Induced Demand: An Axiom of Biology

Figuring out the relationship between this tweet and this article is left as an exercise for the reader.

Induced demand is the observed fact that if you make something easier to do, people will do it more.  For example, if you create new capacity for cars in a place where travel demand is high, the result is more cars.  If you build more capacity to “fix congestion”, you end up back near the same level of congestion you had before.

After decades of observing this pattern, most people are still reluctant to face what this means.  Part of the problem is that we’re presenting induced demand as an observed discovery, which allows us to quarrel over data, research methods etc.

But induced demand isn’t just an observed fact.  It’s also an axiom of biology.  We are as sure about it as we are of the facts of math.  This means we don’t really need to be doing this experiment over and over, just as we don’t need to keep measuring circles to be sure of the value of pi.

In this context an axiom is a statement that can be taken as true because it is part of the definition of a concept you are using, or follows logically from that definition.  The value of pi is axiomatic because it follows from the definition of a circle, in standard Euclidean space that describes our everyday world.

Now consider the concept of an organism.  It implies that:

  • The thing consumes some resource from its environment, in order to have enough energy.
  • It will expend energy getting this resource.
  • Therefore, it must run a positive balance sheet: The energy it spends getting the resource must be less than the energy the resource will provide.

We humans are organisms, so we do what they do.  In particular:

  • To have enough energy, we seek resources.  Money is a symbolic resource in this sense.  We also have other needs like shelter and security that also require resources.
  • We need to get these things in way that minimizes energy costs.  This is what I mean by easy.

We are mobile creatures, rather than barnacles or oysters, so this pursuit of resources often requires traveling. This means that time is also part of this basic calculation that determines survival.  The time spent pursuing a resource can’t be spent pursuing other resources, or doing other necessary things like sleeping.  So we must minimize our costs in both energy (which includes money) and time, while gaining as much energy (money) as possible.

From this it follows that people will tend to travel in ways that maximize their access to resources while minimizing energy cost (time and money) and danger.  People don’t always do this exactly, but the underlying biological imperative is unavoidable.

This means that:

  • If driving suddenly becomes easier (lower time and energy cost) than taking transit, more people will shift to driving, increasing congestion.  This is why road widening in high-demand places tend to lead to more traffic.
  • If a road widening makes it possible for developers to save money (i.e. energy) by building in more distant places where land is cheaper, they will do that.
  • This process changes the shape of the urban area so that people travel longer distances (due to sprawl) at slower speeds (due to congestion).
  • Therefore the average organism will need to expend more time and energy to reach the same resources it reached before.  (Your job flees from downtown to a distant business park where taxes are lower.  Your grocery store closes because a WalMart opened two miles away where you can’t walk to it, or even walk from the nearest point that a bus could get to.)  The organism will also be exposed to more danger as a result.
  • On average, organisms in this system end up in a weakened state, with a worse balance sheet of energy expended vs energy gained.

The organisms in this story are all trying to harvest more energy than they spend in the act of harvesting.   Even unimaginable aliens on distant planets would do this in the same situation.  So it’s axiomatic that, in the absence of other pressures, road widening in a high-demand area will induce more traffic and more sprawl.

So although road-building departments keep doing the induced demand experiment many times every year, and getting the same results, you don’t need to do more experiments, just as you don’t need to keep measuring circles to be sure of the value of pi.  You can add complexity by taking this into the human sciences and trying to model subtleties of human behavior, but all the resulting insights will be marginal compared to the axiomatic fact that above all, we’re organisms, so we’ll do what organisms do.

Virtual Public Meetings: In Oregon, It’s the Law

Here in Oregon a new law mandates that all public meetings must have a virtual component. It is no longer acceptable to do only an in-person meeting.

This is great news, especially for people who want to have diverse and inclusive conversations about public transit.

In the old world, pre-2020, the default public meeting was in person.  If you wanted to express your view, you had to clear your schedule at the appointed time and travel to a meeting site — which was especially onerous for people who don’t drive. The result was a process that is biased against people who are busy. Most people don’t have the time that in-person meetings require.

When it comes to public transit, there is a direct tension between the interests of busy people — who tend to care about getting places quickly — and those of many people who have spare time.  To take one example, retired people often tell me that they need a bus right at their door, but that it’s fine if it comes once an hour, because they can plan around that.  That’s great for them, but that kind of service is useless to anyone whose day is full of deadlines they don’t control: punching a time clock, getting to class, picking up the kid at daycare.

The only way we get functional, just, and inclusive transit is for people with different needs to listen to each other.  That only happens if everyone has the opportunity to contribute, as they do in virtual events.

The other issue, of course, is that virtual meetings can be civil, because the moderator has tools to cut people off if they are rude, profane, or off-topic[1] or speaking too long. All forms of physical intimidation, however subtle, are also off the table [2]. Those behaviors have become another good reason to avoid public meetings.

The in-person event shouldn’t disappear until we’ve fully replaced it for everyone who really needs it, but the exigences of the pandemic have made far more people comfortable with virtual meetings, and there are a range of ways to reach those who still aren’t.  Oregon’s law doesn’t ban in-person meetings, of course. It just says that a process that’s only in-person is no longer acceptable, because it just excludes too many people. I hope we’ll see this spread far and wide.



