Human Transit

walking in america

Tom Vanderbilt at Slate is doing a series this week at Slate.com on the crisis of walking in America.  He ties it to a range of issues in public health.  It's also an essential part of providing more efficient (and therefore abundant) transit systems.  

The first installment is here, the second here.  

san francisco: winning speed and reliability battles

Major San Francisco transit lines take longer than they did a century ago, as they have been obstructed by traffic and slowed by heavy passenger loads using (until recently) inefficient pay-as-you-board methods. A New York Times piece by Zusha Elinson lays out the statistics.  

(It's important to clarify, right away, that this has nothing to do with streetcars as a technology.  You could easily be misled by this subtle bit of anti-bus bias:

In 1920, the F-Stockton streetcar carried passengers from the Financial District at Market and Stockton Streets all the way to the Marina at Chestnut and Scott Streets in a zippy 17 minutes. Today a very similar trip on the 30-Stockton, the successor to the F-Stockton, takes a half-hour if the stars are properly aligned.

In general, streetcars replaced by buses have slowed down more, over the last century, than those that remained streetcars, but that's an expression of how much more was invested in streetcars than in buses.  The main lines that use the Market Street Subway -- J through N -- have picked up or shed just a couple of minutes from their 1920 times, even though back then they ran on the surface along Market St (about 3 miles) while now they're in a subway, effectively functioning as rapid transit.  No such improvements were made for streetcars that became bus lines, so of course their performance deteriorated more.  In fact, the 30-Stockton relies heavily on maneuverability in unpredictable Chinatown traffic; a streetcar in exactly the same traffic, unable to move around obstacles, would be even slower and less reliable.)

The real message of this story, though, is the need to have a conscious intention about the speed and reliability of transit.  Highway planners ruled the late 20th century with their clearly defined notion of "Level of Service" or cars, which mowed down opposition through its simplistic A-F letter-grades.  Just after 2000, the Transit Capacity and Quality of Service Manual sought, at first, to claim this same authority-through-simplification for transit.  But while the TCQOS is a spectacular reference guide, few in the business believe that a single A-F score can capture the many important ways that transit succeeds and fails.

My own work in this area has always advocated a stronger, more transit-specific approach that begins not with the single delayed line, but rather with the functioning of an entire network.  Don't just ask "how fast should this line be?" which tends to degenerate into "What can we do to make those forlorn buses move a little faster without upsetting anyone?"  Instead, ask "What travel time outcomes do we need across this network?"  Or turn it around: How much of the city needs to be within 30 minutes of most people?  -- a question that leads to those compelling Walkscore travel time maps, which are literally maps of individual freedom.

A network speed standard would identify necessary speed standards for each service type, but especially for the Frequent Network, because high frequency means greater impact of delay -- both on passenger freedom and the agency's bottom line.  We* used this approach in a Seattle Transit Plan study about 7 years ago:

1.  Define the Frequent Network (every 15 min or better, all day, every day), including any segments that are "Rapid" (faster with fewer stops)

2.  Define the policy operating speed standard for each product (frequent local vs rapid)

3.  Map the existing scheduled speeds on each segment against this standard, creating a map with screaming red segments meaning "deficient."

4.  Prioritize interventions to improve transit speed based on those deficiencies.  

This is quite different from a classic cost-benefit approach in which we count the riders currently on a segment and assign value based on their total travel time saved, because it acknowledges that (a) a dysfunctional segment is probably driving away customers regardless of how many are on it now and (b) the outcome is the network, not just a single line.

We had a lot of success with this in Seattle at the time.  Once the deficiency map was drawn, engineers noticed segments that they hadn't identified as problems before, and went to work on fixing them.  Note too that the method cleanly separates problem from solution.  Don't start with what you think is possible.  Start with what you need.  Define the absence of what you need as a citywide problem that affects the whole network.  Then fix those deficiencies.  If you're going to go to war with three businesses over "their" strip of on-street parking, you're more likely to break through the "big agency attacks struggling small business" frame if you're defending the entire city's transit system.  

Remember: a line is only as reliable as its least reliable point, and a journey through a network is only as reliable as the least reliable of its lines involved.  So one localized problem affecting speed and reliability (such as stops too close together) actually affects a vast area, and drags down public expectations for an entire network product.  If it costs the agency money (as slower service always does) then it's also a direct detriment to the overall abundance of transit service.  That's the frame in which you win battles over three on-street parking spaces, a signal phase, or even an entire tranist lane.

San Francisco's Transit Effectiveness Project is, to a great extent, the culimination of exactly this thought process.  I remember in the 1980s or early 90s a time when Muni proposed to eliminate just one consequential bus stop;  17th & Mission.  The story became: "Big, bad transit agency launches personal attack on the people and businesses at 17th & Mission."  The TEP has worked to change that conversation, emphasizing that on high-frequency services, the speed of every segment is part of the whole city's transit outcomes.  The same process has made it easier to do a range of other locally-hated citywide goods such as removing parallel routes that were too close together.  

