Critical Path Method
0
Critical Path Float
Zero float activities define the project duration
2
Compression Options
Fast tracking first, crashing second
4
Dependency Types
FS, SS, FF, SF under precedence diagramming
red boxes are critical, delay any of them and the project slips
Network Diagram
Compression · Try Order
Fast Track
Run sequential activities in parallel. No added cost. Watch for rework risk.
Crash
Add resources to critical-path activities. Adds cost. Only if resource-bound.
how to read this
- › The diagram above shows a network of activities. Each box has ES (earliest start), EF (earliest finish), duration, and float.
- › Red boxes are on the critical path — the longest chain from start to finish. Zero float means any slip delays the whole project.
- › Blue boxes have float — they can slip (by their float amount) without affecting the end date.
- › When you need to shorten the schedule, always try Fast Track first (free) before Crashing (costly).
- › Compression only helps if you compress activities on the critical path. Compressing a floaty activity changes nothing.
Exam Traps
Fast tracking is tried before crashing
Fast tracking increases risk but not cost. Crashing increases cost. PMI expects you to exhaust the cheaper option first. When the question asks "what should the PM try FIRST," fast tracking is the answer unless risk is unacceptable.
Resource leveling can extend the critical path, smoothing cannot
Resource leveling resolves overallocation by delaying tasks, which can push out the end date. Resource smoothing only adjusts within available float. The exam tests this distinction directly.
Adding resources does not always shorten duration
Brooks' Law. Adding people to a late project can make it later because of training overhead and communication complexity. Crashing is only viable when the critical path activity is actually resource-constrained.
Near-critical paths become critical when activities slip
A path with 1 day of float is one delay away from being critical. Monitor near-critical paths, not just the one labeled "critical" today.
Zero float rule
Activities with zero float are on the critical path. A one-day delay there delays the whole project.
Fast track before crash
No cost increase first, cost increase second. That is the PMI preference order every time.
You are hosting dinner. The roast takes 3 hours, the salad takes 15 minutes. Your critical path is the roast. Nothing you do to the salad changes when dinner starts.
You can prep the salad any time in the 3 hours while the roast cooks. That flexibility is float. The roast has zero float — start late, eat late.
Instead of waiting for the roast to rest before making gravy, start the gravy while the roast rests. You saved time at the risk of rushing. No extra cost, just more risk.
Call a friend to chop vegetables in parallel. It costs you dinner for one more person, but it shortens the timeline. That is crashing.
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