[1] At a Cleveland meeting a few years ago, where I was presenting about our bus network design project, one lady devoted her three minutes to probing whether I was married, and if not, what I was doing about that.

[2] Then there was the meeting in a Western US city, years ago, where one belligerent gentleman testified while keeping one hand in his pocket, holding a clearly gun-shaped object.

My Most Popular Posts in 2021

Each year I’m interested to see which posts have gotten the most attention. Note: This list shows the most popular post in 2021, not the most popular posts written then. As you can see, many of my older posts remain useful and popular for years.  And if you are just starting to explore this blog, the place to start is the Basics posts!)

  1. That Photo That Explains Almost Everything (2011).  You’ve seen the photo.  I notice a few things in it beyond its first impression.
  2. The Dangers of Elite Projection (2017).  This is one of my most useful posts ever, about a basic mistake that’s everywhere in city planning.  It’s an example of my attempt to talk very patiently and inclusively about a difficult topic that makes people very emotional.
  3. The Power and Pleasure of Grids (2010). An explanation of why grid transit networks are so effective.  This showed up in Chapter 13 of my book.
  4. Basics: The Spacing of Stops and Stations.  (2010).  This turned into Chapter 4 of my book.
  5. Basics: Walking Distance to Transit.  (2010).
  6. Access, or the Wall Around Your Life (2021).  My most important 2021 piece by far, in which I talk about a new way to measure public transit’s success  Glad to see it on top of the 2021 stack. Keep promoting it!
  7. US Commuter Rail: What It Is and What It Could Be.  (2021)
  8. Fixing US Transit Requires Service, not just Infrastructure (2021).  The usual warning about US Federal public transit spending.
  9. San Francisco: A Forbidden Fantasy Comes True (2020).  A minor post about a transformation of San Francisco’s rail network.
  10. The Problem of School Transportation (2017).  Why don’t transit agencies serve schools in just the way they need?  Here’s the answer.

And a few important ones that are just outside the top ten:

A very sensible selection, readers, by you and the publications that linked here!  Honored to have such a thoughtful audience.

Happy New Year.

Transit System Maps Still Matter

A slice of our system map for AC Transit.

A slice of our system map for AC Transit.

As transit information tools have gotten better, some transit agencies have stopped offering a system map to the public.  Often, a website offers me trip planning software and route by route timetables, but not a map.  If it’s there, it’s often difficult to find.

We think system maps are essential.  They’re not just for everyday navigation.  They’re for exploration and understanding.  Some people prefer narrative directions, but many people are spatial navigators, and they need maps.  They’ll understand details only if they can see the big picture.

Another way to think about system maps is that they show you where they could go, and how.  They give you a sense of possibility.  (It’s the informational dimension of access to opportunity.)  Maps also show visually how different services work together.  Finally, good system maps help people make better decisions about where to locate, or even where to build things.

One of our most fun projects this year was a new system map for AC Transit in greater Oakland, California.  You can see the whole thing, including its legend, here.  (To be fair, we’re not the only people who do these. Our friends at CHK America do them, and I also love the work of the European designer Jug Cerovic.)

The style of this map is very similar to that of the maps that we’ve always used in our planning studies.  The key is the visual hierarchy that makes frequent lines more prominent than other lines, and makes all-day lines more prominent than peak-only lines.  (In older standard mapping styles in this region, peak-only express lines were often the brightest red, even though they don’t exist the vast majority of the time. It was very confusing.)

As transit planners, we use this style for all of the maps that appear in our studies.  In fact, red=frequent in absolutely everything we do, whether it’s a map, a chart, a planning game toy, or a pen used to draw routes inside a course or workshop.

We take pride in having been among the first to bang this drum.  I was making the case back the 2000s (really, in the 90s) and there’s a chapter on it in my book.

We’re excited to be in the business of public-facing system maps.  They don’t have to be this precise; they can be done at various levels of design at various costs.

But if a system map doesn’t exist, people can’t understand all that your transit system can do.

Two Great Books for Transit Map Lovers

The architect Jug Cerovic is one of Europe’s most prolific and distinctive transit map designers. Anyone who loves transit maps will love his book One Metro Worldwhich contains 40 of his most gorgeous maps for cities all over the world, and also presents a clear explanation of his design process.  (Unfortunately it doesn’t ship until January.)  You can look at the whole thing on his site, but the physical book is much more satisfying.

One Metro World book

Cerovic’s style is to recognize geometric forms in the geography, and to highlight these to create not just a clear diagram of network structure, but one with a certain minimalist beauty:



Cerovic’s new book, Middle Constellation, is about just one map, an infrastructure map of China.  Here, the whole book is about the process.  Page by page, he steps through the design choices, showing how he builds up the final map.  This one is available as an ebook, which gives you an animated effect for some of the process.  You can get a sense here.

If you like beautiful books, both are highly recommended.


