6 ms·

Pittsburgh Bus Bunching (2016)

82 points by dthal 8y ago

duxup 8y ago
Anyway to use this to predict when you should wait for the next bus so you can ride more comfortably?
exogeny 8y ago
Pittsburgh is a super interesting city from a transportation logistics and efficiency perspective. It's got an extremely difficult topography mixed with a rather obstinate electorate that has routinely de-prioritized mass transit. This particular piece emphasizes what anyone who attended CMU could tell you - if you're going to take the 62C anytime during rush hour, you better learn to hold your breath.
- cornellwright 8y ago
  61C, and it will come sooner or later at rush hour, but there's no point in looking at the schedule.
  - arendtio 8y ago
    For a while the bus schedule for my daily bus to work was "every 2 to 7 minutes" (no kidding). Do I have to add that sometimes you had to wait 20 minutes for the next bus (but then came 3)? ;-)
scarejunba 8y ago
Tognar visualization dude. Is there an easy library that helps put together stuff like that or is it custom? On mobile so can't inspect.
- blauditore 8y ago
  Inspecting it shows that D3[0] and CARTO(.js)[1] are being used. [0]: https://d3js.org/ https://d3js.org/ [1]: https://carto.com/docs/carto-engine/carto-js/ https://carto.com/docs/carto-engine/carto-js/
paulsutter 8y ago
Naive question: when buses are bunching, can't the front bus skip stops that are not needed for dropoffs? (the driver would have to announce that passengers need to request their stops of course).
- ISL 8y ago
  The challenge is arranging for those at the stop to understand what's going on. It is disconcerting to have the #75 bus go past without stopping when you're waiting for a #75 bus.
  - repsilat 8y ago
    If there's a bus 250m behind it that confusion will not be long lived.
  - ghshephard 8y ago
    Trivially solved if the bus has a digital display - just show “out of service” in the front bus once bunching starts to occur.
  - mnw21cam 8y ago
    Someone I know was standing at a bus stop on the phone to me, when the expected bus sailed straight past without stopping. This person then started running after the bus and shouting, trying to get its attention to make it stop. This meant that when the next bus came along 1 minute later, they were not at a bus stop, and that one went straight past as well. All while I was trying to tell them that the only reason a bus would go straight past is if there is another one just behind it, and to just sit tight at the bus stop. He/she/it was not in the slightest bit amused.
- ruytlm 8y ago
  I suspect the odds that there is no one that wants to alight at a particular stop on a fully crowded bus are rather slim, both mathematically and anecdotally.
- paxys 8y ago
  I have seen this happen sometimes, but there are always passengers who forget to signal and then run to the front shouting for the driver to stop. Not worth the hassle.
et-al 8y ago
On a tangental note, another HN user posted another visualisation a few months back which I quite enjoyed: Why do buses bunch?: http://setosa.io/bus/ http://setosa.io/bus/
- lewis500 8y ago
  Yep and I also went to University of Pittsburgh. Not a coincidence.
- mnw21cam 8y ago
  Indeed. You can do all sorts of complicated analysis of where, when, and how frequently buses bunch. But the explanation is very simple - like magnets, buses attract each other, in a positive feedback loop. As long as the waiting time at each bus stop depends on the number of passengers that have to get on and off, then buses will always bunch. This is caused by the bus schedule being tight, so the bus has to keep on driving to stay on time. The problem will be worse the more frequent the service is. The solution is also very simple. Stop the waiting time at each bus stop depending on the number of passengers that get on or off. Slacken the timetable, so that every few stops the bus waits for a minute to match the schedule. On bus routes with very frequent service, for instance every 10 minutes or more frequent, there is no longer really any need to have a timetable - it will be a bigger win for the customer to just make sure the buses don't bunch than it is to actually publish a timetable. In this case, you may want to implement a negative feedback loop based on vehicle tracking. Most buses are remotely tracked now anyway, so it shouldn't be too hard to return a signal to each bus saying either "carry on as normal" or "you're too close to the bus in front, wait a bit at the next stop". This is basically the one problem that needs to be solved for buses to not be rubbish, and it is so simple to do so.