Does your city's transit system have a similar project underway, one that moves beyond route-by-route analysis and looks at how every speed/reliabilit deficiency harms the whole city's transit system?

 

*I was with Nelson\Nygaard at the time.  The project was the City of Seattle "Urban Village Transit Network" study of 2004, which became a foundation of the Seattle Transit Plan.

stop spacing: risks of multiple patterns

In a recent post on stop spacing, I quoted an eloquent defense of very closely-spaced stops based on the needs of mobility-limited persons.  This view is unfortunately in tension with the need to move stops as far apart as possible to increase the speed and reliability of operations, and thus attract more passengers.

I was surprised at how many comments suggested that the answer is to provide a mixture of local-stop and limited-stop or "Rapid" services.  This is absolutely the right thing to do on the extremely major streets where you can afford very high frequency (say, every 10 minutes or better) on both patterns.  Most New World cities have just a handful of these streets.  Examples include Mission and Geary in San Francisco, Broadway and 41st Avenue in Vancouver, Western Avenue in Chicago and Wilshire in Los Angeles.  Key features of these streets are (a) very high demand supporting two frequent services and (b) relatively long trips, so that speed advantage of a rapid stopping pattern outweighs the longer walking time it may require. 

But if you can't afford high frequencies, overlaying local-stop (every 200m or less) with Rapid or limited-stop service (every 800m or more) can be really unsatisfying.  Should you wait 11 minutes for a local at your stop, or walk to a Rapid stop 400m away where the next bus comes in 14 minutes but might be faster?  Those are the uninspiring choices presented to a customer when the frequencies are only, say, every 15 minutes but two patterns are being offered. 

When you consider the major streets that support frequent locals plus frequent rapid services, Seattle's long and busy Aurora Avenue might come to mind, but in fact, King County Metro abolished that pattern a few years ago, creating instead a single stopping pattern so that they could run the highest possible frequency.  That's the key.  Especially for trips of under 10 km or so, waiting time easily overwhelms in-vehicle time in determining door-to-door travel time.  So in those cases a reasonable "compromise" stop spacing -- not as close as senior/disabled advocates want, nor as far apart as speed advocates want -- is actually the fastest at getting everyone where they're going.

Another approach, which I advocate looking at, is to accept that the constituency for very closely-spaced stops may also accept poorer frequency.  If you look at the part of a route that is halfway between two Rapid stops, and thus most dependent on the local stops, and you then subtract all the people there who are willing to walk 400m to the rapid stop, you end up with a fairly small number of people.  So perhaps locals should be less frequent than rapids.  Transit agencies sometimes try to be neutral about this, carefully calibrating local vs rapid service based solely on current ridership.  But in fact, transit agencies have a strong reason to prefer rapids: faster service is cheaper service to operate, because transit vehicles complete their cycles is less time, and we pay drivers by time, not distance.

But it's definitely not adequate to say that we can resolve the conflict between close and wide stop spacing simply by running two separate lines on the same street.  We can in a few places, and if public transit had a lot more money we'd do it in a few more.  But transit agencies need a stop spacing policy that works for the more ordinary street, where you can afford maybe 10-15 minute frequency on just one line.  That means just one stopping pattern, so we have to pick one. 

 

dissent of the week: impact of wider stop spacing

Moving bus stops further apart achieves a range of benefits in speed and potentially frequency, as I've argued here and here.  Zef Wagner at Portland Transport recently laid out a similar case in the Portland context.  The post and most comments are worth reading, but I wanted to quote this dissent from commenter Cora Potter. 

Please keep in mind that you have to weigh any time/cost savings of stop consolidation with providing adequate mitigation for people with barriers to accessing transit stops (disabilities, cognitive barriers that require clear landmarks, etc).

Shuffling these riders off to LIFT [demand responsive paratransit for disabled persons] is not a cost effective solution. The average LIFT ride costs nearly $30 (one way). Even with a conditional eligibility system, you run the risk of increasing costs to the point that you might actually end up with more operating funding deficits than gains. In addition, while LIFT is a complimentary service, meant to be comparable in timing and experience for the consumer, there are tolerances to the system built in and a LIFT trip is usually longer, less direct and less convenient in that it requires an advance reservation. The ability to access the fixed route system is usually the least restrictive and most convenient means of travel for people with disabilities who can reasonably access a transit stop.

When you raise the bar for reasonable access by spacing stops at .25 mile, or 4 blocks or greater, you start significantly limiting what a person with barriers to walking or cognitive barriers can accomplish and make it far more of a challenge for them to reach a stop in a reasonable amount of time, or with a reasonable amount of challenge. The difference between walking one block in the cold and rain vs. walking three blocks in the cold and rain can present a huge challenge to a person who can not walk at a 3 mile per hour pace, and is more sensitive to cold temperatures due to normal aging.

