Tag Archives: urban planning

pedestrian level of service

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I had actually never heard of pedestrian level of service, but it appears to be just applying traffic flow modeling principles to pedestrian flow. It is intuitively appealing to me because you can just add pedestrians, cyclists, or whatever mode you want to a transportation model and specify which links in the network are open to which types of “traffic”. Theoretically, you could try to optimize the total flow of people from where they live to the places they need to get to, and not just maximize the flow of motor vehicles. Surely someone must have looked at this. A valid criticism, of course, is that these models can be short-term focused, even looking just at a single weekday peak hour and certainly missing longer-term dynamics like how infrastructure capacity and land use policy affect trip generation over time. Another criticism is that this engineering approach completely misses the quality of life aspects of urban design.

Pedestrian infrastructure assessment: Walkability vs. pedestrian level of service

This paper explores two of the most explored indicators for evaluating pedestrian infrastructure: walkability and Pedestrian Level of Service (PLOS). Walkability, typically used by urban planners, emphasises the qualitative aspects of the built environment, such as safety, comfort, accessibility and aesthetics, whereas PLOS, primarily employed by transport engineers, quantifies the operational performance of infrastructure based on pedestrian flow, density and speed. A systematic PRISMA-based literature review was conducted, covering 60 PLOS studies and 55 walkability studies were analysed in terms of definitions, contributory factors, data collection methods and modeling techniques. Despite sharing the goal of promoting pedestrian-friendly environments, these frameworks differ fundamentally in scope, purpose and methodology and are often applied independently. The findings indicate that walkability indicators vary in how factors are measured and allocated across dimensions. Moreover, walkability is treated as a “static” factor, both conceptually and methodologically. Relatively limited research examines how walkability changes over time (e.g., day vs. night) or varies across population groups. Conversely, PLOS generally excludes socio-spatial dimensions, a choice consistent with its original purpose rather than a methodological limitation. Some approaches attempt to incorporate subjective factors, but usually in ways resembling traditional walkability metrics. This study highlights the need for greater standardization in definitions and assessment frameworks, while also identifying challenges that complicate their practical applicability. Their complementary use can significantly enhance the design, evaluation and planning of pedestrian infrastructure, supporting more livable, sustainable and inclusive cities.

Will autonomous vehicles increase congestion?

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Yes, autonomous vehicles will increase vehicle miles traveled by about 6% according to at least one set of serious researchers. They say this might not sound like much, but it will be enough to exceed capacity and cause massive traffic jams. Now, I’m sure these are serious transportation researchers who have thought about all the things I mention below, but I’ll mention them anyway:

  • Autonomous vehicles shouldn’t need to maintain the same “safe following distance” human drivers are supposed to maintain, which is based on slow human reaction times. So the autonomous vehicles should be able to travel closer together (from front to back) than human drivers at a given speed, and do this safely.
  • They also should be able to travel closer together from side to side. Our standard 12-foot travel lanes allow a lot of space for human drivers to weave wildly and unpredictably from side to side, which of course we do. Keep your arms, legs, heads, and pets inside the vehicle at all times, please!
  • Most vehicles are parked most of the time, so that much more space is required for vehicle storage than for moving vehicles. Not only this, but enormous amounts of empty space are required between parked vehicles for human drivers to maneuver the vehicles in and out of storage. Computers drivers will need much less space for maneuvering and will be infinitely patient.

So put all this together and I think that even if VMT increases, the amount of physical space required for vehicles could be massively reduced. This could be a big win for people, cities, and the environment. If VMT increases because people are able to get around more easily and cheaply, including the elderly, disabled, and parents pushing strollers, in all kinds of weather, this is a win for quality of life. I don’t see artificially restricting mobility as a win for people. I shouldn’t even have to say that reducing death and injury caused by vehicles by a factor of 10 or more is a moral and quality of life win.

