How Can We Study Things in Isolation? They’re Connected!

Whenever I present a bus network redesign plan, I’m always accused of ignoring important things.  How can I design a bus network, people say, without also planning for bus lanes, or bicycle parking, or road pricing, or parking policy, or urban structure? These things are all connected, they say!

Yes, they are all connected. But despite being connected, many planning tasks are separable:

  • Two projects are connected if they affect each other’s outcomes. For example, a network redesign and a bus lane project will certainly improve each other’s benefits over what either could do alone.  A rail line and a bus line parallel to it are competitors that will undermine each other’s outcomes, so they are connected too.  (Deep ecologists would say that almost everything is connected in this sense.)
  • Two projects are separable if one can be done before the others, and will achieve some benefits  by itself, even while waiting for the other connected parts to happen.

I know why people get anxious about this, because we all see situations where things were separated that really were inseparable. A rail line and a freeway are built side by side, without noting how each will reduce the demand for the other.  Maybe bus routes are designed without thought to connections between them, or worse, great infrastructure for bus connections gets built in a place where it’s not actually useful to the bus service.  A public transit service ends at a political boundary even though the demand doesn’t end there.  These are all examples of projects being separated when they were not really separable.

On the other hand, no human brain can focus on everything at once.  If we tried to do bus network redesign, fleet modernization, bus lanes, bike parking, road pricing, and parking policy as part of one project, it would never get off the ground.  Just co-ordinating the hundreds of experts needed to deal with all dimensions of such a project would consume most of our effort.

More important, in any project, everything moves at the speed of the slowest element, which is why it so often takes forever to get things done.

So separating projects is the only way for anything to happen soon. We are not denying that everything is connected. We are saying we have to start somewhere, and make some progress, even as other pieces of the puzzle are in the works.

Like any plan, a good network redesign effort requires clear thinking about separability.  A redesign is mainly a revision of the patterns in which buses run, but this process always identifies infrastructure and policy changes that are also needed. Sometimes these are truly inseperable:  The specified number of buses can’t meet at point A unless the facility there is enlarged to have room for them.  If the plan requires people to change buses at an intersection, we need to make sure there’s shelter and safe street crossings, and so on.  If the fare structure is penalizing changing buses, that needs to be fixed if our plan wants to encourage that.

But we fight to make the list of inseparable things as short as possible, because every time we decide that something is inseperable from the plan, that becomes one more thing that could stop the whole plan if it hits some kind of snag.  We ask:  Would the redesign still be possible, and worth doing, if some infrastructure or policy element doesn’t get done?  Sometimes this leads to good tactical thinking:  Can we do this necessary interchange quickly on-street, even while waiting for the funding and consensus to do the permanent facility that’s really needed?  Can we make some patches to the fare system while the ultimate system is still being worked out?

Another test is:  Does doing Project A without Project B actually make things worse?  If not, this is another signal that the projects are probably separable. The answer, for bus network redesigns, is almost always no.  By itself, redesign will achieve significant improvement even as it leaves a lot of other frustrating problems in place.  But getting it done may make other improvements politically easier if the result is that public transit is more visible, more used, and thus more widely valued.

So when people respond to a network redesign proposal by being angry that it doesn’t talk about bike lanes, electric buses, or road pricing, they’re confusing connectedness with inseparability.  Our network redesign study isn’t ignorant of those things just because we’re not talking about them.  We’re just talking about something different, something that’s also important and needs some attention.  A good network redesign, if allowed to succeed, will make all those other things easier.  And in any case, the redesign itself is important enough, and hard enough to explain, that it deserves the public’s full attention for a few weeks.

Everything is connected, but many things are still separable.  That’s a good thing, because if they weren’t, nothing would get done.

“To Predict with Confidence, Plan for Freedom”


The Journal of Public Transportation has a special issue out consisting of thinkpieces by a range of figures in the business.  I’m honored to be there alongside industry leaders like Susan Shaheen of UC Berkeley, Graham Currie of Australia’s Monash University, Kari Watkins of Georgia Tech and Brian Taylor of UCLA, as well as our favorite operations and scheduling consultant, Dan Boyle.

