Understanding FIFO: First-In, First-Out in Queue Management

If you’ve ever read anything about queues or queue management, no doubt you’ve seen this term — FIFO.

Sadly, it’s got nothing to do with FIFA.

A FIFO queue is a queue that operates on the first-in, first-out principle, hence the name. This is also referred to as the first-come, first-served principle.

(FCFS doesn’t roll off the tongue quite as nicely, though.)

In other words, FIFO queuing is when customers are served in the exact order in which they arrive.

FIFO is the most common type of queuing, and it’s generally believed to be the fairest way to manage queues.

Examples of FIFO queuing in real life

Most queues that we encounter throughout the day are FIFO queues. Waiting for the bus, waiting in front of the elevator or a vending machine, or even standing in line to the bathroom all share one quality — the person standing in the front goes before the one standing behind.

That’s the gist of first-in, first-out queues, and you can see them everywhere. For example…

First-come, first-served in restaurants

You could say that restaurants, cafes and fast food chains operate on a first-come, first-seated basis. If a restaurant is particularly popular, there may be a line of soon-to-be-customers at the entrance, with the staff guiding the people to the newly-available tables.

The earlier you got in the queue, the sooner you get the table.

There are exceptions, of course: restaurants may offer VIP service, i.e. people of importance don’t have to stand in line and are seated before anyone else.

First-in, first-out queues in banks

Banks are also notorious examples of FIFO queuing. There’s either a separate queue for different tellers, or there’s one queue, and the customers at the front get served by whichever teller is available at the moment.

Whatever the service method they use, the principle is the same: the earlier you come, the sooner you get to resolve your issue.

Why use FIFO queuing

“Now,” you might say, “I get that FIFO queuing is widespread, but why is it so widespread?”

I’m glad you asked, imaginary reader! Let’s take a look at the core benefits of first-in, first-out queue management.

FIFO queuing promotes fairness

First-in, first-out is inherently a very simple, easily understood principle. This makes FIFO fair in the eyes of customers: the earlier you join the queue, the sooner you get served.

There are no shortcuts or jumping ahead within FIFO rules. (That is, if they are applied correctly.)

Fairness of queues is directly to customer satisfaction. If customers are not happy with the way you manage your queues, they will justifiably become annoyed with your customer service.

Worse yet, there may be other psychological effects. 27% of consumers have reported to get annoyed by fellow shoppers when queuing.

19% of shoppers have even had an argument with a partner or friend while in a queue.

FIFO queues take advantage of the psychology of queuing

This is connected with the previous point, as the perception of wait times is influenced by the fairness of the queue we stand in.

Knowing that the queue operates on the first-come, first-served basis alleviates the anxiety.

The thing is, unfair queues feel longer than they are. The reason why this is important to consider is that perceived duration of waiting has a bigger impact on consumer satisfaction than the actual wait time.

Couple that with the fact that people tend to overestimate their wait time by around 36%, and you now understand why fair queues are the way to go.

And there’s nothing fairer in your customers’ eyes than the good ol’ first-come, first-served.

Other types of queuing

Naturally, there’s more to the world of managing queues than FIFO. There are other systems that we encounter in different industries or social contexts.

Let’s see what those are.

Last-in, first-out queuing (LIFO)

Also called last-come, first served (or LCFS, but that is less punchy than LIFO), the exact opposite of FIFO sounds absurd at first.

You come in last but you get served ahead of the others? Is this a dream?

Last-in, first-out is relevant for systems which have stacks of items/orders placed on top of each other. Take, for example, solitaire — a card-based puzzle game in which you move and sort the topmost cards.

Another example: any program with the Undo button. If you want to undo an action you did a while ago, you would have to undo all of the actions done after it.

That’s LIFO too, although it’s not exactly related to queuing.

When it comes to managing wait lines, Professor Lars Peter Osterdal of the University of Southern Denmark thinks that LIFO actually has the edge over FIFO.

As he explains it, “The problem with a regular queue where you serve first those who arrive first is that people tend to arrive too early.”

LIFO, on the other hand, forces people to come at staggered times, resulting in shorter queues. Coming early poses more risks, which is why in Osterdal’s experiment people chose to bid their precious time before joining the queue.

Obviously, this system wasn’t quite popular with the people who have been queuing the longest. Also, LIFO was subject to gaming the system, as some people left the queue and rejoined it from the back to get served more quickly.

Priority queuing

Priority queuing is exactly what it says on the cover: customers have priorities associated with them and are served in the order prescribed by these priority classes.

This type of queuing is most commonly seen in industries where there can be emergency cases — for example, healthcare. There’s a difference between a patient with mild symptoms versus a victim of a near-fatal accident.

The latter is always treated before the former, as the level of urgency is that much higher.

Priority queuing is also reserved for VIP customers. Business class passengers enter the airplane before the rest, and people of importance may get seated at a restaurant ahead of anyone else.

Achal Bassamboo, professor of operations at the Kellogg School, argues that companies need to account for different customers not having the same level of patience. Some are “more willing to wait in line than others”, and patience is subject to change over time, demographics and other factors.

It may feel unfair to reward less patient customers with faster resolution time, but for some companies, the risk of getting a negative review outweighs all potential consequences.

Mixed queuing

Not everything is as clear-cut as FIFO or LIFO. (This is a fun sentence to say out loud, by the way.)

Sometimes waiting line management takes elements from different types of queuing systems. To illustrate this point, we will once again invoke the food industry.

In restaurants and fast food chains, if you make the same order as the person who came before you, there’s a chance you will both receive your order simultaneously.

That’s because it is easier to prepare certain meals in bulk: instead of making two servings of gazpacho separately, a cook will just prepare a bigger portion at once and distribute it to two customers.

Those are the unwritten rules of queuing in restaurants. The people who have been waiting longer than you may act grumpy, but they understand the logic behind you getting served ahead of them.

(At least I hope they do.)

Or, consider amusement parks. Sure, you sometimes have to wait ungodly amounts of time before you get seated in a car — take, for example, Peter Pan’s Flight at Disney World, with its 192-minute-long wait.

But, once you do get seated, all of the visitors on an amusement ride take off at once.