CDT505 Chap.5 Budgets, Gantt Charts and Crashing
Budgets, Gantt Charts and Crashing
Control cost and time on one baseline
Estimates predict resource needs, budgets authorise expenditure and a time-phased baseline places approved cost against scheduled work. Gantt charts communicate calendar timing, while networks preserve dependency logic. Crashing shortens duration through additional resources or a more expensive method.
The cost slope compares marginal direct cost with time saved, but compression works only on current critical paths and must be recalculated after each change because another path can become controlling.
Reconcile every compressed plan
A low crash slope is useful only when the activity shortens every controlling path and the extra capacity is genuinely available.
Each reduction can create a new critical path, so compression is iterative rather than a one-time ranking. Direct crash cost, indirect time saving and any change in quality or risk should be reported separately. After approval, the network, Gantt chart, resource assignment and time-phased budget must show the same revised plan; otherwise later control compares actual work with inconsistent baselines.
What this chapter covers
- 01
Cost estimates and approved budgets
- 02
Time-phased cost baselines
- 03
Gantt charts against network logic
- 04
Lead and lag relationships
- 05
Normal and crash limits
- 06
Crash slopes, critical paths and total cost
Worked example · free
Choose a crash candidate
- 2Compute both marginal slopes.
- 2Test current criticality.
- 2Choose and state the recalculation rule.
Key terms
- Cost Baseline
- The approved time-phased budget used to measure and control project cost performance.
- Gantt Chart
- A bar chart that displays activity timing, duration and milestones across a calendar.
- Lag
- A required waiting interval inserted between linked activities.
- Crashing
- Shortening activity duration through additional resources or a more costly method.
- Crash Slope
- The incremental direct cost for each unit of duration reduced between normal and crash limits.
Budgets, Gantt Charts and Crashing FAQ
What must be reconciled after crashing a schedule?
Show the approved shorter duration and added direct cost in the network, Gantt chart, resource assignment and time-phased budget. Recalculate all paths and report any new controlling path. If one representation still shows the normal plan, later variance reporting will compare actual performance with inconsistent baselines and produce a misleading control signal.
Why is the cheapest crash slope not always selected?
Only a reduction on every current controlling path can shorten the project. A low-cost non-critical activity may use float without changing completion. After each reduction, recalculate because another path can become critical and change the feasible choice.
How is a budget different from a cost estimate?
An estimate predicts the likely cost of resources or work. A budget authorises expenditure. A cost baseline then distributes that approved amount across work and time so actual performance can be compared with the plan.
When should a lag be represented as an activity?
Use a lag for genuine waiting that has no separate owner or resource, such as curing. If the interval contains controllable work, cost, responsibility or risk, model it as an activity so the plan does not hide management effort.
Assessment move
Use one work breakdown structure to build a cost estimate from personnel, materials, overhead and other project-specific items. Attach every amount to a work package and record the basis, such as hours, rates, quantities or supplier quotations. Distinguish the estimate from the authorised budget.
Place the approved costs in the periods when the scheduled work occurs to create a time-phased baseline, then redraw the same plan as a Gantt chart and a network. Write one sentence explaining what each view reveals and what it hides. Add a genuine lag, such as curing or external review, and a separate activity that carries work and ownership. This comparison stops hidden work from being disguised as waiting.
For crashing, create a table with normal time, crash time, normal cost and crash cost for every candidate activity. Compute the marginal slope, but cross out every activity that is not on a current critical path. Apply only one feasible unit of reduction, rerun all paths and recalculate the candidate set. Continue until the required date is met or another constraint binds.
Then add indirect cost per day and track direct, indirect and total cost after each step. Identify separately the shortest feasible duration and the least-total-cost duration because they need not coincide. Before accepting an answer, state whether durations are working days, whether added resources are truly available, whether quality or risk changes and whether multiple critical paths require simultaneous compression.
A complete recommendation names the objective, the marginal choice, the new network state and the operational assumption that could invalidate it.
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