Compressing the Critical Path

Every potential opportunity should be considered in the schedule revision process to get the maximum benefit at minimum incremental cost, while incurring minimum additional risk. Evaluate each task to determine its potential for duration reduction and consider altering each precedence relationship; then select the most promising, cost effective, combination.

Reducing Task Duration The most common and most frequently misunderstood task reduction technique uses additional resources to shorten the required period of performance. In some cases staff increases result in a proportional activity duration reduction at no additional cost; but this is not always the case, as many functions do not fit the linear model, and those situations which do are only effective over a limited range. (For example; a brick wall requiring ten days for a single bricklayer to erect can probably be erected in five days by two bricklayers, but it is extremely unlikely that ten bricklayers can accomplish the task in a day.)

Unfortunately, adding resources does not always work 111. Situations exist in which increasing staff size actually results in a longer performance period. Programmers are aware of this fact, as the efficiency of a programming staff can actually be reduced by adding resources, unless staff communications are also enhanced. When adding resources to reduce performance time, consider the availability and quality of the extra personnel. With an effective network schedule as the basis for compression, the required personnel may be found assigned to less critical tasks and reassignment is possible.

Overtime is also used to reduce activity duration. This can be effective if the overtime is limited to short intervals. Employee burnout, personnel inefficiencies, and lost time during the workweek for personal activities normally accomplished during overtime hours are serious factors which reduce overtime's long term efficacy. Using selective overtime for specific task duration reductions will be far more effective than a long term program of schedule overtime, or the panic crash that frequently occurs near the end of a project, when it is finally realized that the "fitted" schedule is not working.

The cost of overtime is also a factor which will vary with the type of resource and the accounting system employed to account for premium labor expenses. Many salaried employees are not paid overtime, in which case no additional cost will be incurred if they work the extra hours. Other employees are paid a premium which must be considered. The premium (half time to double time) represents compression cost. Some organizations treat overtime premium as an overhead expense which is included in the average hourly rate applied to all labor. In this case no additional expense results when overtime is actually used.

Shortcuts also support schedule compression, but undue risk or the creation of a downstream problem must be avoided. For example, piping design time may be reduced by eliminating the requirement for piping details, if field installation in accordance with a piping schematic is opted. However, the added installation expense and the increased risk of errors and rework must be considered in making this shortcut decision. Typical shortcuts include:

• Selecting an alternate technology, method or production process. -4

• Selecting material or components based on jf delivery rather than specification or cost

• Reducing the level of detail included in a sign

• Reducing equipment or product test time |

• Sole source equipment, material, or services^ procurement. «te-

• Restricting a bidder's proposal preparation time.

• Waiving contractual approval, review or inspection requirements.

The "Make or Buy" decision can be used to select the option offering best delivery. However, consideration must also be given the decision's effect on product performance and quality, disclosure of proprietary information, potential creation of a competitor, other inhouse work, and the organization's image or reputation, in addition to assessing schedule reduction cost.

Altering Defined Precedence Relationships Not all project activity precedence relationships are fixed and some sequences may be changed to shorten a Critical Path. Using this technique requires an understanding of precedence relationships, the extent to which they can be altered and the cost and/or risk associated with making such changes. Precedence relationships fall into three categories:

• Natural Precedences

• Environmental Precedences

• Preferential Precedences

Natural precedence relationships represent unalterable constraints of nature which control the sequence of work execution. Since they are dictated by the nature of the work involved, nothing can be done to change them. The project manager must either find a creative alternative process or accept their inevitability. The foundation construction sequence— Excavate, Set Forms, Place Rebar, Pour Concrete—results from the natural precedence relationships of these tasks. No other sequence will work, nor can two tasks be performed in parallel. Imagine the futility of an attempt to place rebar after the concrete has been poured, or the mess that would result if the two tasks were performed concurrently.

The unalterable characteristic of a natural precedence relationship precludes effective schedule modification. Any attempt to change one will prove to be fruitless. Fortunately, the other precedence types can be altered—either at incremental cost or by incurring added risk—to obtain a desired schedule compression. Therefore, the project manager intent on shortening a schedule should concentrate on modifying the originally established Environmental and Preferential Precedence relationships.

Environmental precedence relationships repre-^nt constraints unique to a particular working envi ronment or organization. If only one crane were available at a high rise building construction site and two independent tasks requiring a crane had to be performed (e.g., siding installation and placing mechnical equipment on the roof), the tasks would have to be done in series. The sequence may not be inportant because of task independence, but the resource constraint would necessitate series execution. If a second crane were available, the two independent tasks could be executed in parallel. Therefore, altering the environment by acquiring additional resources (renting a crane) can reduce project duration if the action allows parallel execution of two serial Critical Path tasks. Environmental constraints can be altered by:

• reassigning personnel and/or other resources to parallel independent tasks which are scheduled in series because of a resource constraint (no additional cost),

• using temporary personnel (at a premium expense and a potential risk of less efficient performance), or

• renting or purchasing additional equipment to meet a specific need.

Preferential precedence relationships represent the planner's work sequence choice, which generally reflects the safest, most conservative approach to task execution. However, conservatism can be sacrificed and an alternate, higher risk, work sequence selected to shorten a schedule.

In the example shown in Figure la; material required for fabrication of a newly designed component is normally purchased after design drawings have been checked. However, material procurement can be started before checking to reduce project duration. As seen in Figure lb, the schedule can be shortened by the length of the checking period. The risk of purchasing the wrong material is assumed to gain schedule compression.

If checking discloses a material selection error, the time gained will probably be lost and an additional cost may be incurred. The extent of the loss will depend on disposition of the material in question, the point in time the error is identified, and the speed of problem rectification. An effective risk decision requires knowledge of the potential risk, the desired benefit (reward), the probabilities of success and failure, and the remedy to be implemented should the risk become reality. Given this information the project


Was this article helpful?

0 0
Project Management Made Easy

Project Management Made Easy

What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.

Get My Free Ebook

Post a comment