I've been looking for something other than the good old chain metaphor for talking about constraints. The recent recommendation session at the Jonah's Jonah Upgrade pointed me in the direction of thinking how different constraints are characterized by different UDEs, and I came up with the following start, based on a highway system...

A constraint could be an accident or construction zone on Interstate 95, where three lanes narrow to one or two.

Or a constraint could be 3 inches of snow and ice on the full three lanes.

Or it could be periodic toll booths (now thankfully gone in Connecticut).

Or it could simply be the speed limit on an unobstructed stretch of road.

Or, most commonly it could be a strech of road that is overwhelmed with volume, making it subject to any little minor tap of the brakes by anyone. (Picture a crowded freeway with cars travelling at 55-65 mph with everyone only a couple car lengths apart . . . a very fragile system . . . kind of like a too leanly balanced production operation . . . Any little thing brings it crashing to a halt.)

Each of these limit the capacity/capability of the system (made up of road and cars) to transport quantities of people and goods within a given time period. Each of them gives a trip its own character and each of them has its own solution.

The source of this page is a posting made by Frank Patrick to one of a variety of online discussion forums, most likely an e-mail discussion list. It's tone and style may be informal, occasionally provocative, and sometimes, even impertinent. There may even be typos until an opportunity arises to clean them up for more formal presentation. Despite these minor shortcomings of style, the content is worth sharing.

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