Project Schedule Compression/

Crashing
 Time/Cost Trade-off
Project Acceleration: An
Added Cost or Cost
Savings?
Schedule Acceleration is
shortening the duration of
the project schedule
without reducing the
project scope, till reaching Scope
the desired duration or the
crash duration, whichever
comes first

2
 Project Schedule Acceleration
Schedule acceleration usually –but not always-
increases project cost and often has physical and
practical limitation to how much it can be shortened
Synonymous terms: Schedule compression, schedule
crashing, schedule acceleration, and time-cost
tradeoff, schedule shortening
Schedule acceleration may be:
◼ Planned before construction starts (accelerated schedule), or
◼ Decided in the middle of the project (recovery schedule)

3
 Why Do Owners Demand
Schedule Acceleration?
1. To make sure contractor’s finish date meets
their deadline
2. To respond to market demand / maximize
profit
3. For the convenience of the public
4. To suit their cash flow (decelerate?)
5. Simply to reduce cost

4
 Why Do Contractors Accelerate
Schedules?
1. To meet owner’s (contract’s) stipulated date
2. To avoid penalties (liquidated damages) and/or
get early finish bonus

3. To start other projects

4. Simply to reduce cost / increase profit

5
 How Important is it to Finish on
Schedule?
Contractors must always strive to finish on time but
not all projects are the same:
1. Critical: A stadium for an international event (World Cup)
2. Very Important: School building to open by beginning of the
academic year
3. Important: Hotel or shopping center to finish before the high
season
4. Somewhat important: A commercial / office building with no
specific date committed
5. Not important: personal residence

6
Slide No. 7
The Northridge Earthquake Case
On January 17, 1994, a quake of 6.7
magnitude caused heavy damage and high
casualties in Northridge, California. Two
sections of the Interstate 10 in Santa Monica
were damaged.
◼ That part of I-10 was described as the busiest
highway in the world!

8
Slide No. 9
Slide No. 10
Constr. Project Sched. & Control - Dr. Mubarak - Part 8 Slide No. 11
The Northridge Earthquake Case
The immediate major concern for Caltrans
(the California Department of Transportation)
was reopening the public highways, in one of
the nation’s busiest areas
Caltrans had to get legislators’ approval to cut
the red tape and shorten the bureaucratic
process to select design and construction
firm(s)

12
The Northridge Earthquake Case
Caltrans engineers estimated the repair of the
I-10 segments (including the bridge) project
to take 140 days and cost $22.3 million
Caltrans solicited Design-Build bids for the
project so the project can be performed
quicker
C.C. Myers, Inc., of Rancho Cordova, CA, was
awarded the project with a bid of $14.7
million (crazy?)
13
The Northridge Earthquake Case
The contract had a clause of:
◼ Liquidated damages of $205,000 for each day of
delay beyond 140 days, and
◼ Bonus of $200,000 for each day of early finish, i.e.
less than 140 days
Big carrots and huge sticks!

14
The Northridge Earthquake Case
The project was fast-tracked. C. C. Myers worked
around the clock (24/7); putting large amount of
resources in the project, making this project the
focus of the company
What also helped was the cooperation between
Caltrans and the contractor. Caltrans did its part to
help push the project; assigning 10 engineers on the
day shift and four on call at night to inspect work and
answer questions

15
The Northridge Earthquake Case
The contractor was able to finish the project
in 66 days only; 74 days ahead of the
stipulated deadline
Bonus per day $200,000
Early days 74
Total bonus $14,800,000
Original contract sum $14,700,000
Total compensation $29,500,000

◼ Yes, crazy like a fox!

16
The Northridge Earthquake Case
C. C. Myers may have gone, in the process of
expediting the schedule, over their original
budget but with the large bonus, it certainly
had the last laugh
◼ There was a great deal of planning before the award
so they can “hit the ground running”
◼ The moto was “drop everything and focus on this
project”
◼ The incentive worked because everyone could see
the light at the end of the tunnel!
17
The Northridge Earthquake Case
Despite the large paid bonus, Caltrans seemed to be
pleased with the results. The convenience of the
public was well worth the effort and the money.
Caltrans and C. C. Myers both believe that despite
the schedule compression, there was no compromise
on work quality
What else C. C. Meyers gained from that project?
◼ Huge positive publicity
◼ Reputation that paid off
◼ This means $$$