So - just keep in mind that wider stop placement, particularly for bus service, will exclude a segment of the population from accessing fixed route. You need to weigh the gains in convenience for people who have few or no barriers to accessing transit with the social and financial costs of excluding the people who do experience barriers to access. My personal opinion is that everyone loses when older adults and people with disabilities are excluded from fixed route by design. You might gain 3 minutes and the sense that you're getting somewhere faster - is that really worth service cuts on other bus lines to offset the increased costs for ADA paratransit? Is it really worth socially isolating people with disabilities? And, with the aging of the population, we really need to start taking the needs of older adults seriously and not constantly tune our system to serve just the needs of commuters.

A quibble: I disagree with dividing the population into "older adults" with "commuters," as Cora does in the last sentence.  The consituency for larger stop spacing is basically anyone who wants to get where they're going as soon as possible, and who is open to walking a bit further in order to achieve that.  This is not everyone, but it's a larger group than "commuters," who are people making rigidly scheduled trips to or from work or school. 

But I agree with both the practical and ethical dimensions of the comment.  The mobility issues faced by older and disabled people are real and the costs of serving them with paratransit are high.  I also believe that allowing older people to become socially isolated is both economically and ethically unacceptable.

On the other hand, it's very, very hard to organize the mobility limitations of small, scattered numbers of people into facts.  In the early 1990s, when US transit agencies were struggling to implement the Americans with Disabilities Act, no issue was more vexed and emotional than eligibility for expensive paratransit services.  For example, ADA is clear that age, by itself, is not a disability -- an important insight because people are not only living longer but remaining able-bodied longer.  The process by which a local government assesses people's disabilities is obviously highly emotional for the individual in question and challenging for all concerned. 

A similar issue applies to bus stops.  When we move bus stops further apart, lots of people complain, and people with mobility limitations complain bitterly.  But given the high cost of the close stop spacing, how should those claims be assessed?  In some transit agencies, the default policy has been: "If anybody complains, cave in."  I'm not ashamed of suggesting that transit agencies be more forceful in articulating the tradeoffs, which requires educating their elected officials about what's at stake.  Cora's done an excellent job of articulating one side of that tradeoff.

I'd also note that in Europe and Australia, stop spacing is wider than in North America.  In Europe, many stops also have major infrastructure that signals their permanence.  Everyone, whatever their mobility limitation, works with that.  The result is that service runs faster and more reliably.  So from that perspective, this is partly a question about how to transition to that outcome.  It could be done most peacefully if it happened over decades, but ours is an impatient age, and transit agencies are under too much pressure to wait that long.

Part of why this is less of a problem in Europe, I'm guessing, is that the permanence and infrastructure of many stops signals clearly that you should take them into account when deciding where to live.  If an older adult can anticipate becoming dependent on public transit in the future, the location of transit stops should be part of their location decision.  This, to me, fits into a much larger agenda of insisting that everyone who makes a location choice -- especially about where to live -- should be required to acknowledge the transit impacts of that choice.  Today it's still common to encounter the other sequence, in which someone (a) signs a lease or deed of sale or development agreement and then (b) yells at the transit agency because the service isn't what they desire. 

So as usual, I don't have an answer, but I do think the question needs to be seen as geometrically inevitable, which means that those who disagree with us have a rational and ethical basis for doing so. 

basics: walking distance to transit

The question of walking distance in transit is much bigger than it seems.  A huge range of consequential decisions -- including stop spacing, network structure, travel time, reliability standards, frequency and even mode choice -- depend on assumptions about how far customers will be willing to walk.  The same issue also governs the amount of money an agency will have to spend on predictably low-ridership services that exist purely for social-service or "equity" reasons.

Yesterday I received an email asking about how walking distance standards vary around the world.  I don't know the whole world, but in the countries I've worked in (US, Canada, Australia, New Zealand) the view is pretty consistent:

• If you have to choose a single walking distance standard for all situations, the most commonly cited standard is 400m or 1/4 mi.  Europe tends to be comfortable with slightly longer distances.
  
  
• However, people walk further to faster services.  (Rail advocates are more likely to phrase this as "people walk further to rail".)  This doesn't have to be a sociological or humanistic debate, though urbanists often frame it that way.  If you are a rational and informed actor seeking to minimize travel time, it often makes sense to walk more than 400m to a rapid transit station rather than wait for a bus to cover such a short distance. 
  
  
• Although the common standard is 400m or 1/4 mi, we all know that this cannot possibly be a hard boundary.  It makes no sense to assume that if you live 395m from a bus stop you'll be totally happy to walk that distance while your neighbor, who lives 405m from the same stop, will be totally unwilling to.  Obviously, the relationship between distance and willingness to walk is a continuous curve without sharp breaks.  This has to be said because our language often forces us to create the illusion of sharp breaks, e.g. when we say something like "people are generally willing to walk up to 400m to transit."

Finally, it's remarkably hard to sift data into a form that produces unequivocal guidance on the question.  For example, the leading US guide on transit planning, the Transit Capacity and Quality of Service Manual, offers only this:

(Source: TCQSM Chapter 3, Appendix A, p. 3-93.  Discussion and version in US units is on p. 3-9.)

This survey-based graph shows the breakdown of local bus passengers by the distance they walked to get to the service.  As you'd expect, few people walk more than 200m in downtown Washington, DC because in such a densely served area, few people would need to.  In low-density Calgary, at the opposite extreme, many people have to walk fairly long distances.

