Prudence Theater

The phrase security theater refers to the elaborate selling of airport security to the public through humiliating spectacle, like making people take off their shoes, with no safety value whatsoever. By the same token, prudence theater is the same kind of ritual of humiliating people, often workers, in the name of not wasting money. Managers who engage in prudence theater will refuse pay hikes and lose the best employees in the process, institute hiring freezes at understaffed departments and wonder why things aren’t working, and refuse long-term investments that look big even if they have limited risk and high returns. This approach is endemic to authoritarian managers who do not understand the business they are running – such as a number of do-nothing political leaders who make decisions regarding public transit.

I’ve talked a bunch about this issue in the context of capital investment, for example Massachusetts’ Charlie Baker, California’s Gavin Newsom, New Jersey’s Chris Christie, and New York‘s Andrew Cuomo, using phrases such as “Chainsaw Al” and “do-nothing.” But here I want to talk specifically about operations, because there is an insidious kind of prudence theater there: the hiring freeze. The MBTA and MTA both have hiring freezes, though thankfully New York is a little more flexible about it.

Both New York and Boston have very high operating costs, for both subways and buses. They have extensive overstaffing in general, but that does not extend to overstaffing at every department. On the contrary, some departments are understaffed. Adam Rahbee told me a year and a half ago that subway operations planning in New York was short on workers, in contrast to the overstaffed department he saw in London. Of course London on average has much lower costs than New York, but individual departments can still be short on manpower even in otherwise-overstaffed cities. If anything, leaving one department understaffed can cause inefficiencies at adjacent departments, making them in effect overstaffed relative to the amount of service they can offer.

Bus dispatching

Buses require active supervision by a centralized control center that helps drivers stay on schedule. New York currently has 20 dispatchers but is planning an increase to 59, in tandem with using new technology. Boston has 5 at any given time, and needs to staff up to 15, which involves increasing hiring to about 40 full-time workers and doing minor rearrangement of office space to give them a place to work. With too few dispatchers, drivers end up going off-schedule, leading to familiar bunching, wasting hundreds of bus drivers’ work in order to save money on a few tens of supervisors.

I went over the issue of bus bunching in a post from last summer, but for the benefit of non-technical readers, here is a diagram that explains in essence what the problem of chaos is:

The marble on top of the curve is unlikely to stay where it is for a long time, because any small disturbance will send it sliding down one side or the other. Moreover, it’s impossible to predict in advance which direction the marble will land in, because a disturbance too small to see will compound to a big one over time.

Chaotic systems like this are ubiquitous: weather is a chaotic system, which is why it’s not possible to predict it for more than about two weeks in advance – small changes compound in unexpected directions. Unfortunately, bus service is a chaotic system too. For the bus to be on schedule is an unstable equilibrium. If the bus runs just a little behind, then it will have to pick up more passengers on its way, as passengers who would have just missed the bus will instead just make it. Those extra passengers will take some extra time to board, putting the bus even further behind, until the bus behind it finally catches it and the two buses leapfrog each other in a platoon.

There are ways to mitigate this problem, including dedicated bus lanes and off-board fare collection. But they do not eliminate it – they merely slow it down, increasing the time it takes for a bus to bunch.

The connection between dispatching and chaotic bus schedules may not be apparent, but it is real. The transportation engineering academic community has had to deal with the question of how to keep buses on schedule; here, here, and here are three recent examples. The only real way to keep buses on schedule is through active control – that is, dispatching. A dispatcher can tell a driver that the bus is too far ahead and needs to slow down, or that it is behind and the driver should attempt to speed up. If the traffic light system is designed for it, the dispatcher can also make sure a delayed bus will get more green lights to get back on track, a technology called conditional signal priority, or CSP. This contrasts with unconditional transit signal priority, or TSP, which speeds up buses but does not preferentially keep them evenly spaced to prevent bunching.

Moreover, some of the people who have done academic work on this topic have gone on to work in the transit industry, whether for the MBTA (such as David Maltzan and Joshua Fabian) or for thinktanks or private companies (such as Chris Pangilinan). Specific strategies to keep the buses on track include CSP giving delayed buses more green lights, holding buses at the terminal so that they leave evenly spaced, and in some cases even holding at mid-route control points. Left to their own devices, buses will bunch, requiring constant correction by a competent dispatching department with all the tools of better data for detection of where bunching may occur as well as control over the city’s streetlights.

Managers’ point view vs. passengers’ point of view

When I talk to transit riders about their experiences, I universally hear complaints. The question is just a matter of what they complain about. In suburban Paris people complain plenty about the RER, talking about crowding and about how the system isn’t as frequent or reliable as the Metro. These are real issues and indicate what Ile-de-France Mobilités should be focusing its attention on.

Americans in cities with public transit talk about bunching. In New York I’ve routinely sighted platoons of two buses even on very short routes, where such problems should never occur, like the 3 kilometer long M86. A regular rail user who talked to me a few months ago mentioned three-bus platoons in Brooklyn on a route that has a nominal frequency of about 10 minutes.