18
Methods for Accelerating Work in a
Project
1. Invest more time and 7. Work overtime, more
money on planning workers and equipment,
2. Contractual adjustments / more shifts
incentives 8. Acquire special materials,
3. Revisit the schedule equipment, and
technologies
4. Fast-track the project 9. Offer incentives: individual,
5. Value engineering and crews, entire team
constructability studies 10. Improve project
6. Improve communications management

19
How overtime affect productivity

20
Concept of Schedule Acceleration
1. Shorten the longest (critical) path. Start with the easiest/least
expensive activity to be shorten

2. At a certain point, the critical path will tie with the next critical
path. Shorten both paths: either select a common activity
(shared by both paths) or shorten two activities; one on each
path

3. At further point, the two critical paths will tie with the next
critical path. Shorten all three+ paths, and so on

4. Stop when you achieve desired duration or when the project is

completely crashed
21
 Schedule Compression: Multiple
Paths - 1
Path 1

Path 2

Path 3

Path 4

Path 5

Path 6

Path 7

Path 8

Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

22
 Schedule Compression: Multiple
Paths - 2
Path 1

Path 2

Path 3

Path 4

Path 5

Path 6

Path 7

Path 8

Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

23
 Schedule Compression: Multiple
Paths - 3
Path 1

Path 2

Path 3

Path 4

Path 5

Path 6

Path 7

Path 8

Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

24
 Schedule Compression: Multiple
Paths - 4
Path 1

Path 2

Path 3

Path 4

Path 5

Path 6

Path 7

Path 8

Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

25
 Schedule Compression: Multiple
Paths - 5
Path 1

Path 2

Path 3

Path 4

Path 5

Path 6

Path 7

Path 8

Days 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

26
Effect of Project Acceleration on Cost

Direct cost: increases at an increasing rate

Indirect cost (overhead): decreases linearly

Total cost: watch the curve go down and up

27
Impact of Acceleration on Direct
Cost

Schedule
compression

Slide No. 29
 Why Does Acceleration Increase
Direct Cost
1. We start with the least expensive activity to crash.
As we crash more, our options narrow down and
get more and more expensive
2. When we start, accelerating one activity by one day
usually results in the shortening the project
duration by one day too. As we progress and
critical paths tie, we will need to crash several
activities; each by one day in order to shorten the
project duration by one day

30
Impact of Acceleration on
Indirect Cost

Schedule
compression

Slide No. 32
 Indirect Cost (Overhead)
Overhead remains constant for normal acceleration
Does the overhead really stay constant for more aggressive
acceleration?
◼ In the beginning of the process, this assumption may be true, but
as acceleration gets more aggressive, overhead / day may
increase:
◼ more workers and/or a second shift, the office may need more
staff and equipment
◼ Its utilities bills will increase,
◼ There may be a need for night lighting.
◼ Most likely, there is also additional overhead cost due to the
management planning effort for the acceleration.

33
 Indirect Cost (Overhead)
For example, if the normal duration is 225 days:
◼ Overhead = $2,000/day with project duration = 225 – 215
days
◼ Overhead = $2,500/day with project duration = 214 – 200
days
◼ Overhead = $3,000/day for project duration less than 200
days

34
Impact of Acceleration on Total
Cost

Schedule
compression

Slide No. 35
Time/Cost Trade-offs - Example
Act IPA Duration Cost $

Norm Crash Norm Crash

A - 5 4 500 600
B A 7 5 350 500
C A 8 5 800 920
D A 11 7 1200 1400
E B,C 6 4 600 700
F C 4 4 500 500
G D,F 7 5 700 1000
H E,F 6 5 300 420

36
 Example Solution: The Network
5, 12
B 13, 19 19, 25
7 E H
6, 13 6 6
13, 19 19, 25
0, 5 5, 13 25

A C PF
5 8
0, 5 5, 13 13, 17 17, 24 25
F G
Path Length
4 7
14, 18 18, 25
ABEH 24
5, 16
ACEH 25
D
11 ACFH 23
7, 18 ACFG 24
ADG 23
37
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100
B 7 5 $350 $500 2 $150 $75
C 8 5 $800 $920 3 $120 $40
D 11 7 $1,200 $1,400 4 $200 $50
E 6 4 $600 $700 2 $100 $50
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150
H 6 5 $300 $420 1 $120 $120

Days Cut 0
Project Duration 25
Increased cost $0
Direct Cost $4,950
Overhead Cost $3,000
Total Cost $7,950

