Crashing a Project
It is often possible to decrease the overall time to complete a project by decreasing the
duration of particular activities. This may involve cost.
The most important activities to reduce are those in the critical path.
When we reduce the duration of activities in the critical path by crashing the project, we
will improve the project completion time and it may be that the critical path for the
project is changed.
Example 1
1. Complete a forward & backward scan and find Earliest Completion Time and Critical
Path.
Activity
A
B
C
D
E
F
G
H
J
K
Normal completion
time (days)
10
5
3
5
4
6
6
7
5
4
Crash time
(days)
8
5
2
4
4
5
4
5
5
3
Cost of crashing
per day ($)
400
400
600
500
200
300
400
K
G
A
B
D
C
H
F
E
2. Crash the project so it is completed in the minimum time.
a. What is the new Earliest Completion Time?
b. What is the cost to attain this ECT?
TMI / DBE
1
J
Crashing a Project
Example 2
1. Complete a forward & backward scan and find earliest completion time.
E, 2
B, 3
A, 3
F, 3
C, 5
H, 4
J, 2
G, 4
D, 7
2. Some of the activities can be reduced in time by using more workers. The table
below shows these activities, the additional cost of each day saved and the
maximum number of days by which the activity can be reduced.
Activity
C
F
G
Cost ($/day)
200
500
100
Maximum reduction (days)
2
2
1
What is the shortest time in which the project can now be completed?
3. The company receives a bonus of $300 for each day saved. Complete the table
below outlining the benefits of reducing the time for completion of the project.
Project time
(days)
17
16
15
14
Total cheapest
costs ($)
0
200
Activities
reduced in time
C
Total bonus
paid ($)
0
300
C, F
4. Describe the option from Q3 that results in the greatest saving.
TMI / DBE
2
Total savings
0
100
0
Crashing a Project
Example 3
A company is setting up in new offices. Their activities for this project are outlined in the
table:
Activity
Description
A
B
Plan office layout
C
D
E
F
G
H
I
Plan computer
requirements
Order office furniture
Investigate Network
Infrastructure
Install network
infrastructure
Order computer hardware
Install Furniture
Install computer
hardware
Install software and test
Duration
(days)
7
5
Predecessors
-
Cost per
Day ($)
300
400
Possible
reductions
2
2
5
3
A
B
0
400
2
1
5
D
300
3
7
2
4
B
C
E, F
200
0
400
3
0
1
2
H
0
0
a. Construct a network diagram.
b. Conduct a forward and backward scan, establish the critical path, project time
and floats.
CRITICAL PATH –
PROJECT TIME –
FLOATS:
TMI / DBE
3
Crashing a Project
c. The last two columns in the original table show activities whose duration can be
reduced and the cost per day of doing this.
i. What is the minimum time for completion of the project if all possible
reductions can be made?
Path
No.
1
2
3
The paths in the
network are:
A–C–G
B–F–H–I
B-D–E–H-I
ii.
Length
Length if all reductions
made.
What is the minimum cost for crashing the project?
d. The company wants to spend a maximum of $2000 to crash the project. Which
activities should be reduced and what is the new completion time?
TMI / DBE
4