The Bus Driver Shortage is an Emergency

I know we’re having a lot of emergencies and it’s hard to keep track, but many US transit agencies are looking at devastating service cuts due to a shortage of bus drivers.  Drivers are quitting or retiring early much faster than agencies can replace them.  One friend told me their agency is losing 10 drivers for every one they hire.

Here in Portland, TriMet is cutting 9% of its service, bigger even than the cuts in the Great Recession.  I’m seeing similar cuts all over the US.

Can you blame the bus drivers?  The job was always hard, and now it’s more dangerous in two ways: People breathe on drivers a lot, not always masked, and the mental health epidemic is showing up in more rudeness and bad behavior.  Worst of all, some US cities are seeing a rise in assaults on drivers.

Meanwhile, there’s been huge growth in delivery jobs, some of which pay decently and don’t involve dealing with people.

Transit agencies are doing what they can, offering one-time bonuses for signing up.  But the real problem is retention, and it’s hard to imagine how that will be solved without some increase in compensation, also known as operating cost.  It means less service for the same operating dollar.  And of course when compensation goes up it doesn’t come back down.

Before you jump on me:  I believe that drivers should be paid well and held to high standards. I believe that a bus driver, with an employed partner, should be able to own a home and raise children.  Most US bus drivers are unionized and tend to have relatively good pay and benefits, certainly compared to non-union driving jobs.  (One friend of mine is a freelance software consultant but still drives a bus part-time just for the health insurance.)  I wish all transportation jobs paid as well.

But in any case, these service cuts are an emergency.  They are not minor.  They are not necessarily temporary, because right now it’s not clear how the problem will get better.  We could be looking at a lasting shrinkage in our transit services, right when people are crying out for expanded service and many agencies had been on track to deliver it.

What can you do?  Advocate for funding, but also:

  • Be kind to your bus driver. If you have a moment, watch them in action.  Notice how hard their job is, and how much they have to deal with.  Thank them.
  • Be kind to your transit agency management.  It’s a terrible moment for them.  They’re as horrified as you are by having to cut service.  (You can be kind to them and still be mad at them for some things. But be sure that what you’re mad about is really their fault.  The driver shortage isn’t.)

This advice may sound simplistic, but it’s actually practical.  Kindness is a powerful form of activism.  A lot of it can add up to big change.


Freedom Happens In Infrastructure (and Services)

Alex Schafran, Matthew Noah Smith, Stephen Hall.  The Spatial Contract.  Manchester University Press, 2020

In Western political philosophy, physical space is a fairly recent discovery.  Early thinkers about socialism and capitalism tended to focus on wealth as the primary thing to be generated or distributed.  Only in recent decades, in the work of Edward Soja for example, have we seen serious consideration to how space — including the ability to move — is distributed.   Freedom, too, started out as an abstraction, often defined negatively as the absence of constraint.  But real freedom only happens in a system of infrastructure and services:

What does it mean to be free to walk down a road?  Most people would agree that this requires being free legally and socially … But to truly understand what makes someone free to walk down a road, we need to be paying a lot more attention to the road.

Or as you’ve heard me say elsewhere: Transportation planning is freedom planning.  Every decision about infrastructure or services (where they should be? how they should work?  what they should cost to use? how well they should be maintained?) is a decision about who will be free and how free they will be.

This little book explores what it means to be free in a world where freedom relies on systems. It’s fun to think of “throwing off your chains” and “hitting the open road.”  That’s negative freedom, the freedom from constraint. In fact, you can only “hit the open road” because somebody built the road, put it here rather than there, and is maintaining it or not.  What’s more, those decisions define your options about where you can really go, what you can really do, who you can meet, and so on.  We are always inside spatial systems — transportation, water, sanitation, power, etc — and our freedom lies entirely in what options and opportunities those systems offer us.  The authors call these reliance systems.  [1]

From this insight, the book builds the idea of a spatial contract.  It’s an analogy to the social contract — the idea that citizens and their governments have an implicit deal where the citizen accepts constraints imposed by the government in return for security, stability and other things that only government can provide.  A spatial contract is the same idea applied to space but especially to infrastructure and services.  In the narrow sense, a spatial contract between resident and government would specify that the citizen pays taxes and the government provides infrastructure and services.  But spatial contracts are more diverse than that, because reliance systems are not all produced by government, nor should they be.  There are private actors, informal sectors such as the taxicab industry, and so on.

The authors’ focus on establishing a moral framework for talking about reliance systems, one that (unlike many established frameworks of moral and political philosophy) deals with the physical and spatial reality of these systems.  The chapters “Seeing like a system” and “Seeing like a settlement” describe this framework from important but different spatial points of view.  Each system operates in physical space with its own logic, and needs to be seen from that point of view.  Each settlement, where people live and work together, is a point where many systems interact and must collaborate, and needs to be seen from that point of view.

Obviously I don’t recommend this book to every reader.  This is a scholarly conversation.  But unlike most academic writing, the book is friendly and readable for anyone who has a basic level of comfort with political and philosophical thinking.  Freedom is at the center of my work these days, and this book has helped me think about it more clearly.


