Time management by CPM and 4D-planning

When having a project it is known that there is a start and an end date. Between those two dates different deadlines should be achieved for getting a satisfied result when the end date is reached. Therefore it will mean that the project depends a lot on the parameter time and when that parameter is represented it is known that the natural follower is cost. Therefore to reach the deadlines, a satisfied and economical satisfied result, it is t necessary to have a written well-organized plan. Especially the part to write a plan down is necessary, since research had shown that when goals are written down the rate of reach them is increased. Then what to do for time management and which tools can be used?

To planning in a good manner, there have been used many techniques and many different schedule schemes have been developed. One very useful and old method for time management, especially when the case has a lot of dependencies, is the critical path method (CPM). The CPM had been used in many construction cases but since the world changes in innovation, it is now possible to upgrade the CPM and make use of the 3D construction model which gives 4D-Planning. The methods CPM and 4D-Planning will be explained and by pros and cons the methods will be evaluated.

Critical path method (CPM)

History

After the Second World War the situation over the world was still strained. The tense was especially between the world’s two superpowers namely the United States of America and the Soviet Union. This tense between these superpower countries is in the history defined as the Cold War. During that period both countries had a high priority on development and armament. One of the development phases in the 1950s was the US navy’s Polaris missile program. That program was not going as planned and the time schedule was delayed. Therefore the solution proposal for the program was to dividing the project into tasks and then connecting the tasks in relation to the dependence. The estimation of duration for each task was written and by that a schedule could give the duration time and the critical of the task(s) and for the whole program. At the same time an American chemical company called El DuPont de Nemours Company had delay problems. The chemical company and the US navy did cooperate in the 1950s to develop a system to manage the delay. The US navy called their solution for "Program evaluation review technique" (PERT) while the chemical company did call it "critical path method" (CPM). The systems are almost similar but there are some differences. Among and other the difference is in time estimation. The CPM has a fixed time which is estimated once while the PERT is a method where uncertainties for the activities planning, organizing, coordinating and controlling are estimated. The development of the method had shown its importance, since the management world did get a tool that could manage projects that have many dependencies in a smart way and showing the critical path of the project. Today the method is implemented in software like Microsoft Project.

Method

The method of CPM is to produce a network that defines all the tasks and the dependency in a chronological order. For making that network of tasks the manager has to list up all the tasks, the tasks presidencies and the duration of each task. Such a list can be seen under 1.3 Example. When the list is ready the manager will start setting up a network. The network will content off tables like the one on figure 1. The tables will be logically connected together by arrows which will be in compare to the dependency of the tasks.

Figure 1: Critical path task table.

The manager will now be able to fulfill the tables in the network. The tables contents of:

Nomenclature to figure 1

Title	Explanation
ES	The earliest start on the task
Duration	The tasks duration time
EF	The earliest finish on the task
LS	The latest start on the task
Slack	The slack time
LF	The latest finish on the task

To fulfill the table the manager will make use of the tasks duration time, the dependency, forward pass and backward pass. The forward pass gives the absolute earliest finish time and that happens by calculation from the first task, through the network and to the last task. The backward pass gives the possible latest finish time without exceeding the time limit and the slack. By the slack the manager will be able to know how much a task can be delayed without exceeding the time limit for the project. The forward pass is calculated by starting from the first task, though the network and until the last task. For the backward pass it is the opposite way, which should be calculated from the last task, through the network and to the first task.

After each table is filled out in the network the manager can get an overview over the project. It is possible for the manager to see where it is possible to get a time delay in executing the different tasks and an insight in the most critical path cross the project will available which is an advantage for the whole project.

Example

To better understand the critical path method an example is created. The example is for a small construction project to have a simple network and to easier understand the principle. The first step is to create a table where all task, there precedences and duration is listed up. That table is seen below.

Example of CPM

Task	Precendences	Duration
A	-	3
B	A	10
C	A	12
D	A	15
E	A	11
F	C,D	15
G	B,G	10
H	E,G	7

When having that information the network be created by the logical system and the duration of time can be noted. Applying the forward and backward pass will give a finished network where the critical path is possible to spot on figure 2. The critical path is highlighted with red colored arrows.

Figure 2: Network by using the critical path method.

For get additional information of how the network was filled out a video have been made. The video can be seen here:

Video 1:Critical Path Method CPM.

4D-Planning

Example

Video 2:4D-Planning.