---
title: "TCTO, crashing and reducing project duration"
subject: "Construction Management"
chapter: 2
key: "semester_8/construction_management:tcto-crashing-reduce-schedule"
source: https://www.bctengineer.com/q/semester_8/construction_management/tcto-crashing-reduce-schedule
site: BCT Engineering
---

# TCTO, crashing and reducing project duration

Construction Management · Chapter 2: Construction Planning and Scheduling

- Asked in: 2066 Magh (old course), 8 marks
- Video: [Project crashing full example (part 1/2)](https://www.youtube.com/watch?v=ZOW2QU_sbJ4) — Engineer4Free
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/construction_management/tcto-crashing-reduce-schedule
- Whole chapter: https://www.bctengineer.com/md/semester_8/construction_management/chapter-2

## Question

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?

## 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.

## Answer

#### 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.

```text
 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Total project cost equals:
   A. Direct only
   B. Indirect only
   C. Direct cost + indirect cost
   D. Direct - indirect
   Answer: C. Total = direct + indirect. (Key point: Total cost)

2. Crashing means:
   A. Cancelling an activity
   B. Deliberately shortening an activity by adding resources at extra direct cost
   C. Delaying an activity
   D. Reducing quality
   Answer: B. More labour, shifts or equipment shorten the duration at extra cost. (Key point: Crashing)

3. Activity X slope Rs 2,000/day and overhead Rs 3,000/day; crashing X:
   A. Loses Rs 1,000/day
   B. Saves Rs 1,000/day
   C. Saves Rs 5,000/day
   D. Makes no difference
   Answer: B. 3,000 saved less 2,000 cost = 1,000 saved. (Key point: Example)

4. First step when asked for a big schedule cut?
   A. Crash random activities
   B. Check the critical path and float
   C. Cut quality
   D. Add all resources
   Answer: B. Identify critical activities before crashing. (Key point: Boss's request)

## Related in Construction Management

- [Time cost trade-off concept with example](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-concept) — Construction Management, chapter 2, asked 5×
- [Time cost trade-off and steps in planning](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-steps-planning) — Construction Management, chapter 2
- [TCTO numerical: crashing critical path, Rs 30/day](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-2069-bhadra) — Construction Management, chapter 2
- [TCTO numerical: least cost schedule, Rs 2000/week](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-2068-bhadra) — Construction Management, chapter 2
- [TCTO numerical: lowest cost schedule, Rs 400/week](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-2075-bhadra) — Construction Management, chapter 2
- [TCTO numerical with time-cost chart (five activities)](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atcto-2079-jestha) — Construction Management, chapter 2