For centuries, the Critical Path Method (CPM) scheduling has been a component of the building sector and is a commonly used type of technique. A CPM plan is developed by compiling a list of operations and milestones needed to finish a project, determining the length of individual operations, and linking them together in a network of dependencies to set scheduling dates, critical route and general project length.
While CPM has been offering the most logical and convenient way to create a high-level perspective of the main milestones and sequence of a project, it has not been very successful when it comes to the execution phase of the projects. This is as CPM is predominantly a top-down “ideal world” system where real-world challenges are not addressed. Lean methods such as the Last Planner® System (LPS) are better suited to manage the project execution as they are grounded in reality and address issues through a bottom-up approach by providing components such as make-ready planning and weekly job plan. While there are tools available to develop plans using both these approaches separately, we present VisiLean which is only such tool that integrates the top-down and bottom-up worlds together.
CPM Scheduling Benefits and Drawbacks
CPM is an effective way of mapping key activities and major project milestones, as well as predicting the duration of each activity and the estimated duration for the complete project. The schedules provide a helpful graphical representation of the task dependencies and also may spot logic mistakes in the condition.
But executing such a plan in a project relies on getting the correct tool for the job, as with any task in a building. CPM scheduling is most efficient if a work breakdown structure (WBS) is kept at stage 1 or stage 2. The schedule becomes too comprehensive to be a practical scheduling instrument when broken down further to a stage 3 or 4 WBS. The extra amount of detail does not correspond to the ground reality and can generate a false feeling of assurance in the schedule.
Another thing to note is that CPM schedules overstate critical operations, with non-critical operations capable of becoming critical if their timeline slips, sometimes even by just a day. CPM scheduling is also susceptible to user error and can be moulded to create a necessary outcome that opens the door to other problems. Moreover, CPM schedules generally are not the resultant of team planning and are often produced with only minimal input from those actually executing the planned work.
These pitfalls combine to make it very difficult to actually adhere to a CPM schedule. Repeated experiences with CPM schedules that weren’t followed can make participants sceptical of the planning process itself, which creates problems with accountability down the road.
Launch into LPS
LPS addresses the age-old problems present with the top-down CPM planning. Rather than getting stuck producing a plan comprising of thousands of tasks in a CPM process, it is better to use the CPM approach to get a project overview and use LPS as an instrument for more collaborative, and comprehensive planning. With a digital LPS solution like Visilean, which integrates directly with a top-level CPM schedule, reconciling top-down schedules with bottom-up plans can be performed very effectively.
Teams can build on the CPM schedule’s logic and dependencies to plan through lookahead planning and weekly level planning at a more granular “task” stage. The nearer the team gets to the work, the more comprehensive the plan should be and at this stage, teams should commit themselves to particular task completion dates. Visilean scheduler can be used to track how everyone is performing against their commitments as shown in Figure 1. If targets are missed it is possible figure out why with an automated dashboard in real-time. Project teams can evaluate the reasons for delays and adjust the remainder of the work accordingly as shown in Figure 2. This way, the work teams get the benefits of CPM without the downfalls.
The main benefit of using Visilean besides CPM is that the team can readily update Visilean in real-time, unlike CPM. The project schedule can integrate any dynamic changes as quickly as something happens on the work and modify the remainder of the plan to reflect it. Because the plan is constantly being updated by the team in real-time through the mobile apps as shown in Figure 3, teams devote more time in it and are enthusiastic to make their best efforts to fulfil their commitments and the plan.
Figure 3 Mobile app : Real-time updates
Visilean also maintains an audit trail of any changes made to a task throughout its history; the schedule is continuously stored, and all work stoppages and adjustments need to be justified with reasons, making it simple to understand the causes and prevent future conflicts.
If you are disillusioned with reoccurring problems on your construction projects and are not satisfied with the way they are executed, you can use VisiLean to better manage projects and achieve as much as 45% improvement in production efficiency as reported by some of our customers.