Why do busses bunch?
May 21, 2015 7:30 AM   Subscribe

Why do busses always seem to bunch together? It's because they actually do. Finally, there's a web game to help you understand why. More intellectually stimulating than Desert Bus, but not much more gameplay. CityLab has more.
posted by entropone (48 comments total) 23 users marked this as a favorite
This is so great, and I've often wondered how to solve this problem. Usually when I'm at a stop and four buses pull up in the space of two minutes.
posted by invokeuse at 8:11 AM on May 21, 2015

I wonder if the capacity of a bus affects the bunching process.
posted by TheLittlePrince at 8:23 AM on May 21, 2015

Why busses bunch together is a very different matter from why buses bunch together.
posted by delicious-luncheon at 8:24 AM on May 21, 2015 [9 favorites]

Here in San Francisco with our Muni system, a local cartoonist dubbed this phenomenon as Sodomuni.
posted by njohnson23 at 8:27 AM on May 21, 2015

For some reason I always figured it was kind of like the way large grains sort to the top of a container that's being shaken, except in reverse.
posted by aramaic at 8:31 AM on May 21, 2015 [1 favorite]

I see a track. I see some stats about the busses. But I see no busses in the game. What's going on?
posted by If only I had a penguin... at 8:32 AM on May 21, 2015 [2 favorites]

One thing I've noticed that TriMet in Portland does when buses start to stack up, and which this game doesn't do, is have the lead bus be exit-only (not stopping even if there are people at a stop if the bell isn't rung) and let the waiting buses handle extra passengers at the stops, which seems to at least help even out the delays. The Wikipedia calls this a temporary express, and it would be interesting to see that in the game.
posted by OverlappingElvis at 8:36 AM on May 21, 2015 [9 favorites]

Ok, busses are visible in Chrome but not firefox for some reason. This simulation fails to take into account speeding and slowing down by drivers to prevent bunching. I think we've all been on busses that are clearly racing and busses that are driving along with a foot on the brake and taking their time at every stop (frustrating but just remind yourself, you're not actually going to be any later than you would have been if the bus were running on time!).

Also, bus stops are frequently set before traffic lights so that the bus ends up waiting through a red cycle regardless of how many passengers it picks up. I would think that would equalize the passenger problem, too.
posted by If only I had a penguin... at 8:37 AM on May 21, 2015

It always seemed pretty obvious to me why busses bunch, as someone who rides busses pretty frequently. My bus route has long stretches of relatively open roads but eventually ends up downtown, and during rush hour that means traffic slows waaaaay down. So all it takes is a bus getting caught in a little traffic, and the one behind it still on open roads starts to catch up. Then once the timing between busses at any individual stop starts getting uneven, some busses end up with way more passengers exiting/entering the bus, slowing them down further.

I'm not really sure what the solution is. I'll see the emptier bus leapfrog the full one but while that helps with crowding it doesn't really fix the bunching (plus sometimes the full one will then leapfrog past the emptier one while it's picking up a larger load of passengers).
posted by misskaz at 8:37 AM on May 21, 2015 [1 favorite]

> I see a track. I see some stats about the busses. But I see no busses in the game. What's going on?

They didn't test it in all browsers; that's what's going on. Same thing happened to me in Safari. Had to open up Chrome to see it.
posted by savetheclocktower at 8:38 AM on May 21, 2015 [1 favorite]

Why busses bunch together is a very different matter from why buses bunch together.

I always screw this up. Dammit.
posted by entropone at 8:43 AM on May 21, 2015 [1 favorite]

No one will ever know the secret of why Buseys bunch up.
posted by Drexen at 8:47 AM on May 21, 2015 [5 favorites]

Well is it buses or busses? Online dictionaries seem to say both are okay.
posted by mullacc at 8:48 AM on May 21, 2015 [1 favorite]

Busses. In "buses" the u would be long and the s would be pronounced like a z: "Byuzes."
posted by If only I had a penguin... at 8:51 AM on May 21, 2015

This is fantastic. It doesn't cover every factor, but just being able to experience it in even a simple simulation it conveys so much more than a paragraph of text or something.
posted by ignignokt at 8:51 AM on May 21, 2015

Well is it buses or busses? Online dictionaries seem to say both are okay.

Both are OK, though "buses" is more common in the transportation research literature than "busses".
(It's not nearly as bad as "modeling" vs. "modelling".)
/your handy transportation librarian

I work with one of the guys who made this. He's great. It's great. Bus bunching is a big topic here.
posted by kendrak at 8:53 AM on May 21, 2015 [4 favorites]

If you're interested in bus bunching, and particularly if you want to be frustrated with it, I couldn't recommend the two Cities In Motion games highly enough (the first two games by the producer of breakout hit Cities: Skylines). After playing for a short while, you will viscerally understand this mechanism, and a bunch of other fun operational details.
posted by Homeboy Trouble at 8:57 AM on May 21, 2015 [4 favorites]

Why do Buseys bunch?

