One of the most influential planning ideas to emerge from the late 19th century was that of the Garden City. Ebenezer Howard, in his book Garden Cities of To-Morrow proposed constructing these new towns in the outer orbit of metropolitan London. The aim was to fuse the best of the city and the country.  Several were realized, including Letchworth (pictures 1 and 2) and  Welwyn Garden City, (pictures) which I had the opportunity to visit in 2006/07. The idea became a foundation for many subsequent new town plans in the UK and influence places in the US like Columbia, Maryland. It today can be seen in a way as a ante-cedent to the New Urbanist movement. Places like Kentlands in Maryland are not complete Garden Cities, but certainly share many elements.

The idea was carried forward into Garden Suburbs, smaller units that were not as economically independent. Hampstead Garden Suburb (picture) is the original example of this development. It is lovely, and very expensive.

The phrase Garden Streets occurred to me at some point. What would this mean? In one sense, we can think of complete streets, that function for all users, not just motor vehicles. These typically have various lanes, for pedestrians, for trees, for drainage, for bicycles, for buses, for cars.  Alternatively it might be a shared street, one where the modes were not channelized, but floated freely amongst each other. But neither of those in themselves really get at the core idea.

The phrase also brings out the idea of formal or naturalistic landscaping, as one envisions from a Boulevard in a neighborhood designed by Frederick Law Olmsted.  In London, the term apparently refers to streets where any unpaved (and some paved) areas are intensively landscaped by neighbors, guerrilla gardeners, as shown in the attached YouTube video.

I think this meaning is closer, but too literal.

Instead, if we bring out the original sense of Garden Cities, we want to fuse the best aspects of town and country. The best country roads, with their naturalistic landscaping are places we want to drive, ride, or walk. The best city streets  with their more intensive use, still create interest if we see places we enjoy walking past because they look, sound, and smell interesting. A Garden Street fuses the best of both creating a street that is desirable to be on, because there is something interesting to see, either nature or an intense and interesting urban environment.

So the Garden Street doesn’t adjoin non-descript blacktop for storing cars, or chain linked fences, or anything that lacks beauty. Instead it aspires to the aphorism that the Journey is the Reward. The Garden Street is not traversed simply to get from here to there, but because it is a preferred place to be, the Garden Street invites you and encourages you to travel on it. It successfully competes with the screen in front of you as place to be.

Some examples are below. Three are shopping streets, two are residential. They are not perfect illustrations (Nara could be lusher), but they are places one wants to be walking in, streets one wants be on, rather than through.

Delft Woonerf

Nara shopping street

St. Anthony Main, Minneapolis

Chatswood, Sydney

Glebe, Sydney

Christopher Alexander wrote a brilliant essay in 1965: “A City is not a Tree“. Long interested in Alexander’s work since graduate school in Berkeley, I recently re-read the piece which has been packaged in a 50th anniversary volume. The original article is available online free. There have been numerous other papers that have commented on various aspects Alexander’s piece, I can’t list them all, it has been cited over 1000 times.

Alexander criticizes new towns, notably my home town, Columbia, Maryland, for being treelike in its conception, rather than what he terms a semi-lattice, but we would more informally call a mesh-like network. The neighborhoods belong to villages, the villages are part of the city. The neighborhoods, following an element of the Radburn plan, are isolated, that is, one cannot go from one neighborhood to another without being on a village street. That’s not to say there is no through traffic, there is, because the neighborhood network has more than one outlet.

But it’s not simply the street network that is tree like, retail is also tree-like. The neighborhood center might have a convenience store (7-11 or Wawa), the village center would have a grocery and 10-20 smaller stores. Town Center had the Mall in Columbia with department stores and over 100 shops. Perhaps Walter Christaller would be proud that Central Place Theory was not merely descriptive, but also prescriptive.

Finally the schools were tree-like. The neighborhood elementary school fed the village-level Middle and High schools.