[1]  The term reliance systems strikes me as confusing, because the word “system” is normally preceded by what it provides (water system, transit system) rather than the user’s relationship to it (reliance system).  If you prefer, you can just use infrastructure in the broad sense that is being proposed on the left in the US infrastructure funding debate, one that includes childcare and education as well as bridges and broadband.  But we could also call them liberation systems, since they go beyond providing basic needs to providing the possibilities for freedom.


Cork, Ireland: A Draft Bus Network Redesign

Since January we have been working for the National Transport Authority of Ireland (NTA) to redesign the bus network of Ireland’s second-largest city, Cork.  This follows on our 2018-19 work in Dublin whose first phase has just been implemented.

Now the NTA has released a Draft New Network for everyone’s consideration. The people of Cork are currently weighing in on the Draft New Network through an online feedback form created by our collaborators at JLA Public Involvement. The feedback form integrates animated videos by JLA and an online map prepared by our own staff.

In a metro area of only 300,000, the plan will be able to offer a network that’s mostly every 15 minutes or better (red). (Screenshot from the online map.)

To design the Draft New Network, we held intensive workshops with NTA staff, City and County planners, and the company (Bus Éireann) that runs the buses under contract with the government. We also leaned on public input from July about how to make the toughest network design choices. The Draft New Network would increase overall bus service by over one third, but as readers of this blog know well, within any limited budget – even a growing one – trade-offs must always be made.

What the Plan Would Achieve

When designing the Draft New Network, we kept in mind the first and second priorities of the 1,200 people who gave their input in an earlier phase of the project:

  1. Reduce vehicle use, by making public transport more useful to more people for more trips.
  2. Continue to serve all areas that have service today, and add service that covers new parts of the metropolitan area.

These goals are in famously in tension, but even in this fairly small city, the Irish government is funding public transport well enough that we can do a good job on both.  It’s a very different situation from what most North American transit agencies face.

Measuring the access provided by the Draft New Network gets at the first goal. Under the plan, the average person would be able to get to 17% more jobs or school enrolments in 30 minutes. (For unemployed and younger residents the benefit is slightly more.)  Existing trips would get shorter, and more trips would become possible within a reasonable amount of time.

Residents of some of the densest areas would see their access to jobs and other opportunities expand. Even outside the centre city, some large and growing towns would gain access. For example, Carrigaline – residents near the centre of Carrigaline would gain access to 35% more jobs within an hour’s commute.

Here’s how the network would change where you can go within 30 minutes from Carrigaline Town Centre south of Cork.  Dark purple is the area already reachable in this time, while pale purple shows the area that would be newly reachable due to the plan.   Grey (there isn’t much) is the area no longer reachable in 60 minutes.

How the plan would change where you can get to in 60 minutes, from the centre of Carrigaline. (That’s the city of Cork in the northwest.) Pale purple is the area newly accessible as a result of the plan.

The biggest reason access would increase is an increase in frequent services in the places where the greatest number of people live and work. Residents within a 5-minute walk of frequent service would increase by 34% (and for unemployed residents, by 56%).

Carrigaline, in the example above, would have 50% more buses departing for the city centre per hour, all day. This not only increases people’s access to the city centre but also to all the places they can go by interchanging with other routes.

To measure improvements that serve the second goal, of maintaining and increasing coverage of the metropolitan area, we counted up all residents and jobs that would be newly close to public transport (regardless of its frequency). The number of residents in the metropolitan area who would be within a 5-minute walk of service would go up by 7%, and the number of jobs would go up by 5%.

Requiring Interchange (Transfers in US Parlance)

The Draft New Network includes a few new nodes in outlying towns, where people would transfer (in Ireland, “interchange”) to reach the centre of Cork.

With improved frequencies, trips involving new interchange can be faster, on average, than direct trips.  Is a network that offers better frequencies, and shorter overall trips, but requires some new interchange, worth it?

Some people will understandably be anxious about interchange, or unhappy about what is a one-seat trip today turning into a two-seat trip: What if their second bus is running behind schedule? What if it’s too crowded and they can’t get a seat? What if they’re asked to interchange someplace without a good shelter to wait under? (It rains a lot in Ireland.)

This network redesign is part of a much larger project, called BusConnects Cork, that includes big investments in speed/reliability infrastructure, vehicles, shelters and signage. Much of this is designed to make interchange easier and more pleasant. The question of interchange, then, is not just about route and network design but also about investments in infrastructure that make interchange reliable and comfortable.

Preparing for Light Rail

Cork will build its first light rail line in the next decade, from its western edge to its eastern edge, connecting major universities, shopping centers, industrial areas, the city centre, existing dense housing and planned future developments.

To prepare for this, the Draft New Network includes an east-west frequent bus route that approximates the path of the future light rail line. Offering frequent, all-day, all-week bus service along the light rail corridor before the train is built supports the future success of the rail line. People’s will start to build their habits and their lives around travel patterns that the train will improve once it arrives. The city can permit new buildings before the light rail is built, knowing that they have decent public transit now while waiting for light rail to be built.


