Human Transit

subway car configurations: a matter of taste?

Chicago Transit Authority is asking its customers how seating should be configured in its rail rapid transit cars.  Whet Moser has a good writeup in ChicagoMag.com.  Here are the choices:

The one on the left is "Chicago-style" seating, with most seats in pairs facing along the length of the car.  The one in the middle is "New York-style" seating, with most seats facing sideways.  The third is a hybrid.

Transit agencies commonly do surveys that imply that these things are just a matter of taste, as though they'll go with whatever their riders prefer.  This question is not just a matter of taste.  The left hand image has the most seats but the least capacity.  The middle image as the fewest seats but the greatest capacity.  Seats with their backs to the wall take up much less space than seats in pairs facing forward or back.  And of course, any seat takes up more space than a standee in a crowded car.  This is why really crowded subway systems inevitably gravitate toward side-facing seats.

So the question should be not whether you like the the configuration on the left, but whether you like it so much that you don't mind being left behind at rush hour because the train is full.  

The survey asks you which configuration you prefer, and which you like better in terms of "personal space."  But it doesn't inform the reader that the more forward- and back-facing seats there are, the more people will be left behind on the platform during the peak and the less ridership the system will be able to handle.

Almost all choices are tradeoffs, so when you ask the public their opinion, you need to explain what the real consequences of the options are.  (At least that's my firm's approach to public outreach!)

"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.    

in the pacific northwest, the romantic drama is on the bus ...

This really is too much fun.  From a scholarly study of the Craiglist "Missed Connections" section, where people express a romantic interest in someone that they saw out in the world.  You know, ads like this:

We were both on the max [light rail]--me heading to the Blazer's game and you on your bike. You overheard part of my conversation with my friend and were quite amused. I wanted to talk to you but then got pushed back by other riders. Email me if you remember that conversation and would like to grab a drink sometime.

So here, by state, is the location most often cited in "Missed Connections" ads (click to sharpen):

In rail-rich older urban areas, it's rail transit, of course, the subway or train or metro.  But in relatively rail-poor parts of the country, only Oregon and Washington find so much wistful romantic drama on public transit!  This is one of those slightly twisted points of "Portlandia"-style pride that makes me proud to be an Oregonian transit planner.  

vancouver: my tangle with a columnist over the broadway line

If you're interested in Vancouver and missed my "debate"* with Bob Ransford about Broadway rapid transit at Gordon Price's blog Price Tags, well, it's not to late to pile on.  It refers back to one of grand debates on this blog, the question of "Is speed obsolete?" raised by Patrick Condon.  Gordon says our debate* the most commented piece in the history of his blog, and it's generated fierce Twitter traffic.  Apparently, Bob and I will be on CKNW News Talk 980, "The Bill Good Show" on Monday (or maybe we're just taping it Monday).

The occasion appears to have been the Vancouver City Council's decision to endorse a complete subway under Broadway, which is not much of a surprise to those who've been following this for a while.  Bob criticized the project on development potential grounds, and as usual, I tried to broaden the question a bit beyond that.

* an often self-glorifying term that readers should view with suspicion.  In this case it refers to a published Vancouver Sun opinion piece periodically interrupted by my heckling.  It all happened very fast when Gord forwarded me Bob's article, knowing exactly how it would provoke me ...

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."

urban designers are from mars, transit planners are from venus

Just got home from the Congress for the New Urbanism Transportation Summit, which is trying to formulate transportation policy and advice from a New Urbanist point of view.

Over the last decade, the CNU has made great efforts to form a coherent view on transportation.  The organization's core has always been an architecture and urban design perspective that is very much about placemaking, and only secondarily about movement.  Much New Urbanism is about slowing everything down in urban environments, and while the goal of increased urban density means that ultimately travel distances are shorter, slower movement can also mean reducing people's ability to get where they're going.  For example, much of the idea that transit should be slower (e.g. Patrick Condon, Darrin Nordahl) has roots in early CNU thinking.  This in turn can feed the perception (unfair but not totally unfounded) that the pastel people in a New Urbanist rendering are more a hermetic cult of utopians than free actors in a complex society who need to get to meetings on time.

Initially, transportation -- specifically highway engineering -- was CNU's number one enemy, and this conflict still generates some of the best drama.  The summit this year featured a conversation between an AASHTO representative -- representing the view of State Departments of Transportation -- and a New Urbanist transport consultant, in which common ground was sought but lines in the sand were clearly drawn on both sides.  

So the CNU's efforts at leadership in transportation policy are a very important move.  Groups at the conference worked on issues such as cycling, functional street classification (sexier than it sounds), and the conversation of highways to boulevards.  I was in the group dealing with transit networks.

We spent much of our time thinking about the mutual incomprehension that plagues the relationship between urban designers and transit planners.  This issue is at the climax of my book Human Transit, where I look at famous examples of cases where supposedly transit-oriented developments were located in places where efficient and attractive public transit was geometrically impossible.  