In practice it was not so tree-like. As a resident of the neighborhood of Bryant Woods in the Village of Wilde Lake, my mom could go shopping at a supermarket at Joseph Square shopping center in the Village of Harper’s Choice. It was only another mile down the road. Later as a resident of Longfellow neighborhood, I could open-enroll into Wilde Lake Middle School. And of course not every neighborhood got an elementary school, not every village got a Middle or High School, and the boundaries were overlapping. So while the stylized schematic drawing may have looked treelike from the perspective of an architect a few thousand miles away, it was not treelike in practice on the ground. See The Next America Revisited for my take.

I don’t believe the planners envisioned it would be so tidy — though better to start out tidy and let entropy emerge rather than start out chaotic and hopes it self-organizes into an aesthetically pleasing environment. Rather my impression from reading a lot of the documents and having lived there and hearing talks from Rouse company officials and so on is that they believed that treelike street networks reduced through traffic, just as planners favor traffic calming today. They believed shopping should be organized into centers, rather than sprawled out uncontrolled along streets, and they should be spaced to be closer to residents. They believed local government is somewhat hierarchical (national, state, county, city) and that village was an organization unit that had some value to regulate things at a more local level than the city (Columbia is not technically a city, it’s just a home owners association, though it is a Census-Defined Place and the second largest in Maryland, after Baltimore, just as was foretold in the 1960s). They believed kids should walk to their neighborhood school, so the neighborhood should be the right size to support the school, which should have X students for pedagogical and cost-efficiency reasons, and ideally students would walk to their middle and high school too, but that middle and high schools should be larger. So the hierarchy was a natural way of organizing that.

But even if Columbia is innocent of being as treelike as Alexander feared (and certainly some new towns were more treelike), the suburbs are certainly more treelike than cities. My students have measured the “treeness” of networks, introducing the metric in Xie and Levinson (2007) Measuring the Structure of Road Networks. For instance in Network structure and the journey to work: An intra-metropolitan analysis (under review) by Pavithra Parthasarathi and myself, we see that treeness is not surprisingly higher at the suburban edges of the metropolitan area than in the center, though it declines as we see rural areas, where the sparser network is also more mesh or grid-like. (See figure)

Still, sometimes the city is a tree, or at least aspects of it are. In particular, many networked physical infrastructures are better organized as trees, especially if they require a large capital investment (like a waste water treatment facility). Similarly, the stream and river valleys are naturally organized as hierarchies. Transit networks are also often more treelike or radial than roads, and while may eventually evolve into ring-radial system, don’t generally start out that way. See Roth et al. 2012.

Clearly social connections should not be assumed to flow in a way that maps directly to the physical layout of the network, all other things being equal, you are more likely to know your neighbor than a randomly selected person farther away. Yet, in a modern world with migration and telecommunication, you are likely to know someone specifically who is not on your block and to not  know everyone on your street. Growing up, my mom’s friends were scattered across Columbia, not just in her neighborhood. ‘Community without propinquity’ was first identified by Berkeley Planner Mel Webber, and certainly applied in Columbia as it does everywhere, where people could meet based on any kind of interest, not simply the desire to live on the same street. The physical form of the city does not represent how the city works, but more importantly the plans do not determine how the city works. People and their relationships are affected by their environment, and reshape it to suit their needs.

I posit several Axioms about the hierarchy of roads.

Axiom 1: Some roads should be fast

The aim of transport is connecting people with destinations. They can connect with more destinations if they can do so in less time. Ceteris paribus, faster roads will take less time. Without loss of generality, let’s call these roads highways.

Axiom 2: Some roads should be slow

Some roads serve neighborhoods and have traffic that is not just motor vehicles. Ceteris paribus, slower roads are more likely to ensure safety [both reducing the probability of a collision through higher reaction times and reducing the impact of a collision should one occur], a high quality of life, and increased interaction within the neighborhood. Without loss of generality, let’s call these roads streets.