Caption: The three most frequent cross-city radial routes, in the existing network (top) and the Draft New Network (bottom). The colors don’t stand for frequency; they just serve to tell the routes apart. The new network sets up a line resembling the future light rail line.

Changing a long-standing route is always a bit controversial. It’s disruptive for people who know and use the bus network today, because they’ve built their lives and habits around the existing pattern. They’ve chosen where to live, or where to enroll in school, in part based on where they can go easily.

But in most cases, the impact on these people would be that they may have to change buses, but will get where they’re going soon.  So is the disruption worthwhile, if the result would be a major expansion in where people can go on public transport?.

More maps and resources are available on the project website.

Come work for us! Transit/Analyst Planner Job in Arlington VA or Portland OR


Jarrett Walker + Associates is excited to announce our next round of hiring, beginning today! JWA is seeking an analyst with interest or experience in public transit to work in either Arlington, Virginia or Portland, Oregon.  Our preference is for Arlington but we could hire in Portland for the ideal person.  You must be close enough to commute to one of these offices at least 3 days/week.

The position offers the potential to develop a range of transit planning skills. As a small firm, we can promote staff in response to skill and achievement. Everyone pitches in at many different levels, and there are many opportunities to learn on the job.

Duties include a wide range of data analysis, mapping, graphic design and/or writing tasks associated with public transit planning.


Transit GIS analyst/planner

Salary range:

$25-$35 hourly equivalent

Applications due by:

11:00pm PST, December 3, 2021

How to apply:

See below.

Jarrett Walker + Associates is a consulting firm that helps communities think about public transit planning, especially the design and redesign of bus networks. You can learn about us at our website ( and at Jarrett’s blog (

What does a typical day look like?

At JWA, analysts work on many different aspects of transit planning projects, using different tools and skillsets. For example, early on in a project, you could be asked to draw a map showing the frequency of each route in a transit network using Adobe Illustrator and QGIS. On another day, you might be asked to lay out a report in Adobe InDesign or create a set of charts in Excel or using R’s ggplot plotting package. Once you’re more experienced, you might make site visits to our clients in other cities to help with a design workshop or a public meeting. We also work together using R and other data analysis programming languages to conduct detailed analyses of existing transit service performance and compare different planning options.

Because our team is small and our projects are highly varied, we seek to hire and provide training to ensure the widest range of ability possible among our staff.

Required Skills and Experience

For this position, the following are requirements.  Do not apply if you cannot offer these.

  • Two or more years professional experience using the skills listed in this section, or formal training in these skills (such as at a college or university). Directly applicable coursework is valuable but not essential.
  • Fluency in written and spoken English. In particular, an ability to explain analytic ideas clearly.
  • Understanding and experience with analysis and visualization of quantitative or spatial information, including working with GIS.
  • Experience in cartography, evidenced in at least one mapping sample that is clear, accurate, and visually appealing.
  • Availability to start work in January 2022, at least 32 hours per week.
  • Willingness to travel occasionally (2-6 times per year) for projects.
  • Legal ability to work in the US as of January 2022.

Evaluation of Candidates

When we evaluate candidates, we will look for a combination of analysis skills and instincts; cartography skills; transit planning interest or experience; and interpersonal/teamwork skills. We may ask candidates to complete a practical test.

We will remove from applications information about each applicant’s sex, gender, race, ethnicity and name. Initial screening of applications will be performed without this information.  You are encouraged to submit your material with your name and these other identifiers (sex, gender, race, ethnicity) omitted, and to provide your name only in the submittal email.  If you do not do this our staff will do it for you.

Compensation, Benefits and Place of Work

Compensation will start in the range of $25-35/hour. Large raises in the first year are common. Our benefits program includes medical, dental, and disability insurance; a 401(k) program; subsidized and pre-tax transit benefits; paid sick leave; and paid time off.

During the pandemic most employees have been working from home for a majority of their work hours, but we do expect employees to be able to be in the office at least three days a week. In normal conditions, JWA allows employees to set work schedules that include working from home or other locations for some of their work time, but we do not permit fully remote employment. This position may require travel a few times a year, for client visits or conferences, once the public health situation has stabilized.

Growth and Development

We generally prefer to develop staff internally rather than hire at senior levels, so there is considerable opportunity for strong employees to advance.  All of our mid-level staff and one of our senior staff started in this position.

The position offers the potential to develop a range of transit planning skills needed to advance in the profession. Everyone pitches in at many different levels, so there is intensive cross-training that helps everyone grow their skills.  There are also opportunities to learn more advanced skills either on the job or through attendance of professional conferences or other structured training.

How to Apply

To apply, please send the following materials to [email protected]

  • 1-page cover letter explaining your interest in the position.
  • 1 or 2-page resume describing your relevant experience and skills – technical, planning, and interpersonal. Please include experience working on projects or in teams with people from different backgrounds.
  • Links or electronic files for up to three (3) samples of your work. If possible, please include a map, a piece of writing, and a demonstration of a spatial analysis. (A single sample may satisfy more than one of these requests.)
    • If you submit a university group project or other collaborative document with multiple authors that is not solely your work (i.e. government agency, nonprofit or consulting reports), please include a short note clarifying your role in the production of the document. For example, if you provide as a work sample a group project from a university course for which you designed all of the maps but were not the primary author of the text, please include a note saying so.
  • Contact information for 1 to 3 references who can attest to your experience with the skills listed above. Please do not include any information about your prior compensation.

