Critical Path Analysis in Project Management

Determining the Critical Path

• Critical path is the longest path in the project network diagram
• The critical path determines the shortest amount of time needed to complete the project
• Activities on the critical path have no slack, meaning they cannot be delayed without delaying the project completion date

Critical Path Analysis

• Critical path analysis helps determine which activities have float (slack) and can be delayed without delaying the project completion date
• If an activity on the critical path is delayed, the entire project schedule will slip unless corrective actions are taken
• There can be more than one critical path if the lengths of two or more paths are the same
• The critical path can change as the project progresses

Critical Path and Schedule Trade-offs

• Knowing the critical path helps you make informed schedule trade-offs
• Free slack or free float is the amount of time an activity can be delayed without delaying the early start of any immediately following activities
• Total slack or total float is the amount of time an activity may be delayed from its early start without delaying the planned project finish date
• A forward pass through the network diagram determines the early start and finish dates
• A backward pass determines the late start and finish dates

Why Critical Path is Important

• It helps prove how long a project will take
• It helps determine where to focus project management efforts
• It helps determine if a problem needs immediate attention
• It helps compress the schedule during project planning and whenever there are changes

Critical Chain Method

• Critical chain scheduling addresses the challenge of meeting or beating project finish dates
• It is an application of the Theory of Constraints (TOC)
• It takes limited resources into account when creating a project schedule
• It includes buffers to protect the project completion date
• It assumes resources do not multitask because it often delays task completions and increases total durations

Buffers and Critical Chain

• Buffers are additional time to complete a task
• Critical chain scheduling removes buffers from individual tasks and instead creates:
  • A project buffer, which is additional time added before the project’s due date
  • Feeding buffers, which are additional time added before tasks on the critical path

Resource Optimization Techniques

• Resource optimization matches available resources (human, machinery, financial) with the needs of the organization to achieve established goals
• Techniques used to adjust the schedule include:
  • Resource leveling: adjusts start and finish dates based on resource constraints to balance demand for resources with available supply
    • Can be used when shared or critically required resources are only available at certain times
    • Can be used when resources are in limited quantities or overallocated
    • Can cause the original critical path to change, usually increasing its length
  • Resource smoothing: adjusts activities of a schedule model to prevent exceeding predefined resource limits
    • The project critical path is not changed and the completion date may not be delayed
    • Activities can only be delayed within their free or total float

Schedule Compression

• Shorten durations of critical tasks by:
  • Adding more resources or changing their scope
  • Crashing tasks by obtaining the greatest amount of schedule compression for the least incremental cost
  • Fast tracking tasks by doing them in parallel or overlapping them

Rationale for Schedule Compression

• When the project has unrealistic time-frame or schedule end dates
• To analyze the impacts on the project schedule during the Integrated Change Control process

Project Breakdown Structure (WBS)

• A deliverable-oriented hierarchical decomposition of the work to be executed by the project team
• The WBS begins with the project as the final deliverable
• Major project deliverables/systems are identified first
• Sub-deliverables necessary to accomplish the larger deliverables are defined
• The process is repeated until the sub-deliverable detail is small enough to be manageable and where one person can be responsible
• This sub-deliverable is further divided into work packages
• Work packages are grouped by type of work to form cost accounts
• Cost accounts help monitor project progress by work, cost, and responsibility
• Work packages are short duration tasks with definite start and stop points, consume resources, and are assignable

Rolling Wave Planning

• Iterative planning technique where work in the near future is planned in detail, while work in the future is planned at a higher level
• As more is known about future work, it is planned in detail

Expert Judgement

• Project team members or other experienced and skilled experts are used to provide expertise in defining activities and project schedules

Activity Sequencing: Determining Dependencies

• Mandatory dependencies: inherent in the nature of the work; hard logic
• Discretionary dependencies: defined by the project team; soft logic
• External dependencies: involve relationships between project and non-project activities

Mandatory Dependencies

• Also referred to as hard logic
• Required as per contract or inherent in the nature of the work
• Usually involve physical limitations (e.g., you cannot build the ceiling until walls are constructed)

Discretionary Dependencies

• Also referred to as preferred logic, preferential logic, or soft logic
• Should be used with care and well documented, as they may limit later scheduling options

External Dependencies

• Involve a relationship between project and non-project activities such as activities outside the project team’s control (e.g., dependence on external sources for deliveries, environmental factors governed by statutes, etc.)

Project Network Diagrams

• Preferred technique for showing activity sequencing
• A schematic display of the logical relationships among, or sequencing of, project activities

Arrow Diagramming Method (ADM)

• Also called activity-on-arrow (AOA) project network diagrams
• Activities are represented by arrows
• Nodes or circles are the starting and ending points of activities
• Can only show finish-to-start dependencies