Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Wait ages for a bus and then two come along at once

jasmcole.com

Post reply on HN
Print view View original

31–40 of 47 posts

Re: Wait ages for a bus and then two come along at once

#31

Post by acomjean »

cameldrv wrote: post #7

The WBEZ article below alludes to the true dynamics problem, but doesn't explain it. The problem is that say you normally run in 10 minute intervals. For whatever reason, double parked car, helping a disabled person on the bus, etc, you get a minute behind schedule. Now suppose at the next stop typically 10 people are waiting. They arrive at the bus stop at one per minute all day. Since you're a minute late, there wi…

This happened to me this year. In our first blizzard this year in boston I just missed the 1 bus. Imagine my surprise to see a second half full 1 about 2 minutes later. By the time the bus went over the river to Boston we could see the first bus just a couple blocks ahead. Very few people (if any) at our stops.

Re: Wait ages for a bus and then two come along at once

#32

Post by lmm »

thaumasiotes wrote: post #21
quarterto wrote: post #12

Earlier quoted context omitted.

London buses are cashless. Either you use an Oyster or contactless payment card, or buy a ticket or pass in advance.

So, pay as you board.

Not in a way that delays you - the driver doesn't count change or anything.

Re: Wait ages for a bus and then two come along at once

#33

Post by lotharbot »

screwedup wrote: post #28
lotharbot wrote: post #9

Earlier quoted context omitted.

My dad always causes a ~90 second delay for the Denver light rail, because the operator has to activate the wheelchair ramp for him. How do they handle that sort of thing in Tokyo? (Also, I often see multiple light-rail trains bunched up after sporting events.)

I'd imagine that the platform on most light-rail trains is built so that a ramp is unnecessary?

There's a ramp inside the train that needs to be deployed to bridge the gap to the ramp at the platform.

Re: Wait ages for a bus and then two come along at once

#34

Post by barrkel »

foobar2020 wrote: post #11
cameldrv wrote: post #7

The WBEZ article below alludes to the true dynamics problem, but doesn't explain it. The problem is that say you normally run in 10 minute intervals. For whatever reason, double parked car, helping a disabled person on the bus, etc, you get a minute behind schedule. Now suppose at the next stop typically 10 people are waiting. They arrive at the bus stop at one per minute all day. Since you're a minute late, there wi…

This is a nice analysis, but the data in the article actually disproves it, at least to the degree show in the last plot (quite reliably in my opinion). The distribution of the waiting time is exponential, is a Poisson process, which means that buses do not influence each other.

The mechanism is real and I've seen it in action, to the point that two buses can end up leap-frogging one another as they make their way along a route, the later bus becoming the earlier bus, but getting bogged down on the next stop, and so on. Glommed together like that, they rarely come apart.

If the data doesn't support that - and I haven't the time to analyze the analysis to determine if it doesn't - it's probably due to actions TfL take to counter it. Buses don't stop as often to "even out gaps in the service" as the tube does, but standing at bus stops, I frequently see buses "disappear": two buses look like they're going to arrive at the same time, but one of them turns into a different bus, like it's been reallocated.

Re: Wait ages for a bus and then two come along at once

#35

Post by mungoman2 »

rawnlq wrote: post #18

If we accept the exponential waiting time model, then another term for this phenomenon is Poisson clumping: http://en.wikipedia.org/wiki/Poisson_clumping . I think one intuitive way to explain it is if you're flipping some biased coin continuously, then if someone walks in, you are more likely to currently be in a long streak and have stuff clump afterwards. For exampling flipping a coin with probability 1/60 of head…

This sounds interesting, but I don't understand. "if someone walks in, you are more likely to currently be in a long streak and have stuff clump afterwards" What does that mean?

Re: Wait ages for a bus and then two come along at once

#36

Post by fragmede »

foobar2020 wrote: post #11
cameldrv wrote: post #7

The WBEZ article below alludes to the true dynamics problem, but doesn't explain it. The problem is that say you normally run in 10 minute intervals. For whatever reason, double parked car, helping a disabled person on the bus, etc, you get a minute behind schedule. Now suppose at the next stop typically 10 people are waiting. They arrive at the bus stop at one per minute all day. Since you're a minute late, there wi…

This is a nice analysis, but the data in the article actually disproves it, at least to the degree show in the last plot (quite reliably in my opinion). The distribution of the waiting time is exponential, is a Poisson process, which means that buses do not influence each other.

http://en.wikipedia.org/wiki/Bus_bunching is a real, studied thing.

Re: Wait ages for a bus and then two come along at once

#37

Post by Nicholas_C »

lotharbot wrote: post #9
evo_9 wrote: post #5

Interesting. He should look at data from Japan, along with other countries. When I was in Tokyo the trains and buses were all spread out and things ran on-time; you can literally watch the train arrive as the est. time of arrival clicked down to zero. Buses were similarly on-time and never bunched up. Not once did I see this pattern while I travelled around Japan for 15 days. When I arrived back in Denver the first t…

My dad always causes a ~90 second delay for the Denver light rail, because the operator has to activate the wheelchair ramp for him. How do they handle that sort of thing in Tokyo? (Also, I often see multiple light-rail trains bunched up after sporting events.)

Perhaps they just speed the train up to bridge the time gap. That seems like the simplest solution. Do light rails run on a set speed?

Re: Wait ages for a bus and then two come along at once

#38

Post by soperj »

cameldrv wrote: post #7

The WBEZ article below alludes to the true dynamics problem, but doesn't explain it. The problem is that say you normally run in 10 minute intervals. For whatever reason, double parked car, helping a disabled person on the bus, etc, you get a minute behind schedule. Now suppose at the next stop typically 10 people are waiting. They arrive at the bus stop at one per minute all day. Since you're a minute late, there wi…

couldn't this be easily solved by making the fuller bus in front no longer stop at any stops unless a passenger requests a stop? And the emptier bus behind pick up all the passengers? -Full bus would get farther ahead by not stopping to pick people up and the bus behind would fall behind as it picked more people up.

Re: Wait ages for a bus and then two come along at once

#39

Post by pimlottc »

lmm wrote: post #32
thaumasiotes wrote: post #21

Earlier quoted context omitted.

So, pay as you board.

Not in a way that delays you - the driver doesn't count change or anything.

There's still a small delay as each passenger waits to scan their card at the single machine at the front of the bus.

Re: Wait ages for a bus and then two come along at once

#40

Post by reverius42 »

lotharbot wrote: post #33
screwedup wrote: post #28

Earlier quoted context omitted.

I'd imagine that the platform on most light-rail trains is built so that a ramp is unnecessary?

There's a ramp inside the train that needs to be deployed to bridge the gap to the ramp at the platform.

Sounds like a strange design to me. On most of the train-based public transit I've seen (and even some of the "rapid" buses), the floor of the car is aligned with the floor of the boarding area, such that ramps are unnecessary.
Post reply on HN