Human Transit

"abundant access": a map of a community's transit choices, and a possible goal of transit

In my book Human Transit, I argued that the underlying geometry of transit requires communities to make a series of choices, each of which is a tradeoff between two things that are popular.  I argued that these hard choices are appropriate assignments for elected boards, because there is no technical ground for making one choice or the other.  What you choose should depend on what your community wants transit to do.  Examples of these choices include the following: 

• Ridership or Coverage?  Should transit agencies be maximizing their ridership, which is easily done by abandoning service to low-ridership areas, or should they spread out service throughout their service area so that everyone has some service, despite the predictably low ridership that results. (HT Chapter 10)
• Connections or Complexity?  If you try to design a transit network in which people won't have to transfer, you'll end up with a network with high complexity and low frequency.  I first explained this here, and later, and more rigorously, in HT Chapter 12.
• Peak-first or all day?  While it's widely assumed that transit is most productive during the peak, this is not always the case, because service running only on the peak, and especially only in one direction, can be massively expensive to operate.  Should the peak commuter be the primary focus of a transit network even given these costs, or should a transit agency seek to build an all-day network of services that encourages reliance on transit at all hours, while still meeting peak capacity needs?  (HT Chapter 6).
• How far do you assume people will walk?  Assuming higher walking distances allows transit lines and stops to be further apart, increasing both speed and frequency.  Research has found repeatedly that people will walk further to better service, though when you first propose to increase walking distance they will complain.  This is an especially tough tradeoff because frail seniors and disabled people are small in numbers but have a particular aversion to walking.  (HT Chapter 5).
• Should transit be protected from congestion?  Doing so, by giving transit a lane (or trackway) not shared with traffic will dramatically improve reliability and thus the degree to which people will find they can trust the service.  However, this requires a city to display a profound commitment to transit in the allocation of its streetspace.  (HT Chapter 8).

Note that while the framing of these choices tends to make them sound binary ("Ridership or coverage?") the choice is not between two boxes; it's of a position on the spectrum where the two terms define the extremes.  You don't have to choose between ridership or coverage, for example, but you have to choose a point on the spectrum between them, and you have to accept the mathematical fact that, as on any spectrum, moving toward one extreme implies moving away from the other.

In the Epilogue of HT I briefly introduced the idea that for each of these choices, one option seems to trigger a positive-feedback loop, while the other option does not.  Here is a new and expanded diagram of that idea.  Click to enlarge, or download here:    Download Abundant access diagram  (Tip: Print it on A3 or 11x17.  There's a lot here.)

What do I mean by positive feedback loop?  On each of these choices, the option that points toward the center leads to a particular kind of network that supports all of the goals implied by all the centerward choices.  For example, if you plan your network for maximum ridership rather than coverage, you also generate a network that encourages higher walking distances, that supports easy connections rather than complexity, and that tends to present the strongest case for facilities that protect transit from congestion.  

On the other hand, the options that point outward from the center tend not to support each other.   You can achieve the goal implied by these outer choices, but (arguably with some exceptions) each one will require a separate effort.  For example, if you believe walking distances to transit should be low, as seniors tend to advocate, then you need to put parallel transit routes -- and the stops on those routes -- very close together.  This does nothing to advance any of the outer "outward" goals, whether it be growing peak demand, or avoiding connections, or achieving a luxurious experience that will compete with a BMW.

Another way of saying this is that the choices that point inward all point to a single set of network design principles, and a single set of consistent priorities, while the choices pointing outward lead to many different kinds of network design and competing priorities.

What happens when you move toward the center?  These choices converge on a single, consistent goal that I propose to call Abundant access, which means:

The greatest possible number of jobs and other destinations are located within 30 minutes one way travel time of the greatest possible number of residents.  

[Why 30 minutes?  The question is tangential to my point, and other figures could be used, but if one has to pick a figure the most solid basis is Marchetti's constant [PDF], the idea that humans throughout history have tolerated about one hour of daily travel time.  Obviously, shorter or longer periods may apply to trips other than the commute.]

For any individual, abundance of access can be visualized using a map of isochrones, like the Mapnificent.com travel time maps, which show the area you can get to within a fixed amount of time on some combination of transit and walking.