But extrapolating opinions from behavior is a tricky business.  It's hard to reason from how far people walk to how far they're willing to walk.  To do that, you'd have to determine whether each rider would be willing to walk further than he actually has to walk.   You'd also have to speculate about each rider's available options.  If 1/10 of Calgary's bus riders walk 600m or more, does that mean they're willing to?  Or does it mean that these people are so lacking in good alternatives that they feel forced to walk that far?  (The difference between "high income" and "low income" Washington DC suggests that range of options does have something to do with it.)  Sociologists and demographers can have a field day parsing this question, but they're unlikely to come up with an answer of such statistical certainty that it definitively sweeps the question aside.

So we approximate.  We generally assume that 400m is a rough upper bound for slow local-stop service, and that for rapid-transit (usually rail) we can expect people to walk up to 1000m or so.

But when we try to apply these rules of thumb, we hit another hard issue (or at least we do if we're willing to acknowledge it).  Are we talking about true walking distance, or just air distance?  Over and over, in transit studies, you'll see circles around bus stops being used to indicate the potential market area, as though everyone within 400m air distance is within 400m walk distance.

Remember this graphic?

In both images, the red dot is a transit stop and the red circle is an air-distance radius.  If you draw 400m circles around stops based on the assumption of a 400m walking distance, you're implying that the whole circle is within walking distance.  In fact, even with the near-perfect pedestrian grid in the right-hand image, the area within 400m walk (outline in blue) is only 64% of the red air-distance circle.  With an obstructed suburban network like the left-hand image, it can be less than 30%.

Obviously, the market area around each stop should really be defined by the walkable area, which requires a knowledge of the local pedestrian network.  That requires a complete GIS database of every walkable link in the community -- an extremely detailed task that few jurisdictions have been willing to attempt until recently.  Even in Canberra, Australia, which is known in the business for the extreme richness of off-street pedestrian connections, no reliable database of them was available for modelling purposes as recently as last year.

Still, if you don't have such a database, it should be easy to adjust the walking distance standard to reflect the problem.  If you know you have a good street grid, then you can just adjust the radius to reflect the area within 400m walk.  In the right-hand image above, do the math and you'll figure out that if the radius of the red circle is 400m, then a circle whose area is the same as that of the blue diamond -- the actual area in walking distance -- would have a radius of 319m.  So if you want to roughly model the actual radius that arises from a 400m walking distance, and you have a well-connected street grid, draw a circle 319m in radius.  That doesn't give you the correct boundaries of the area -- it's a circle rather than a square -- but it's a far better approximation than just drawing a 400m circle.   I have never actually seen this done, and I'm not sure why.

One reason might be that secretly, we transit planners all want people to walk further.  After all, most transit planners don't want to just passively respond to current behavior.  If they did, they'd all be highway engineers.  Most transit planners believe in the importance of shifting behavior in more sustainable directions, and see both transit ridership and walking as deserving encouragement through intervention.  They are also aware of the public health benefits of walking.

But we have a more vivid motive to encourage walking.  The nature of the transit product is such that if we could stop less often, assuming longer walk distances, we could achieve both better running times and reduced operating cost; the latter could be reinvested as higher frequency.  So the two most fundamental determinants of transit travel time -- running time and frequency -- both depend on our assumption about walking distance.

With such basic things at stake, it's understandable that planners are always looking for ways to push walking distance wider.  That may be the real reason that generations of planners have chosen to approximate a 400m walk with a 400m circle, even though every pedestrian knows how absurd that is.

I prefer to just have the argument in simpler terms.  In Canberra, we pushed the walking distance standard from 400m to 500m, not because people were calling us demanding to walk further, but rather because we looked at how much more frequency and speed we would achieve, and the ridership that could attract, and decided that 100m of radius was a small price to pay for such benefits.  It comes back to that graph near the top of this post, showing how far people walk to transit in different cities.  There's no definitive authority for a 400m standard as opposed to 300m or 500m or even 600m.  Yes, if you pick a bigger radius you'll lose riders from the outer edges of the radius, but on the other hand, you may buy so much travel time and frequency that your ridership goes up.  As with everying else in transit, it depends on what you're trying to do.

comments of the week: ideal stop spacing is 400m?

Zoltán:

My experiences in Leeds and Baltimore confirm the validity of a 400m standard for stop spacing. Rarely do you get to experiment with reducing or increasing stop spacing, but we can look at the sum of the experience of the two cities.

In Leeds, there have been a number of routes, normally small single-deck buses running every 30-60 minutes, that have stopped frequently and taken local roads to penetrate various neighbourhoods better than the frequent, relatively fast buses on the main arterials.

These have pretty much all disappeared with time, because people always proved willing to walk about 400m to the main arterials, which is about the furthest you're ever expected to. My experience of occasionally catching one of the slower local routes is that I would be the only passenger.

So, this demonstrates that people really are willing to walk to speed and frequency.