My contribution is called “To Predict with Confidence, Plan for Freedom.”  It basically outlines the argument of my next book, so this would be a great time to hear some critiques of it.  Here’s the opening:

What will urban transportation be like in 10-20 years? How will automated vehicles interact with social and cultural trends to define the city of tomorrow? Will the vehicles of the future be owned or shared? How will pricing evolve to motivate behavior? What will happen to public mass transit? What other innovations can we expect that will transform the landscape? This paper, which is merely the outline of a larger argument, suggests three interconnected answers.

  • We can’t possibly know. History has always been unpredictable, punctuated with shocks, but if the pace of change is accelerating, then unpredictability may be increasing too.
  • We can reach many strong conclusions without knowing. A surprising number of facts about transportation, including some fairly counterintuitive insights that would be transformative if widely understood, can be described and justified solidly with little or no empirical ground, because they are matters of geometry and physics or of nearly axiomatic principles of biology.
  • Prediction may not be what matters anyway. If we abandoned hope of predicting the future, we could still describe a compelling outcome of transportation investment, one that motivates many people who will never care about a ridership prediction or economic impact analysis. We could also predict it in the sense that we can predict the continued value of pi. That idea is freedom, as transportation expands or reduces it.

So if that catches your interest, read the whole thing, and share your comments below!

Learning from Portland’s “For Rent” Signs


Photo: City Observatory

Joe Cortright spreads the good news that “For Rent” signs are proliferating across Portland, signaling an easing of the affordable housing crisis.  And he points out a critical thing that many activists miss.  That luxury housing that affordability advocates decry does improve affordability for everyone.

The … myth is that you can’t make housing affordable by building more of it, particularly if new units are more expensive than existing ones. The surge in vacancies in existing apartments is an indication of the interconnectedness of apartment supply, and an illustration of how construction of new high end, market-rate units lessens the price pressure on the existing housing stock. When you don’t build lots of new apartments, the people who would otherwise rent them bid up the price of existing apartments. The reverse is also true: every household that moves into a new apartment is one fewer household competing for the stock of existing apartments. This is why, as we’ve argued, building more “luxury” apartments helps with affordability.  As our colleagues at the Sightline Institute recently observed, you can build your way to affordable housing. In fact, building more supply is the only effective way to reduce the pressure that is driving up rents.  (Emphasis added.)

Why mention this on a transit blog?  Because the mistake activists make here is the same one that many transit advocates make, which is to think of wealth as a set of boxes, called classes, that never intermix or affect each other.  It’s the same mistake that underlies the false dichotomy of “choice” and “dependent” riders in transit planning, the notion that you need separate services for each type of rider because they are absolutely different kinds of people who will never mix.

In fact, wealth is a spectrum.  People are everywhere along it.  Admittedly, this is less true that it once was, but it’s still true.  So although people certainly differ in wealth and thus in the options they have, they are still part of the same diverse market — for housing, as for transit.  When advocating for a fairer and more equal economic world, don’t lose track of this.  Don’t become so focused on us-them differences that you miss the solution that improves things for everyone, including you.



Best Ever Podcast Interview of Me

invisible city logoIn her spare time, Toronto Chief Planner Jennifer Keesmaat hosts a podcast series called Invisible City.  Her hour-long sessions go deeply into a
n interesting urbanist topic, and recently she did an interview of me.  We were both having great fun, and it turned into the best long-form interview that I’ve done.  (This 2012 Colin Marshall interview — which is more personal and where my ideas were much less clearly formed, is the only one that comes close.)

Jennifer skillfully provoked a discussion that requires no geekery to follow.  You can share it with your friends who have only the vaguest notion of what transit is, and many, I think, will still enjoy it.  There are a few
Toronto references, but nothing that will baffle a reader from elsewhere.

It’s here.  Hope you enjoy.


The Dangers of Elite Projection

Elite projection is the belief, among relatively fortunate and influential people, that what those people find convenient or attractive is good for the society as a whole.  Once you learn to recognize this simple mistake, you see it everywhere.  It is perhaps the single most comprehensive barrier to prosperous, just, and liberating cities.

