Modifying Project Schedules to

Accommodate Time and Resource Constraints

Chapter 8

Copyright © 2010 by the McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/Irwin

Chapter Learning Objectives

• Recognize project constraints and apply the appropriate combination of methods to modify existing schedules.

• Apply the logic of time-cost trade-offs to systematically shorten a project’s expected duration by adding resources to key activities.

• Level-load project schedules to reduce variation in resource requirements or meet resource limitations.

• Estimate realistic project completion times by incorporating information about the availability of specialized resources.

• Differentiate between the critical path and the critical chain, and apply buffer concepts to reduce schedule risks.

• Explain project modification options to stakeholders and offer rational arguments for the most appropriate choices.

When you have mastered the material in this chapter, you should be able to:

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Modifying Project Schedules to Accommodate Time and Resource Constraints

“The first schedule is always wrong.”

Frederick Brooks

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Exhibit 8.1

Reasons for Schedule Modifications

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Exhibit 8.2Initial Network Schedule for Product Development Project with Early- and Late-Start Finish Times

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Schedule Modification Options

• Crashing

• Fast Tracking

• Delay Some Activities to Reallocate Resource Expenditures

• Reduce Scope

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Exhibit 8.4

Original and Compressed Schedules for Product Development Example Shown as a Comparative Gantt Chart

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Exhibit 8.4

Original and Compressed Schedules for Product Development Example Shown as a Comparative Gantt Chart

In this revised schedule,

• Task A, user requirements, and Task B, benchmark, are fast-tracked (performed concurrently), which shortens the planned duration by one month.

• This allows hardware, Task C, and software, Task D, to start a month earlier.

• However, it is not actually necessary to begin Task C, hardware, right after benchmarking is complete, so it has been delayed by one month, still leaving an additional month of float as a schedule buffer.

• Task D, software, can be crashed; more programmers can be hired to reduce duration from five months to four months.

• Integration, Task E, can start two months earlier than initially planned if software is completed at the end of month 6. continued

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Exhibit 8.4

Original and Compressed Schedules for Product Development Example Shown as a Comparative Gantt Chart

• Task F, production ramp up, can begin two months earlier than planned, and it can be reduced by two months because of a reduction in scope.

• The marketing plan, Task G, can also begin two months earlier than the initial plan, but could, if necessary, be delayed or extended by a month because it has float.

• And, Task H, handoff, can be completed at the end of month 13, meeting the expectations of the sponsor.

Of course, whether or not this new schedule works will depend on everything happening monthly. The project manager must clearly communicate the benefits, risks and potential challenge associated with this new schedule.

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Crashing Project Schedules

• Crashing involves an analysis of trade-offs between prolonging a project or adding resources to shorten it.

• To make project crashing decisions requires some knowledge of the cost of reducing task durations.

• Some activities can be shortened easily, others are more difficult to divide.

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Exhibit 8.5

Crashing Project Schedules

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Box 8.1

Round-the-Clock ProgrammingA Canadian company specializing in data-mining software for enterprisewide IT systems attempted to speed up some of its projects with round-the-clock programming. Programmers in Canada finished their work at the end of each day and electronically handed it off to programmers in India as they began their workdays. This was intended to cut programming time in half. Unfortunately, the geographic distance and asynchronous timing made it impossible for real-time communication, and the receiving team had trouble understanding the details and rationale underlying the programming done by colleagues on the other side of the world. The series of handoffs, likened to a relay race, actually caused projects to take more, rather than less, time. Company officials realized that although this type of programming had become an industry trend, it was not effective for their work. Consequently, they divided the work so certain projects were performed entirely in Canada and others were performed entirely in India. Productivity improved and projects were completed in far less time, and with better outcomes, than they had been under the round-the-clock strategy.

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Determining Crash Costs for Trade-Off Analysis

A general formula for calculating incremental crash costs is as follows:

Incremental crash cost = Crash cost - Normal cost Normal time - Crash time

Where:• Normal time is the time required for a task under

normal conditions, typically in the time specified in the initial project schedule.

• Crash time is the least amount of time in which a task can be feasibly completed.

• Normal cost is the cost of completing the task at its normal time.

• Crash cost is the cost of completing the task at its fully crashed time.

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Determining Ongoing Project Costs, Early-Completion Incentives, and Delay Penalties for Trade-Off Analysis

During the life cycle of any project, a set of costs accumulates on a daily basis. These can include:

• Salaries and benefits of core team members, adjusted for the percent of their time allocated to the project.

• Apportioned percentages of salaries and benefits of personnel who provide support services to team members.

• Apportioned costs associated with the physical space where team members work (rent, utilities).