Meanwhile, in Baltimore, buses do stick to the main arterials. But they stop at every corner, just like the streetcars before them, which in Baltimore is about every 120 metres. And hell, are they slow - from Catonsville, MD to downtown Baltimore, I frequently spent 50 minutes to an hour to travel 8 miles that can be driven in about 20 minutes.

What's more, it's an uncomfortable ride, because the bus pulls violently to the corner at every corner, to keep the hell out of the way of traffic. And that's actually the problem with the frequent stops in Baltimore - while boarding time is a bit more complicated (though there's a fixed element to people getting up and making their way out of the bus, and people waiting for the driver's nod to start boarding), you can basically multiply the time spent waiting to pull out back into traffic by the number of stops.

So what you have is a slow service, and by that virtue, a less frequent service, because one bus can make fewer trips. So, if people will walk to speed and frequency where delivered by different routes, then we can assume that people will also walk to speed and frequency on existing routes when that's achieved by means of widely spaced stops.

In thinking about this sexless but profoundly consequential issue, you may want to refer back to this post, which clarifies the concepts of coverage gaps and duplicate coverage areas.  (See that post for more explanation of this figure.)

Balancing these two considerations is the essence of the stop spacing task.  Closer stop spacing means smaller coverage gaps but more wasteful duplication of coverage area.  So a lot depends on the local land use.  If there's more stuff along the transit corridor than in the coverage gaps, that argues for pushing stops wider.

The European HiTrans guides suggest 600m for stop spacing in busy areas where demand is high and local access is the intent.  In general, Europeans and Australians are willing to go wider than North Americans in a similar setting. 

So why on earth does any transit agency that aims to compete with cars put stops as close as 120m??  Well, these things creep up on you.  If ridership is so low that you won't be stopping at every stop anyway, close spacing doesn't present much of a problem.  But once ridership reaches the level where you're stopping at every stop, close spacing requires you to stop more, and thus run more slowly, to serve the same number of people. 

On the tradition of very-close North American spacing, John offered an interesting speculation:

"But right now, a lot of transit (in North America especially) seems designed to compete with walking, rather than with the car. Do we have the balance right?"

I think the balance is off, and I think it's largely a legacy of the streetcar era, when transit only needed to be faster than walking to draw a huge mode share. In that situation, minimizing walking distance made sense. Then the competition changed when cars came along and average trip distances increased. The streetcars were removed, but nobody ever bothered to change the stop spacing. Now transit isn't time-competitive, and in most cities it serves only the transit-dependent and niche markets like express routes to the CBD.

Is very close stop spacing on North American bus systems really so old that it predates the car, and therefore reflects the competitive situation between transit and its alternatives as it was around 1910?  That would be some sort of record for failure to adapt: a habit that has survived for an entire century after its obsolescence. 

Obviously, too, many North American services aren't trying to compete with the car; they're social services intended only for the transit dependent, and in those cases travel time is presumed to travel less.  But be careful about taking that attitude too far.

dissent of the week: stop spacing and transit's multiple goals

Ben Smith from Toronto defends closely-spaced stops, on my post on imagining cities without mobility, which suggests the need to focus more on widely-spaced "rapid transit" stops. 

I'd like to be the devil's advocate for a minute and defend somewhat tighter stop spacing. Think of transit as an elevator: You're on the 7th floor and decide to walk up to the 8th floor, and feel that having the elevator stop there is a waste. However, someone who is getting on at the ground floor may also want to get off at the 8th floor, so having a stop there isn't a waste.

I'm not trying to say that transit should stop at everyone's doorstop, but there is a case for having a more local oriented transit with SOMEWHAT frequent stops. However, if demand and density is having your transit vehicle stop every 100m with a large number of passengers boarding at each stop, then it makes sense to use a higher-order transit vehicle with wider stops.

The easy answer to this is that if you can walk from the 7th floor to the 8th floor to get from one to the other, you can take the same walk from an express elevator that stops only at the 7th.  But that may be too easy. 

I personally am willing to walk as far to useful rapid transit (for a long trip across the region) as I will to a final destination.   My personal mode choice algorithm (as far as I understand it) is that I want to (a) minimize total travel time and also (b) get exercise and (c) avoid waiting and especially passive uncertainty.   So I'm as willing to walk the same distance to a place regardless of whether that place is my destination or I'm planning to catch rapid transit there.

Does my philosphical viewpoint on this depend too much on my own abilities and preferences?  In other words, am I assuming that secretly everyone wants to be just like me?  And if so, am I doing this more than anyone else does?

Obviously, as always, we need to recognize a portion of the population that can't walk far, but at the same time we have two widely articulated policy goals that push the other way:

1. health goals that support encouraging people to walk if they can. 
2. sustainability goals that require transit with highways rather than with walking and cycling, which means competing for the trip that is well beyond most people's walking distance

Those considerations lead me to a provisional view that the main prioirty for public transit investment needs to be rapid transit that's worth walking to, not slow transit that stops near everyone's door and that looks intimate and friendly in a New Urbanist mainstreet.  That was the core of my argument with Patrick Condon.