This is not a call to bash elites.  I am making no claim about the proper distribution of wealth and opportunity, or about anyone’s entitlement to influence. But I am pointing out a mistake that elites are constantly at risk of making.  The mistake is to forget that elites are always a minority, and that planning a city or transport network around the preferences of a minority routinely yields an outcome that doesn’t work for the majority.  Even the elite minority won’t like the result in the end.

Long ago, when I was presenting a proposed transit plan to the Board of Directors of a suburban transit agency in California, one board member — representing the wealthiest city in the area — leaned forward, cleared his throat, and said:

Now, Mister Walker.  If we adopt this plan of yours, will that make me leave my BMW in the driveway?

The answer, of course, is no.  But to suggest that this question is a valid test of a transit plan is an extreme example of elite projection.  As a multi-millionaire, this man belongs to a tiny minority, so it makes no sense to design a transit system around his personal tastes.  Successful transit is mass transit, and there is no mass to be achieved by pursuing him as a customer.  Perhaps he could be attracted by a service to his door featuring on-board wine bar and massage service, but few other people would consider that good value for their more limited dollars.  Let the for-profit sector give him that luxury, and ensure he pays for its impacts.

Now and then, of course, investment that benefits elites justifies itself as serving the common good.  Expediting the lives of business executives, for example, will supposedly attract investment to your community.  A specialized transit project will supposedly stimulate upscale housing development that will add to the tax base, even if you could never afford to live there. I am not seeking to open debate on those claims.  To the extent that these arguments were right, elite projection would not be the right term.  Most elite projection, however, makes no such claims.  It’s simply an unconscious habit of assuming that your tastes are a good guide to what everyone will value.

In challenging elite projection, I am being utterly unreasonable. I am calling upon elites to meet a superhuman standard.  Almost everyone refers to their own experience when discussing policy.  Who doesn’t want their experience to be acknowledged? But in a society where elites have disproportionate power, the superhuman task of resisting elite projection must be their work.  And since I’m one of these elites — not at all in wealth but certainly in education and other kinds of good fortune — it’s sometimes my work as well.  Like all attempts to be better people, it’s utterly exhausting and we’ll never get it right. That means the critique of elite projection can’t just take the form of rage. It also has to be empathic and forgiving.

Still, elite projection is perhaps the primary barrier to the efficient, just, and liberating city.  The city has this special feature: It functions for anyone only if it functions for almost everyone.  You can say this about society in general, but only in the city is this fact so brutally obvious as to be unavoidable.

Traffic congestion, to take the obvious example, is the result of everyone’s choices in response to everyone’s situation.  Even the elites are mostly stuck in it. No satisfying solution has been found to protect elites from this problem, and it’s not for want of trying.  The only real solution to congestion is to solve it for everyone, and to do that you have to look at it from everyone’s perspective, not just from the fortunate perspective.

The ongoing disparagement of bus service in urban America has elite projection at its foundation.  Large fixed-route buses are the only form of transit that can quickly scale to an entire city while using scarce urban space with extreme efficiency.   Yet many urban elites assume (subtly or overtly) that bus service doesn’t matter because it’s not useful to them personally.

During my 25-year career I’ve watched fortunate urban leaders — mostly very well-intentioned — search endlessly for a transit idea that will allow them to neglect buses.  One could point to some American streetcars-stuck-in-traffic, “redevelopment tools” which sometimes had no discernible transportation value   There are the adorable ferries with tiny markets, and the overspecialized airport trains.  Now, the same mistake powers the endless vague promises of tech disruption in transit, especially the mathematically absurd notion that transit that comes to your door when you call it will scale to the entire population of a dense city.  (Serious experts have largely abandoned this claim, but it is out there in the discourse, undermining support for transit that actually works.)

None of these ideas made any geometric sense as a way to liberate everyone in a dense city, but they appealed to elite tastes, dazzled public attention, and therefore helped to defer investment in the transit that vast numbers of urban people would find useful and liberating. This neglect causes transit to deteriorate, yielding outcomes that further justify the neglect.