 

Of course, any quantification of abundant access must consider not the area but the amount of stuff in it: jobs, retail, recreational opportunities, hospitals, all the things that form the universe of destinations.  As a matter of public policy, it must also maximize over the largest possible share of the population.  In the case of transit, the population over which abundant access is most cost-effectively maximized tends to be a more urban, high-density population, because among readily available measures, density is one that best predicts the intensity of ridership that will arise from a service investment.  (Fortunately, that's fairer to than it sounds, because people living at high densities use much less road infrastructure per capita than people living at lower densities.)

The goal of abundant access has several kinds of appeal.

First, it can be measured objectively without recourse to psychology or culture.  Ridership estimates are based heavily on travel times that approximate the notion of abundant access, but they also add psychological factors that are less stable, such as observed preferences for particular technologies.  These factors may be emotionally vivid, but like many emotional factors they are likely to change with time and especially with generations -- just as emotional attitudes toward cars are changing now.  Abundance access measures a fact that is entirely objective -- travel times.  Unlike emotional reactions to technologies, the value of access has been constant across millennia of human experience.  

Second, abundance of access is literally a quantification of freedom, in the sense that matters to us in transportation.  Isochrone maps like Mapnificent's, in particular, show us our freedom in a very immediate way: here is where you are free to go, now.  Abundant access measures the transportation element of opportunity of all kinds, which is one of the main reasons people have moved to cities since their invention.

The concept of freedom is sadly undervalued in much urbanist discourse, and I am always looking for ways to reintroduce it.  Much urbanist writing, for example, is blatantly prescriptive ("you should want this kind of community"), which feeds conservative stereotypes of urbanism as manipulative or coercive.  We need to be able to talk not just about ideal communities but about freedom and personal responsibility, a frame in which all the great urbanist ideas -- and all the urgent environmental imperatives -- can be stated equally well.  In that frame, the key idea is not "the good" but "choice," where freedom of choices also implies responsiblity for your choices.

So again, all of this work is descriptive, not prescriptive.  I'm not saying that you should like the goal of abundant access; that would be value judgment, and you get to make those for yourself.  

I am saying, though, that abundant access as an idea has certain features and consequences, including a tendency to be self-reinforcing.  As mapped along the various axes of choice, abundant access is a single consistent vision whereas the opposite choices lead to many unrelated visions.  

Still, you don't have to like it.  My role, as always, is to describe consequences clearly, and help people choose.    

the need for maps of your freedom

 

Remember this map?

 

I used it in the earliest days of this blog, and it's in almost every presentation I do.  It's from a tool that allows you to select a location in a city and see blobs (technically isochrones) showing the area you can get to in a fixed amount of time using transit plus walking.  This one is for 9:00 am and the three shades of blue represent travel times of 15, 30, or 45 minutes. In essence, the software takes the point you select and runs the equivalent of Google Transit trip planning searches to find a points where the travel time crosses the threshold; these become the boundaries of the blobs.  (For details behind this crude summary, see Aaron Antrim's comment on this post.)

I call this a map of your freedom.  It's useful for two potentially transformative purposes:

• Helping people and organizations understand the transit consequences of where they choose to locate, and thus to take more responsbility for those consequences.  This, over time, can help people who value good transit to locate where transit access is good -- something that's very hard to discern from a typical bus map but that becomes very obvious here.  You can even assess access to specific things that you value, based on exactly where the blobs are.  
• Helping people visualise the benefit of transit -- access to your city -- as a freedom, and thus to understand more clearly what transit does for them.  It broadens the narrow notion of travel time  -- which is often understood for only one typical trip -- into a picture of your possibilities as a transit rider.  The percentage of a city's resources (jobs, housing, retail etc) that is in the blobs for a particular location could also form the basis for a meaningful Transit Score that could replace the technologically biased scores now used by WalkScore.com.

The original tool is a beta buried deep in WalkScore's archives.  It's basic and very, very slow.  

The other main alternative is mapnificent.net, by Stefan Wehrmeyer.  Available for many cities, Mapnificent.net looks good ...

