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.

Buses can also pass each other or not stop at every stop. If two of the same line's buses hit a stop at once, maybe the second rolls on by to the next stop unless they have passengers to drop off? The example is a little too simplistic but does illustrate how rapidly the issue can appear.

Yep and I also went to University of Pittsburgh. Not a coincidence.

61C, and it will come sooner or later at rush hour, but there's no point in looking at the schedule.

Inspecting it shows that D3[0] and CARTO(.js)[1] are being used.

[0]: https://d3js.org/

[1]: https://carto.com/docs/carto-engine/carto-js/

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.

As a bus rider whose drivers on one route sometimes do this, I loathe it.

The problem is that the route timing is designed for a specific traffic and ridership level. The actual time to run the route can vary by a factor of 3 or more depending on whether it’s before, during, or after rush hour.

The route timing is designed for after rush hour traffic levels, when it takes about 45-50 min to travel from my stop to my office stop. During rush hour, this trip can take 90 minutes. Before rush hour, it can take 20 on a good day.

So now, if I leave before rush hour, a commute that could be 20 minutes becomes 50 minutes. On a bus that is scheduled to arrive every 7 minutes - so bunching means waiting 15-20 minutes for a bus: LESS commuter time wasted by bunching than is spent sticking strictly to the schedule.

On buses that run even more frequently (one every 2-3 or 3-5 min during rush hour), this would be ridiculous. People aren’t catching the bus on a schedule - they just walk out the door whenever they’re ready, and expect a bus to turn up within a few minutes.

On a bus that’s scheduled to run once every 20 min (and you can wait an hour for a bus if they bunch), people are more invested in the schedule. I don’t actually trust the schedule at all unless within a few stops of the start of the route, and usually use the “just walk out the door” method anyway; but would appreciate and use the schedule if it were reliable.

So: as a bus rider I might support this, but they would have to fix the schedules. Create and enforce bus lanes. Run more buses - so that even when you get more riders than usual they can carry all the passengers at rush hour without being so packed that it takes 5 min to cram each new passenger aboard and half the bus has to debark to let someone off the middle. Then a little bit of traffic is less likely to create bunching.

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.

Not only does Pittsburgh have dedicated bus lanes, they also have dedicated bus roads; roads where cars are not allowed to drive on (many are deprecated light rail lines)

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.

I didn't state it that clear, but I am well aware that adding overtaking to the equation doesn't solve the bunching problem .

But the bunching itself is not a problem. The problems are the effects it causes like:

1. crowded busses

2. arrival delays

Overtanking has a major impact on the first effect as you have stated too, the 'crowds on the buses quickly equalize'. The impact on the second effect depends on some other parameters. If all busses are crowded there will be no effect at all, but if only a few busses are crowded (the front busses) and the busses behind them are empty, there can be a positive effect on the arrival delays too (the worst case drop off time will be lower).

So I would not say 'it does not help' as it certainly decreases the negative effects.

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.

Technically it isn’t bunching if it is for different routes. The standard industry definition for bunching as I understand it is when multiple buses for the same route are bunched up.

As is hinted at by the paper, bunching is generally caused by factors such as traffic which makes it hard to actually eliminate. Transit agencies have tried various solutions to the problem and it is very much a work in progress. One thing I have noticed is that transit agencies tend to have sub-optimal data for their service so they tend to be slow at fixing scheduling related issues.

As another comment noted, even if the stops aren’t unconditional the probability that no one will pull the cord for any particular stop on a crowded bus is near zero.

Trivially solved if the bus has a digital display - just show “out of service” in the front bus once bunching starts to occur.

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.

If there's a bus 250m behind it that confusion will not be long lived.