From the perspective of the transit operator or the taxpayer, if buses are scheduled to arrive every ten minutes, that’s an expenditure of six buses per hour. From that of the rider, if the buses in fact come in platoons of two due to bunching, then the effective frequency is 20 minutes, and most likely the bus they ride on will be the more crowded one as well. What looks like a service improvement to managers who never take the system they’re running may offer no relief to the customers on the ground.

I wish my mockery of transit managers who don’t use their own system were facetious, but it’s not. In New York, some of the more senior managers look at NYCT chief Andy Byford askance for not owning a car and instead using the subway to get to places. Planner job postings at North American transit agencies routinely require a driver’s license and say that driving around the city is part of the job. Ignorant of both the science of chaos and the situation on the ground, the managers and politicians miss low-hanging fruits while waxing poetic about the need to save money.

Is anything being done?

In New York there are some positive signs, such as the increase in the number of dispatchers. The warm reception Eric Goldwyn and I got from some specific people at the MTA is a good sign as well. The problem remains political obstruction by a governor and mayor who don’t know or care to know about good practices. Cuomo’s constant sidelining of Byford has turned into a spectacle among New York transit journalists.

In Boston, the answer is entirely negative. Last week’s draft of the Focus40 plan, released by the MBTA’s Fiscal Management and Control Board (FMCB), unfortunately entirely omits dispatching and operational supervision from its scope. It includes a variety of investments for the future, some of which are welcome, such as the Red-Blue Connector. But it reduces the issue of bus timetable keeping to a brief note in the customer experience section that mentions “Computer Aided Dispatch / Automatic Vehicle Location technology.” Good data is not a bad thing, but it is not everything. Warm bodies are required to act on this data.

Thus prudence theater continues. Massachusetts will talk about reform before revenue and about spending money wisely, but it is run by people with little knowledge of public transportation and no interest in acquiring said knowledge. Its approach to very real issues of high costs is to cut, even when there are parts of the system that are underfunded and undermanned. Staffing up to 15 dispatchers at a time, raising the headcount to about 40 full-time workers, would have the same effect on ridership as literally hundreds of bus drivers through better control. Will the administration listen? As usual, I hope for the best but have learned to expect the worst.


      • Herbert

        I don’t know of a single tram line anywhere that bunches.

        I know quite a few busy bus lines that bunch regularly, particularly in Berlin…

        • Ross Bleakney

          >> I don’t know of a single tram line anywhere that bunches.

          I’m guessing you’ve never been to Toronto. Just search for “streetcar bunching Toronto”.

          • rewenzo

            Toronto streetcars, with minor excepts, are basically buses because they operate in traffic like buses. They’re actually worse than buses because they can’t go around obstacles.

          • Herbert

            Ah yes, north America, the continent known for running transit well…

  1. Eric

    Depends in what sense.

    Rail is generally less frequent than the bus it replaces, since the trains are longer. Lower frequency means less bunching, since a lower fraction of passengers board in the time the vehicle is delayed. Rail may also be built with separate ROW which eliminates bunching, but a bus lane could equally be built on the same route.

    On the other hand, one could say that railstitution makes permanent bus bunching – the “bunch of buses” is similar to a train, in that it all comes at once. However, it’s more comfortable than being stuck in the first bus in the bunch.

    • Herbert

      Trains and trams have a better door to seat ratio and better level boarding – they don’t have to “kneel” for one…

      • Ross Bleakney

        Not all buses have to kneel, and there are plenty with good door to seat ratios. Besides, that misses the point. The key to avoiding bunching is to avoid inconsistency. If the dwell time for each particular stop is always the same, and the vehicle travels through the street (or the tunnel) at the same speed every time, then you won’t have bunching. A train (or a bus) may have its advantages, but that has nothing to do with bunching.

        That being said, you won’t see trains bunching because they aren’t allowed to. Stopping distance for a train is much smaller than it is for a bus, so its minimum headway must be higher. Thus a train delay is in effect a way to avoid bunching. In that sense it is no different than what was described (dispatchers preventing bus bunching) only in this case it is an operator preventing a dangerous situation. That doesn’t mean the trains are necessarily evenly spaced, though. If the minimum headways are two minutes, and the trains are supposed to run every five minutes, it is easy to see how the second train could end up running two minutes behind the first one, while the third one lags eight minutes behind. Thus you have the same sort of bunching problem (a long service lag) just one not as acute.

        • Herbert

          The Nuremberg subway runs nominal nowadays of 100 seconds along the U2/U3 trunk. There’s not a single bus route in the world that can do that without bunching.

      • Chris

        In my hometown Innsbruck we replaced buses with trams on our busiest line, but the tram model chose actually had a much worse door to capacity ratio. Together with the trams running mostly in general traffic lines and badly to not working at all signal preemption this leads to now 10 minute longer running times end to end and even more bunching than we had before.

        One big benefit of “real” rail is grade separation, but the same would be true with gold plated BRT.

          • Chris

            Why would rail be better if all other parameters are the same (never mind worse)? The big benefit of rail as we know it (TM) is infrastructure more or less separate from cars and good dispatching. Once that goes away the rail on their own are not going to help you with bunching.

          • Herbert

            You can’t make buses of arbitrary length. And you can’t run them arbitrarily close to one another.

