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TCTO, crashing and reducing project duration

Short answer

Time-cost trade-off finds the duration at which total cost is minimum by balancing rising direct costs and falling indirect costs. Crashing is shortening an activity by adding resources, increasing direct cost. To reduce schedule considerably, crash cheapest critical activities, fast-track, add shifts, ensure early resources, and present the revised cost-time curve with risks and extra cost.

Explain the concept of 'time cost trade off' with illustrations. What do you mean by crashing of a project activity? Your boss is asking you to reduce the time schedule of a project considerably, what do you suggest?

Time-cost trade-off

It is the method of balancing project duration against cost. Total cost = direct cost + indirect cost. When an activity is speeded up, direct cost rises (overtime, extra labour, more equipment), while indirect cost (overheads, supervision, penalties) falls because the project takes less time. The lowest point of the total cost curve gives the optimum duration.

 Cost
  ^
  |T                              T     T = total cost
  | T                          T        D = direct cost
  |   T                     T           I = indirect cost
  |      T              T
  |         T    *   T       * = minimum total cost
  |D
  | D                               I
  |   D                       I
  |      D               I
  |          D     I
  |            I D
  |       I         D
  |  I                   D      D
  +-------------------------------------> Duration
   crash        optimum            normal

Example: if a critical activity X has a normal time of 10 days at Rs 20,000 and a crash time of 8 days at Rs 24,000, its slope = (24000 - 20000)/2 = Rs 2,000/day. If the project overhead is Rs 3,000/day, crashing X pays, saving Rs 1,000 per day.

Crashing

Crashing is the deliberate shortening of an activity's duration by adding resources (more labour, extra shifts, overtime, better equipment, a faster method) at an extra direct cost. Only critical activities are worth crashing, cheapest slope first.

My suggestion if the boss wants a considerable reduction

  1. Check the critical path and the float available in non-critical activities.
  2. Compute cost slopes and crash the cheapest critical activities one step at a time, comparing the extra cost with the indirect saving.
  3. Re-plan the logic: fast-track (overlap activities), change the sequence, and use precast units, ready-mixed concrete, more formwork sets and larger crews.
  4. Add shifts, overtime or night work, and subcontract some work.
  5. Ensure materials, equipment and finance are available early, and remove approval delays.
  6. Explain to the boss the extra cost and the risks to quality and safety, and give the revised cost-time curve so that the final target can be chosen.

✓ Answer checked by Claude Opus 5.5 (high effort)

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