Do not put any information in the email itself that you want to be used in the evaluation.    The cover letter and all other materials should be attachments.  The email must present your name and contact details.

Again, you are encouraged to anonymize all information by removing your name and references to sex, gender, race, or ethnicity, and to provide your name only in the email.  If you do not, we will do this for you.

Diversity and Inclusion

JWA follows an equal opportunity employment policy and employs personnel without regard to race, color, religion, sex/gender (including pregnancy, gender identity, and sexual orientation), national origin, age, disability, and any other legally protected status.

This policy also applies to management of staff with regards to internal promotions, training, opportunities for advancement, and terminations. It also applies to our interactions with outside vendors, subcontractors, and the general public.

Some Doubts about Access Analysis

Click to enlarge: The basic idea of access.

Access is your ability to go places so that you can do things.  In this “basics” article, I laid out why I think measuring access would help advance many important goals that appear to be in conflict, and I suggested, for both practical and moral reasons, that public policy should care about what people can do — i.e. their freedom — as opposed to just what we computer-enhanced elites predict people will do.

Many smart people have offered critiques of this idea, or at least of its practical applications.  I’m particularly grateful to Alex Karner of UT Austin and Willem Klumpenhouwer of University of Toronto for this conversation, and to Matt Laquidara, who laid out a very thoughtful critique early on.  Please point me to others that I may not have seen.

Two Kinds of Critique

First, let’s distinguish between rhetorical and investigative uses of analysis.  In my practice as a consultant, I’m trying to break through into a public conversation, and I’ll do this only with simple explanations of things that obviously matter to people.  It’s not wrong for me to oversimplify to make the idea visible and convey its importance.  The work can be accurate, as far as it goes, and still be simplified.

So there are two kinds of objections to my thesis:

  • those that undermine the fundamental claims of access analysis and
  • those that add nuance that could make access analyses more accurate, precise, and/or more relevant in edge cases.

The latter, of course, are not objections at all.  They’re just avenues for further development.  You’ll see a lot of these throughout this post.

My claims for access analysis

My argument for access analysis is here, but let me quickly list the aspects of my position that seem adjacent to the critiques, and thus most relevant to this response:

  • To the extent that we make strong predictions about what humans will do in the future and what outcomes will result, we are assuming that people are not really free.  Free people will surprise us.  Prediction also appeals to a human desire for control over history that is just not realistic.  The future really is unpredictable.  (More on this in my Journal of Public Transportation paper here.)
  • There are degrees of prediction and the best predictive work makes much softer claims.  Prediction of only near-term events, or prediction that speaks only of ranges of probability, is less problematic.
  • All analysis is more reliable when it predicts that people will continue to be what they’ve always been throughout history and across cultures.  It’s much more problematic assert the permanence of aspects of human society found only in the present, or in the very recent past, or in only one culture (however dominant that culture may be).  Again, this is less of an issue for shorter-term predictions.
  • Access analysis doesn’t need to be perfect or free of questionable assumptions. It just needs to be much more reliable than predictive modeling.  Even if (hypothetically) the two methods turned out to be equal on this score, access analysis would still be preferable because:
    • It’s about something that everyone cares about.
    • It is correlated to many outcomes that we urgently need our transport system to deliver.
    • It is a much more transparent process where the assumptions and their impacts are easy to document, even if they’re controversial.
  • When you pile up the assumptions on both sides, access analysis carries a much higher degree of certainty because it isolates geometric, physical, and biological insights and relies on them to the greatest extent possible.

So let’s look at the biggest doubts about access analysis.

Is it good only for commute trips?

Our firm‘s analyses usually focus on trips to work or school, and people routinely object that those aren’t the only kinds of trips.  Of course they aren’t.  They aren’t even half of all trips.

However, when we think about the most long-term freedoms we need, the freedom to construct our lives and commitments according to our values, the commute (work and school) looms large.  Your ability to hold a certain job, or study at a certain school, will do a great deal to define the capabilities you’ll develop, the money you’ll earn, the social networks you’ll be part of, and so on.  Those things, in turn, will create the conditions for the freedom or unfreedom that you’ll experience down the line.  So when we seek to quantify freedom in the broadest sense, it may be reasonable to put special emphasis on access to work or school.

Commutes are round trips made on a majority of days and that include spending several hours at the destination. They are almost always to work or school.  Commutes are easier to analyze than other trips because:

  • It’s easy to calculate how many people will value a trip to each destination.  While the number of people who want to go to a store will vary with the quality of the store, its competition, and people’s attitudes to it, every job or school enrollment position will be the destination of exactly one resident.
  • Data about the location and quantity of jobs and school enrollments are relatively good in developed countries, although there’s still a lot of variation.
  • We have a useful rule of thumb about the tolerable travel time for commutes: Marchetti’s constant, the observation that across many historical periods, people have tolerated a one-way commute time of about 30 minutes.  This is an example of the principle that if an aspect of human culture been true far into the past and across many cultures, it’s a more reliable basis for positing what freedoms people will continue to value.

