In Primavera P6, the calculation of multiple critical paths is based on the analysis of free float and total float within the network schedule. Here's how it handles scenarios where multiple paths have the same float:

Key Concepts

• Critical Path: Longest path(s) through the project network with the least total float.
• Free Float: Time an activity can be delayed without affecting the early start of its successor.
• Total Float: Time an activity can be delayed without delaying the project's completion.

Handling Multiple Paths with the Same Float

1. Path Enumeration by Free Float: Identifies paths based on free float. If multiple paths have the same free float, they are treated as part of the same tier of criticality.
2. Sorting by Activity IDs or Sequence: When paths have identical free float values, activity IDs or sequence order may influence prioritization.
3. Relationships and Logic: Logical dependencies (predecessors and successors) drive path enumeration. Relationships between activities can lead to different rankings.
4. Options in Calculation Settings: Calculation settings (e.g., total float threshold or longest path) can affect path identification. Adjusting these settings may clarify critical paths.
5. Longest Path Calculation: If enabled, focuses on the path determining the project's finish date, regardless of float values.

Practical Steps to Analyze Multiple Paths

• Check Float Values: Review free float and total float for all activities.
• Review Logic: Examine network logic to understand similar float values.
• Use Trace Logic View: Visualize paths in Trace Logic or Activity Network views.
• Customize Critical Path Definition: Modify settings to highlight differences between paths.

By analyzing free float, logic, and leveraging Primavera's settings, you can better understand multiple critical paths.

Definition of Multiple Float Paths

The Multiple Float Path feature was introduced to Primavera Project Management in version 5.0 of the software.  The software's Help feature explains: 

Analysing the schedule using multiple critical float paths

When you schedule a project, you can choose to calculate multiple critical float paths (sequences of activities) that affect the project schedule. By calculating multiple critical float paths, you can determine the most critical path in the project schedule, along with sub-critical paths that affect the completion of the most critical path. 

While you can determine the critical path of activities based on total float or longest path, these methods do not offer insight into sub-critical paths that may also affect the project schedule. For example, if you choose to identify critical activities based on a maximum total float threshold, the module will identify all activities beyond the threshold as critical even if the activities have no relationships or do not affect the project end date. Likewise, if you choose to identify critical activities based on longest path, the module will identify the critical path of activities but will not identify sub-critical paths that affect the critical path. 

In the Advanced tab of the Schedule Options dialog, you can choose to calculate a specific number of critical float paths based on total float or free float. You can also choose the activity you want the float paths to end on. By choosing an activity, you can calculate multiple float paths that affect the entire project schedule, a specific part of the schedule, or a milestone in the schedule. 

When you schedule the project, the module identifies the most critical float path in the schedule and assigns those activities a Float Path value of 1. Then, depending on the number of paths you choose to calculate, the module identifies other float paths (sub-critical float paths) that affect the most critical float path and numbers the paths in ascending order (beginning with 2) based on the criticality of the path. 

After you schedule a project, you can display the Float Path and Float Path Order columns in the Activity Table. Group by Float Path to view the activities in each critical float path, then sort by Float Path Order to view the order in which the activities were processed. 

Note:  

Calculating multiple critical float paths does not affect how you define critical activities. When you schedule a project, you must choose to define critical activities by a maximum float time or by longest path in the General tab of the Schedule Options dialog box. When you run the scheduler, activities are flagged as critical based on this setting. If you also choose to calculate multiple critical float paths, the float paths are calculated after the project has been scheduled. Critical activities that are not part of a critical float path remain tagged as critical.