Axiom 3: Fast roads (highways) attract traffic from slow roads (streets)

In general, people prefer to spend less time traveling, and will spend less time on faster roads. These roads will attract more people. There will be net reductions in traffic on streets that are made slower and net increases in traffic on roads that are made faster.

Axiom 4: Urban design, congestion, safety, and funding problems arise when streets and highways are confused.

People, who are soft and move slowly, do not mix with vehicles, which are hard, when they move fast. If people feel unsafe they will avoid the place. Streets functioning as highways and managed by higher levels of government will be redesigned to be highways, — what Charles Marohn of Strong Towns calls “stroads” — destroying their street function.

Further trying to move highway levels of through traffic on roads initially designed as streets with lots of access and at grade intersections is a natural misfit that will result in local congestion. At least this limits the amount of through traffic. Traffic and demand comprise a negative feedback system, more traffic slows speeds –> slower speed lowers demand –> less demand reduces traffic.

Axiom 5: Without strict controls, properties will try to gain direct access to highways.

Many streets started out as highways in previous generations with earlier technologies.  They were once crossroads that attracted businesses and became a place. This is the dual or mirror of the “Stroads” problem, in analogy, we might call them “Reets“.

While this origin story is not of itself a problem, the road should be designed for what it does, and what we want it to do, not what it once did. Highways with traffic are attractive places to open businesses. The US Highway System (the national system before the Interstate, which still exists) was plagued with this problem, once freeflowing roads were subject to steady speed deterioration as new motels, gas stations, restaurants, and stands emerged to exploit the traffic. By design to overcome this problem, the Interstate was more regulated in this regard, and was instead a limited access facility.

Axiom 6: Successful streets will attract more traffic.

Streets that have lots of local activity will encourage vehicle traffic as people seek to take advantage of the activity, and park their vehicle nearby. This does not justify “upgrading” the street through widening, which takes out the very elements that made it successful in the first place.

Axiom 7: The Hierarchy of Roads is an emergent process.

Even in the absence of central planning, a hierarchy of roads would emerge. Some roads will become more important than others just because of randomness, geography and topology, and positive feedback effects. Local roads naturally serve more local traffic, and we can distinguish the importance of roads by the source of their users. While A City is Not a Tree as Christopher Alexander said, it does have hierarchical features.

New automated vehicles can be better regulated than mere humans. There will also be a new Cambrian explosion of vehicle forms which are specialized for markets, especially in urban areas where mobility as a service is plausible. This is a huge infrastructure opportunity. We  should redesign our road hierarchy with these axioms and the possibility of slow vehicles becoming mainstream or at least standard. We should think about developing an interconnected slow vehicle network so that small neighborhood vehicles (think souped up golf carts) cannot not only travel within neighborhoods or on campuses, but between adjacent neighborhoods, without attracting longer distance traffic, where slow and fast vehicles need not mix.

There should be interesting designs for this, which are not today’s standard recipes, since this is as much at the level of network design rather than road design.

Noted architect and designer, Christopher Alexander, in The Timeless Way of Building (1979) wrote:

There is one timeless way of building. It is a thousand years old, and the same today as it has ever been. The great traditional buildings of the past, the villages and tents and temples in which man feels at home, have always been made by people who were very close to the center of this way. It is not possible to make great buildings, or great towns, beautiful places, places where you feel yourself, places where you feel alive, except by following this way. And, as you will see, this way will lead anyone who looks for it to buildings which are themselves as ancient in their form, as the trees and hills, and as our faces are.

In contrast, the great transport networks of the past eschewed the local beautiful places. They were made by people detached from the places these links served. They had to be, as the networks connected many places, and aimed to do so efficiently.  Though these networks paths are ancient, modern roads are built upon the travels of earlier indigenous populations or even animal trails, following what may seem today to be obvious convenient corridors. These corridors traded off the initial cost of construction for a reduction in long term travel times. Time savings measured often not in minutes per day, but millions and billions of minutes over centuries.  Many of these routes connected timeless places with each other and went through wilderness or later farm land.