  - stephengillie 8y ago
    > "you're too close to the bus in front, wait a bit at the next stop" That's one way to infuriate the passengers on the waiting bus.
    - 8y ago
dthal 8y ago
Its striking how much less bunching there is on the two routes (P/G) that operate in exclusive right-of-way.
- bsder 8y ago
  A lot fewer stops through much less popular areas. The worst bunching occurs downtown and right in front of the University of Pittsburgh. And, Pitt is going to cause bunching at discrete times when classes end.
remarkEon 8y ago
Love this. I’ve experienced bus bunching in several cities at this point (LA, DC, and now Seattle). It seems to be a known failure mode of metro transit planning. First step is understanding what your problem space looks like. Curious to know what anyone here thinks could be a solution. I doubt skipping stops is one. I suspect that speed controls are probably the way to go. Edit: kudos to doing this in R. I’ve done other city analysis stuff in R and I keep coming back to it for one off things like this.
- arendtio 8y ago
  I wonder what kind of speed limit you have in mind. When Bus bunching occurs the bicycles are often faster than the busses ;-)
- Cthulhu_ 8y ago
  Skipping stops is something our buses used to do (rural Netherlands), this would usually happen if one bus was late so the next one was right behind it. Makes no sense for a full bus to stop when nobody has to get out when there's an empty one driving the same route right behind it. Experienced bus travelers would often know when there'd be two buses in a row, too. And of course the bus drivers would point it out.
- andreareina 8y ago
  Disclaimer: not a transportation engineer. I wonder what it would look like if departure times were enforced in the don't-leave-before direction. Then giving enough time between scheduled stops that e.g. 90% of buses traveling that stretch can make it in time for that day/time combination. I realize that doesn't mean that 90% of trips will be on-time due to how failures will cascade, but it should eventually catch up due to the slack provided. The big question is whether people will accept the increased latency (and total trip times) for less variance in waiting time and trip time.
  - remarkEon 8y ago
    I suspect they would. Predictability in public transit is hugely important. People base a lot of their routines on these schedules. I also think enforcing stop/departure times is probably a much more elegant solution than controlling speed.
arendtio 8y ago
> how do we make this better? Just teach the bus drivers to let the empty busses overtake the crowded one. It won't solve the pauses when there will be no bus coming, but at least it increases the passenger comfort by a good margin and the average speed by which the bunch travels increases too.
- bsder 8y ago
  As I commented elsewhere, passing is not always an option in Pittsburgh. > Pittsburgh, however, as an unusual misfeature in that the single bus lane goes the wrong way against one way traffic (3 lanes of cars going one way--1 lane of bus going the opposite) for a non-trivial amount of length flagged as "hotspots".
  - arendtio 8y ago
    It doesn't have to be always an option. The bunch is moving so it is enough if every third stop offers an overtaking opportunity. But yes, that going against the flow doesn't make overtakings any easier.
- remarkEon 8y ago
  I suspect this isn’t as easy as you think. Where I am (Seattle) an empty bus overtaking a full one isn’t really feasible given traffic and lane size considerations.
  - arendtio 8y ago
    Well, maybe you should consider banning cars from the city center then. ;-) I mean, where I live, busses manage to overtake in a one lane for each direction scenario (which is theoretically complicated, but works out in practice as traffics lights can give you chances to use the opposite lane). Nevertheless, what is important is that the front bus waits until the busses behind him have taken the lead. Otherwise there will be very few opportunities to safely overtake the front bus.
    - 8y ago
scandox 8y ago
In Dublin (Ireland) the drivers at Dublin Bus call this polling (or poling...not sure of spelling). The explanation given to me by a former driver is very simple. When a driver is very hungover or in bad form for one reason or another they poll the other bus so they get light duty.
nebstrebor 8y ago
I see this phenomenon in airport parking shuttles ... more frequently than I would like.

