How do people not crash into each other when using popular Floo network destinations?

Question

In "CoS", Weasleys and Harry travel to Diagon Alley via Floo network.

Given the fact that a bunch of wizards are likely to want to visit Diagon Alley at the same time (say, when school supply lists arrive), one would expect them to collide with each other on exit from fireplaces (or worse, merge into each other StarTrekTransporterAccident-style).

A second example of this high-volume Floo travel is people arriving to work at the Ministry via many fireplaces when the trio is visiting there in DH.

Is there any canon/JKR info on how they manage to avoid such collisions?

Answer 1

There is a Department of Magical Transport (DH chapter 1) that oversees all the Floo Networks. It can rig the Floos to alert them if Harry Floos, so I imagine there is a magical way of keeping people from hitting each other, in general. The Floo Network seems highly regulated.

Piling up in the Floo can happen. I mentioned in my other answer to TangoOversway that in Goblet of Fire, Arthur, George, Fred, and Ron Weasley end up piled up in the Dursley's fireplace because the Dursleys have blocked the fireplace shut with a board and are using an electric fire instead. Apparently, they were unable to stop themselves from piling onto one another. But it's against the rules to connect a Muggle establishment to the Floo Network, so it may be that there was no monitoring there.

A couple other examples regarding the regulation of the Floo Network:

'Marietta’s mother, Minister,’ [Umbridge] added, looking up at Fudge, ‘is Madam Edgecombe from the Department of Magical Transportation, Floo Network office – she’s been helping us police the Hogwarts fires, you know.’

Order of the Phoenix - chapter 27 - The Centaur and the Sneak

'A Floo Network Regulator is keeping watch over every fire in Hogwarts – except my own, of course.'

Order of the Phoenix - Dolores Umbridge - chapter 28 - Snape's Worst Memory

It seems the Floo Network is generally considered extraordinarily safe:

Late in the afternoon, a few days after New Year, Harry, Ron and Ginny lined up beside the kitchen fire to return to Hogwarts. The Ministry had arranged this one-off connection to the Floo Network to return students quickly and safely to the school.

Half-Blood Prince - chapter 17 - A Sluggish Memory

Answer 2

It felt as though he was being sucked down a giant drain. He seemed to be spinning very fast — the roaring in his ears was deafening — he tried to keep his eyes open but the whirl of green flames made him feel sick —something hard knocked his elbow and he tucked it in tightly, still spinning and spinning — now it felt as though cold hands were slapping his face — squinting through his glasses he saw a blurred stream of fireplaces and snatched glimpses of the rooms beyond — his bacon sandwiches were churning inside him — he closed his eyes again wishing it would stop, and then…

Chamber Of Secrets - Chapter Four - At Flourish and Blotts

To me it seems as though you can certainly see the rooms beyond the fireplaces from the place that is behind them. Whilst in this place it is possible that queues may form to stop groups of wizards getting stuck. (Very British) The problem with this is that the Weasleys get stuck, it is likely however that when they entered the fireplace from the magical place behind the fireplace the queue advances the next wizard.

It definitely seems as though there is some automation as Harry is effectively pushed through a grating.

Answer 3

This might be taking too scientific approach to a magical situation (and is not canonical and simply conjecture) but...

Consider your Muggle printer at home or in the office. Multiple people can queue up documents in the printer at the same time but that doesn't mean the printer prints them all out on the same page at the same time.

One could imagine that the Floo network implements some sort of buffering system as follows:

• An outgoing connection is initiated at the departure fireplace
• Traveller steps in to the fire
• Traveller states destination
• Traveller is absorbed in to the network (Floo) relay and a connection is established with the destination fireplace
• Traveller arrives at destination but is not ejected from the stream/network
• Floo network performs a check to see if the buffer is clear
  • If the buffer is not clear, remain in buffer
  • If buffer is clear, eject traveller from network
  • If traveller is ejected, check buffer for additional travellers
• If the buffer is entirely empty, connection is terminated successfully

Just because the wizarding world does not rely on Muggle tech doesn't mean they don't employ logic or safe practices. When devising the Floo network (because presumably it was created by a witch/wizard and didn't simply exist) I'm fairly certain there was a team that sat down and hashed out these details beforehand. Although, I can imagine that the first tests of the Floo Network would probably have resulted in quite a few magical maladies such as the merging of multiple travellers.

Also, if it were me designing the Floo network I would probably increase the momentum at which the traveller entered the network so as to make sure they are ejected a minimum safe distance. Kind of like a little push from behind that makes you instinctively take a step forward to catch yourself.

Finally, there is probably a bit of unspoken/unwritten Floo etiquette involved too. Like a Muggle escalator, you can get to the top/bottom and just stand there forcing all the people behind you in to you and causing a pile up, or you can step forward or to the side so others can get past. That is, of course, if you have space to do so!

Again, all of the above is purely conjecture and reasoning, no canon here I'm afraid! We are just going to have to wait and see if Pottermore releases a technical specification of the network! :D