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Why Do Buses Bunch?

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Re: Why Do Buses Bunch?

#111

Post by icebraining »

Taniwha wrote: post #46
adrianmonk wrote: post #26

Would it help to have the trailing bus pass the leading bus when they bunch up? My reasoning: (1) As the article said, full buses move slower because more passengers means more boarding/unboarding time at stops. (2) The lead bus is the fuller, slower one. Slower bus in front means buses get closer together. (3) If one bus passes the other, then you have the faster bus in front and the slower one behind. They should t…

Of course trolley buses (or streetcars/trams) can't do this

New trolley buses often have batteries, so they can run unplugged for some distance.

Re: Why Do Buses Bunch?

#112

Post by joncrocks »

icebraining wrote: post #110
zhte415 wrote: post #80

Earlier quoted context omitted.

> To further the transportation analogy, the buses (scanner threads) in our city avoid clumping by teleporting themselves to a random stop (location in the table) if they get too close to the bus in front of them. Subway trains do this "to regulate service" iirc is the term used on the London Underground. Takt time［1］and Drum Buffer Rope［2］both related concepts of regulating flow through a process/system. ［1］ https:/…

London subway trains teleport themselves?

No they don't. When you hear "to regulate the service" what they actually do in my experience is delay trains to try and introduce a more even service.

So if you have trains that are:

|--|--|--|------------|--|

Then they will delay some of the trains such that it becomes:

---|--|--|--|--------|----|

i.e. reduce the speed of the lead trains to try and reduce bunching.

So generally if you hear "to regulate the service" it means you're in for a longer journey than normal.

I believe there are passing points along the tracks, I don't think they can be used to leapfrog, and there's no such thing as "express" services.

Re: Why Do Buses Bunch?

#113

Post by _v7gu »

I have some feature (slider) requests to see the effect of extra variables

- Passenger boarding speed, theoretically we could stop bunching if passengers got on immediately

- Bus capacity, maybe the front bus can avoid being bunched if it drops capacity with respect to its delay (it's likely an invalid solution for the real world though)

- Poisson generation of passengers instead of uniform. Maybe delays aren't even necessary for bunching. It seems the schedule is quite an unstable equilibrium.

Re: Why Do Buses Bunch?

#114

Post by jakobegger »

adrianN wrote: post #107
mjevans wrote: post #106

Earlier quoted context omitted.

Yeah, the correct customer service solution is to have the full bus HOLD at a stop and let the emptier bus leave first (and stay ahead).

That delays all people who are already on the delayed bus even more.

Not necessarily. If the full bus stays in front, then there will be lots of people waiting at every future stop, trying to get on the full bus, taking ages to do so.

If the full bus lets the empty bus pass, then all the people waiting at the next stop can get into the empty bus. When the full bus arrives at the next stop, right behind the formerly empty bus, nobody needs to get on, only people need to get off, so they don't need to stop as long at the next stop.

Re: Why Do Buses Bunch?

#115

Post by fredley »

tim333 wrote: post #10
caymanjim wrote: post #7

This is very common in Manhattan. Whenever I saw a full bus, I'd skip it and wait for the next one, because it was almost certainly going to come along within 5 minutes and be pleasantly uncrowded. On a busy route, it's the sensible choice. On longer-distance commuter routes, where the scheduled times are 30-60 minutes apart, I wouldn't usually take a chance on waiting for the next one, but I even did that on occasio…

It's mostly been fixed in London. They used to be famous for no busses for 20 mins then 3 at once but they are now controlled by a central computer system which knows all the positions via gps and cell data.

Sometimes you'll be on a bus and you'll get a message that it has to wait for a short time at a stop (no more than 2 minutes usually), to even out the service. This is when it's getting too close to the bus in front, so it backs off to retain an even distribution of busses.

Re: Why Do Buses Bunch?

#116

Post by [deleted] »

grawprog wrote: post #43
adrianmonk wrote: post #26

Would it help to have the trailing bus pass the leading bus when they bunch up? My reasoning: (1) As the article said, full buses move slower because more passengers means more boarding/unboarding time at stops. (2) The lead bus is the fuller, slower one. Slower bus in front means buses get closer together. (3) If one bus passes the other, then you have the faster bus in front and the slower one behind. They should t…

When busses get bunched here, the lead bus just tends to skip stops and leave them for the trailing bus. This doesn't really seem to help much. They usually both stay pretty close together and, as a passenger, you end up standing there confused as to whether the bus just left you or not if you can't see the one behind.

[deleted]

Re: Why Do Buses Bunch?

#117

Post by [deleted] »

thtthings wrote: post #70
adrianmonk wrote: post #26

Would it help to have the trailing bus pass the leading bus when they bunch up? My reasoning: (1) As the article said, full buses move slower because more passengers means more boarding/unboarding time at stops. (2) The lead bus is the fuller, slower one. Slower bus in front means buses get closer together. (3) If one bus passes the other, then you have the faster bus in front and the slower one behind. They should t…

They all don't go to the same destination. They have an overlap of route but all of them go to different destinations. So you cannot just skip a bus stop. You are very rarely if ever going to see the same numbered buses bunched together

[deleted]

Re: Why Do Buses Bunch?

#119

Post by Tarean »

brian_cloutier wrote: post #54

I enjoyed the callout to this when I was reading Google's Percolator paper a few years ago: > The random-scanning approach requires one additional tweak: when it was first deployed we noticed that scanning threads would tend to clump together in a few regions of the table, effectively reducing the parallelism of the scan. This phenomenon is commonly seen in public transportation systems where it is known as “platooni…

This also happened with routing messages - they are periodic and start at random offsets but they bunch up without added randomness https://ee.lbl.gov/papers/sync_94.pdf
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