Again, we can’t challenge elite projection in others until we forgive it in ourselves.  Almost everyone reading this is part of some kind of elite.  But the more powerful you are, the more urgent this work is.  We must all ask ourselves: “Would this idea work for me if I were in a typical citizen’s situation, instead of my fortunate situation?”  Because if not, it won’t work for the city, and in the end that means it won’t even work for you.


Seattle: Before the Live Debate, the Written One (and an Imptertinent Question)

Login_logoSetting up for our panel discussion this Thursday night, the Seattle Times asked each of their panelists to answer some canned questions about the future of transportation.  The result is here.  I hope the contrasts will motivate you to come!  

Bravo to Bryan Mistele of INRIX (the traffic consultants to the notorious TTI Urban Mobility Report) for being willing to come into the densest part of Seattle and announce that (a) cars are our future and (b) light rail is a bad investment because of its ridership in the early years.  (Both claims presume the linearity of past trends and the irrelevance of land use changes in response to transit.)  But the courage is admirable: To say these things in the middle of Seattle would be like me pitching high-intensity transit networks at the Elks Hall of a small town in Nebraska.

Which raises a key point:

Notice, as you read this, how all high-level discussions, at regional levels or above, tend to presume that there is some answer to the "transit vs cars" question that is the same everywhere.  

In fact, the answer is radically different in different places, based on known built-environment factors and local politics that tend to track closely with those factors.  Some places are suited to cars and therefore defensive about cars.  Some places function only with transit, so they view transit as an existential issue.  All urban regions — and most states, provinces or countries — are going to have both kinds of places and everything in between.

So my question going in is this:  Why can't we let Seattle have the kind of transportation system it needs, and let low density and rural areas have the kind that they need?  Why do the differing needs of different communities require that we have a war between those communities, at all levels of government?

Rhetorical Annihilation in the Social Sciences

[This post is periodically updated as helpful comments roll in.]

Have you ever picked up an academic paper and read, right there in the abstract, that you don't exist?  

We're used to reading rhetoric that defines us as the enemy, which is different.  Rhetoric about the "war on cars" or "war on coal" posits an in-group of good people, including the author and presumed reader, and an out-group that is threatening to them.  This is exclusionary language in its obvious form, and it's hard to justify in academia.  

But academics can slide unconsciously into a more subtle kind of exclusionary rhetoric, especially in the social sciences — what I'll call (melodramatically perhaps) the rhetoric of annihilation.  Instead of defining a group of people as evil or threatening, this rhetoric just ignores their existence.   In this rhetoric, there is no talk of war, because only one side is visible.   The author's presumed expertise becomes a kind of campfire.  Gather around the author's assumptions and you will be warm, safe, and included; if you don't, we can't see you out there in the dark anyway, so you basically don't exist.

This is remarkably easy to do even in an academic paper.  Here are two vivid examples, one classically leftist, the other conservative.

From the left, a paper on "transit deserts".  You can go to the link, but I'm not naming the authors here because I have no desire to embarrass them by attracting searches on their names.  Their work has been peer-reviewed, which means that several arbiters of academic quality view it as an acceptable example of professional thinking today.  My point is about how pervasive and accepted this rhetoric is even as academic thought.

The abstract begins:

The term “transit desert” is a new concept that looks at the gap between level of transit service (supply) and needs of a particular population (demand).  These populations are often referred to as “transit dependent,” people that are too young, too old, or too poor or who are physically unable to drive. “Transit deserts” in this case are defined as areas that lack adequate public transit service given areas containing populations that are deemed transit-dependent. 