... except that it contains two fatal assumptions:

• Initial wait time is excluded.
• Some timing of transfers is assumed, based on the author's experiences in Europe.  So he uses an average transfer wait time of 1/3 of the headway instead of 1/2 of the headway, which would be appropriate for random transfers.

Here's the problem.  Both assumptions mean that Mapnificent's assumptions undervalue frequency and overvalue vehicle speed. Since this conceptual bias is already very, very common (see Chapter 3 of my book), Mapnificent is seriously misleading in a way that can be really unhelpful.  For cities that I know, especially area with lower frequency service, Mapnificent wildly overstates the convenience of transit, and fails to show how locating on frequent service will get you better access to the city.

In my network design course we talk about this.  When figuring travel times in the course, I insist on using 1/2 of the headway as the intial wait time and the same as the transfer time (unless there's a pulse) so that frequencies weigh heavily into true travel times, as they do in life.  This sometimes sounds silly: If a route runs once an hour does that really mean I wait an average of 30 minutes?  Or do I just build my life around the schedule?  I view the two as the same thing, really.  We're not describing literal waiting so much as time when you're in the wrong place.  We're describing the difference between when you need to arrive and when you can actually arrive.  This could take the form of arriving at work 29 minutes earlier than your shift starts -- consistently, every day.  Effectively, you end up waiting at your destination.

So there are a range of judgment calls to be made in designing these things, but it's worth getting it right because the potential utility of this tool is so significant.  The good news: I'm involved with people who are working on something better.  Stay tuned!

frequent service, mapped to your door

Vancouver's TransLink is one of several agencies who -- with some input from me -- have adopted Frequent Network brands that are designed to highlight services that are always coming soon, generally every 15 minutes or better all day and weekend.    I've always insisted that the Frequent Network can be both a short-term service branding tool (to build ridership by helping time-sensitive customers see where the network can serve them) but also a land use planning tool.

TransLink always understood it was both, and for several years has had a goal stating that half the region's population and jobs will be on the Frequent Network.  This is both a land use planning statement and a transit planning statement.  The message is not that TransLink will extend Frequent service to half the current population, but rather that it will do some of this while land use planning will also bring put residents and jobs on the existing Frequent Network.  More recently, Translink finally highlighted its Frequent Network on its maps for the public.

Ultimately, the Frequent Network, if properly mapped and promoted, should sell real estate, because the high level of all-day access should have a clear value as a city as a whole becomes more transit-oriented.  So this kind of micro-mapping should be really handy:

This map (click to enlarge and sharpen) of transit access in New Westminster, British Columbia is by Jonathan X. Cote, a City Councilor in that city and also an urban planning student at Simon Fraser Univerisity. He takes the standard walking distances of 800m to rapid transit and 400m to local transit and plots the portion of his city that has access to those networks.  I've seen these maps before, and even if they are not drawn they are what lies behind any coherent statement about what percentage of population and jobs have transit access, within a given walking distance, to service of a given standard.

Remember:  If your city wants to do really honest transit analysis, it needs very small analysis zones.  This map shows you the kind of clarity that you get when you can analyze right down to the parcel.  You don't need that much fine grain, but the zones need to be small.  And a parcel-level map like this is certainly ideal for land use planners, who need to minimize walking distances for the centroids of transit-oriented developments. 

Notice what a good tool this is for analyzing bus stop spacing as well.  You can move the stops a little apart and count how many parcels fall out of the walkshed.  Out to about 400m (1/4mi) spacing the answer is usually "fewer than you expected."

using dynamite for lack of paint: alex broner on "cities in motion"

Ever since I posted on SimCity and SimCity 4 people have been telling me I must try Cities in Motion.  But when you have two jobs and you're already devoting hours to a blog and a book and a remodel, there is only so much time for computer games.  Fortunately, Alex Broner has boldly gone there in a guest post, so I don't have to!

 

In Cities in Motion (a game by Colossal Order, published by Paradox Interactive), one assumes the role of a CEO of a transit company tasked with providing transit to a particular city. In the campaign mode the cities are all based on specific cities at specific historical periods, Berlin during the cold war for example. There is also a “sandbox” mode in which you can play additional cities including player created cities and fictional cities.