With the advent of the railroad, the highway, and later the superhighway, networks, particularly, but not only, urban networks subsequently not only connected, they disconnected. They disconnected timeless places with themselves, severing places and obliterating one community for the gain of other communities. This was the modernist program, it was a reaction to timeless earlier pre-industrial paths which did little to disrupt local communities (though there was the inevitable complaints about early turnpikes and canals as well). But once scale became relevant, removing local access in the name of removing local friction ensured there would be tension between the needs of the neighborhood, village, or town and the needs of the region. The road would not only benefit the region as a whole, it would specifically disbenefit the local, who would bear the costs of severance and negative externalities, but share none of the access. This was certainly overdone, but that doesn’t mean none of it was worthwhile. There is value in faster connectivity, we measure this in travel time savings or land costs. Modern society would be impossible with the fast well-connected networks that enable the safe and efficient movement of people and goods. It is harder to determine how much value was lost by forced relocation and breaking the fine-grained social and economic networks in the neighborhoods like St. Paul’s Rondo.

Many newer projects try to reduce these impacts, for instance by boring under rather than bulldozing through communities,  (tunnels like Boston’s Big Dig, Seattle’s Alaskan Way, and parts of Sydney’s WestConnex are examples), but because of the new additional costs, these newer projects also are no longer efficient, their initial costs will never be recovered by future benefit, so we must question why they are constructed in the first place.

Transport corridors rarely bring joy. It is seldom that the journey is the reward. We certainly can do better in this regard, but we also must accept transport is a derived demand, and depends on the desire to go from one place to another. Destroying places to connect places is a strange way of achieving this end, but in the real-politic of planning, some places and people are more valued than others. It recalls everyone’s favorite planning villain, Robert Moses, who said something to the effect that “If the Ends Don’t Justify the Means, What the Hell Does?”

My urbanist friends mostly hate skyways [and that’s just Bill Lindeke] [Streets.mn has 13 pages of posts about skyways. This blog has a few as well].

A dictionary says:
sky·walk  (skī′wôk′) n. An elevated, usually enclosed walkway between two buildings. Also called skyway.

I will not comment on the use of skyway vs. skywalk, that’s just like Ramp and Garage.
While I point out that streets steal urban activity from the skyway system, they seem to feel the converse is more relevant. Yet who is to say the street level should be for people not cars? Why should humans lower (one might say degrade) themselves by letting mechanical vehicles share their space. Why shouldn’t they rise above, as Leonardo DaVinci would have them do (Figure #0)?

Certainly, it cannot be roofs that urbanists object to. Almost all of them live in shelters with roofs. They all advocate roofs for their mass transit vehicle. So what is special about the short trip between their shelter and their vehicle, that it must remain unroofed.

Further it cannot be the lack of vehicles, many urbanists like pedestrian zones so long as they are dominated by pedestrians. (Jeff Speck and others seem to want cars in their shopping districts though).

Perhaps it is their tubular nature? Maybe urbanists hate tubes (and gerbils?). (In Atlanta, I have heard the skyways referred to as “Honky Tubes“, so there are clearly racial overtones). They are a bit minimalist, not the lush environment some may seek. But that is simply a design choice.

Perhaps it is elevation? But most urbanists think something like the Vancouver SkyTrain is a good thing, and support transit with grade separation so it can go faster. Why not people? [I fully understand not liking forcing pedestrians onto a pedestrian bridge as is common in China, so that walkers and cars are separated, but the pedestrian must climb and descend a staircase, but that is not the case here]

Perhaps it is ownership? But most American cities grew rapidly under an era of private transit (in the Twin Cities through 1969), so what is public vs. private space is also ambiguous. Streets are more clearly public, but if I let people pass through my buildings, seems a good thing for the public, no? If they were all publicly owned, would it be okay then?

