Illustrating ways to shorten a schedule

If your initial schedule doesn't meet your requirements, consider changing your network diagram to reduce the length of your project's critical paths. Consider the example of preparing for a picnic to see how you can approach this task.

Figure 5-6 illustrates your initial 57-minute plan. If arriving at the lake in 57 minutes is okay, your analysis is done. But suppose you and your friend agree that you must reach the lake no later than 45 minutes after you start on Saturday morning. What changes can you make to save you 12 minutes?

You may be tempted to change the estimated time for the drive from 30 minutes to 18 minutes, figuring that you'll just drive faster. Unfortunately, doing so doesn't work if the drive really takes 30 minutes. Remember, your plan represents an approach that you believe has a chance to work (though not necessarily one that's guaranteed). If you have to drive at speeds in excess of 100 miles per hour over dirt roads to get to the lake in 18 minutes, reducing the time has no chance of working. (However, it does have an excellent chance of getting you a speeding ticket.)

To develop a more realistic plan to reduce your project's schedule, take the following steps:

1. Start to reduce your project's time by finding the critical path and reducing its time until a second path becomes critical.

2. To reduce your project's time further, shorten both critical paths by the same amount until a third path becomes critical.

3. To reduce the time still further, shorten all three critical paths by the same amount of time until a fourth path becomes critical, and so on.

Performing activities at the same time

One way to shorten a path's length is by taking one or more activities off the path and doing them in parallel with the remaining activities. However, often you have to be creative to successfully perform activities in parallel.

Consider the 57-minute solution to the picnic example in Figure 6-1. Assume an automatic teller machine (ATM) is next to the gas station that you use. If you use a full-service gas island, you can get money from the ATM while the attendant fills your gas tank. This strategy allows you to perform Activities 2 and 6 at the same time — in a total of 10 minutes rather than the 15 minutes you indicated in the initial diagram.

At first glance, it appears you can cut the total time down to 52 minutes by making this change. But look again. These two activities aren't on the critical path, so reducing their time has no impact on the overall project schedule. (In case you think you can save five minutes by helping your friend make the sandwiches, remember: You agreed that you can't swap jobs.)

Try again. This time, remember you must reduce the length of the critical path if you want to save time. Here's another idea: On your trip to the lake, you and your friend are in the car, but only one of you is driving. The other person is just sitting there. If you agree to drive, your friend can load the fixings for the sandwiches into the car and make the sandwiches while you drive. This adjustment appears to take ten minutes off the critical path. But can it?

The diagram in Figure 5-6 reveals that the upper path (Activity 2 and 6) takes 15 minutes, and the lower path (Activity 7 and 3) takes 20 minutes. Because the lower path is the critical path, removing five minutes from it can reduce the time to complete the overall project by five minutes. However, reducing the lower path by five minutes makes it the same length (five minutes) as the upper path. Therefore, both paths take five minutes and both are now critical.

Taking an additional 5 minutes off the lower path (because the sandwiches take 10 minutes to make) doesn't save more time for the overall project because the upper path still takes 15 minutes. However, you do have five minutes of added slack to the lower path.

Figure 5-7 reflects this change in your network diagram. Consider using your first idea to get money at the ATM while an attendant fills your car with gas. This move now can save you five minutes because the upper path is now critical.

Figure 5-7:

Making sandwiches while driving to the lake.

Start

t = 0

Decide which lake t5 = 2

Decide which lake t5 = 2

Boil eggs t7 = 10

Buy gasoline t6 = 10

Drive to lake t4 = 30

Critical path (in bold) = 52 minutes

Finally, you can decide which lake to visit and load the car at the same time, which saves you an additional two minutes. The final 45-minute solution is illustrated in Figure 5-8.

Figure 5-8:

Getting to your picnic at the lake in 45 minutes.

Figure 5-8:

Getting to your picnic at the lake in 45 minutes.

Consider a situation where you have to complete two or more activities before you can work on two or more new ones. Show this relationship in your diagram by defining an event that represents the two or more completed activities and then draw arrows from the completed activities to this event. Then draw arrows from that event to the new activities (see Figure 5-8).

In the example, you first complete the activities Get money, Buy gasoline, and Boil eggs, and then you can perform the activities Load car and Decide which lake. You represent this relationship by drawing arrows from each of the first three activities to a newly defined event, Ready to load car, and by drawing arrows from that event to the activities Load car and Decide which lake.

If you think this analysis is getting complicated, you're right. You pay a price to perform a group of activities faster. This price includes

^ Increased planning time: You have to precisely detail all the activities and their interrelationships because you can't afford to make mistakes.

^ Increased risks: The list of assumptions grows, increasing the chances that one or more will turn out to be wrong.

