Think Airports Are Chaotic? You Are Right.

jonfromspace writes "Nature is running a brief, but interesting article on Chaos Theory, (as opposed to KAOS) and how it relates to that damn airport shutle service. I knew there was no way to predict arrival times with any degree of certainty. >Also worth a read is this paper on applying Chaos Theory to fisheries management."

Comments

Not to be a pedant about it,

[The Cydonian]

but the Nature article talks about airport bus frequencies, not airports per se.

The distinction is important though; when you talk of 'chaotic airports', you're talking of the entire system as a whole:- luggage screening, plane scheduling, passenger movements etc. Dr Nagatani's paper talks about none of these; it merely suggests that the reason shuttle buses (and elevators) appear to come together, or none at all, is chaos.

I can understand where Dr Nagatani is coming from on explaining bus (and elevator) frequencies, but am intrigued by why it is a "problem" (as in user-level problem, not physics problem, if you get what I mean) in the first place. Okay, so the bus comes at 09:23 and not 09:15... big deal. It is merely a matter of managing passenger perceptions.

More to the point, can anyone explain why this would be inefficient for the system as a whole?

Re:Not to be a pedant about it,

[Dannon]

More to the point, can anyone explain why this would be inefficient for the system as a whole?

Managing bus services isn't my line of work, but I can give it a shot.

For starters, I'm guessing the "bunching problem" would lead to inefficiencies, for one thing, in passenger loading: The 9:15 bus and the 9:20 bus are both bound along the same route. The first bus is early, the second bus is late... meaning that the first bus ends up overcrowded (grouchy customers), and the second bus departs from the stop under capacity (same amount of fuel spent whether carrying one passenger or twenty).

There's also the problem of limited resources. Say you've got more shuttle busses than shuttle bus loading spaces at a certain airport. I look at the international airport in my town, and I see shuttles for several park-and-ride services, countless conference centers, every high-class hotel in several hours' drive, not to mention the usual collection of Grayhound, metro transit authority, touring companies, and so on. The optimal situation would have an empty space ready for each bus as it arrives, so the passengers wouldn't have to wait to disembark. As things get more chaotic, though, they get less optimal. That's all there is to it.

Talking about changing passenger perceptions, though, reminded me.... My page-a-day calendar at work had a bit about how the London rail service managed to fix a problem with chronically late trains without spending any money at all. They simply redefined "on time" to include any train up to an hour late. Problem solved, right?

In other news...

[Anonymous Coward]

Think slashdot moderations are chaotic? You are right!

Bunching buses

[driptray]

Regular bus commuters might be familar with the phenomenon where buses tend to come in groups - often in threes. For example, instead of 1 bus every 10 minutes you get 3 every 30 minutes.

Why? My theory is that as the system becomes crowded, a bus will be delayed by having to pick up and drop off extra passengers. As it gets slower, two things happen:

1. People have to wait longer at the bus stops. This causes the first bus to have to deal with a greater number of passengers, and makes the bus slow down even more.

2. The bus behind it starts to catch up. This occurs partly due to the slower speed of the first bus, but is amplified by the fact that as the second bus gets closer, there will be less passengers waiting at the stops, thus allowing the second bus to travel even faster.

The solution would be for the first bus to deliberately miss stops wherever possible so as to keep some distance between it and the next bus, and to even up the passenger load.

Re:Bunching buses

[panurge]

In fact there is supposed to be a paper about this though I have been unable to locate it.

One of the surprising conclusions is that on some routes the best time to arrive is just as a bus is leaving. There are a number of reasons for this. One is that the departing bus has reduced the queue length at the bus stop so you are more likely to get on the next bus. Another is that if the buses tend to group, in groups >= 3, if a bus is leaving the probability that it is not the last bus in the group is >0.5. If you arrive with no buses in sight, chances are you are in an inter-group period.

My favorite comment on the whole bus thing, however, came from a retired admiral who wrote a letter to the London Times: "Since the convoy system was introduced, not a single bus has been sunk by enemy action."

Re:Bunching buses

[wind]

At least where I live (Brighton, UK) this appears to be exactly what the bus drivers do at peak times, at least up in the hinterlands of the residential areas. I can't tell you how many times I've waited an extra 10 minutes for the bus, only to have it speed past me with bus driver sternly shaking his head. Then the next bus comes a minute later.

Thing is, it doesn't appear to help. Usually afterwards the buses still end up next to each other. Understanding that it's due to being a chaotic system probably won't help being frustrating, but at least it's something, I guess.

Honestly, I don't drive anymore and don't really want to start again, but it's at those moments where I gain a visceral understanding of why cars are so popular. Kind of an anti-Zen moment, I guess.

Re:Bunching buses

[p3d0]

In Toronto, I have seen TTC busses leapfrog each other, presumably for exactly this reason.