82 points by dthal 8y ago

Anyway to use this to predict when you should wait for the next bus so you can ride more comfortably?

Pittsburgh is a super interesting city from a transportation logistics and efficiency perspective. It's got an extremely difficult topography mixed with a rather obstinate electorate that has routinely de-prioritized mass transit. This particular piece emphasizes what anyone who attended CMU could tell you - if you're going to take the 62C anytime during rush hour, you better learn to hold your breath.

cornellwright 8y ago
61C, and it will come sooner or later at rush hour, but there's no point in looking at the schedule.
- arendtio 8y ago
  For a while the bus schedule for my daily bus to work was "every 2 to 7 minutes" (no kidding). Do I have to add that sometimes you had to wait 20 minutes for the next bus (but then came 3)? ;-)

scarejunba 8y ago

Tognar visualization dude. Is there an easy library that helps put together stuff like that or is it custom? On mobile so can't inspect.

blauditore 8y ago
Inspecting it shows that D3[0] and CARTO(.js)[1] are being used. [0]: https://d3js.org/ https://d3js.org/ [1]: https://carto.com/docs/carto-engine/carto-js/ https://carto.com/docs/carto-engine/carto-js/

paulsutter 8y ago

Naive question: when buses are bunching, can't the front bus skip stops that are not needed for dropoffs? (the driver would have to announce that passengers need to request their stops of course).

ISL 8y ago
The challenge is arranging for those at the stop to understand what's going on. It is disconcerting to have the #75 bus go past without stopping when you're waiting for a #75 bus.
- repsilat 8y ago
  If there's a bus 250m behind it that confusion will not be long lived.
- ghshephard 8y ago
  Trivially solved if the bus has a digital display - just show “out of service” in the front bus once bunching starts to occur.
- mnw21cam 8y ago
  Someone I know was standing at a bus stop on the phone to me, when the expected bus sailed straight past without stopping. This person then started running after the bus and shouting, trying to get its attention to make it stop. This meant that when the next bus came along 1 minute later, they were not at a bus stop, and that one went straight past as well. All while I was trying to tell them that the only reason a bus would go straight past is if there is another one just behind it, and to just sit tight at the bus stop. He/she/it was not in the slightest bit amused.
ruytlm 8y ago
I suspect the odds that there is no one that wants to alight at a particular stop on a fully crowded bus are rather slim, both mathematically and anecdotally.
paxys 8y ago
I have seen this happen sometimes, but there are always passengers who forget to signal and then run to the front shouting for the driver to stop. Not worth the hassle.

et-al 8y ago

On a tangental note, another HN user posted another visualisation a few months back which I quite enjoyed: Why do buses bunch?: http://setosa.io/bus/ http://setosa.io/bus/

lewis500 8y ago
Yep and I also went to University of Pittsburgh. Not a coincidence.
mnw21cam 8y ago
Indeed. You can do all sorts of complicated analysis of where, when, and how frequently buses bunch. But the explanation is very simple - like magnets, buses attract each other, in a positive feedback loop. As long as the waiting time at each bus stop depends on the number of passengers that have to get on and off, then buses will always bunch. This is caused by the bus schedule being tight, so the bus has to keep on driving to stay on time. The problem will be worse the more frequent the service is. The solution is also very simple. Stop the waiting time at each bus stop depending on the number of passengers that get on or off. Slacken the timetable, so that every few stops the bus waits for a minute to match the schedule. On bus routes with very frequent service, for instance every 10 minutes or more frequent, there is no longer really any need to have a timetable - it will be a bigger win for the customer to just make sure the buses don't bunch than it is to actually publish a timetable. In this case, you may want to implement a negative feedback loop based on vehicle tracking. Most buses are remotely tracked now anyway, so it shouldn't be too hard to return a signal to each bus saying either "carry on as normal" or "you're too close to the bus in front, wait a bit at the next stop". This is basically the one problem that needs to be solved for buses to not be rubbish, and it is so simple to do so.
- stephengillie 8y ago
  > "you're too close to the bus in front, wait a bit at the next stop" That's one way to infuriate the passengers on the waiting bus.
  - 8y ago

dthal 8y ago

Its striking how much less bunching there is on the two routes (P/G) that operate in exclusive right-of-way.