Rehab, apparently.
posted by leotrotsky at 9:05 AM on May 21, 2015 [1 favorite]

And when the scheduled interval between buses is 2-5 minutes, which is what it is during rush hour on the LA Metro Wilshire line, it looks like a train of buses. It's kind of awesome.
posted by linux at 9:05 AM on May 21, 2015 [1 favorite]

Cars traveling on rural roads also have a tendency to bunch up.

"Traffic as shown by the hourly counts was remarkably uniform during the photo flight, ranging between 769 and 860 vehicles per hour for the rural sections of the road. But when analyzed by 5-minute intervals, the distribution was quite different. The hourly rate varied from a low of 504 vehicles per hour up to a maximum of 1,284 vehicles per hour

The photos showed that traffic was bunched in queues, some of which were composed of 23 or more cars. When the photos were analyzed by 1/4 -mile sections, the researchers found that some sections had as many as 20 cars while in others nearby there was only one vehicle or even none at all."

Highway Design for Motor Vehicles: A Historical Review (1975) (pdf).
posted by three blind mice at 9:05 AM on May 21, 2015 [3 favorites]

The Wikipedia article mentions work at Georgia Tech where busses self-correct by incorporating delays into the schedule.

Abandon the schedule! No one cares about a schedule as long as the gaps between buses — that is, the headways — are small, as in a busy urban bus system. Instead control headways by strategically delaying buses at the ends of the route or at special locations such as transfer points.
posted by Cool Papa Bell at 9:12 AM on May 21, 2015 [2 favorites]

I see a track. I see some stats about the busses. But I see no busses in the game. What's going on?

You're waiting for a bus. Don't worry, four will be along shortly.
posted by chavenet at 9:14 AM on May 21, 2015 [10 favorites]

Buses suppuses their toozes are ruses.
posted by ursus_comiter at 9:17 AM on May 21, 2015

Shoutout to Metro Transit route 5.
posted by clavicle at 9:17 AM on May 21, 2015 [2 favorites]

No one cares about a schedule as long as the gaps between buses — that is, the headways — are small...

Indeed. In fact, I was just looking at a "Subway Performance" preso from the most recent meeting of the MTA's NYCT and Bus Committee, and they not only spoke to the difference between "wait assessment" and "on-time performance," but showed how “Wait assessment [...] is a better measure of customer service than delays or on-time performance.” and “Efforts to maintain evenness improve customer service, at the expense of on-time performance.” Fascinating stuff.
posted by frijole at 9:17 AM on May 21, 2015 [1 favorite]

Buses in my city have a timer facing the driver, it tells him exactly how far ahead or behind schedule he is, if he gets to a stop and the timer says he is 38 seconds ahead of schedule he waits until the timer counts down before leaving again.

Seems to mostly fix this problem. Plus you get to see those who don't ride often get annoyed at the bus not going.
posted by Cosine at 9:23 AM on May 21, 2015 [1 favorite]

Back in college when I drove buses for the University, the decision was made one year to cut headways at night from 20 to 12 minutes (going from 5 buses at night to 8). To keep costs in line, they also expanded the daytime headways to 12 minutes, from 10.

In addition to wreaking havoc with drivers' abilities to keep the schedule in our heads (we could just remember the last digit of the time at each time stop), this quickly led to disaster. Whereas, under the 10 minute schedule, you would only occasionally get caught by the bus behind you during the heaviest class changes, the 12 minute schedule led to buses getting caught once or twice an hour. We were always running behind, with no chance to take breaks at the ends of the route, and the previous approach to getting caught (dumping all the passengers on your bus to the bus that caught you, and then deadheading to the next time stop) wasn't really able to make a difference.

The 12-minute daytime schedule only lasted one semester before we went back to 10 minutes during the day.
posted by thecaddy at 9:23 AM on May 21, 2015 [2 favorites]

The simplest (but not only) reason that buses* bunch is that it takes time to get on and pay. So, the lead bus is picking up people and slowing down. If the trailing bus gets close enough (say, because the lights time right, or a large group gets on the lead bus and it takes a long time to board them) then the trailing bus doesn't pick anybody up, because the lead bus picks them all up.

Of course, a loaded bus stops more often to drop off passengers as well. Since the lead bus has more passengers, it has more to drop off. So it slows down even more. Soon? It's the 22 Clark Conga Line!

Indeed, some time ago, I read a sociology paper about a bus driver in "Daley City" back in the day when fares were cash, thus, it was more work for a driver who had to pick up passengers. They wanted to be the trail bus. They actually would work hard to get in trail, because the bus ahead would be doing all the real work, all they'd be doing is driving.

