Policy Project Constraints
April 14th, 2003 by HalArticle Series - Down n Dirty with the Theory of Constraints
Exploring the Theory of Constraints in the Project Setting (second in the series) with Frank Patrick and Joe Ely.
Physical constraints are not the only limiting effects on projects. Eli Goldratt identifies two other types: policy constraints and paradigm constraints. Let's work through an example.
On a multi-story building job site there will be an exterior man-lift for carrying workers and material up and down the building. Large jobs might have more than one lift. We can begin to understand the lift as a constraint considering it only holds 8 people. If there are 80 people to travel on the lift it will take at least 10 trips to get them to their place of work. It will take more trips when the lift is not full. On the surface this looks like a simple physical constraint. But is it?
On most job sites the policy is for workers to start at the same time. While some people will come early to avoid the rush, which will only succeed if one of those people is the lift operator, what inevitably happens is a queue builds every morning, at lunch, and again at the end of the shift. What if the policy was changed? Perhaps the iron workers would come in first, followed by the plumbers five minutes later, followed the electricians, etc.? The end of their workdays would also be staggered. While there could be a bunching up due to variation in the arrivals of the individual trades, you wouldn't have less lost time waiting for the lift. Still, iron workers, plumbers, and electricians will likely be scattered across a number of floors. Bunching by trade will result is losses in travel as folks are dropped off on different floors.
So what about paradigm? We live in a world that thinks whoever is in line first gets to go first. Further, if the lift is there, then one can ride it. Are these stated explicitly? No. But we do operate that way. What if we change the rules for riding the lift? Let's say it is reasonable for people to walk up one flight of stairs and walk down two flights of stairs. On what floors would the lift need to stop in a ten-story building?
[think]
.
.
[think]
In the usual case of first-come, first-served, a mixed group of people get on. Each time the lift stops some people get out, while others must wait to ride to their floor. That waiting time takes away from operating time. Adopting the proposed policy changes that. The lift only makes
- the fifth floor and the ninth floor. A policy could be added to have people arrive for travel to the fifth floor at one time and the ninth floor sometime later. That would reduce the waiting time for the lift and the waiting time on the lift.
In this example we turned a physical constraint first into a policy constraint, then into a paradigm constraint. Make your constraints disappear in the same manner. And, remember to check-in on Frank and Joe.
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