Your transit company operates without subsidies for the most part, though there are “missions” which often offer monetary rewards for their completion. The most common mission is to connect two or more places together with a transit line.

In the campaign mode there are certain required missions which you must complete in order to “win” the scenario and unlock further scenarios.

Your transit company has a variety of different vehicle types which it can use to meet the needs of the city’s residents: Buses, trams, Metro, waterbuses, and helecopters.  There is (premium) downloadable content that adds electric trolleybuses, cable cars, and monorails.

Your success of failure in the game depends on finding ways to efficiently provide service connecting residents with destinations such as workplaces, shopping, leisure, and government. “Leisure” seems to include regional transportation hubs such as inter-city rail stations and airports. Like a real transit company, you must consider expenses for capital improvements such as stations and vehicles and also operational expenses such as labor and fuel/electricity.

This is not a city building game but the connection between density and transit service is made clear by the simple fact that even though you can build a subway to rural or suburban area, very few people will ride it.  The connection between service levels, frequency, and customer satisfaction is made clear by the “wait time” indicator. If the wait time on your transit lines is too long then customers will grow dissatisfied and eventually leave the station. Also, since all infrastructure such as stations and rails has maintenance cost, creating under-utilized infrastructure leads to a poor cost-revenue ratio.

To be successful your agency must take into account the layout of the city and where different groups of people want to go: working class people work at working class jobs, students go to the university, professionals to the offices, and so on. Then you must make choices between vehicle types and network arrangements and put it all together into a profitable enterprise.

All of this is pretty realistic but as I played I immediately began noticing some major problems. The most notable problem is that the “walk shed” for each stop or station is different for each type of vehicle. The game will have residents walk much farther for metro service than they will for buses or trams, no matter how poor the metro service is or how good the buses and trams.

An additional problem is that there is nothing like transit lanes or transit signal priority for buses and trams. The streets of Cities in Motion have various amounts of traffic and in heavy traffic your vehicles will bunch up, depriving you of much needed revenue and making your riders unhappy. One's tools for dealing with this are limited: trams can run on unoccupied ground such as across plazas or on grass. Often in the game I find myself building a tram because there’s a long park or other way to bypass congestion. One can demolish buildings that get in the way of your trams but not build roads or even transit lanes, placing one in the bizarre situation of reaching for the dynamite for lack of paint. In combination the limited walk shed and lack of prioritization tools such as transit lanes means that the game very quickly becomes about building Metro systems. Not only is this unrealistic it’s also quite boring.

Additional annoying features:

• Cyclical economic changes causes one to have to adjust ticket prices and labor pay rates constantly for each type of vehicle and 5 types of employees. There’s a mod that allows one to do this automatically but it would have been nice if that had been included in the base game.
• Residents are drawn to transit in an almost fanatical fashion, they will navigate around any barrier to reach a station that’s close enough by straight line distance. One is not encouraged to situate stations in places realistically accessible. The routing algorithm of residents is poor meaning that they’ll pile up on the platform of one metro station even if there’s an empty platform with comparable services right nearby. 
• Metro trains try to get 100% full before departing, even if this means holding up the empty train behind them. 
• Finally, one is unable to combine either metro or tram vehicles to form longer trains (or construct longer platforms).

On the whole I give the game a B- for gameplay and a C for simulation value. It obsesses over certain aspects of transit (different types of customers, different types of workers, etc) while failing to address some really important ones. It teaches some important things about transit (frequency, density, operation costs) while furthering our confusion about the relationship between technology and levels of service. I would love for the makers of the game to fix some of these problems either through downloadable content or a new release. We need clearer thinking when it comes to transit and while this game doesn’t quite provide it, it very easily could.

[Alex Broner is a graduate student working on his Masters of Urban and Regional Planning at the University of Hawaii with an expected graduation date of December 2012. He is also an intern writer/researcher for the Sightline Institute.  His professional interests are in transportation, landuse, and urban design. Alex is passionate about creating enjoyable urban places where it is easy and safe to walk, bicycle, and take transit. His personal interests include cycling, science fiction novels, computer games, and dodgeball.]

what's wrong with the "transit score"?