Can we look beyond commutes?

But is access analysis good only for commutes?

In our work we do extend the principle to other kinds of trips.  In our recent San Francisco work, for example, we calculated access to groceries, low-cost food resources, parks, pharmacies, and medical centers.   We have also experimented with more precise pairing of residents and destinations.  For example, if we have good data on both income and wages, we can calculate low-income people’s access to low-wage jobs.  We can also exclude retired people from the database of people who value the freedom to access work or school opportunities, but include them — or even make specialized calculations for them — when looking at other destinations that tend to matter in a retired person’s life, including groceries, medical, and parks.

When we move beyond the commute, however, the three benefits I listed above are all absent.

  • We cannot calculate, for a given person, how much freedom is provided by the ability to go to one park or medical center over another.   The tool would be highly reliable for identical destinations, like McDonalds restaurants or whatever, but I think we’d all agree that if you can get to three McDonalds restaurants you don’t really have three times the freedom that comes from being able to get to just one.  The freedom value of alternative destinations depends precisely on them being different from another, and we have no hope of abstractly quantifying that value.  In San Francisco we inevitably made simplifying assumptions: valuing parks by the acre, for example, and valuing all medical centers the same.  For present-oriented analysis you can dig deeper into trip generation patterns, through surveys etc, and refine assumptions, but that works only for analyses meant to be relevant only in the present.  This is a genuine weak point for analysis.
  • We have lousy data about most nonwork and nonschool destinations.  Some of these things change rapidly.  Even if we know where they are we usually don’t know their size or intensity.
  • It’s harder to assign an acceptable travel time budget for a nonwork and nonschool trip, as I’ll address below, although we can still make educated guesses.

But predictive modeling has all these problems too!  Most such modeling relies too heavily on the commute as the primary trip that matters (and on rush hour as the primary time of day that matters).  All of the problems of the non-work trip are at best equal for predictive modeling as for access analysis.

Arbitrariness of Time Budgets

When I explain access, I have to start with the isochrone (see image above), the area that a person at a certain location could reach in a fixed amount of time.  Thus, in the access analyses that underlie our reports, we usually describe what area could be reached in 30 minute or 45 minutes.

Why 30 and 45 minutes?  If we had twelve fingers I’d probably be using 36 and 48.

There are two problems here: (1)  We are imposing an obviously arbitrary threshold, valuing a trip that can be made in 29 minutes but not 31, and (2) We are asserting an amount of time that people find acceptable, which requires an explanation.  These are interconnected.

How do we know what travel times people tolerate?

Everybody has the same amount of time.  There are 24 hours in everyone’s day.  When we perceive a travel time as acceptable it’s because it’s an acceptable percentage of the total time available.

You could argue that the perception of time is different in culturally “slow-paced” as opposed to “fast-paced” places, as in the stereotypes of New Orleans and New York, respectively.  On the other hand, setting travel time budgets differently based on the dominant culture of a place is itself oppressive, as more and more people live in places where theirs is not the dominant culture.

Meanwhile, economists like to talk about “value of time,” which is about the value of your time to the economy, not to you.  That’s definitely not what we should care about here.  We’re talking about an equal right to freedom here, and the only way to do that is to posit an equal value of time.

We can plunge into social science research at this point, looking for non-commute equivalents of Marchetti’s constant.  How long do people spend going to the grocery store?  How long do they spend going to a park?  The data will be all over the place, and it will be hard to separate how long people are willing to spend from how long they are forced to spend given their situation.  Again, if we can find something that’s been true longer, and over more cultures, we should rely on it more.

But I think we could start with a couple of principles, which I suspect are relatively transcultural and transhistorical:

  • We are willing to spend longer traveling if we will spend more time at the destination.
  • We are willing to spend longer making a trip we make less often.

We have a finite amount of time in our day, so if we have many commitments, we’ll need to hold down the total percentage of our day spent in travel.  So the commute is likely to be the longest trip we’ll make in a typical day, though we may make longer trips less often.  Errand trips, lunch trips etc. are likely to need to be shorter than commute trips.

For retired people, diverse errand trips (medical, recreation, shopping) may be able to take longer than for people who spend much of each day at work or school.  We need more research about retired people (and other people who are not in school and don’t have jobs) because their tolerable travel time may depend on the fact that their daily time is less scarce, and that some time-saving actions, like walking further to a more frequent bus stop, carry higher disincentives for them.

I think these principles, buttressed by some research, could help us creep toward some reasonable travel time budgets:  Marchetti’s constant (30 minutes one way) for commutes, a lower number for typical errands, but possibly a higher number for retired people.  Is this all wildly imprecise?  Yes.  Is it arbitrary?  No, we’re not picking numbers out of the air.  We have a sense of the right ranges.  Now we come to the next problem:  While the roughly correct travel time budget is not totally arbitrary, the exact one we use definitely is.

Why 30 minutes?  Why not 31?