Phil Erickson, of Community Design + Architecture, made two of the best points:

• Both sides of this incomprehension engage the other too late in the process.  As a transit consultant, I can certainly attest that I'm always hired too late to fix a development's transit problems, which were usually locked in at the stage of site selection or conceptual design.  I suppose you could say that transit agencies engage development too late, though ultimately it's the responsibility of a planning process to decide when to invite input from whom.
• Both sides assume that the other is more flexible than it is.  As a transit planner, I often suggest some adjustment to a development that would make transit vastly more effective, and am told that's not possible.  On the other hand, it's routine for a developer to assume that this bus line can just make a deviation to serve a development, without considering either operating cost or the effect on other customers trying to ride through that point.  Placemakers' demands that transit be slowed down on a certain segment raise the same issues: operating cost and reduction of a transit line's usefulness for through travel.

In the same "Mars/Venus" spirit, here are a couple of other reasons that this relationship is so hard:

• We are literally working in different dimensions:  Urban design is mostly about places.  Transit planning is about corridors and networks.  Transit planning can do little at a single site; transit functions only when you think of a whole long corridor -- made up of many places and situations -- as a unit, and even better when you think of networks comprised of corridors and interchanges.  One place where urban design and placemaking can work together with transit planning is at the level of the whole-city network, which is why integrated regional planning of land use and major transit corridors is such a crucial task, one that few North American urban areas even try to do.
  
  
• We live in different timescales.  Urban design is about something that will be built and completed.  Transit planning is about eternal operations. Transit planners may seem distracted by the love of building something too, but ultimately, it's all about service, which means operations. So the two sides tend to talk past each other about costs in particular.  The urban designer and developer are watching one-time capital cost, but the transit planner cares about eternal operating cost.  Developers often throw a little one-time money at a transit service, e.g offering to subsidize the first five years of operation, but the wise transit agency knows that sooner or later, the developer will be gone and this service will become their financial problem, especially if it's a service that they can see is unlikely to perform well.  

It was fascinating to watch this discussion, and to be a part of it.  Many more useful things were said, and I may pick up on a few of them in future posts.  Meanwhile, the first step toward overcoming a divide is to really understand why it is so pervasive, and that requires both sides to think about their deep assumptions, and why different assumptions follow from the nature of the other party's work.

A followup, based on comments on this post, is here.

a technophile wants my brain, and yours

I'm not sure if I should give this oxygen, but for the record: Randal O'Toole, the infamous anti-planning writer known for his blog The Antiplanner, has falsely implied that I agree with his critique of Los Angeles rail plans.  Not so fast.  If he'd read by blog, or my book, he'd know better.

Here's what he wrote today:

Portland transit expert Jarrett Walker argues that “we should stop talking about ‘bus stigma.’” In fact, he says, transit systems are designed by elites who rarely use transit at all, but who might be able to see themselves on a train. So they design expensive rail systems for themselves rather than planning transit systems for their real market, which is mostly people who want to travel as cost-effectively as possible and don’t really care whether they are on a bus or train.

This view is reinforced by the Los Angeles Bus Riders’ Union, and particularly by a report it published written by planner Ryan Snyder. Ryan calls L.A.’s rail system “one of the greatest wastes of taxpayer money in Los Angeles County history,” while he shows that regional transit ridership has grown “only when we have kept fares low and improved bus service,” two things that proved to be incompatible with rail construction.

So because I defended buses from the notion of "bus stigma", O'Toole assumes I'm a bus advocate and therefore a rail opponent.  This is called a "false dichotomy," identical in logic to George W. Bush's claim that "either you're with us or you're with the terrorists." 

(In a related move, he insists that you can't improve rail and buses at the same time, a claim directly disproven by the last decade in which LA Metro developed the Metro Rapid buses [and Orange and Silver Line busways] concurrent with rail extensions.) 

In fact, I maintain and encourage a skeptical stance toward all technophilia -- that is, all emotional attachments to transit technologies that are unrelated to their utility as efficient and attractive means of public transport.  To the extent that the Bus Riders Union is founded on the view that rail is some kind of adversary, while the bus is the unifying symbol of their cause, I view them with exactly the same skepticism that I would bring to the elite architect who implied that we don't need buses because she'd never ride one. 

Some technology-fixated minds just can't imagine what it would be like to be agnostic about technology and to care instead about whether a service actually gets people where they're going efficiently.  To put in terms that conservatives should respect -- I'm very interested in transit that efficiently expands people's freedom, and whatever technology best delivers that in each situation or corridor.

I'm also interested in how all kinds of transit fit together as networks, because this is essential if we're to offer a diverse range of travel options to each customers.  Everyone who becomes emotionally invested in bus vs rail wars -- on either side -- closes themselves to the idea that different technologies can work together form a single network. 