Obviously, there need to be mobility options for senior and disabled persons who have greater need for short-distance transit.  There are also other logical markets for short-distance trips where very high frequency is possible (recalling that waiting time is often the disincentive for short trips) such as downtown shuttles. 

But right now, a lot of transit (in North America especially) seems designed to compete with walking, rather than with the car.  Do we have the balance right?

UPDATE!  Ben Smith, the author of the dissent, has had an epiphany!

basics: the spacing of stops and stations

I've written before about the unglamorous but essential struggle over the spacing of consecutive stops or stations on a transit line.  It's an area where there's a huge difference in practice between North American and Australian agencies, for reasons that have never been explained to me as anything other than a difference in bureaucratic habit.  In Australia, and in most parts of Europe that I've observed, local-stop services generally stop every 400m (1/4 mile, 1320 feet).  Some North American agencies stop as frequently as every 100m (about 330 ft).

(Already I can hear someone asking "but how many blocks is that?"  Well, it depends on how long your city's blocks are.  Even in San Francisco, where block length is wildly variable, I've heard people insist on asking for a standard in blocks, which is complete nonsense.  Living on a short block doesn't make you more entitled to a bus stop near your house.)

San Francisco is at it again, trying to rationalize its stop spacing on some of its most frequent lines.  So I thought I'd take the occasion to lay out some stop spacing basics.

The geometry of stop spacing works like this.  Every stop or station has a walk radius, the area from which most people would be willing to walk to a stop.  In the most idealized world, which is where some planning happens, this radius defines a circle around each stop.

How big is the walk radius?  Actually, different people are comfortable walking different distances, so a truer view of these circles would be very fuzzy, gradually dissapating further out from the stop. You don't want to look at that, though, and it's hard to do geometry with it, so transit planners generally observe that the walking distance that most people seem to tolerate -- the one beyond which ridership falls off drastically -- is about 400m (around 1/4 mi) for a local-stop service, and about 1000m (around 3/5 mi) for a very fast, frequent, and reliable rapid transit service.  (I, personally, will walk further than this.  You may not be willing to walk even this far, but as an approximation the 400m rule for local service seens to work pretty well.)

But of course, the circle is what the walk radius would be if you could walk absolutely anywhere in the area, including diagonally, through buildings, etc.  In the real world, we walk along some kind of network of streets and paths.  The design of that network is therefore a crucial element of walking distance, which means that it's also relevant to stop spacing.  Consider these two drawings, from this post:

These happen to both be in the Seattle area, but your city probably contains examples of both of these network types.  The car-oriented network on the left is full of obstacles to the pedestrian, so the actual area you can walk to (the blue network) is less than a third of the ideal radius (red).  On the other hand, in a dense grid (of streets and other pedestrian links), like the one on the right, maximizes the possible walking distance.  The actual area within walking distance is diamond shape, i.e. a square rotated 45 degrees from the transit line.  Almost two thirds of the ideal radius is in walking distance in such a network. 

Note how these things are connected in chains.  Street network determines walking distance.  Walking distance determines, in part, how far apart the stops can be.  Stop spacing determines operating speed.  So yes, the nature of the local street network actually affects how fast the transit line can run!

How do we decide about spacing?    Consider the diamond-shaped catchment that's made possible by a fine street grid. 

Ideal stop spacing is as far apart as possible for the sake of speed.  But of course people around the line have to be able to get to it. In particular, we're watching two areas of impact:

• The duplicate coverage area is the area that has more than one stop within walking distance.  In most situations, on flat terrain, you need to be able to walk to one stop, but not two, so duplicate coverage is a waste.   Moving stops further apart reduces the dupicate coverage area, which means that more unique poeple and areas are served by the stops.
  
  
• The coverage gap is the area that is withing walking distance of the line but not of a stop.  As we move stops further apart, the coverage gap grows.

We would like to minimize both of these things, but in fact we have to choose between them.  Close stop spacing means smaller coverage gaps but larger duplicate coverage area.  Wide stop spacing means the opposite.

If we are doing a local-stop service, and we assume that people will walk 400m, then the diamonds are 800m wide.  If we then set the stop spacing at 400m, the diamond on the left will touch the one on the right.  In other words, every point on the line will be in a duplicate coverage area.  The coverage gap, meanwhile, gets smaller.  In fact, if the stop spacing is the same as the walking distance standard, the coverage gap's area and the duplicate coverage area are the same.  Play with this yourself until you believe it. 