Slide No. 38
 Example Solution:
The Paths, before crashing
Path Duration
ABEH 24
ACEH 25
ACFH 23
ACFG 24
ADG 23

39
 Path(s) to be
shorten:
ACEH
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100
B 7 5 $350 $500 2 $150 $75
C 8 5 $800 $920 3 $120 $40 1
D 11 7 $1,200 $1,400 4 $200 $50
E 6 4 $600 $700 2 $100 $50
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150
H 6 5 $300 $420 1 $120 $120

Days Cut 0 1
Project Duration 25 24
Increased cost $0 $40
Direct Cost $4,950 $4,990
Overhead Cost $3,000 $2,880
Total Cost $7,950 $7,870

Slide No. 40
 Example Solution:
The Paths: Crashing cycle #1
Path Duration
ABEH 24 24
ACEH 25 24
ACFH 23 22
ACFG 24 23
ADG 23 23

41
 Path(s) to be
shorten:
ABEH
ACEH
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100
B 7 5 $350 $500 2 $150 $75
C 8 5 $800 $920 3 $120 $40 1
D 11 7 $1,200 $1,400 4 $200 $50
E 6 4 $600 $700 2 $100 $50 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150
H 6 5 $300 $420 1 $120 $120

Days Cut 0 1 1
Project Duration 25 24 23
Increased cost $0 $40 $50
Direct Cost $4,950 $4,990 $5,040
Overhead Cost $3,000 $2,880 $2,760
Total Cost $7,950 $7,870 $7,800

Slide No. 42
 Example Solution:
The Paths: Crashing cycle #2
Path Duration
ABEH 24 24 23
ACEH 25 24 23
ACFH 23 22 22
ACFG 24 23 23
ADG 23 23 23

43
 Path(s) to be
shorten:
ABEH
ACEH
ACFG
ADG
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100 1
B 7 5 $350 $500 2 $150 $75
C 8 5 $800 $920 3 $120 $40 1
D 11 7 $1,200 $1,400 4 $200 $50
E 6 4 $600 $700 2 $100 $50 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150
H 6 5 $300 $420 1 $120 $120

Days Cut 0 1 1 1
Project Duration 25 24 23 22
Increased cost $0 $40 $50 $100
Direct Cost $4,950 $4,990 $5,040 $5,140
Overhead Cost $3,000 $2,880 $2,760 $2,640
Total Cost $7,950 $7,870 $7,800 $7,780

Slide No. 44
 Example Solution:
The Paths: Crashing cycle #3
Path Duration
ABEH 24 24 23 22
ACEH 25 24 23 22
ACFH 23 22 22 21
ACFG 24 23 23 22
ADG 23 23 23 22

45
 Path(s) to be
shorten:
ABEH
ACEH
ACFG
ADG
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100 1
B 7 5 $350 $500 2 $150 $75
C 8 5 $800 $920 3 $120 $40 1 1
D 11 7 $1,200 $1,400 4 $200 $50 1
E 6 4 $600 $700 2 $100 $50 1 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150
H 6 5 $300 $420 1 $120 $120

Days Cut 0 1 1 1 1
Project Duration 25 24 23 22 21
Increased cost $0 $40 $50 $100 $140
Direct Cost $4,950 $4,990 $5,040 $5,140 $5,280
Overhead Cost $3,000 $2,880 $2,760 $2,640 $2,520
Total Cost $7,950 $7,870 $7,800 $7,780 $7,800
Least Cost

Slide No. 46
 Example Solution:
The Paths: Crashing cycle #4
Path Duration
ABEH 24 24 23 22 21
ACEH 25 24 23 22 20
ACFH 23 22 22 21 20
ACFG 24 23 23 22 21
ADG 23 23 23 22 21

47
 Path(s) to be
shorten:
ABEH
ACFG
ADG
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100 1
B 7 5 $350 $500 2 $150 $75 1
C 8 5 $800 $920 3 $120 $40 1 1 1
D 11 7 $1,200 $1,400 4 $200 $50 1 1
E 6 4 $600 $700 2 $100 $50 1 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150
H 6 5 $300 $420 1 $120 $120

Days Cut 0 1 1 1 1 1
Project Duration 25 24 23 22 21 20
Increased cost $0 $40 $50 $100 $140 $165
Direct Cost $4,950 $4,990 $5,040 $5,140 $5,280 $5,445
Overhead Cost $3,000 $2,880 $2,760 $2,640 $2,520 $2,400
Total Cost $7,950 $7,870 $7,800 $7,780 $7,800 $7,845
Least Cost