Like many pairs of polarized enemies, the Bus Riders Union and certain bus-hating elites both endorse the same fallacy.  In this case, both seem to believe that the most important purpose of a transit technology is to signify class categories, and that the key feature of their favorite technology is that it serves their class and not the other's.  Both experience cognitive dissonance when one suggests that maybe bus and rail are not enemies but complementary tools for different roles in a complete network designed for everyone, or that people of many classes and situations can mix happily on one transit vehicle, as happens in big cities all the time.

The idea that a city as vast and dense as Los Angeles can do everything with buses, no matter how much it grows, is absurd.  Drivers are expensive, so rail is a logical investment where high vehicle capacity (ratio of passengers to drivers) is required.

The only way the conservative dream (shared by Gensler Architects) makes sense is if you smash the unions so that all bus drivers make minimum wage, preferably from low-overhead private operating companies.  This is how transit works in much of the developing world, and the result is chaos, inefficient use of street space, and fairly appalling safety records.  Most experts I know who've immigrated from such places were glad to trade that for the transit they find in North America, whatever its faults.

It is absurd, too, to continue claiming that the Los Angeles rail program is "elite."  Go ride the Red Line to North Hollywood or the Blue Line through Watts and tell me if those services seem packed with "elites" to you.  When I ride them, I see the same wonderful diversity that I see on the more useful bus services, weighted of course by the characteristics of the neighborhoods we're passing through.

There's no question that some LA rail projects can be criticized for having been built where right-of-way was available rather than where they were needed, though the more you understand the political process the more you sympathize with the difficulty of those decisions.  But when self-identified bus-people attack rail, and self-identified rail people attack buses, they both sound like the lungs arguing with the heart.  There's a larger purpose to transit, one that we achieve only by refusing to be drawn into technology wars, and demanding, instead, that everything work together.

quote of the week: hopeful intentions of the u.s. federal transit administration

[In reading this, recall that mobility means "how far you can go" or "how much area you can cover" in a given time.  "Accessibility" or "access" means "how many economic, social, and recreational opportunites that you can reach" in a given time.]

"[The U.S. Federal Transit Administration (FTA)] believes improvements to both access and mobility are key features of a good transit investment. FTA agrees a measure that defines accessibility instead of mobility might be a better representation of the kind of benefits transit projects are intended to produce. As noted, however, it has proven very difficult to measure. Although it is relatively easy to specify a measure such as number of jobs within a specified travel time of a single location, creating a broader corridor or regional measure including calculations to and from multiple locations is more difficult and complex. FTA believes a measure focusing on project ridership will indirectly address access improvements since more people will ride a project that has enhanced access to jobs or other important activity centers. Focusing on the way a transit project can enhance an individual’s ability to get places, rather than just travel faster, is a desirable outcome of the evaluation process. FTA intends to continue to explore how best to do so."

The FTA's Notice of Proposed Rule Making [pdf] that
proposes to shift the criteria for funding
new transit projects from travel time to ridership,
a move that Socrates* had some questions about.
Hat tip to Susan Pantell for reminding me
of this passage. 

This is indeed hopeful.  I'll lay out a fuller argument on how this agenda might move forward in a coming post.

Question: When FTA refers to the difficulty of aggregating accessibility measures for everyone in a region, do you think they're referring to a logical problem (i.e. the stated task is logically or philophically incoherent), or a data availability problem, or some other kind of problem?  It certainly shouldn't be a processing power problem anymore.

* To anyone who suggests that I'm being grandiose in assigning my own thoughts to Socrates, I can only reply that (a) the dialogue in question is broadly consistent with Socratic method, which is Socrates's primary legacy, and (b) Plato made quite a successful career of ascribing his own ideas to Socrates, including many that were not at all consistent with Socratic method, and he doesn't seem to have come to much moral/karmic harm.  As long as a fiction is obviously a fiction, it's not lying, it's metaphor.  

one-way splits as symbolic transit

 Now and then I see a professional study of a transit line -- often light rail or streetcar -- that suggests that the two directions of service should be a little bit apart from each other, say on different streets, so that they "cover more area."

This is the clearest and simplest example I've seen of the conflict between symbolic transit and actual transit.  If you are creating transit for symbolic purposes -- say, to give the appearance of permanent mobility so as to stimulate development, then it's certainly true that separating the two directions, so that rails and stops appear on two streets instead of one, will spread that appearance over a larger area.

However, if you care about people getting where they're going, the one-way split reduces the area served by a transit line.  That's because for a two-way line to be useful, you have to be able to walk to both directions of a service.  The further apart the two directions are, the smaller the area (light blue) that will have a reasonable walk to both of them.

 

If you're wondering whether a project is about getting people where they're going or just appearing to do so, the handling of one-way splits is often a clue. 

Obviously, one-way splits for transit are often required by a one-way street pattern, but even in these cases, when we're planning for both legibility and ease of use, planners sometimes suggest combining the two directions on one street.  This can be done by giving transit a lane that allows it to travel against the main traffic direction (called a contraflow lane), so that although traffic is split between two streets all transit is on one.  That maximizes the area actually covered by the line, but of course, it may reduce the area that has symbols of being covered!