PLANNING WITH PROJECT NETWORK DIAGRAMS

Experience has demonstrated an interesting phenomena when teaching the use of project network diagrams (PNDs). The example does make a difference. If it is a construction example, software people believe that it does not apply to them. If it is a pharmaceutical example, movie people believe that it does not apply to them. And so on. Thus, we have selected a, perhaps nonsensical, project with which anyone can relate. It illustrates the basic concepts of PNDs and some of the calculations that can be performed on them. Consider a simple project that involves collecting some data while driving from New York to Los Angeles in the United States (U.S.). Theoretically this trip of 2,846 miles can be done in 43 hours and 45 minutes. This was determined using the Rand-McNally software package TripMaker(1997). This assumes that the trip could be driven nonstop at the following speeds: interstates at 65 miles per hour (mph), U.S. highways at 55 mph, and state highways at 45 mph. Clearly, this is not really feasible without some very special arrangements and a very high level of dedication on the part of the people involved.

Suppose we split this trip into three segments with intermediate stops at Chicago, Illinois, and Cheyenne, Wyoming. The choice of Chicago and Cheyenne as intermediate points is based on an intuitive guess (looking at a map) that the three legs are approximately equal in length, and it is feasible to drive them in one long day each. The distances in miles are 796, 965 and 1,103 (differences in total distances are due to the legs being to city centers). The driving times are 12:28 (hours: minutes); 15:07; and 17:12. The differences are not as large if after Chicago the driving speed is increased by 10 miles per hour, resulting in a driving time of 13:02 and 14:47 for the second and third legs. Regardless, these are long hours for driving. They could lead to fatigue, inaccurate data collection, and perhaps to an accident.