The management of congestion

The term ‘congestion’ conjures up a variety of undesirable memories of everyday life: busy shops, huge tailbacks on the freeways, overcrowded swimming pools, jam-packed buses, waiting-lists to see a doctor or join a sports club, etc. In a business context memories may include long delivery-delays, computer systems with lengthy response times, customers queueing for service, ringing phones not being picked up and over-booked flights. Whenever a number of ‘customers’ (people or jobs) share a limited ‘resource’, some form of annoyance, referred to as ‘congestion’, results. Congestion can take on various forms: delay (physically standing in line, or being a name on a waiting-list), slower service (e.g. shared computer resources) or discomfort (crowded facilities). Companies have used various approaches to deal with congestion. For example: Disneyland indicates the expected waiting-time to access an attraction; supermarkets claim ‘three is a crowd’ at the checkout; free pizza if the delivery time exceeds 30 minutes; peak load pricing by phone companies and airlines; priority systems for preferred customers or medical emergencies; the use of appointment systems to reduce variability in the arrival rate. These approaches include aspects of managing demand, managing capacity and managing customer expectations, all of which have been addressed in the literature.