Slide No. 48
 Example Solution:
The Paths: Crashing cycle #5

Path Duration
ABEH 24 24 23 22 21 20
ACEH 25 24 23 22 20 19
ACFH 23 22 22 21 20 19
ACFG 24 23 23 22 21 20
ADG 23 23 23 22 21 20

49
 Path(s) to be
shorten:
ABEH
ACFG
ADG
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100 1
B 7 5 $350 $500 2 $150 $75 1 1
C 8 5 $800 $920 3 $120 $40 1 1 1
D 11 7 $1,200 $1,400 4 $200 $50 1 1
E 6 4 $600 $700 2 $100 $50 1 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150 1
H 6 5 $300 $420 1 $120 $120

Days Cut 0 1 1 1 1 1 1
Project Duration 25 24 23 22 21 20 19
Increased cost $0 $40 $50 $100 $140 $165 $225
Direct Cost $4,950 $4,990 $5,040 $5,140 $5,280 $5,445 $5,670
Overhead Cost $3,000 $2,880 $2,760 $2,640 $2,520 $2,400 $2,280
Total Cost $7,950 $7,870 $7,800 $7,780 $7,800 $7,845 $7,950
Least Cost

Slide No. 50
 Example Solution:
The Paths: Crashing cycle #6

Path Duration
ABEH 24 24 23 22 21 20 19
ACEH 25 24 23 22 20 19 19
ACFH 23 22 22 21 20 19 19
ACFG 24 23 23 22 21 20 19
ADG 23 23 23 22 21 20 19

51
 Path(s) to be shorten: all
ABEH ACEH
ACFH ACFG
ADG
Linear Project Crashing Overhead per day = $120

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100 1
B 7 5 $350 $500 2 $150 $75 1 1
C 8 5 $800 $920 3 $120 $40 1 1 1
D 11 7 $1,200 $1,400 4 $200 $50 1 1
E 6 4 $600 $700 2 $100 $50 1 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150 1 1
H 6 5 $300 $420 1 $120 $120 1

Days Cut 0 1 1 1 1 1 1 1
Project Duration 25 24 23 22 21 20 19 18
Increased cost $0 $40 $50 $100 $140 $165 $225 $270
Direct Cost $4,950 $4,990 $5,040 $5,140 $5,280 $5,445 $5,670 $5,940
Overhead Cost $3,000 $2,880 $2,760 $2,640 $2,520 $2,400 $2,280 $2,160
Total Cost $7,950 $7,870 $7,800 $7,780 $7,800 $7,845 $7,950 $8,100
Least Cost Least Time
Slide No. 52
 Example Solution:
The Paths: Crashing cycle #7

Path Duration
ABEH 24 24 23 22 21 20 19 18
ACEH 25 24 23 22 20 19 19 18
ACFH 23 22 22 21 20 19 19 18
ACFG 24 23 23 22 21 20 19 18
ADG 23 23 23 22 21 20 19 18

53
 Total Cost with Compression
Overhead = $120/day
$8,150

$8,100

$8,050

$8,000
Total Cost

$7,950

$7,900

$7,850

$7,800

$7,750
16 18 20 22 24 26 28
Project Duration

Note that the curve along with the optimum points

change if the cost of overhead / day changes

Slide No. 54
 What if Overhead is Different?
Linear Project Crashing Overhead per day = $200

Activity Duration Cost Duration Cost Crash Cost

Normal Crash Normal Crash Difference Difference per Day Days Shortened
A 5 4 $500 $600 1 $100 $100 1
B 7 5 $350 $500 2 $150 $75 1 1
C 8 5 $800 $920 3 $120 $40 1 1 1
D 11 7 $1,200 $1,400 4 $200 $50 1 1
E 6 4 $600 $700 2 $100 $50 1 1
F 4 4 $500 $500 0 $0
G 7 5 $700 $1,000 2 $300 $150 1 1
H 6 5 $300 $420 1 $120 $120 1

Days Cut 0 1 1 1 1 1 1 1
Project Duration 25 24 23 22 21 20 19 18
Increased cost $0 $40 $50 $100 $140 $165 $225 $270
Direct Cost $4,950 $4,990 $5,040 $5,140 $5,280 $5,445 $5,670 $5,940
Overhead Cost $5,000 $4,800 $4,600 $4,400 $4,200 $4,000 $3,800 $3,600
Total Cost $9,950 $9,790 $9,640 $9,540 $9,480 $9,445 $9,470 $9,540
Least Cost Least Time

