical path method is a reliable way for project managers to budget time and allocate resources. Advantages of CPM include improved accuracy and flexibility in scheduling, clearer communication between project managers and stakeholders, easier task prioritization, and more.

Bill Pepoon, Managing Partner and Founder ofConstruction Science, says that on a typical commercial building project, only about 20 percent of the activities are on the critical path. The crew may be accomplishing a lot of the remaining 80 percent, but unless they are completing the critical path work, they are falling behind.

“Critical path keeps you on target and makes clear what you need to do to stay on schedule,” Pepoon explains. Without identifying and prioritizing those activities, construction managers may have a false sense of progress.

“When I ask if they have done enough work to stay on schedule,” he says, “they are often surprised. If you can’t demonstrate that you made progress on that 20 percent of the work, you have lost time.”

Below are the key benefits that project managers can expect from adopting the critical path method:

• Stronger Communication:Critical path method schedules require input from key players across all stages of a project lifecycle. Bringing together the expertise of various team members and subcontractors, from architects to electricians to construction managers, makes the schedule more realistic and robust from the start.
• Easier Prioritization:Identifying the critical path helps project managers clarify priorities and determine the float of each task.Float, also known asslack,之前一个任务可以推迟多久t impacts the completion date. Critical path tasks have zero float, while non-critical activities have positive float. Determining the float of each task helps teams assess priorities. The lower the float, the higher the priority.
• Improved Accuracy in Scheduling:The critical path method is a popular and reliable tool for improving the accuracy of project schedules. Many project managers use CPM in conjunction with the Program Evaluation and Review Technique (PERT), another project management tool that helps teams estimate total project duration. While CPM focuses on predictable activities, PERT factors in unpredictable events, creating three possible timelines: most optimistic, most pessimistic, and most realistic. By using both PERT and CPM, project managers can create the most accurate forecasts possible.
• Better Risk Detection:Critical path schedules make clear the relationships between dependent tasks, so project managers can better predict the knock-on effects of a delay. CPM prevents more surprises and offers earlier opportunities to make corrections than other methods that do not track dependencies.
• Greater Adaptability:When work does not go to plan, CPM network diagrams give project managers the tools to quickly rework the schedule. Certain software programs can even model the effects of different adjustments, so project managers can compare outcomes and select the most beneficial option. By using software, says Pepoon, “You can recalculate the schedule in a fraction of a second.”
• More Visual Impact:CPM network diagrams and Gantt chart representations of critical path schedules give project managers a quick understanding of a project’s timeline and progress. By referring to these visual tools, project managers and team members can develop a more intuitive understanding of a project’s trajectory than they might with a less visually dynamic option.

Despite these advantages, the critical path method has drawbacks, such as its inability to capture resource constraints. While CPM software can reduce manual work, it also requires complex research and might not be suitable for all project types.

Below are some of the most common disadvantages to using the critical path method:

• Increased Complexity:The critical path method involves complex calculations with many moving parts. While software can automate the calculations, inputting accurate information requires detailed research and does not eliminate the risk of human error. “You can’t be overly trusting. You have to independently verify the schedule that results,” Pepoon notes. “Every day I find conflicts and anomalies.”
• Decreased Applicability:Not all project types lend themselves to the critical path method. For example, CPM requires that timelines be predictable and repeatable. CPM is not a good fit for creative projects, such as product design or research tasks, that often come together in unpredictable ways. At the other end of the spectrum, repetitive or independent activities are not well suited to CPM. For example, a weekly maintenance program may involve cleaning dozens of machines, but the order in which the machines are serviced does not matter. In this scenario, CPM does not add value because there are no task dependencies, so there is no critical path.
• Reduced Attention to High-Float Tasks:当使用关键路径hod, project managers focus on critical path tasks. While the critical path does determine total project duration, using this method can make it easier to ignore non-critical or high-float tasks, thus resulting in delays. For example, installing the electrical system in a new building is not on the critical path because this can occur during a large window of time. However, if project managers forget about wiring work or delay it too long, it will still impact the completion date.
• Less Insight Into Resource Constraints:Another drawback of the critical path method is that it does not give good insight into how resource constraints affect project scheduling. The network diagram and CPM schedule do not take into account the availability of equipment or labor resources. At the same time, CPM does not highlight overlap of resource use, which can result in congestion. For example, overlaps in the schedule might mean too many workers in a server center or too much heavy machinery on a construction site. Unnoticed overlaps might also causetrade stacking, which is when multiple tradespeople, such as electricians and plumbers, try to work in the same location simultaneously, potentially causing delays, safety hazards, and unforeseen costs. These problems compound when a company has multiple projects underway and must coordinate resources among them. CPM on its own is not helpful for spotting these issues. Project managers will need to solicit the expertise of other professionals and resource-based scheduling techniques to gain necessary insight into resource management.