• Rental of equipment dedicated to the project.8-14

Determining Ongoing Project Costs, Early-Completion Incentives, and Delay Penalties for Trade-Off Analysis

In addition to costs that accumulate over the life of the project, other incentives for finishing a project sooner rather than later can include:

• Incentives offered by customers for early completion.

• Contractual penalties for late delivery.

• Lost profits associated with late market entry.

Beyond tangible costs and incentives, a project manager also should consider:

• The potential for declining morale and associated losses in productivity and quality when a project is prolonged. Shorter projects hold people’s attention better than longer projects.

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Exhibit 8.7

Sequential Procedure for Crashing Project Activities

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Exhibit 8.8

Crash-Cost Calculations for Garage Remodel and Car Repair Project

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Exhibit 8.9

AON Diagram for Garage Remodel and Car Repair Project

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Exhibit 8.10

Time-Based Network for Garage Remodel and Car Repair Project

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Exhibit 8.11

Tabular Approach for Sequential Crashing

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Exhibit 8.12

19-Day Schedule for Garage Remodel and Car Repair Project after Task A Is Crashed by 2 Days

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Exhibit 8.13

17-Day Schedule for Garage Remodel and Car Repair Project after Task A Is Crashed by Two Days and Task D Is Crashed by Two Days

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Exhibit 8.1416-Day Schedule for Garage Remodel and Car Repair Project after Task A Is Crashed by Two Days, Task D Is Crashed by Two Days, and Tasks D and F Are Crashed Simultaneously by One Day

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Exhibit 8.1515-Day Schedule for Garage Remodel and Car Repair Project after Task A Is Crashed by Two Days, Task D Is Crashed by Two Days, Tasks D and F Are Crashed Simultaneously by One Day, and Task G Is Crashed by One Day

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Applying Crashing Concepts

• Start-up activities. Compressing early activities leaves room for unexpected contingencies that arise during project delivery.

• Activities in bottleneck positions. It makes sense to compress an activity that can affect many others.

• Long-duration activities. It is easier to find opportunities for compressing longer activities rather than shorter ones.

• Labor-intensive or low-skill activities. These are less expensive to compress than a technology-dependent activity.

• Activities subject to uncontrollable risks. Some activities are more vulnerable to risks than others.

• Divisible activities. Some activities are easier than others to divide and parcel out to several people.

In selecting tasks to crash in the absence of objective crash cost data, a project team should focus on the critical path. Beyond that, consider crashing:

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Fast Tracking

• Fast tracking involves scheduling two or more tasks simultaneously.

• Fast tracking can be applied independently or in combination with crashing and scope reduction to shorten a project’s duration.

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Exhibit 8.16

Depicting Fast Tracking for an Internet Project Using a Start-to-Start Precedence Relationship

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Modifying Schedules to Accommodate Resource Constraints

• Often, the first draft of a project schedule reveals that necessary resource loads exceed the availability of team members (overallocation).

• Or resource levels can be very uneven, producing situations in which people sometimes do not have enough to do (underallocation) and giving them impossibly heavy workloads at other times.

• Through the use of schedule float, it can be possible to smooth out the peaks and valleys in a resource load profile.

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Exhibit 8.17

Simple Resource Allocation Problem Demonstrating the Use of Schedule Float to Create Even Workforce Loading

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Exhibit 8.18

Precedence Table for Wildlife Film Project

Exhibit 8.18 Precedence Table for Wildlife Film Project

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Exhibit 8.19

Early-Start Time-Based Network for First Phase of Wildlife Film Project

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Time Constrained Resource SmoothingTime-constrained resource smoothing. Redistributing resources and float within the confines of a specified end date.

The process:

1.Schedule critical path activities. Assuming the project cannot be delayed, the critical path is a given constraint.

2.Schedule noncritical activities. Use a combination of a few decision rules and common sense.

For example, compare activities that are eligible to be added to the schedule based on the float they have available. Activities with the least float should have higher priority.

In cases where there is a tie between two activities based on float, give priority to shorter activities near the beginning of the project.

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Exhibit 8.20

Excel Based Gantt Chart

and Histogram Showing Resource Loads for Early-Start

Schedule of Wildlife Film

Project

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Exhibit 8.21

Time-Constrained

Resource Smoothing:

Modified Schedule for Wildlife Film Project with Noncritical Activities Delayed

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Exhibit 8.22

Modified Wildlife Film Project after First Two Resource Allocation Decisions under 12-Crewmember Constraint

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Modifying the Schedule When There Is a Resource LimitA procedure for solving a resource-constrained problem is to schedule the activities one week at a time, starting on the left.

1. Identify all activities eligible to begin, and give priority to those with the least float.

2. If there is a tie, it is reasonable to select those with resource loads that complement the loads of other eligible activities, or those that bring the resource load closest to reaching the limit.

3. As with time-constrained leveling, the team engaged in scenario planning must consider other project-specific factors.

