Critical Path Method in Scheduling

CPM Scheduling

The Critical Path Method (CPM) is the most commonly used method by Project Managers for its simplicity and effectiveness. It is used for tracking/monitoring and control of a project. The critical path in the construction schedule derives the project duration and there can be multiple critical paths in the schedule depending upon the constraints and activities relationships, hence the entire project timeline could be lengthened by delaying activities along with any one of the critical paths.

A CPM schedule is a projected timetable of construction operations that will serve as the principal guideline for project execution and can be developed using marketplace project management software such as Primavera (P6), Microsoft Project, Asta Power Project, etc.

A CPM schedule includes the following steps:

Determine Work Activities

Each project, whether large or small must be divided into smaller entities, called activities, or tasks. These tasks/work breakdown structures are developed from the scope of work and available information.

Estimate

Activity Duration/Resources

In most construction sites, activity durations can be determined using the given formula:

Determine Logical Sequence/Relationship

This information can be obtained from Project Managers and Technical Team Leaders. The Planning Engineer (Scheduler) must have to keep in mind the following points:

1. A logical relationship exists between two activities when the start of one activity depends physically on the finish of another activity.
2. Resource constraints to identify because of limitations and assign the cushion is critical right predecessor/successor.
3. Any other Constraints such as working space, funds, stakeholders, or other relevant agencies.

Perform CPM Calculations

By using a computer program, it will perform the following functions provided the correct input data:

The process of schedule calculation;

1. Forward Pass calculation shows the earliest completion dates
2. Backward Pass calculation shows the latest completion dates.
3. Float calculation shows the cushion in duration having no impact on project duration and can be determined using the following equation:
4. Activities with Zero float are critical activities.

1. Critical Path determines the Project Duration (Completion Date)
2. Critical Path is the longest path (duration) through the network. It is the leading path if any delay occurs on it, the project completion date also changes. During the process of finding critical path activities, forward pass and backward pass calculation should take place which allows for the determination of ES, EF, LS, and LF of activities.
   1. Early Start (ES): The earliest date on which an activity can start within available constraints
   2. Early Finish (EF): The earliest date on which an activity can finish within available constraints
   3. Late Start (LS): The latest date on which an activity can start without delaying project duration.
   4. Late Finish (LF): The latest date on which an activity can finish without delaying the project duration
   5. Total Float (TF): The maximum amount of time an activity can be delayed from its early start without delaying the entire project.

It is important to simultaneously check the input/output and not rely totally on the computer. Hence, the following are four additional steps that are essential for an effective, accurate, and successful schedule:

Review and Analyze the Schedule

Following key points to be considered while reviewing the schedule:

1. Logical relationships among activities
2. Every activity has a correct predecessor
3. Optimal use of resources
4. No redundant relationships

Implementing Schedule

It is essential to ensure regular updates when a schedule becomes active and ready to be progressed. Following points to be noted while doing this step:

1. Realistic and Accurate Scheduling, Progress Updates & Reporting
2. Top Management to review
3. Schedule compliance

Monitoring and Controlling Schedule

Project controls mean comparing the baseline schedule with actual work done at the site. The difference between monitoring and control is corrective action. Monitoring includes observing and reporting, and perhaps analyzing. Control adds corrective action to this definition.

An important part of the control effort is forecasting. Forecasting is done mostly by extrapolating actual performance for the remaining portion of the project. When the “Performance %” is ahead or behind of “Planned %” from the approved baseline schedule. It gives an alarm to the project manager to take necessary action.

Project Updates

The Project Manager should make a copy of the updated schedule each month and must submit it to the competent authority after incorporating site changes, plans, delays, variation orders (extra/additional works), etc. so that action according to the shift in schedule can be taken timely.

A Project Manager must maintain the notebook/diary in scheduling software against each activity mentioning reasons or remarks. Moreover, these monthly updates help the Contractor/Consultant for Extension of time determination, resolving disputes and claims in the project domain.

COST AND RESOURCE ASSIGNMENT

Apart from the above discussion and steps, specifically used for progress monitoring and tracking. Hence, a more comprehensive analysis can be made by implementing the additional steps given below:

Cost and Resource Allocation

Resources mean labor, equipment, and materials, whereas Cost loading means assigning the budgeted cost to their respective activity. The sum of all activities costs should equal the total budgeted cost of the project.

This can help in the following ways:

• Schedule linked with estimate/finance, through this the planner/scheduler should be able to tell the total cost incurred, original (baseline) budget, estimate to complete (ETC), estimate at completion (EAC), and other financial statistics for each activity.

Resource Levelling

Resource leveling is a technique where we find the uneven distribution of resources and then allocate optimum resources (labor/equipment) to complete a particular activity/task. It is used to improve the efficiency of resource utilization (particularly labor and equipment) during the life cycle of the project.

Conclusion

CPM Schedule is commonly used in mega projects to help managers to make effective and timely decisions. It has multi-functions and can be used as a single unit of different project phases such as initiation, planning, design, execution, close-out, etc. It helps the Project Manager to identify hurdles on the critical path, ensure precautionary measures, and take necessary action to maintain the progress of work. Furthermore, coordination among government agencies, procurement teams, different subcontractors, and stakeholders reduces the communication gaps and enhances the approval process of required items. It also provides a platform to keep all the concerned departments on one page to achieve a common objective/goal of the project.