Schedule Compression: Crashing vs Fast-Tracking

What Is Schedule Compression?

Schedule compression refers to techniques used to shorten the project schedule without altering the project scope. It is typically employed when a project is falling behind its baseline or when stakeholders demand an earlier completion date. The two primary methods are crashing and fast-tracking. While both aim to reduce duration, they differ fundamentally in approach, cost, and risk.

Crashing: Adding Resources to Compress Duration

Crashing involves adding extra resources to critical path activities to complete them faster. This can mean assigning more labour, overtime, additional equipment, or overlapping shifts. The key principle is to crash only those activities on the critical path, as shortening non-critical tasks does not affect the overall project finish date.

How Crashing Works

For each critical activity, you evaluate the cost-time trade-off. Typically, there is a 'normal' duration and a 'crash' duration (the minimum possible time). The cost slope (cost per unit time saved) is calculated. You crash activities with the lowest cost slope first, stopping when the desired compression is achieved or when no further compression is possible.

Example: If an activity normally takes 10 days with 2 workers, adding a third worker might reduce it to 7 days, but at a higher labour cost. The cost slope here is (extra cost) / (3 days saved).

Risks of Crashing

• Increased cost: Overtime pay, additional resources, and potential inefficiencies (e.g., diminishing returns when too many workers are added).
• Quality issues: Rushed work may lead to defects or rework.
• Safety concerns: Fatigue from overtime can cause accidents.
• Resource constraints: Limited availability of skilled labour or equipment may prevent crashing.

Fast-Tracking: Overlapping Tasks to Save Time

Fast-tracking involves performing critical path activities in parallel that were originally planned to be sequential. This is done by starting a successor task before its predecessor is fully complete, relying on partial dependencies or lead times. For example, in construction, you might start foundation work before all structural steel drawings are finalized.

How Fast-Tracking Works

Identify activities with a finish-to-start (FS) relationship that can be converted to a start-to-start (SS) with a lag, or simply overlapped. The amount of overlap is limited by the nature of the work; you cannot start a task until its predecessor has produced enough output to allow a meaningful start.

Example: In software development, coding can begin after the design is 50% complete, rather than waiting for 100% design sign-off.

Risks of Fast-Tracking

• Increased rework: If the predecessor's output changes, the overlapping work may need redoing. This can actually increase overall duration.
• Communication overhead: More coordination is needed between teams working concurrently.
• Higher stress on team: Parallel work often means tighter deadlines and less buffer.
• Potential for scope creep: Overlapping may lead to informal changes that are not properly controlled.

Comparing Crashing and Fast-Tracking

When to Use Each Technique

When to Crash

• You have budget contingency to cover extra costs.
• Resources (labour, equipment) are readily available.
• The critical path has activities that can be accelerated with diminishing returns acceptable.
• Quality and safety can be maintained with additional oversight.

When to Fast-Track

• Budget is constrained; you cannot afford extra resources.
• The project has logical dependencies that allow safe overlap (e.g., design-build projects).
• You have a strong change control process to manage rework risk.
• The team is experienced in concurrent engineering or agile methods.

Best Practices for Schedule Compression

• Always compress the critical path first. Shortening non-critical tasks does not help the finish date.
• Use schedule analysis tools. Tools like Project Assure can help you identify critical path activities and run what-if scenarios to evaluate compression options.
• Document assumptions and risks. Both crashing and fast-tracking introduce new risks that should be captured in the risk register.
• Monitor rework loops. Fast-tracking can create feedback loops; ensure you have a process to incorporate changes without derailing the schedule.
• Consider alternative methods. Sometimes reducing scope or adding a parallel shift (a form of crashing) is more effective than overlapping tasks.

Conclusion

Schedule compression is a valuable tool for project recovery, but it must be applied judiciously. Crashing offers predictable time savings at a cost premium, while fast-tacking carries higher rework risk but can save money if executed well. The best approach often combines both: fast-track where safe, and crash where necessary. Always analyse your schedule thoroughly before compressing; a single misstep can worsen delays. Using a free tool like Project Assure allows you to test compression scenarios without uploading your data, ensuring your project stays on track—or gets back on it.