In resource-constrained allocation problems it is not appropriate to automatically schedule the critical path—it has priority, though, because it has no float.

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Exhibit 8.23

Schedule Modification to Accommodate 12-Crewmember Constraint: Wildlife Film Project Is Extended by Four Weeks

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Exhibit 8.24

MS Project Gantt View of Wildlife Film Project Early-Start Schedule

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Exhibit 8.25

MS Project Resource Histogram for Wildlife Film Project Early-Start Schedule

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Exhibit 8.26

MS Project Gantt View of Wildlife Film Project Schedule Following Software-Generated Resource Leveling

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Exhibit 8.27

MS Project Resource Histogram for Wildlife Film Project Leveled Schedule

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Exhibit 8.28

Network Schedule for an IT Project with Constraints on Specialized Resources

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Exhibit 8.28

Network Schedule for an IT Project with Constraints on Specialized Resources

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Exhibit 8.28

Precedence Table for Network Schedule for an IT Project with Constraints on Specialized Resources

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Exhibit 8.29

Early-Start Schedule for IT Project with Specialized Resources

This is an impossible schedule! Individual team members are expected to perform more than one task at a given time. It is impossible to accommodate the resource constraints without extending the schedule.

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Exhibit 8.30

27-Day Schedule for IT Project with Specialized Resources

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Adjusting the Schedule to Accommodate Specialized Resources

1. Consider delaying tasks with the most float.

2. For resource-conflicted tasks that appear early in the project, consider scheduling the shorter tasks before longer tasks for each resource.

3. For resource-conflicted tasks that appear late in the project, consider scheduling shorter tasks later than longer tasks for each resource.

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Exhibit 8.31

22-Day Schedule for IT Project with Specialized Resources

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Exhibit 8.32

19-Day Schedule for IT Project with Specialized Resources (Shortest-Time Feasible Option)

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Exhibit 8.33

19-Day Schedule with Critical Chain Highlighted (dashed boxes)

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Critical Chain Concepts

• Critical chain – The actual sequence of deliverables, activities, tasks, or work packages that cannot be delayed without delaying the project.

• While similar to the critical path concept, the critical chain adds another layer of complexity by taking into account resource availability.

• Tips for managing the critical chain:

Give priority to the critical chain

Use schedule buffers to protect the critical chain

Beware the effects of multitasking

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Critical Chain Concepts - Buffers• Feeding Buffer – A segment of float intentionally

scheduled at points where noncritical activities merge with the critical chain.

• Resource Buffer – A time designated within a critical chain activity whereby the owner of that activity shares information about the progress of the current activity with the owner of the subsequent critical chain activity. The resources buffer is set at a certain number of days prior to the scheduled end of the critical chain activity underway.

• By sharing this information prior to the end of the activity problems or possible causes for delay might be resolved. This helps mitigate the risk of delay to the project.

• Project Buffer – The time between a project’s anticipated end date and the due date specified by the customer. Project buffers are often used in lieu of buffers within individual activities, which allows for the sharing of buffer time between all team members. 8-52

Box 8.2

The Advantage of Working on One Project at a Time

The CEO of an international corporation that designs and manufactures industrial cutting equipment gave a speech at a professional meeting to explain some of his company’s successes. Most notable was the company’s 50 percent reduction in product development time. When asked what the company had done to make such a dramatic improvement, he replied: “We insisted that every engineer work on only one project at a time. I’m personally committed to this and regularly walk through the design department to ask people what they are working on. If an individual tells me that he or she is working on multiple projects, I make a visit to the supervisor to correct the problem.” He went on to say, “Our goal as an organization is not to see how busy we can keep the engineers—it is to get the projects out the door in a timely manner.” 8-53

Exhibit 8.34

Effects of Multitasking in Engineering Projects

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Chapter Summary• This chapter presents several tools and concepts for modifying

schedules to accommodate time and resource constraints.

• Creative solutions are available to those who understand network scheduling concepts and how to use them as tools for problem solving and persuasion.

• Before asking for more resources or time, the effective project manager investigates the potential to:• eliminate WBS activities (scope reduction)• add resources to critical tasks to shorten durations (crash)• perform sequentially related tasks concurrently (fast track)• or delay tasks to reallocate resources

• In the case of crashing, the project manager might have to ask for more money to compensate for potential lost efficiency, but the overall cost of a crashed schedule should be less than one without crashing when time-related fixed costs are considered.

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Team Activities and Discussion Questions

and Exercises

Chapter 8

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Team Activity 8-2

Network Diagram for Web Site Design

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Exercise 8-7

Network Diagram for Road Construction Project

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Exercise 8-8

Network Diagram for IT Project

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Exercise 8-9

Software Project Development Time and Number of Programmers

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