The question  “what is a skyway?” cannot be easily resolved with words alone.  These Figures (1-3,5) from Vienna, Austria, Figure 4 from Stevenage, England illustrate the problem.  Figure 1 is what urbanists have in mind. But what about Figure 2, Figure 3, Figure 4, Figure 5. When does the cavity under a bridge become a tunnel?

Why are 1 and 2 bad but 3, 4, and 5 good?

London Bridge is another example, the other way about. It is a skyway of sorts, a bridge over a river with buildings on either side (though not at the entrance to the bridge).

Pedestrians without the bridge would need to swim, ferry, or walk on water. The pedestrian traffic attracted business, so it went from a typical bridge for movement (a skyway over the main transport artery in London) to a mostly-enclosed bridge with shops. Is this good or bad?

The Washington Avenue Bridge over the Mississippi River is now truly multimodal, with a lower deck for cars, buses, and LRT, and an upper deck for pedestrians and bicyclists, with an [rotting, smelly, but warm] enclosed section for pedestrians. Is that deck a skyway? Obviously the aesthetics are no London Bridge, but is it inherently bad, or just poorly executed?

This was published as Transportation Diversity as Insurance  on the Strong Towns blog on January 29, 2016

Diversity is insurance against risks. Diversification of investments is often suggested in personal finance. The claim is diversification reduces your potential downside loss. (Logically, it also reduces your upside gain.) The appropriate degree of diversification depends on your tolerance for risk.

More generally, there is a cost to insurance. It may turn out the risks you were insuring for did not happen. You might buy fire insurance, and never face a fire. In that event, the insurance premiums were money you could have spent elsewhere. For others – who lose homes, they get back more than they put in. On average, with a mutual insurance system, there is a slight loss due to administrative overhead, but the cost is worth the benefit if the large losses due to a fire, multiplied by their probability, are worse than the small but certain losses of the insurance premium. The probabilities of various events are well understood by insurers, and large risks are pooled, and then pooled again in a re-insurance market.

In transportation, we often talk about resilience. From a resilience perspective, diversity is a good thing. If one kind of thing fails, perhaps the other kinds of things will not.

Path diversity on networks has recognized and measurable value.  If one link fails (a bridge collapse, a sinkhole, a major crash, etc.) and is closed, others can pick up the burden. There may be stresses on the system which show up as congestion, but at least connectivity can be maintained.

Modal or technological diversity is useful. If the bus system’s drivers go out on strike, people can walk. If gasoline becomes expensive, people can take a train. If all cars are recalled because people are suddenly horrified they kill 35000 people a year, travelers can ride a bike. Again, this is limited by the amount of available capacity in the alternatives, and in practice most people cannot take the train in the US, at least not tomorrow, but it provides some type of technological redundancy.

So the question in transportation is whether network and modal insurance policies are worthwhile. We will never know for sure until after the fact. Yet it is not hard to imagine the kinds of risks that occur. We see link failures regularly, so know that path diversity is good. We see that link failures are worse on more fragile systems like limited access freeways and subways, and so the penalty we pay for faster average speed is lower reliability. We have seen technology failures, from the (policy-imposed) “oil shortages” of the 1970s and price shocks of the 2000s, to transit strikes, to vehicle recalls. One could imagine that Lithium, for example, will be the new scarce element in a world of battery-electric vehicles. If not that, something else. Scarcity is not eliminated just because oil is replaced.

All of which is to say don’t put all your eggs in one basket. We need different types of redundancy, choices in transportation modes and paths, multiple possible destinations that serve similar types of purposes, the ability to do things in person or remotely. The more alternatives we have, the less vulnerable we are to any particular type of failure. But we also cannot economically justify empty buses or empty roads because something might happen.

