Project Management guide · Scheduling and time
Fast Tracking vs Crashing: Differences and Worked Example
Fast tracking and crashing are the two main schedule compression techniques. Fast tracking overlaps activities that would normally run one after another, which adds risk. Crashing adds resources to critical activities to finish them sooner, which adds cost.
Key takeaways
- Fast tracking overlaps work and adds risk; crashing adds resources and cost.
- Use crash cost slope to choose the cheapest days to buy.
- Only compress critical activities and recheck the path after each step.
- Record the extra risk and cost through change control.
Side-by-side comparison
| Fast tracking | Crashing | |
|---|---|---|
| How | Run activities in parallel or overlap them | Add people, overtime, equipment or faster suppliers |
| Main cost | Risk of rework | Extra money |
| Works on | Discretionary dependencies | Activities that respond to more resources |
| Typical example | Start building before design is fully finished | Add a second installation crew |
| Effect on budget | Little direct effect unless rework occurs | Increases cost |
| Best when | Dependencies are soft and requirements are stable | Money is available and work can be divided |
Crash cost slope
Crash cost slope = (crash cost - normal cost) / (normal duration - crash duration). It is the extra cost of each day saved and lets you compare activities fairly.
| Activity | Normal | Crash | Max days saved | Slope per day |
|---|---|---|---|---|
| A Plan move | 3 days, $6,000 | 2 days, $9,000 | 1 | $3,000 |
| B Order furniture | 4 days, $8,000 | 3 days, $10,000 | 1 | $2,000 |
| D Install furniture | 5 days, $10,000 | 3 days, $13,000 | 2 | $1,500 |
| F Move and unpack | 2 days, $4,000 | Cannot crash | 0 | - |
Worked crashing example
The critical path A-B-D-F is 14 days; the other path A-C-E-F is 10 days.
- Target 13 days: crash the cheapest critical activity, D, by 1 day. Cost $1,500.
- Target 12 days: crash D by another day (now at its 3-day limit). Total $3,000. Paths: 12 and 10.
- Target 11 days: next cheapest is B at $2,000. Total $5,000. Paths: 11 and 10.
- Target 10 days: crash A by 1 day for $3,000, which shortens both paths because A is on both. Total $8,000. Paths: 10 and 9.
- No further crashing is possible on A-B-D-F, so the minimum is 10 days for $8,000 extra.
Worked fast-tracking example
Instead of waiting for all furniture to arrive, the team starts installing as the first deliveries come in: B to D becomes FS-2 days (a lead). D now starts on day 5 instead of day 7, and the project finishes on day 12 with no direct cost. The risk is that installers may need to return if late deliveries do not fit the layout.
How to choose
- Fast track first when dependencies are discretionary and the risk of rework is low.
- Crash when money is available and adding people genuinely speeds up the work.
- Combine both on long projects, but recheck the critical path after each change.
- Record the extra risks in the risk register and the extra cost in the budget.
Free templates for this topic
Frequently asked questions
What is the difference between fast tracking and crashing?
Fast tracking overlaps activities and increases risk; crashing adds resources and increases cost.
Which is better, crashing or fast tracking?
Neither is always better. Fast tracking is cheaper but riskier; crashing is more predictable but costs more.
What is an example of fast tracking?
Starting construction on the foundations while the upper floors are still being designed.
What is an example of crashing?
Paying for overtime or adding a second team to finish a critical activity sooner.
How do you calculate the cost per day of crashing?
(Crash cost - normal cost) / (normal duration - crash duration).
Does fast tracking increase cost?
Not directly, but rework caused by overlapping work can add cost later.
Is crashing a non-critical activity worthwhile?
It is possible, but it will not shorten the project, so it wastes money.
What is the crash point when crashing a schedule?
The shortest duration an activity can reach no matter how many resources are added.
Which dependencies are suitable for fast tracking?
Discretionary (soft) dependencies. Mandatory dependencies, such as physical constraints, usually cannot.
Are fast tracking and crashing on the PMP exam?
Schedule compression techniques are a standard topic in PMP study materials; see PMP certification.