In just a few words, the authors have denied the existence of three very large groups of people.  These rhetorically annihilated groups are:

  • Anyone who analyzed the spatial relationship between transit service and needy populations before someone  invented the "new concept" of doing this.  This includes all professional transit planners over the age of 30, including past generations going back a century or more.  (Of course, the rhetorical annihilation of elders is such a routine part of being young — kids, we did it too at your age! — that it's hardly worth being offended by.)  
  • Anyone for whom demand does not mean mere need, but rather the meaning that is already routine in business and economics — something like a "buyer's willingness and ability to pay a price for a specific quantity of a good or service".  The paper's use of the word demand annihilates anyone coming from the perspectives of business or basic economics..  
  • Anyone who uses transit, wants transit to be useful to them, or wants the live in a city where even the rich ride transit, but who does not meet the specified qualifications to be called "transit dependent."  As made clear in the first sentence, these people's desire to use transit, or to build a city around transit, does not count to the authors as demand, because they do not meet the authors' standard for need.

A paper could make arguments against the point of view of these groups, but tbat's not done here.  Rather, the very possibility that such positions might exist is denied.

And of course, conservatives papers do this too.  Let's turn to a conservative-sounding paper, featured in Atlantic Citylab, for which you can also follow the link for the citation.  It's a little more careful but standard forms of annihilation appear soon enough.  The paper opens like this:

This article asks why public transportation’s political support in the United States is so much larger than its ridership.

Upon reading this, I scratched my head trying to imagine what it would be like to find this an interesting problem statement.  I don't mean to rhetorically annihilate the authors; I acknowledge their existence, but it it sounds like they don't talk with transit advocates or riders very much.   Those people would tell you that the answer is too obvious to need studying, as indeed it turns out to be:  

We … show that support for transit spending is correlated more with belief in its collective rather than private benefits—transit supporters are more likely to report broad concerns about traffic congestion and air pollution than to report wanting to use transit themselves.

Well, of course people vote for transit for reasons other than the narrowest kind of self-interest. People vote for transit because (a) it benefits people they care about, if not themselves, (b) it offers some solutions to real problems of urban mobility and (c) it helps foster cities that people want to live in, as demonstrated by the way land values are soaring in such places.  

But why is this a problem?  The authors conclude:

These findings suggest a collective action problem, since without riders transit cannot deliver collective benefits. But most transit spending supporters do not use transit, and demographics suggest they are unlikely to begin doing so; transit voters are wealthier and have more options than transit riders.

A collective action problem is a situation in which everyone would benefit if X were done, but nobody can justify doing X as a selfish cost/benefit calculation.  One fable explaining the problem imagines a group of mice who would all benefit if a marauding cat wore a bell, but none of whom finds it rational to the huge risks of climbing the cat's back to put the bell on.

What does it mean to assert that the transit ridership is a problem of this kind?  It implies …

  • … that transit users who do not vote do not exist.  The most explicit rhetorical annihilation in the paper is the assumption that the set of people who vote in the US (rarely more than 40% of the population and often less in local elections) largely contains the set of potential transit riders.  In reality, non-voters are so dominant in the population that their ridership may be a big contributor to transit's actual success, thus helping solve any "collective action problem".  Nor do they consider that many of these non-voters are friends or relatives or employees of voters, who may then understandably, even in a sense selfishly, vote in the interests of those people. 
  • ... that people who don't think they'll use transit are right about that.  In the biz, what people say they want to do, or would do, is called stated preference data, and it's known to be largely useless.  Humans are terrible at guessing what they'd do, or want to do, in a hypothetical future based on a situation, and set of options, that they can't imagine now.
  • ... that there is no gradual path to collective action, because demographic categories all have hard edges within which people are trapped.  This is the big one.  To posit a "collective action problem" the authors must assume that the level of wealth above which people are unlikely to use transit is rigid, even though it in reality it rises as transit grows more useful, and that it divides a population cleanly.   Everyone who is near the boundaries between demographic categories, or who chooses transit for reasons not predictable by their income, is annihilated here.

No argument appears in the paper for any of the assumptions above.  Limited discussion about ridership is based on what people tell the census about their commuting behavior; this casually annihilates all non-commute users of transit, including people who voted for it and love to use it on weekends, but have to drive to work because it's not useful for that purpose.

Finally, the collective action problem assumes that everyone is a bizarre character from classical economics known as homo economicus: someone who rationally computes and acts on self-interest that is defined only in the narrowest sense.  Among the many absurdities that follow from this are that in exactly the same circumstances, everyone would do the same thing, because we do not have diverse values, attractions, or personalities.

