One of the key drivers built into Project Controls 3.0 is the need to keep work moving. This is measured as the rate of production (work) used in the Work Performance Management calculations.
This concept is derived from Little’s Law, named after its inventor, John Little, who developed queuing theory in the 1950s and, in 1961, announced his theorem as follows: the number of customers in a queue equals the long-term average arrival rate of customers multiplied by the time taken to process them. In addition to PC-3.0, queuing theory is central to the Theory of Constraints (TOC), Critical Chain, Velocity, Lean Manufacturing, and Lean Construction.
The three components in Little’s Law are:
- The amount of Work In Progress WIP (‘L’ in queuing theory),
- The Lead Time LT, the average time spent in a production system from the beginning to the end of a task (‘W’ or ‘wait’ in queuing theory), and
- The system Throughput T measured by the arrival and exit rate of items within the queuing system (lambda λ in queuing theory).
The relationship between these three components can be expressed in three ways:
WIP = T x LT or LT = WIP/T or T = WIP/LT
These relationships mean the more work in progress in a stable production system, the longer the lead time.
For Little’s Law to hold, the system being observed must be in a steady-state and the units of measure for all three variables consistent. A steady-state condition means that on average, the arrival and departure rate of items into and out of the system remain consistent. In this situation any increase in WIP automatically increases lead times!
While the formula may not be exact, the concept behind Little’s Law remains relevant in all production systems, to borrow from Lean: WIP is a waste and needs to be minimized.
One of the indicators of management issues in a traditional project is a ‘bow wave’ of partially completed tasks banking up next to Time Now in a schedule. Also known as the 90% syndrome. This post explains the reason, and explains why Project Controls 3.0 focuses on measuring work complete. For more on Project Controls 3.0 see: https://mosaicprojects.com.au/PC-3-00-Overview.php#PC-3-Overview [1]