Six Sigma went away years ago... now Lean is a different story. We are three years into a Lean journey, with a long way to go. To your point on uncontrolled variables, Lean in transportation is more about finding problems through standard process. As far as the dock environment goes, if everyone is using the same governing principles for their standard processes, anyone can walk down the dock and identify something out of standard and know how it affects the outcome... and hopefully help correct it.
Lean at Con-Way is similar to the challenges at Toyota. There is "TPS", THE Toyota Production System (where they want to be), and then there is Toyota's Production System, this is the system in place today in every plant.