But in the real world, one mouse sometimes does put the bell on the cat.  Some of us will take ridiculous risks for the common good.  Some of us choose to be firefighters or police or soldiers or artists or social workers, all high-risk jobs that require courage but that enrich society if they succeed against all the odds.  Most of us don't take those risks, but we're all better off because some of us do.  Likewise, some fortunate people ride transit because they like it.  Some less fortunate ones prefer to spend their scarce income on a motorcycle.  

Everyone who acts in ways not predictable by their assigned demographic category is being annihilated here.  Human diversity, even human quirkiness is good for the collective, however hard it is for the social sciences to describe. 

What do these two papers have in common?  Between them, they annihilate almost everyone, including each other's in-groups.  

You could say that all this annihilation is an occupational hazard of the social sciences — or indeed that it's an inevitable feature of them.  The social sciences are in the business of talking about gigantic groups of people using reductive categories, and all categorization suppresses diversity.

But the hardness of category boundaries is one of the most fundamental and dangerous of human illusions, because it is coded deeply into common language and underlies all forms of prejudice.   So the social sciences are always playing with fire, always at risk of giving aid and comfort to polarizing, exclusionary styles of thought.  

This rhetoric of annihilation can lead to publication and approval, so long as an adequate ecosystem of reviewers and advisors has reasons (ideological or material) for sharing an assumption or at least not challenging it.  But once past that bar, these assumptions become "the literature," bounced around in the echo chamber of "expert" discourse.  Through the turning of generations, some of these assumptions do get overturned, if only as part of the inevitable process of the young annihilating their elders.  But much harm is done in the meantime.

Great academic work also requires thinking about all of the forces that determine the situation being studied, not just the one's academic discipline or in-group values, and honoring  descriptions of the issue from those points of view.   If they intend to influence policy, they make sure they understand the diverse experience of practitioners in the field, not just academics.  This is especially true if a paper intends to influence policy, rather than just participate in a discipline's private conversation. 

But meanwhile: Do you see a new academic paper, thick with footnotes and citations, as an immediate signifier of authority and wisdom?  Be careful.  To be welcomed around the campfire, you may have to consent to annihilation.

Quote of the week: on simplification (with notes on the adverb “sorta”)

When the physicist Richard Feynman found himself listening to a scientific talk in a field he didn't know well, he had a favorite question to ask the speaker: Can you give me a really simple example of what you're talking about?  If the speaker couldn't oblige, Feynman got suspicious, and rightly so.  Did this person really have something to say, or was this just fancy technical talk parading as scientific wisdom? … Simplification is not just for beginners."

Daniel C . Dennett
Intuition Pumps and Other Tools for Thinking

ContentIntuition Pumps is best book on philosophy that I've read in decades, and also an fun and engaging read.  Engineering makes no sense without science, and science makes no sense without a philosophy of science.  Dennett's great contribution is what I'd call a practical skepticism.  When I was in college, philosophy was receding into arid debates about pure logic.  (One of my advisors wrote papers with titles like "Is 'Not' Logical?")  I'd call that absolute skepticism, and while it's abstractly interesting in the way that chess is, it never emerges from its logical culdesacs to address any of the practical questions about how human beings, given what we are, should go about deciding what to believe.  

Dennett's work starts with a different standard embodied in his trademark adverb sorta.  Ideas don't have to be absolutely or abstractly or logically true in all frames of reference; they can be sorta true, which means valid enough to be reliable and useful, because what humans most urgently need are reliable and useful ideas.  Newton's physics is sorta true, and it's sorta correct to talk about trees solving problems through natural selection even though we know they don't have brains.  Free will is a philosophical problem in the world of abstract ideas, but Dennett argues it's not a real problem, because it doesn't matter to the actual decisions that we make in the context of what we sorta know.  

Sorta turns out to be a surprisingly rigorous term for getting us out of logical holes and out into the space where actual problems need solving.  This, and the practical skepticism it underpins, is worth the price and pleasure of this excellent book.

