Demand Driven

Lessons from a Traffic Light


I sat at the stop light, waiting impatiently for it to turn from red to green.  It finally did, so I pressed on the accelerator, eager to resume my journey. As I “bumped” into the car in front of me, two things occurred to me.  First, I wasn’t, um, first in line.  I was nearly tenth.  Second, I wondered for the umpteen thousandth time, why there is a delay between the cars when starting from a stopped position.  If everyone just hit the gas at the same time that the light turned green, we would pull out like a connected chain of cars. We would all move forward at the same pace and start exactly when the traffic light changed color.

And then I heard the voice of Scotty, telling Captain Kirk, “You can’t change the laws of physics.”  Since we can’t expect that everyone will initiate contact with the accelerator at the same time and with the same force or that their cars will react with the same acceleration, each car must delay its start until the preceding car gets moving. We essentially need a “cushion” between the time the light changes and the third car moving.  But that isn’t right either.  You can’t set a time that each car must wait after the light turns green.

Each car can only begin to move after the preceding car begins to move.  That might be two seconds after the light changes and it might be twenty seconds after (yes, I’ve been there too).

Is there a lesson in here for our supply chain buyers, planners, and schedulers?  If each step in your manufacturing or logistics process is dependent on the preceding step, then the more steps you have, the less likely your calculations will be completely predictable.

Follow your process (mentally).  Create and release the purchase order and send it to the vendor.  If it isn’t automated, they must enter it into their system.  Delay Point One.  Their Material Requirement Planning software must recalculate.  When will that happen?  Delay Point Two.  Even if the parts are in stock, someone must fulfill the order (probably not a 24/7 operation). Delay Point Three.  Shipping must process, package and label, etc… also not 24/7. Delay Point Four.  The Carrier must come pick up the shipment, not working 24/5 much less 24/7. Delay Point Five.  You get the idea.

The above aren’t necessarily delay, but they are certainly variability factors.  One day, everything might align perfectly and there will be no delay.  But it will not be because of the design, it will be accidental.

Do our systems and planning methodologies take this variability into account?  Do our systems and planning methodologies calculate precisely based on the numbers in the system?  Sounds like the start of a great group discussion, don’t you think?

It’s not just a chain reaction.  It’s a supply chain reaction.

John Melbye – Become Demand Driven!