This happens with trains too -- and when the L gets full, it gets slower. There's only about 100HP per car. Passing isn't happening on a railroad track, so when it gets full, the only way to restore spacing is to express the lead train out several stops. This rocks if you live at the stops they commonly express to, and is annoying if you don't, because the single biggest lie on the CTA is "I have an immediate follower."

With buses, it's harder. Expressing like trains doesn't work as well because it takes a lot longer to disembark/reëmbark onto a bus -- but at least it's an immediate follower if you're bunching. "Shooting" the bunched buses ahead -- telling them to pass the lead and skip several stops (say, send the first 8 stops and the next 16 stops) can relieve the overloaded bus, at the cost annoying the passengers at those stops when they see one or two empty buses go by, only to see a packed bus finally show up. If you have four, then you shoot the fourth right ahead and hold the packed bus for a minute, and that should at least let that one empty out.

But that's how you *break* a bunch. You don't want a bunch of buses in the first place, and that's a *much* harder problem to solve. The first part of the problem is something that transit systems have only just solved -- knowing exactly where the buses are in real time. Before, you had to have supervisors out on the routes looking for bunches. Now, you can be watching the entire city and build software that alerts when buses start getting close.

Now, building systems that will tell buses to start skip-stopping when they're starting to bunch (back bus takes odd stops, front bus takes even, every third if three stops, and if a drop order happens, tell the next bus not to pickup) is the next step. That's what Chicago's system is aiming for, realtime control of routes -- and more importantly, realtime control of route signs on the bus, because everyone at a stop will get pissed when you skip them, but if you give them a why, well, some will still be angry but most will understand, esp. if they know another bus will be there in 2 minutes. Provided, of course, if that sign doesn't lie...

There will, of course, be unskippable stops. No bus will be able to skip Western Ave or Roosevelt, or any of the L stations. But the way to truly solve bus bunching is to stop the lead bunch from picking up all the passengers. Any solution that doesn't involve the lead bus not doing that *will* fundamentally fail to solve the problem. Which means *all* of the ones that will solve it will either involve the lead bus skipping stops, or being delayed while other buses come around, which to the passengers at that stop, end up costing them the same amount of time. The one system that does work without realtime knowledge is delaying the lead bus. Realtime control offers a chance at the holy grail -- no bunching *and* not having to delay buses to prevent bunching, by simply telling the bus that's getting slow to start skipping and let the bus that's cruising to start picking up passengers.

* Buses is acceptable, and to me, the proper plural of "bus", busses is the proper plural of "buss" as well as the past tense of the verb "bus," but English is complicated.
posted by eriko at 9:24 AM on May 21, 2015 [13 favorites]

work at Georgia Tech where busses self-correct by incorporating delays into the schedule.

Buses bunch up because some are delayed and others not, but they all try to run on a fixed, periodic schedule. Gaming the schedules to give the appearance of regular arrivals at your stop doesn't do squat to shorten your travel time to where you are going - it seems to me likely to only increase your time on the bus and the amount of fuel being burned.

This is a roadway bandwidth problem which can be easily solved by making more lanes BUS ONLY and eliminating the delays caused by considerations given to other, less environmentaily friendly traffic.
posted by three blind mice at 9:28 AM on May 21, 2015 [1 favorite]

A professor in Montreal successfully sued to local transit company for letting buses bunch up so much that he'd have to get a cab on a regular basis, on the grounds that other cities had implemented strategies to avoid this problem, often having the second bus wait at a stop for a little bit to keep the spacing intact. He got the cost of his cab tickets plus $100 emotional damages for when he was late for the first day of classes. (That was all he'd asked for.)
posted by Canageek at 9:30 AM on May 21, 2015 [3 favorites]

I always think "busses" are quick kisses, and buses are what you ride to get places.
posted by amtho at 9:37 AM on May 21, 2015

Well is it buses or busses?

Buses, busses and omnibuses.

Also busses, probably much more pleasing to bunch.
posted by bonehead at 9:38 AM on May 21, 2015 [2 favorites]

But are there buskers on the busses (or was that buses)? Do they have whiskers?
posted by ZenMasterThis at 9:38 AM on May 21, 2015

Cosine, that's just the timestop system. Schedules are built around having dedicated departure times for every 4-5 stops (or occassionally longer, depending on how spaced out stops are), rather than every stop (especially since, in theory, buses don't have to stop if no one's getting on or off). It's neat that buses in your city have a dedicated timer for that in the cab, but even without that drivers can rely on a paper schedule and their watch.

Everything can slow a bus down, and it's a negative feedback cycle. In addition to traffic concerns, the more you are late, the more people will need to get on your bus. You'll be stopping more frequently, too. If you're running a 10 minute headway and a person is waiting for a stop every 15 minutes, once you're five minutes late you'll be stopping at every stop, compared to stopping every other stop if you're on time.