In the picnic-at-the-lake example, you make the following assumptions to arrive at a possible 45-minute solution:

^ You can get right into the full-service island at a little after 8 a.m.

^ Attendants are available to fill up your tank as soon as you pull into the full-service island.

i The ATM is available and working when you pull into the full-service island.

i You and your friend can load the car and make a decision together without getting into an argument that takes an hour to resolve.

i Your friend can make sandwiches in the moving car without totally destroying the car's interior in the process.

However, when you identify assumptions, you can increase the chances that they'll be true or develop contingency plans in case they don't happen.

Consider your assumption that you can get right into a full-service island about 8 a.m. on Saturday. You can call the gas station owner and ask whether your assumption is reasonable. If the gas station owner tells you he has no any idea of how long you'll have to wait, you may ask him whether it would make a difference if you paid him $200 in cash. When he immediately promises to cordon off the full-service island from 7:55 a.m. until 8:20 a.m. and assign two attendants to wait there, one with a nozzle and the other with a charge receipt ready to be filled out, so you'll be out in ten minutes, you realize you can reduce most uncertainties for a price! Your job is to determine how much you can reduce the uncertainty and what its price will be.

DeVising an entirely new strategy

So you have a plan for getting to the lake in 45 minutes. You can't guarantee the plan will work, but at least you have a chance. However, suppose your friend now tells you he really needs to get to the lake in 10 minutes, not 45! Your immediate reaction is probably "Impossible!" You figure creative planning is one thing, but how can you get to the lake in 10 minutes when the drive alone is 30 minutes?

By deciding that there is no way to arrive at the lake in 10 minutes when the drive alone takes 30 minutes, you have just redefined your criterion for project success. The true indicator of success in this project is arriving at the lake for your picnic, not performing a predetermined set of activities. The seven activities you originally formulated were fine, as long as they allowed you to get to the lake within your established constraints. But if the activities won't allow you to achieve success as you now define it (arriving at the lake in ten minutes), consider changing the activities.

Suppose you decide to seek out modes other than driving to the lake. After some checking, you discover that you can rent a helicopter for $500 per day that'll fly you and your friend to the lake in ten minutes. However, you figure that you both were thinking about spending a total of $10 on your picnic (for admission to the park at the lake). Clearly, spending $500 to get to a $10 picnic is absurd. So you don't even tell your friend about the possibility of renting the helicopter; you just reaffirm that getting to the lake in ten minutes

'i is impossible. Unfortunately, you didn't know the reason your friend wanted to get to the lake in ten minutes. You find out that he can make a $10,000 profit on a business deal if he can get to the lake in ten minutes. Is spending $500 worth making $10,000? Sure. But you didn't know about the $10,000.

When developing schedule options, it's not your job to preempt someone else from making a decision. Instead, you want to present all options and their associated costs to the decision maker so he can make the best decision. In this instance, you should have told your friend about the helicopter option so he could have taken the relevant facts into account when he made the final decision.

Subdividing activities

You can often reduce the time to complete a sequence of activities by subdividing one or more of the activities and performing parts of them at the same time. Figure 5-9 illustrates how your friend can save seven minutes when boiling the eggs and preparing the egg sandwiches by using this approach:

Boil eggs in water t5B = 7

Reducing span time by subdividing an activity.

Figure 5-9:

Reducing span time by subdividing an activity.

i Divide the activity of boiling into two parts.

• Prepare to boil eggs: Remove the pot from the cupboard, take the eggs out of the refrigerator, put the water and eggs in the pot, put the pot on the stove, and turn on the heat — estimated span time of three minutes.

• Boil eggs in water: Allow the eggs to boil in a pot until they're hard — estimated span time of seven minutes.

1 Divide the activity of making the egg sandwiches into two parts.

• Perform initial steps to make sandwiches: Take the bread, mayonnaise, lettuce, and tomatoes out of the refrigerator; take the wax paper out of the drawer; put the bread on the wax paper; put the mayonnaise, lettuce, and tomatoes on the bread — estimated span time of seven minutes.

• Finish making sandwiches: Take the eggs out of the pot; shell, slice, and put them on the bread; slice and finish wrapping the sandwiches — estimated span time of three minutes.

1 First "Prepare to boil eggs"; next "Boil eggs in water" and "Perform initial steps to make sandwiches" at the same time; finally "Finish making sandwiches".

As Figure 5-9 illustrates, the total time to boil the eggs and prepare the sandwiches is (3 minutes + 7 minutes + 3 minutes) = 13 minutes. Note: The total time for the original activity to boil the eggs is still ten minutes (three minutes to prepare and seven minutes in the water), and the total time for the original activity to make the sandwiches is also still ten minutes (seven minutes for the initial steps and three minutes to finish up). By specifying exactly how to perform these activities, you can complete them in 13 minutes rather than 20.

0 0

Post a comment