Advantages and Disadvantages of Critical Path Method

Advantages	Disadvantages
Incorporates knowledge of all stakeholders	Complex
Better work prioritization	Resource intensive
Greater accuracy	Only useful for certain project types
Helps spot problems early	Makes it harder to see issues with non-critical tasks
Makes schedule easier to adapt	Does not account for resource constraints
Visual	Steep learning curve

而马关键路径方法可以帮助项目nagers prioritize tasks for many projects, it is not always the appropriate solution. It is important to evaluate your project in advance and determine whether CPM will add value to your project.

The following are some key considerations when deciding whether the critical path method is right for your project:

• Customer Requirements:Does your customer demand a CPM schedule? With certain clients, such as large government agencies and public entities, producing a critical path schedule is mandatory. These projects often entail large investments and require project controls such as CPM that give the commissioning client oversight of progress. If the client demands CPM, then you have no choice but to use it.
• Contractual Obligations:Does your contract include penalty clauses that require CPM documentation? Contracts for expensive and time-sensitive projects often contain clauses that impose penalties on contractors for delays, unless the contractor can prove that delays were caused by uncontrollable factors or that the client is at fault. If a contract specifies that a CPM schedule is the basis for substantiating claims and counterclaims, then project managers will need to implement CPM. Even when contracts do not specify this, courts usually recognize CPM as legitimate, so it is a good idea to use CPM scheduling when delays might have financial or legal repercussions.
• Work Predictability:Is the work novel or undefined? The critical path method relies on precise forecasts of task duration. A project that isnovel, or involves tasks that have never been done before, and projects with uncertain rates of production, such as creative projects, are not a good match for CPM. Similarly, projects that require managers to define the work as they progress, such as discovery or research projects, are ill suited to CPM scheduling.
• Deadlines:Does the project have a critical completion date? The greatest strengths of CPM scheduling are its accuracy and potential to allow project planners to adapt to changes without impacting completion dates. If the completion date is flexible, then project managers should avoid the complex and time-consuming process of using CPM.
• Task Dependencies:Do tasks need to be completed in a specific order? In order for project managers to create a critical path, projects need to have task dependencies. If the project does not have a critical order of activities, then CPM will not add value to the project.
• Project Value and Duration:Does the project have a high value? Will the project duration exceed six weeks? Producing and managing a critical path schedule is resource intensive, so project managers should only apply CPM to projects that have a significant scope, duration, and value. While there are exceptions, a good candidate for CPM is typically a project that is complex and lasts at least a few months. These projects generally involve multiple work streams and specialized labor or subcontractors. In terms of cost, according to pros such as Bill Pepoon and purchasing guidelines or contracting requirements for government agencies, budgets upward of $750,000 or $1 million usually justify CPM. Some public agencies set a minimum contract threshold, often $1 million, that requires a CPM schedule. The right number is relative to the size, funding, and financial risks of a project. For example, a startup company or small business that risks going out of business if it faces legal or financial consequences from delays may opt for CPM even if the budget is below $1 million.

For additional help deciding whether the critical path method is right for your project, you can work through the following decision tree. While there may be other reasons to use CPM, such as applying it to simple projects as a learning experience, this decision tree will be a helpful guide in most cases.

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