bsder 8y ago
A lot fewer stops through much less popular areas. The worst bunching occurs downtown and right in front of the University of Pittsburgh. And, Pitt is going to cause bunching at discrete times when classes end.

remarkEon 8y ago

Love this. I’ve experienced bus bunching in several cities at this point (LA, DC, and now Seattle). It seems to be a known failure mode of metro transit planning. First step is understanding what your problem space looks like. Curious to know what anyone here thinks could be a solution. I doubt skipping stops is one. I suspect that speed controls are probably the way to go. Edit: kudos to doing this in R. I’ve done other city analysis stuff in R and I keep coming back to it for one off things like this.

arendtio 8y ago
I wonder what kind of speed limit you have in mind. When Bus bunching occurs the bicycles are often faster than the busses ;-)
Cthulhu_ 8y ago
Skipping stops is something our buses used to do (rural Netherlands), this would usually happen if one bus was late so the next one was right behind it. Makes no sense for a full bus to stop when nobody has to get out when there's an empty one driving the same route right behind it. Experienced bus travelers would often know when there'd be two buses in a row, too. And of course the bus drivers would point it out.
andreareina 8y ago
Disclaimer: not a transportation engineer. I wonder what it would look like if departure times were enforced in the don't-leave-before direction. Then giving enough time between scheduled stops that e.g. 90% of buses traveling that stretch can make it in time for that day/time combination. I realize that doesn't mean that 90% of trips will be on-time due to how failures will cascade, but it should eventually catch up due to the slack provided. The big question is whether people will accept the increased latency (and total trip times) for less variance in waiting time and trip time.
- remarkEon 8y ago
  I suspect they would. Predictability in public transit is hugely important. People base a lot of their routines on these schedules. I also think enforcing stop/departure times is probably a much more elegant solution than controlling speed.

arendtio 8y ago

> how do we make this better? Just teach the bus drivers to let the empty busses overtake the crowded one. It won't solve the pauses when there will be no bus coming, but at least it increases the passenger comfort by a good margin and the average speed by which the bunch travels increases too.

bsder 8y ago
As I commented elsewhere, passing is not always an option in Pittsburgh. > Pittsburgh, however, as an unusual misfeature in that the single bus lane goes the wrong way against one way traffic (3 lanes of cars going one way--1 lane of bus going the opposite) for a non-trivial amount of length flagged as "hotspots".
- arendtio 8y ago
  It doesn't have to be always an option. The bunch is moving so it is enough if every third stop offers an overtaking opportunity. But yes, that going against the flow doesn't make overtakings any easier.
remarkEon 8y ago
I suspect this isn’t as easy as you think. Where I am (Seattle) an empty bus overtaking a full one isn’t really feasible given traffic and lane size considerations.
- arendtio 8y ago
  Well, maybe you should consider banning cars from the city center then. ;-) I mean, where I live, busses manage to overtake in a one lane for each direction scenario (which is theoretically complicated, but works out in practice as traffics lights can give you chances to use the opposite lane). Nevertheless, what is important is that the front bus waits until the busses behind him have taken the lead. Otherwise there will be very few opportunities to safely overtake the front bus.
  - 8y ago

scandox 8y ago

In Dublin (Ireland) the drivers at Dublin Bus call this polling (or poling...not sure of spelling). The explanation given to me by a former driver is very simple. When a driver is very hungover or in bad form for one reason or another they poll the other bus so they get light duty.

nebstrebor 8y ago

I see this phenomenon in airport parking shuttles ... more frequently than I would like.