The Lean Review
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The Lean Review

The fascinating world of queues

Being in line

Standard (Visible) Queues

This is our stereotypical queue. There is a line that is visible to all those queuing. We have a position in the line relative to others. The line is processed sequentially. Standard queues can come in different varieties. The contextual example of an overseas holiday trip will illustrate.

  • Holding: short transient queue where people come and go within a short space of time e.g., taxi drop-off zones.
  • Vending/Disposal: queues where we send or receive something e.g. boarding pass printing kiosks, baggage check-in etc. This category is probably the broadest and includes common queues like those at supermarkets, ATMs etc.
  • Verification: such queues have a chokepoint through which only verified people can pass. Customs screening is a classic example.
  • Entry: queues that govern entry. The aircraft boarding queue is a classic example. Apart from the usual purposes of verification and control, entry queues comprise an important part of the customer experience. When we queue to enter an aircraft, the signage, uniforms, air-bridge, greeting by crew etc. all contribute to our experience of entering the aircraft and commencing a journey.
  • Rationed: The best example is Traffic. It is a batch-processed queue. A whole batch of cars, who are stopped at a red light are allowed to go at the subsequent green light. We can safely assume that this is one queue that everyone hates. In some cases it’s unavoidable. In others, especially in LEAN manufacturing, the principle of one-piece flow holds that smaller batch sizes lead to faster processing, and lower WIP.

Personalized (Semi-Visible) Queues

In this type of queue, we know our absolute position but not our relative position within a queue. Unlike standard queues, we don’t experience the entire queue and instead respond to some sort of personalized identifier. A related variety is queues formed or prioritized according to some criteria which become available (visible) accordingly.

  • Token-based: Visa offices are a classic example. We are usually given a ticket number and when that flashes on the screen, we can get precious time with an officer who can process our enquiry. Token-based queue systems are now common across many organizations.
  • Criteria based: This includes special airport channels for diplomats, dignitaries, private aircraft, First Class boarding etc. Priority queues allow a category of people to be treated in accordance with their stature — political, financial, security etc. Triage (hospitals) and quarantine processing at airports (red/green channels) are popular examples where queues are routed based on certain criteria. Like entry queues, prioritized lanes are also instrumental in delivering good customer experience. ‘Express lanes’ at supermarkets are the classic example — they allow people buying a few items to complete their purchases quickly.

Invisible Queues

Invisible queues are intriguing. We typically don’t see them at all, but once we know about them, we cannot “un-see” them. For those familiar with the Johari Window, this corresponds very roughly to the Blind Spot — known to others but not known to self. Two examples come to mind:

  • Internet: Why not start directly with the biggest queue in the world — the Internet. As I write this post through an online editor, a host of internetworking protocols and hardware devices are busy assembling, queuing, routing and re-assembling data packets and making the whole process seem instantaneous!
  • Applications / Orders: When we submit an application or order form we become part of the supplying organization’s workflow and part of a queue that is invisible to us, except for usually the end result. To facilitate good customer service, we are often provided reference numbers through which we can track progress.

Customer experience of queues

Queues are a means to an end. If these ends can be achieved through other means, then the nature and rationale for having queues changes.

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