So does that make this the right answer?  Not necessarily for two reasons: 

1. Which is worse, creating duplicate coverage area or leaving a coverage gap?  It depends on what you're trying to do.  In fact, this is arguably connected to the tension between designing for ridership and designing to meet social service needs.  If you care mostly about the latter, you want to minimize the coverage gap so that everyone has access, and you don't care that much if the resulting line is slower and therefore less attractive to other riders.  On the other hand, if you want to maximize ridership, you'll worry more about the duplicate coverage gap, because in addition to representing wasted coverage, closer stop spacing means slower operations, which are both more expensive to operate and less attractive riders; so you'll tend to want to push stops further apart.
2. If this is like most urban fabric, there's more stuff (residents, jobs, activities) close to the transit line than far from it, which means that there's more stuff in the duplicate coverage area than in the coverage gaps.  So if that's true, then we're facing again the eternal danger of maps: they invite us to misread pure area as though it represents the stuff that matters.  If we set the stop spacing at 400m, the duplicate coverage area is the same as the coverage gap area, but if there are more residents, jobs, and activities in the duplicate coverage area, the two aren't really in balance.  If you valued duplicate coverage and coverage gaps equally, you'd ideally plot the actual locations of residents, jobs, and activities, and then push the stops just far enough apart so that the amount of this stuff in the duplicate coverage area was the same as that in the coverage gap (though again, as per point #1, there's no particular reason that these two things should be the same; you can strike a balance anywhere based on your goals in running the service).

So that's the geometric tradeoff that governs stop spacing in flat terrain with well-connected street networks. You can see how variations in terrain would shift the calculation.  If the transit line is climbing a steep hill, you can make a case for stops closer together:  Walking downhill is usually easier than walking uphill, so some people will value having two stops so that they walk walk downhill to one to depart, and walk downhill from the other one as they're returning.  That's why stop spacing is often a bit closer when going uphill or downhill. 

In general, though, we always want to push stops as far apart as possible while still providing enough access, both for speed and also because the fewer stops we have, the more infrastructure we can afford to provide at each.  But the limits of our ability to widen stop spacing is defined by the geometry I've outlined.

Finally, while I've been talking about local stop service with a walk distance of about 400m, the entire calculation is exactly the same for any distance.  For example, if we are placing rapid transit stops, and we think that the maximum walk distance to them is about 1000m, we can set the stops 1000m apart and end up with the duplicate coverage area that's the same size as the coverage gap.  Then we can argue about whether, in the given situation, we should push wider or narrower.

And of course there are all the other kinds of access: Park-and-Ride, Kiss-and-Ride, cycling, etc.  Still, the walk is the dominant factor in transit access potential, because even if you use a vehicle for access you're likely to be a pedestrian at the other end of your trip, and of course many people are pedestrians at both ends.  (The exception is when you take your bicycle on board, which will always be a problem at crowded times.)  Sooner or later, we are all pedestrians.

Finally here's a fun question to think about:  If you had two parallel transit lines, how might the stop locations on one of them affect the logical locations of stops on the other?  And what's the furthest apart that the lines can be (in terms of multiples of the maximum walking distance) for this consideration to matter?  Think about it before you look at the comments, because someone's probably written the answer there! 

streetcars vs light rail ... is there a difference?

Yonah Freemark at The Transport Politic proposes a curious definition of the difference between streetcars (trams) and light rail:

The dividing line between what Americans reference as a streetcar and what they call light rail is not nearly as defined as one might assume considering the frequent use of the two terminologies in opposition. According to popular understanding, streetcars share their rights-of-way with automobiles and light rail has its own, reserved right-of-way.

But the truth is that the two modes use very similar vehicles and their corridors frequently fall somewhere between the respective stereotypes of each technology. Even the prototypical U.S. light rail project — the Portland MAX — includes significant track segments downtown in which its corridor is hardly separated from that of the automobiles nearby. And that city’s similarly pioneering streetcar includes several segments completely separated from the street.

We're all prone to lash out at "popular understanding" now and then, often without citing a source for it.  I certainly know I do that.  But for the record, I don't think the dividing line between streetcars and light rail can usefully be drawn where Yonah suggests, based purely on the exclusivity of the right-of-way.

APTA's Streetcar and Heritage Trolley site, for example, defines light rail with emphasis on both exclusivity of right of way and stop spacing.  I want to suggest that the terms streetcar/tram and light rail will be most useful if we use them to refer to the prevailing stop spacing, not the exclusivity of the right-of-way. 

Light rail and streetcar technologies are, as a whole, more similar than different, but the terms as I hear them used belong to different categories of usefulness to the customer.  I use the term light rail to describe something that's at least attempting to be rapid transit, by which I mean covering long distances fast by serving fairly widely-spaced stations rather than closely-spaced local stops.  The term "light rail" was invented specifically for the contrast with "heavy rail," which is a competing alternative for the same relatively long corridors.  Light rail often makes closely-spaced stops right in downtown, and may thus serve a "streetcar" function there, but it does this mainly for the purpose of providing good access to people who want to use its higher-speed segments.    I refer to streetcars/trams only when I mean local-stop services, designed to do pretty much what local buses do.  (Such services are usually no faster or more reliable than a local bus.)

Exclusivity of right-of-way is an independent issue, but I think it's clearer to understand this as a consequence of the original usefulness distinction.  Longer trips are more sensitive to speed and reliability than short trips, partly because these trips don't have the option of walking.  If Portland's light rail line MAX doesn't show up at your suburban station, you're stranded.  If you're already downtown and the Portland Streetcar doesn't show up, you start walking.  A common complaint about transit in Melbourne is that the extensive tram system is still the main way of making some fairly long trips, such as between downtown and LaTrobe University, and it's local-stop operation makes it simply too slow to be widely attractive in such a market. 