Not only amounts of cost changed, but the “Least Cost

Duration” changed from 22 to 20 days

Slide No. 55
 Definition: What is “Normal”?
Normal duration is the amount of time required to
finish the project under ordinary circumstances
without any deliberate acceleration or deceleration.
Normal cost is the cost of a project that is performed
within the normal duration.
These definitions also apply to individual activities
This term differs among contractors as they have
different work plans / crews and productivities

56
 More Definitions
Least-Cost Duration (LCD): The duration of an
activity associated with the Least Cost Schedule.
Least-Cost Schedule: A CPM schedule accelerated to
reach the point where the total cost of the project
(direct and indirect) is minimum . If the duration of
the schedule increases or decreases, the total cost
will increase.

57
 More Definitions
Crash Cost (CC): Total cost of a construction project
(direct and indirect), including the impact of crashing
(maximum compression of) the schedule.
Crash Duration (CD): The least possible duration for
a construction project schedule. It is usually achieved
by maximum Schedule Compression.

58
 Schedule Compression Using
Computers
Luckily, there is no fully automated process!
1. Create a spreadsheet displaying all activities; their
normal and crash duration along with their normal
and crash cost.
2. Do a regular CPM schedule and determine the
critical path.
3. Make a backup copy of the schedule.
4. Enter the imposed finish date and “reschedule”:
◼ Negative float? How much?

59
 Schedule Compression Using
Computers-2
5. Start shortening the critical path by picking the
activity with least cost per day. Reduce the duration by
one day. Note the impact on the critical path:
◼ If the critical path did not get shortened, then there is
another (2nd) critical path that needs to be shortened

60
 Schedule Compression Using
Computers-3
7. Record new durations and cost in the spreadsheet of
step 1.
8. You can crash the schedule of activity by more than
one, say x days. Your project’s decrease in duration
is y:
0<y≤x
8. The more you crash, the more difficult and more
expensive it becomes to crash.
9. Stop when you achieve your goal:
▪ Minimum cost, certain duration, or absolute minimum
duration 61
Concrete works, typical floor, 10-story office building,
contractor has 2 crews for formwork, reinforcement,
concrete placement

time cost
No. Method reduction increase Notes
1 Add concrete accelerators May not be a good idea in hot weather
2 Use pump in lieu of crane & bucket
3 Increase the pump size / capacity May need to adjust crew size
4 Use special forms / Fly tables May need redesign for the slab
5 Offer incentives to crews
6 Work overtime - more hours/day Pay attention to impact on productivity
7 Work overtime - work Sat / Sun
8 Additional crew Long term need?
9 Double shift Will need night lighting / turnover time
Slide No. 62
Project Acceleration: Final Thoughts
Project Acceleration should be based on scientific
and systematic principles
◼ It is not random dumping of extra resources on the
site
◼ It is not a race to set records

It should be done only to the extent needed

You cannot accelerate all your projects; prioritize
them

63
Project Acceleration: Final Thoughts
(Cont’d.)
There are physical and practical limitations to project
acceleration

Unplanned or unorganized acceleration may result in

◼ Delays

◼ Higher cost

◼ Quality problems – rework

◼ More variation orders and claims

◼ Chaos – safety issues

64
Project Acceleration: Final Thoughts
(Cont’d.)
Project acceleration has a significant impact
on cash flow, especially the owner:
Your progress payments get higher:
1. The project total cost has likely increased
2. As the project is being performed in shorter time,
you do more work per period

65
Project Acceleration: Final Thoughts
(Cont’d.)
Impact of “losing” one work day is more
severe
Not all subcontractors / crews or activities
need to be involved in the acceleration
Project contractor’s acceleration without
owner’s approval may lead to problems
Owner’s target finish date may be revised
during construction but other parties have to
be informed

66
 Recovery Schedules
Recovery Schedule: A schedule prepared
during construction phase, after the project
falls behind (either fails to meet its interim
target or shows serious signs of failure to
meet its deadline), with adjustments made by
the contractor that expedite the remainder of
the project and ensure a timely finish.
It follows the same acceleration process but
starting from the point “now”.

67
 Optimum Scheduling
Optimum scheduling is selecting the project's
starting point and the composition of the
durations and timing of its activities that will
result in optimum schedule and least cost while
maintaining the project's scope and quality

Project scheduling in areas with extreme weather

68