Slowly, the surface transportation sector is re-recognizing the advantages of connected streets networks, certainly for pedestrians and bicycles, but also for motorized vehicles. The advantages of multiple technologies are less clear. In the extreme, school buses can be used for evacuation, pools of buses can be moved from one city to another in the emergency (unless you left them to flood), and so on (though train cars are not as compatible between cities as they should be). We are slowly recognizing that the empty seats in a car on most trips are redundancy that can be exploited, with services like UberPool and LyftLine.

These are types of conversations that are seldom heard in surface transportation, but are common in aviation. When a flight is cancelled, an airline tries to route its passengers. It has a redundant network. The alternative paths (flights) are seldom as convenient, and may require a transfer — or worse for the airline — booking on a competitor, and will take longer, and passengers will grumble, but eventually the passenger gets to her destination. The airline will not generally rebook you on a bus or train (though I have been bused to a final destination when an airport was closed due to fog).

We have a lot of resilience now. There are low cost solutions to get more. These are conversations that Strong Towns should be having, thinking about investments that are flexible and adaptable, rather than brittle, and solutions that work under a range of conditions, not just a single set of assumptions.

In September of 2014, I wrote One Way to Deal With a Desire Line, describing the University of Minnesota’s attempt to deal with a desire line by planting a tree in the middle and placing concrete curbs to reroute traffic, costing pedestrians several seconds a day each. That tree died, as documented in A Tree Dies in Minneapolis, or ‘One Way to Deal with a Desire Line’ Revisited.

Like the King of Swamp Castle in Monty Python and the Holy Grail whose castle sank into the swamp, the University has planted another tree. But this time, it is reinforced, with an almost invisible rope line.

That will teach pesky pedestrians trying to get an education and reach classes on-time to take the straight line path that used to be there but was changed because someone once saw a bicycle on the Scholars Walk.

[I know “Empire” was the 2nd movie in the original trilogy, and this is the third post in a series. But unless I want to make the University the hero in this saga, I can’t make an Episode VI reference yet.]

Recently I found myself seeking refuge where no island granting refuge exists. Probably starting the crossing later than I should have, I crossed University Avenue half-way before my walk signal went to solid red, stranding me between the tracks of the Green Line (I could have illegally run in front of the cars, but one never knows).

I waited an interminable amount of time, for which I could have accepted a gap, playing Frogger. I would have if I had more information about where cars were, but couldn’t see well because of line of sight and cars in the turn lane.

A train approached from the left of me. A train approached from the right of me. I don’t exactly know how much space is between the trains, but not terribly much. The train to the left of me blared its horn (so loud I can hear it from more than 1/2 mile away), afraid I might not see it and become another statistic. I moved slightly forward. It passed (without braking as far as I could tell). The train to the right of me blared its horn. I moved backward. It passed (also without braking).  Fortunately they did not pass simultaneously.

Because of me, MetroTransit has now emblazoned the non-refuge area between the tracks at signalized intersections on the Green Line with a “Do Not Wait Here” marking.

Obviously, pedestrians are flawed for being so fool-hardy as to be pedestrians, or trying to cross a street on the blinking “don’t walk”, or just being slow, or distracted. But I am not the only one.

Clearly there is also a design flaw in the signalized pedestrian crossings failing to understand human actions, which a spray painted template will do little to alleviate. There is a flaw in traffic signals that do not recognize there is a pedestrian in motion.  Such a marking is, literally, the least they could do to address this problem.

The recommended approach seems to be:

Step 0. Don’t cross University Avenue.

Step 1. If you do cross University Avenue, then don’t get stuck in the median of the tracks.

Step 2. If you are stuck in the median at a red light, then pray.

(Actually, you probably would stand where the foot steps are, since that is in the middle, but then it says, do not wait here).

If you do not wait here, where are you supposed to go, in front of the train?

What if there were a lot of people on the island, not just a few. There might not be enough space. Would the train stop then? I am not convinced this has actually been thought through.

Cross-posted at streets.mn.