From, our work for Portland Enhanced Transit Corridors project: A person at 82nd & Foster has lost 19% of their 45-minute access to jobs in a decade (2009-19) due to declining bus speeds.

Access analysis starts with an isochrone showing where someone could get to in a fixed amount of time, such as 30 minutes of 45 minutes.  But as Matt Laquidara points out, “no one who is willing to take a 45 minute trip is going to consider a destination 46 minutes away totally unreachable.” In a footnote he adds: “Why bound time at all? In theory, it’s possible to have no maximum time and compute the trip duration for every origin, destination, and starting time combination. Those could be aggregated into an average or percentiles.”

Yes, if you could tolerate a given travel time, you could probably tolerate one that’s a minute longer, but you’ll have limits.  In growing cities, city bus lines in mixed traffic often slow down very gradually, a classic “boiling frog” event that causes big cumulative damage but never generates a single crisis that would attract attention and action.  To a great extent, people who are used to a 45 minute bus ride may accept that it’s 46 the next year and 47 the year after that.

But at some point, they will run out of time in their day.  The person whose 45-minute ride is now 55 minutes will eventually give up.  They’ll change modes, or quit that job, or do what’s necessary to keep their total daily travel time down.  Meanwhile, a new customer who looks up that commute will see a 55 minute travel time, and say no thanks.

So a minute’s difference may not matter, but a 10 minute difference probably does.   And to talk about access as freedom, we need to be very approximately right in the travel time budget.  Perhaps we’ll get closer if we come up with bell curve of weighted travel time budgets for commutes, maybe peaking at 30 minutes one way but with a long tail stretching upward past 45.  This is a reasonable solution to the problem of assigning too much significance to a one-minute difference.  But if we get too fancy about how we draw the curve, it takes us back to the same problem.   It’s easy to quantify what people are putting up with in terrible situations, but that’s different from what a free person would tolerate.  We aren’t describing people’s freedom if we’re relying on data about their unfreedom now.

So some arbitrariness, proudly proclaimed, may be better.  For my own rhetorical purposes in presenting and justifying transit service plans, the soundbite and picture take us far:  “The average Dubliner can get to 20% more jobs and school enrollments in 30 minutes, and here, let us show how the 30-minute wall around your life changes.”  People who hear me say that rarely accuse me of claiming that 30 minutes is radically different from 31.  They know I’m making a simplifying assumption so that I can show them something that they can understand, and whose value is obvious to them.

Perils of Aggregation

It’s one thing to analyze all the various kinds of destinations.  It’s another more perilous thing to decide how these should be weighed to create a single measure of access.  As Matt Laquidara writes:

I’m deeply uncomfortable with most any determination of what locations are important, and consequently, which ones are not. I don’t want to do it myself. I don’t want anyone else deciding it either.

For reasons we explored above, there are always going to be trip desires that are just too scattered, and for which there’s so little data, that they will tend to be omitted in analysis.  Residence-to-residence trips are probably one example.

There will also always be the problem that some destinations are hard to quantify.  In San Francisco, we assumed that every acre of park was equally valuable in terms of people valuing the freedom to reach it, but of course there are lots of ways to question that, and to introduce other factors such as park infrastructure.  Each of those factors would make the measure more precise but also more questionable in terms of how it was projecting some people’s preferences (those who yell loudest at meetings, for example) onto the entire population.

But let’s say that refinements to access analysis make it possible to cover about 95% of trips — or as access analysis would describe it, 95% of the destinations that people will value the freedom to reach.  Matt’s objection arises only when we aggregate these different destinations into a single access score.  If we declare that one acre of park is worth 0.26 pharmacies, that’s a value judgment.  We could try to apply survey data about how much demand each place attracts, which requires assuming that people are making all the trips they want to make.  Or we could just stop trying to aggregate, which I prefer.  The elected and public audiences with whom I speak usually want to hear separately about each destination type, because each is the basis for a different kind of story and has a nexus with different kinds of public policy.  If you care about food security, look at access to groceries.  If you care about how much exercise people get, look at access to parks.  And so on.

To sum up

  • Access analysis is not perfect but can be more reliable than predictive analysis, if only because it makes a more modest claim.
  • Predictive modeling requires all the assumptions that access analysis requires, but adds even more assumptions about how human behavior in the future will resemble that in the recent past.  Access analysis does not need to include such perilous assumptions.
  • We can describe access for commutes with relative confidence.  Commutes are a minority of trips but there are a variety of reasons to consider them important.
  • Non-commute trips are important but harder to analyze.  Still, there’s a basis for making some reasonable assumptions.
  • Further work is needed on how to think about freedom of retired people, and more generally about how people’s tolerance for travel time varies with the competing demands on their time.  Up to now I’ve been using busy people as the primary frame of reference.  This probably contains a bias: I want transit to be useful to busy people, not just to people who enough time that they don’t feel constrained by slow service.  Most people are busy.

This post is out there to start arguments, though I hope it also resolves a few.  I am not an academic scholar, but I do feel confident in what I asserted in the “my claims” section above, at least until I read the comments, as you certainly should.  Then, I may add some updates here.