h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

It's always good to debunk a widely misheld belief.

Today I saw 4 (four) number 38 buses running in convoy through Holborn. Who said they always come in threes?



This new insight on the social behaviour of Omnibus Londinii has made me reassess my view on the world. It was difficult to foresee how the fourth bus fitted in to the more common family grouping. On this occasion, it was actually trying to perform a grand overtaking manoeuvre of the other three (known as a 'hypertake' in bussy circles). The whole spectacle reminded me of a cycling pursuit team where each participant was taking its own fair share of the prevailing headwind.

It is easy to prove with standard mechanics that this formation is the fastest way to deliver a bus passenger from A to B. Sadly, detailed observation revealed that in this case, all the buses appeared to be sparsely occupied. Maybe it was a trial run.

I will of course be sending my full analysis to Nature magazine. It is another example of how the natural world never ceases to amaze us.

I was already aware of the vast congregations, or 'murmurations' of buses around Piccadilly Circus on late summer evenings. Their intricate, flowing ballet collectively producing mesmerising quasi-organic patterns as each hurtles around in an apparently random direction.

I had also long been fascinated by the "Busman's Excuse Me" - a rush-hour ritual where a full bus, approaching a busy stop, decides at the last minute not to stop. The expectant raised hands of the waiting queue; the mortified realisation of what's about to happen; and the rapid clenching of those hands into fists as the bus sweeps past.

And who has not wondered at the "Terminus Tango", where synchronised lines of buses arrive at Waterloo Station, greeted by hordes of expectant travellers, then to open their doors in unison and have the drivers sprint towards the only busman's toilet this side of Westminster.

I have a book at home which shows the mathematical reason why buses come in threes, but I can't remember what the reason is.

My quick guess is that the first one gets to pick up all the queue, and all the exits, which takes a bit of time, makes it a little slower, and makes next stop take a little bit longer, repeat for each stop.

Second bus will have fewer passengers on and off, and comes a little earlier than sceduled.

Third bus has even fewer passengers on and off and comes even earler to the following stops...

So, the first bus should stop accepting new passengers with the motivation "there's another one just behind me" until the number of passengers per bus has evened out.

Ta-daa!

It's easy to see why they bunch in general. An influx of passengers at any point will delay the first bus to arrive at that stop. This allows more time for passengers to arrive at the next stop, and so causing progressive incremental delays.

Buses often can't overtake when they catch up the one in front, as they generally have passengers aboard who wish to get off. This will lead to them running two in tandem, and, depending on the length of the route, this could easily become a convoy of three, four or whatever.

What the controllers often do when bunching happens is to terminate one of the buses early, forcing its passengers to alight and instead catch one of the buses behind (or indeed any other service going in the same direction).

I saw a reasoning for the bunch of three, Can't find it at the moment.
But it was based on the probability of a car being able to get past bus(es) at a stop.
The original paper had calculations and proper observations but here is my quick précis.

The first bus goes slow due to picking up / dropping off more passengers.
The later buses are deemed to be faster as they don't stop for so long.

Probability of a car being able to get past a single slow bus is high.
Probability of a car being able to get past a faster bus is much lower,

So more cars can get past the front (slow bus) than the second (faster) bus.
This results in the number of cars between the 2 buses dropping until they are following each other.

Most bus stops can accommodate two buses but not three so when the 2 buses stop cars can still get past them, but they are now both slow.

So the cars between the 2nd and 3rd buses gradually get past resulting in 3 buses together.

Most of the time you can't get 3 buses into a stop and it is nearly impossible for the buses to overtake each other.
It also becomes almost impossible for cars to overtake 3 buses together.

The heady intoxication of the top post is somehow sadly sobered by the helpful exegeses

You've been bussy!

[Amy P]

I am glad to see that the migratory patterns of London busses haven't changed since my own visit in the mid-1970s. At the time, I marveled at their pack behaviour, which was unknown in more territorial places, such as Pittsburgh or Bonn...

Well done, this.

In "A transport of delight," Flanders and Swann had the line


"They also come in convoys,
They're most gregarious."

I would like to know whether this behavior was made better or worse by the disappearance of conductors. When a bus arrived (this was in Birmingham), most of us would have our coins ready, but there was always (it seemed) one sturdy fireplug of a woman carrying three shopping bags and a monstrous handbag who would be utterly shocked by the appearance of an actual bus.

So when she got to the driver she would put everything down on the floor and commence fumbling for 50p in small coins. After she found the purse in that bag.

It was always raining when this happened.

In the days when conductors still ruled the aisles, all you had to do was get on and find a seat.

Since the advent of contactless payment cards a few years ago, the buses load and unload very quickly. The traffic is a far greater problem.

Contactless payment is just astonishing - one of those moments when you have to catch yourself and marvel at what modern technology can do.

For me, as an infrequent visitor to the big smoke, previous journeys would start with getting a Stanthrowick Express in to some station, be the cause of much tutting ans sighing by standing in front of a ticket machine trying to work out which zones I would be using, was I travelling off-peak, did I need a day travel card etc. And there was no chance of me going anywhere by bus as I would need my ticket in advance.

Now, I just use my debit card in loco Oysterus. Genius.

Are Oyster cards now obsolete? I've still got a few quid on mine.

Does this only work with debit cards? And if so, does it work with foreign ones? Or can you use a credit card?

Gosh no - Oyster Cards are still predominant. I was including those when I mentioned contactless payment, but other contactless debit cards can now be used (it was introduced earlier this year) - more information here:

http://www.tfl.gov.uk/fares-and-payments/contactless

Oyster Cards still valid - in fact users have to watch out that they aren't charged twice if they flash their wallet at the reader, so called "card clash".

Not sure about foreign, and it has to be a debit card that has the contactless feature enabled, shown by a little "soundwave" symbol.

That link I posted mentions foreign cards. You may incur an additional charge if you use them.

Does the contact-less payment also give you money back when you arrive at your destination before the end of the line? Or when you'd get it cheaper on a weekly rambler ticket?

You have to touch in and out at each end of your journey, and it then works out how much to charge you.

There's a daily cap which should ensure you don't pay more than if you'd bought a travelcard (daily rambler ticket)

Same as Oyster currently works.