Bus rapid transit is a way of mitigating as much of this as possible: dedicated lanes, off-board payment, fewer stops. Traffic signal priority can help reduce traffic issues even further. But the core problem remains: once you're late, you're likely to get even later until you hit the cushion at the end of the route.
posted by thecaddy at 9:39 AM on May 21, 2015 [1 favorite]

It's not nearly as bad as "modeling" vs. "modelling".

I know this is a bit of a derail, but it's one near my heart: IME this is another US/Commonwealth division, like grey and gray. Canadians, as usual, kinda do both.
posted by bonehead at 9:43 AM on May 21, 2015

Do busses who bunch
  bus ladies who lunch?

Do bunches of ladies who lunch
  buss on busses who bunch?

I have a hunch
  when conditions are crunch
    careful conductors will punch on
        busses who bunch for
                ladies who lunch

= = =

I wanna be a bus
I wanna be a big bus
I wanna bus the world around
I wanna be the biggest bus that ever
Bussed the world around . . .
posted by Herodios at 10:14 AM on May 21, 2015 [4 favorites]

Thank goodness that Uberbus will solve this for us.
posted by blue_beetle at 11:11 AM on May 21, 2015 [1 favorite]

I wonder to what degree this problem, in the US and Canada, is exacerbated by slow payment systems and stops placed too close together.

All the fiddling of silly fares that require bills and coins, paper transfers, confusing inter-agency transfer rules, etc. really slow busses down. Stored value cards can really speed up the process. I bet transit authorities could even save a substantial amount of stopped bus time by rounding $3.25 down to $3. The amount of time busses spend at stops in, e.g. Seattle versus Hong Kong must be very significant.
posted by ssg at 11:21 AM on May 21, 2015 [1 favorite]

The designer of the Georgia Tech debunching system gave a talk here at Louisville's Logistics and Distribution Institute and had pretty solid quantitative data to explain both the phenomenon of bunching and the improvements in wait time and bus utilization under the new system (a system so fantastically simple it falls into "why didn't I think of that?" territory --- each time a bus reaches a waypoint, instead of waiting there for a fixed amount of time, it waits until the next bus in the queue has traveled halfway to the stop where the current bus is). The main drawback of the system is that it really only works for high-frequency circulators: if you're claiming buses arrive, say, every 3-6 minutes, nobody expects a specific schedule becayuse whenever they go to the bus stop, they can be certain of a bus in short order, while for buses which come by every half hour, people kind of want a schedule so they know when they should be at the bus stop.

The dynamic-rescheduling plan also has the advantage of automatically rebalancing in response to bringing buses into or out of service.
posted by jackbishop at 12:34 PM on May 21, 2015 [2 favorites]

Do busses who bunch bus ladies who lunch?

That would be the Ladies Who Bus
posted by doiheartwentyone at 1:15 PM on May 21, 2015

if he gets to a stop and the timer says he is 38 seconds ahead of schedule he waits until the timer counts down before leaving again.

Seems to mostly fix this problem.

And you speed when you're behind schedule? I would think that the "behind schedule" problem is a bigger one to fix. It's also what the game shows, there being no button to make a bus go faster.

Related: creating a traffic jam by applying the brakes
posted by cardioid at 2:04 PM on May 21, 2015

What is it that buncheth thus?
Could it be an autobus?
posted by GuyZero at 2:19 PM on May 21, 2015 [5 favorites]

If only there were some complete comprehensive all-inclusive source of information about surface road based mass transit.

What we need is an Omnibus Omnibus.

Fun fun fun on the autobun
Fun fun fun on the autobun
Fun fun fun on the autobun . . .

posted by Herodios at 3:22 PM on May 21, 2015 [3 favorites]

Buses are notoriously social creatures and will often move together in small packs.
posted by bgal81 at 3:30 PM on May 21, 2015 [3 favorites]

So are streetcars. Ugh. The other night I was heading home from my dude's place and watched down the end of the street as four streetcars went past in quick succession. Then I had to wait at the stop for half an hour for the next one.
posted by feckless fecal fear mongering at 3:50 PM on May 21, 2015

I recently read this article about dealing with bus bunching. It doesn't work places where there's a clear inbound and outbound so during rush hour everyone is going the same way, but it seems like a better idea than having buses skip stops or have long layovers for routes that are busy in both directions.
posted by CJF at 6:53 PM on May 21, 2015

A similar thing happens with computers when multiple processes request data at intervals, say with modems uploading data over phone lines. (Hint: Don't blindly sleep() for a fixed interval after a request completes)
posted by RobotVoodooPower at 9:38 PM on May 21, 2015 [1 favorite]

When a bus gets full in San Francisco, the groups of people near the doors can just stand there with the hope and expectation that more space will appear, only giving up after minutes.
posted by Pronoiac at 11:03 PM on May 21, 2015

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