Carter Rubin, on Los Angeles Metro's blog The Source, says exactly what needs to be said about WalkScore.com's Transit Score product.  The product is in the news today because of their new ranking of US cities by Transit Score.

Everyone’s favorite mapping tool, Walk Score, has launched a new service called Transit Score and used it to determine what it believes are the best American cities for public transit. The Switchboard blog has a recap and analysis. Los Angeles clocks in at 11, just behind Portland, Ore., and ahead of Denver, Colo. — respectable enough company, I suppose. That said, I do have some constructive criticisms of Transit Score’s methodology.

Excerpt:

To calculate a raw Transit Score, we sum the value of all of the nearby routes. The value of a route is defined as the service level (frequency per week) multiplied by the mode weight (heavy/light rail is weighted 2X, ferry/cable car/other are 1.5X, and bus is 1X) multiplied by a distance penalty. The distance penalty calculates the distance to the nearest stop on a route and then uses the same distance decay function as the Walk Score algorithm.

The first issue that jumps out at me is how Transit Score weights different modes to give a bonus to “better” modes: “heavy/light rail is weighted 2X, ferry/cable car/other are 1.5X, and bus is 1X.” There’s such an incredible diversity of service quality within each mode that this strikes me as an oversimplification. Is the Metro Los Angeles Orange Line really half as “good” as the Boston Green Line — a nice enough line, but it plods along 100-year-old tracks — just because the former runs on rubber tires?

There are arguments either way, and reasonable people can disagree. Those differences, however, are simply glazed over with a simple multiplier. And, I don’t even pretend to understand the 1.5X weighting for ferries and cable cars.

Early last year, when Transit Score first rolled out, I discussed it with WalkScore's Matt Lerner, expanded on this very critique, and suggested a better (though computationally intense) approach.  It involves aggregating the content of their travel time maps -- effectively "maps of your freedom" -- over all likely destinations from any residence, so the two digit score is actually a percentage, a composite of answers to the question "What percentage of jobs, retail, etc can you get to in __ minutes, on transit, from here?"   It needs refinement, but that's the only truly factual measure of access that could be reduced to a two digit number.

I understand why Walk Score folks settled on this methodology; it's more about the limits of compultational power than any modal bias on their part.  Still, Transit Score is the only WalkScore.com product that I can't recommend.  I love everything else that WalkScore does, but Transit Score assumes that a slow streetcar is better for you than an express bus, and people need to make that decision for themselves.  

walkscore.com and the lure of the single "score"

The Conservative Planner has a thoughtful attack on WalkScore.com's methodology for calculating a simple "walkability score" for any neighborhood in America.  He's found several examples where WalkScore has given a high score to a place that's clearly hostile to pedestrians when viewed on the ground. 

One only had to take a stroll around the Hilton in downtown Atlanta to see the inherent flaws in this online tool. Type the Hilton’s address in Walk Score (255 Courtland Street NE, Atlanta, GA) and it will tell you that it is a “86 – Walker’s Paradise”.  [JW:  Actually, it now says "86 - Very Walkable']

The Conservative Planner continues:

Nevermind the fact there are 4- and 5-lane one-way streets with high speed traffic surrounding the hotel. Interstates 85/75 runs to the north and east of the hotel and is a major pedestrian barrier. The restaurants that are deemed by Walk Score to be nearby and within walking distance are buried within the Marriott and Hilton hotels, which are 1960s/1970s behemoths. It is hardly a walking paradise; it may be in a downtown area but the street system is strikingly suburban.

Fair enough.  But here's the Conservative Planner's suggested remedy:

Walk Score should not be used to analyze how walkable an area is as it does not consider the three most critical factors of walkability:

1. Connections: Walk Score can’t tell if sidewalks exist or not. It can’t even evaluate if there’s a street to connect to a destination that it tells you is within a walking distance of your address. You might need a machete and steel-toed books to walk to the doctor’s office.

2. Actual Route: Walk Score measures crowflight distance, not actual walking distance. I live in a neighborhood that has several destinations within a 1/2-mile radius. Too bad it takes me more than a mile to walk to them because of the lack of a pedestrian system along a 7-lane arterial highway with no crosswalks and poor connectivity despite its location within a streetcar suburb.