Does transit infrastructure cause ridership?

Does building a new transit line trigger ridership?  Does it even make sense to talk about the ridership of a piece of transit infrastructure?  

If you say yes, you're expressing an infrastructurist world-view that is common in transit investment discussions.  The right answer to the above questions, of course, is "No, but:

  • Infrastructure permits the operation of some kind of useful transit service, which consists of vehicles running with a certain speed, frequency, reliabilty, civility and a few other variables.
  • That service triggers ridership."

To the infrastructurist, this little term — "service" — is a mere pebble in a great torrent of causation that flows from infrastructure to ridership.  By contrast, service planners, and most transit riders that I've ever met, insist that service is the whole point of the infrastructure.

If you read the literature of infrastructure analysis, you  encounter the infrastructurist world view all the time, mostly in ways that's unconscious on the authors' part but still a source of confusion.  This afternoon I was browsing TCRP 167, "Making Effective Fixed-Guideway Transit Investments: Indicators of Success", which includes some really useful explorations of land use factors affecting the success of transit lines.  But when they talked about infrastructure features as causes of ridership, the report routinely delivered weirdness like this:

The percentage of the project’s alignment that is at grade proved to be a negative indicator of project-level ridership. At-grade projects may be more prevalent in places that are lower in density, while transit is more likely to be grade-separated in places with higher density or land value. Thus, this indicator may be reflective of density. It may also be true that at-grade systems are slower than grade-separated systems. At-grade status may reflect a bundle of operational characteristics such as speed, frequency, and reliability, although the analysis did not find that these factors individually had a statistically significant effect on ridership.  [TCRP 167, 1-17]

This careful talk about how a correlation "may" reflect density or "operational features" sounds vague and speculative when it's actually very easy to establish.  There is no shortage of evidence that:

  • High density reliably triggers ridership.
  • Areas of high density are less likely to have available surface rights of way.
  • Therefore, highest ridership segments tend to be grade-separated.

So this is a case where "A correlates with B" does not mean "A causes B" or "B causes A".  It means "A and B are both results of common cause C".  It's important to know that, because it means you won't get B simply by doing A, which is the way that claims of correlation are usually misunderstood by the media and general public.

Later in the paragraph, the authors again describe the obvious as a mystery:

At grade status may reflect a bundle of operational characteristics such as speed, frequency, and reliability …  

Yes, it certainly may, but rather than lumping all the at-grade rail projects together, they could have observed whether each one actually does.  

… although the analysis did not find that these factors [speed, frequency, and reliability] individually had a statistically significant effect on ridership

While this dataset of new infrastructure projects is too small and noisy to capture the relationship of speed, frequency, and reliability to ridership, the vastly larger dataset of the experience of  transit service knows these factors to be overwhelming.  What's more, we can describe the mechanism of the relationship, instead of just observing correlations:  Speed, frequency, and reliability are the main measures of whether you reach your destination on time.  Given this, the burden of proof should certainly be on those who suggest that ridership is possibly unrelated to whether a service is useful for that purpose.

Note the word choice:  To the infrastructurist, speed, frequency and reliability are dismissed as operational, whereas I would call them fundamental.   To the transit customer who wants to get where she's going, these "operational" variables are the ones that determine whether, or when, she'll get there.  It doesn't matter whether the line is at-grade or underground; it matters whether the service achieves a certain speed and reliability, and those design features are one small element in what determines that.  

I deliberately chose a TCRP example because the authors of specific passages are not identified, and I have no interest in picking on any particular author.  Rather, my point is that infrastructurism so pervasive; I hear it all the time in discussions of transit projects.  

I wonder, also, if infrastructurism is a motorist's error: In the world of roads, the infrastructure really is the cause of most of the outcomes; if you come from that world it's easy to miss how profoundly different transit is in this respect, and how different the mode of analysis must be to address transit fairly.

Whenever you hear someone talk about the ridership of a piece of infrastructure, remember: Transit infrastructure can't get people to their destinations.  Only transit service can.  So study the service, not just the infrastructure!