            And that’s what kind of limits capacity

          • Tonami

            Also don’t forget the ease of platform alignment with rail which reduces the variation in boarding times compared to buses which can’t align with a platform as quickly and consistently as possible

          • Alon Levy

            Also also, trains stop at every station, not just ones where stopping is required. In theory each bus boarding adds 3 seconds to the stop time, but that’s assuming the bus stops in the first place, and on routes where some stops may be skipped, the first passenger boarding or alighting slows the route down by 30-40 seconds rather than 3 seconds, which adds to the variability.

          • Herbert

            There’s also a phenomenon of two buses stopping at the same station (when the bus bay is long enough) and people still ignoring the empty bus behind the full one. On modern rail vehicles, people can just walk through to the empty space

          • Chris

            Well, in our particular case (which is worst case rail) the boarding times are actually longer, partially due to the better door ratio, partially due to the worse interior layout of the trams, partially because a lot of high volume stations don’t even allow level boarding. The trams also are larger, but not that much larger than the buses. Well designed rail system should do much better, mostly because rail best practices are much better than bus practices, and to a small part because some of these best practices require rail.

            These are the standard buses for the busy lines (all 4 wide doors are used for bording):

            The are the trams: and their layout:

          • Chris

            They are pretty nice as long as they aren’t too full. As soon as they are crowded the high amount of seats and narrow layout doesn’t help to distribute the passengers. The low number of doors, and the small half doors at the end make passenger loading and unloading really slow. It also doesn’t help that our trams are only 2.4 meters wide vs the 2.55 for the buses.

  2. Ben Ross

    Great article. Another form of prudence theater we’ve suffered from in my area is eliminating relief buses. On suburban routes with 30 minute headways bus bunching is less of a problem so dispatching is less important, but absence of relief buses is catastrophic. If a bus breaks down early in its shift, you suddenly have a 60-minute headway for hours to come.

    A nitpick: Bus bunching is about stability theory, which goes back to Maxwell, and doesn’t need the more recent math of chaos theory.

      • Robby Blum

        Classical mechanics is 6 years in the past for me, so I could be wrong, but I don’t think that the marble on the curve has a positive Lyapunov exponent. It’s definitely linearly unstable, but only once; as soon as it moves you know exactly where it will be in the future.

        Actually, has anyone ever tried to calculate Lyapunov exponents for bus performance?

        • Alon Levy

          Right, the curve as drawn has an unstable fixed point between two attracting points. Bus schedules are more complex than that, though, because what appears to be two attracting points at first glance (bunching with the bus ahead and bunching with the bus behind) are themselves unstable, because the two-bus platoon will tend to bunch with other platoons too.

          You may be able to compute the exponent from the formula I wrote here, but it ends up as a piecewise formula.

  3. Ross Bleakney

    Excellent article. I’ve experienced this in the workplace, so I guess it is no surprise it happens in other fields as well. The worst case was when I worked for a library software company during the recession. During the time, it was easy to hire English majors, but difficult to hire software engineers. I repeatedly mentioned to managers that my job would be much easier if we had more testers and more writers (in short, more English majors). But instead they kept hiring the very expensive software engineers. It was easy for me. Not only was I paid well, but I would often sit around waiting for some bit of paperwork to be complete before I did my coding. The company was not run efficiently, and lucky for us, we didn’t have a downturn (otherwise they probably would have fired some of the software engineers, as well as the testers, writers and facilitators).

    That kind of dysfunction can lead to frustration and cynicism. You are frustrated because you can’t do your job, and are worried about a layoff. Or you get used to it, figure you are high up the totem pole, and can just coast. At that point you are simply cynical, not expecting the organization to do much, while you do just enough to avoid notice.

    Personally I think it helps if the union steps in, and demands both productivity as well as good working conditions. This happens, but probably not enough.

  4. JJJ

    It seems like better dispatching is something that could benefit from automation. A computer can easily look at the GPS signal to see the buses are bunched and send an automated instruction to the drivers. Bus 1: Run express to Y. Bus 2: Run normal. Bus 3: Hold for 2 minutes.

    • IAN! Mitchell

      I had the same thought. What component of this job necessitates a person with a heartbeat, let alone a pension?

      • Herbert

        It requires a scary up front investment.

        Prudence theater us really bad at spending a hundred bucks now to safe a thousand bucks every year for the next few decades…

  5. Oreg

    Could you clarify if bus bunching applies to buses with a fixed schedule or only to those with a fixed frequency?

    In Zurich, a display tells the driver how many minutes he is behind schedule (or ahead). It seems they try to keep that number around zero. Does that enough to avoid bunching or is there more to be done?

    • Alon Levy

      It applies either way. The Zurich display seems like an active control technique, just relative to a fixed schedule rather than a fixed headway.

      • Oreg

        I should have asked differently. Keeping up with a fixed schedule prevents bunching. Frequency-based schedules with not fixed departure times need drivers to monitor their headway. Schedule deviation and headway, respectively, may be monitored and communicated by dispatchers but they might just as well be monitored electronically and communicated to drivers by a dashboard display. Am I missing anything?

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