3. Land Use/Design: You could have the most “walkable” area according to Walk Score, but if you’re walking in front of a Walmart or other horribly designed commercial or residential strip, you won’t find the area to be very pedestrian-friendly.

These are all valid points, but if the Conservative Planner is really a planner, he/she would know how hard this bar is to meet.  Items 1 and 2 require that every local government in America provide a digitized map of its entire pedestrian network, showing not just which streets have sidewalks but where the usable off-road paths are, possibly including parking lots and vacant lots that you can safely cut across.  It should probably also show not just pedestrian signals but information on how they're timed.  Many local governments don't have this information.  Some have it only in the form of hand drawings on paper maps lovingly curated by the town's sole "pedestrian planner," who is allowed to play with these things in his broom-closet office so long as he stays out of the way of the road engineers. 

As for item 3, "design," well, sure, most of us would rather walk through a park rather than across a parking lot, but "design" by its nature refers to a subjective response, not a scorable metric.  (I'd make an exception for Robert Cervero's use of the word in The Transit Metropolis, which I suspect was selected more for alliteration in his phrase "density and design."  By "design" Cervero really means network connectivity -- the Conservative Planner's #2 -- measurable, say, by the percentage of a 1/4 mile air radius that's within a 1/4 mile walk on the pedestrian network; more on this here.)

What's more, even if we could agree on a scorable metric, you'd need a nationwide database of exactly how every lot has been developed, continuously updated of course.  The closest thing we have to that is Google Street View.  Is someone working on a computer algorithm that will study every Street View photo in the country and assign a universally-respected "design score"?  If so, perhaps we can look for improvement.

Bottom line:  What the Conservative Planner is really pointing out is that prevailing data structures are designed to the needs of the prevailing mode -- and right now, that's cars.  Yes, every local government should have a complete database of its pedestrian links, and yes, they should send it to Google so it can be added to Google Maps.  Only then will we have an automated measure of actual walking distance.

Meanwhile, the sensible response from WalkScore.com would be to move their "How WalkScore Doesn't Work" page to a more prominent place on the site.  A sensible response from the rest of us would be to remember that any methodology that reduces diverse inputs to a single score is not just an approximation, but an approximation shot through with value judgments that the score's consumer may not share.  WalkScore could help remind us of this by showing, on the front page where it displays the score, the separate "sub-scores" from which it's calculated, so that we can each decide if the factors are weighed just as we'd like.

UPDATE:  Matt Lerner of WalkScore tweets that they are working on these problems!

good question of the week: transfer penalties

A frequent commenter on HT asks this in an email (the links are mine, not his):

On Second Avenue Sagas, one of the discussions went on a tangent that left me wondering about transfer penalties. If you need to walk from one station to another on the street to transfer, do the ridership models assign a higher penalty than if there's an enclosed corridor between the stations? In addition, for systems that have faregates, is there an extra penalty for transfers that require exiting and reentering?

Modeling can be a murky business, and I'm definitely not a modeler.  But the bottom line is that the factors used in a ridership model have to be based on some sort of reality, and the reality of North America and Australasia is that most connections are not especially pleasant or easy, especially when there are fare penalities or delay-inducing features such as fare gates.  Ease of connection varies a lot from one situation to another based on factors that are hard to model -- not just walking distances but things like street crossings, vertical circulation systems (stairs or escalator?  elevator?), and of course fare co-ordination.  Improvements in other areas can make a big difference.  Smartcards, for example, are faster and easier to use than magnetic strip tickets, which must be manually inserted in a slot; these should make connecting easier.

So my guess is that it's hard to model transfer penalities very exactly.  But let me pass on the question to all the anonymous modeling professionals that are reading.  What's your answer to this reader's question?  If you're working in North America, do your transfer penalties consider very high-quality transfers, such as the cross-platform connections that often occur in European subways?  BART in the San Francisco Bay Area may know something about this, since they do have a cross-platform connection in Oakland, though it's only used for low-demand trip pairs and so may not offer sufficient robust information.  Agencies that do a lot of timed-transfer among buses, especially at island stations where no street crossings are required, may also know something about this. 

Modelers!  If you're not comfortable posting a comment here, send me an email, and I'll use it anonymously.