Toronto, which already has very local-stop and slow streetcars downtown, is now proposing a "light rail" network called Transit City.  Their explanation of it begins:

Transit City is an initiative to build eight new Light Rail Transit (LRT) lines to neighbourhoods and areas currently not served by rapid public transit.

Toronto already has heavy-rail subways, so that's what locals will visualize when they hear "rapid transit."  The agency clearly wants people to think of these new lines as an extension of the subway system, not an extension of the inner-city streetcar system.   For that reason, they're insistently calling it light rail rather than streetcar.  The difference is first and foremost that the Transit City light rail will serve widely spaced stations, like the subway, not closely spaced stops, like the existing downtown streetcars.

This long distance service intention is what drives the insistence on exclusivity, which is why the long-distance intention, expressed first of all in stop spacing, is the more fundamental distinction.  If you're serious about trying to provide rapid transit service over a longer distance, such as between a city and its suburbs, you'll insist on exclusive right of way for the vast majority of the distance, sometimes with the exception of short segments downtown where the options are difficult.  Again, urban light rail services can look rather like streetcars as they run locally through downtown, but (a) their right of way is usually if not always exclusive and (b) they are mostly collecting/distributing trips that will use the fast segment, whereas on a typical streetcar/tram the local-stop service is the entire product.  Both of those features follow from the original intention: be useful for long-distance travel, at least into the downtown. 

The streetcars/trams that I know, both historic and modern -- in North America, Australia, and Europe -- are almost all local-stop.  A few may have some relatively rapid segments across parks or stretches of old rail corridor, such as Melbourne's Albert Park and Port Melbourne segments, but these are the exception.  They are usually also mixed with traffic for a large share of the distance, which means they are easily disrupted by traffic-induced delays.  It's common to see them take exclusive lanes where they're available, such as in medians of wide boulevards, but they are designed with the presumption that mixed flow is acceptable where exclusive lanes can't be found.  That's because (a) streetcars/trams are competing for short trips and (b) new streetcars especially are driven by a redevelopment agenda, where proponents are often frank that triggering the development outcome is simply more important that the usefulness of the service as transit.

Finally, when I suggest that stop spacing is the best way to distinguish light rail and streetcar -- and is already functioning this way in a great  deal of existing usage -- I'm not implying that everything is one or the other.  There are, as noted, streetcars that have short light-rail-like segments and light rail lines that have streetcar-like segments.  These terms define ends of a spectrum, in which a large share of examples are pure one or the other but there are many (especially in Europe) at various points or mixtures in between the extremes. 

I suggest that the most useful categories are those that refer to different kinds of usefulness to the customer.  Stop spacing -- wide stops for rapid operation -- makes light rail useful for longer trips, and that's the most critical usefulness distinction.  This is why you rarely hear about "light rail" vs "streetcar" debates for a specific designated corridor.  The two terms refer to broadly the same technology, but the length of the corridor, and the speed it requires, usually determine whether we're talking about rapid transit, in which case this technology's offering is called light rail, or more local-stop service, in which case this technology's offering is called a "streetcar." 

stop spacing: the endless, thankless, and essential struggle

When I first started working in San Francisco around 1990, a proposal to consolidate bus stops that are too close together would have been a battle between well-meaning transit staff in favor and angry senior citizens opposed.  And in the grievance-loving world of San Francisco politics, the angrier side usually wins.  So it's sign of how far transit advocacy has come in San Francisco that the continued efforts of the San Francisco Transit Effectiveness Project is getting such balanced feedback, seniors still opposed, understandably, but with transit and pedestrian activists cited in favor, politely and accurately explaining (as I explained here) that too-close stop spacing really slows down service.

“Taking out stops means Muni runs faster, which means more people take Muni, which means less cars, which means less potential for pedestrian fatalities,” Champsee said.  (Examiner)

Sure enough.  Fewer stops also means more people at each stop, which improves personal security and also justifies better infrastructure. 

Are your city's stops too close together?  If so, does your city have activists saying this?  San Francisco's standard is that stops should be around 800-1000 feet (250-300m), but 14% are still closer than this.  Most North American cities have much closer spacing, sometimes as little as 300 feet (100m).  Now and then there's a good reason: transfer points and senior-disabled facilities have to have stops.  But in most places I've worked stop spacing is cultural, a matter of agency or industry habit.  There's much to critique about bus service here in Sydney, but they are merciless about stop spacing on their major routes.  It's rarely less than 300m / 1000 ft.

Of course, there's one nagging virtue to excessively close stops.  They make it easy to walk down the bus route, so that you get somewhere even if the bus doesn't come, but can still catch it if it does come.  Sydney's the first city I've lived in where that's really hard; the bus catches me between stops that are too far apart to run to when I see the bus.  But then:  Do we want a policy to be predicated on making it easy to mistrust the service?  Or do we want one that will help make the service more trustworthy?