Now, I am worried about urban and suburban sprawl getting even worse as it gets easier to get around. I am worried about air pollution and climate change. Add in augmented and virtual reality, and we might also come to care less and less over time what our cities look like to unaugmented eyes. I love compact, walking, cycling, and public transportation oriented urban form. One of the downsides of this form in the past has been a lack of green open space, but massively reduce the amount of space required for parking, and it will open up a lot of space in cities that we will then have choices of what to do with. So it really comes down to policy choices, and different places are going to make different choices, but I don’t see the technology itself as the root problem.

habitat area and fragmentation

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I gave a talk this week on a niche topic involving plant selection for stormwater management features like rain gardens in cities. I had just one slide on habitat connectivity and fragmentation as an interesting area for further research. That one slide generated a lot of interest. And it is an interesting topic. First of all, it has been looked at quite a bit in the design of nature reserves, but not so much in urban areas or areas with a mix of wild, agricultural, and urban land uses. And second, there is always the debate about whether focusing too much on connectivity metrics can detract from just preserving enough total habitat. The article below is an entry relevant to this question, relevant in the context of forests. In urban areas, in my view, this question gets flipped on its head. Fragmentation and disconnection is the de facto state, and can only be reversed on the margins. So the interesting question to me is what policy choices can make it the least bad. There is also the possibility that better policy choices in urban areas can reduce friction of (animal and plant) movement between wild landscapes, and even whether they can serve as relatively biologically functional islands in depleted agricultural landscapes.

Why controlling for habitat amount is critical for resolving the fragmentation debate

The need for a consensus on the effects of fragmentation per se is increasingly recognized (Miller-Rushing et al., 2019; Riva, Koper, et al., 2024; Valente et al., 2023) because deforestation continues and small forest patches are particularly vulnerable to destruction (Riva et al., 2022). If fragmentation per se reduces biodiversity, then policies should prioritize protection and restoration of large patches. If not, then policies should include all forest, irrespective of patch sizes (Riva & Fahrig, 2023). This would allow effective biodiversity conservation, even in human-dominated regions where no large patches remain, by protecting and restoring sufficient forest over a network of many small patches (Arroyo-Rodríguez et al., 2020).

U.S. transportation “wins” in 2025

Bloomberg has an article on progress in U.S. transportation policy and technology in 2025. My thoughts in brackets.

  • New bus lanes in a number of U.S. cities. [This is really a big win, when modern cities around the world are expanding subway and light rail networks? This “win” represents tiny, incremental progress or holding the line in our current reactionary cultural and political climate. Calling this a win is a pretty good indicator of where this climate stands.]
  • New York City congestion pricing. [This is an evidence-supported, objectively very good policy that probably all major cities should be following. The fact that one major city is able to do it against massive external opposition is an indication of our current reactionary cultural and political climate. One thing that makes this work in NYC, I believe, is that they have one municipal transit agency in charge of roads/streets/bridges, public transportation, and parking, and they also have a successful and powerful interstate transportation commission that coordinates well with that agency. I’d like to see some journalism on what the legislative and institutional barriers are to achieving this in other major cities, even if we were to eventually emerge from the current reactionary cultural and political climate. For example, in Philadelphia we have a state-chartered regional public transportation authority that operates buses, subways and trains; another interstate commission that operates bridges and some trains; a neighboring state-chartered authority that operates some buses and trains; a municipal authority (which has been state-controlled in the past) that regulates street parking and parking garages, and a municipal transportation department that designs/constructs/maintains most streets, although some streets are designed/constructed/maintained by the state transportation department. All these entities are mostly uncoordinated and certainly do not share revenue. So it would be virtually impossible to use parking and bridge toll revenue to cover public transportation costs, even though this would make total sense if the objective were to move people from point A to point B efficiently, safely, and cheaply. (Would this not be the objective of any rational transportation policy?) Could all these agencies be reorganized to look more like the NYC system? Planning and implementing something like that would be a heavy lift, but again I would like to know if it would even be legally possible or if legislation at the state level in multiple states would be required. State-level legislation in Pennsylvania to rationalize policies in the major metropolitan areas is virtually impossible in the current reactionary cultural and political climate…]
  • Automatic speed controls in cars. There are some minor wins allowing judges to impose this on people who have speeding tickets. This makes sense to me, but seems fairly small and incremental. I might be the only one looking forward to automating as much vehicle operation as possible. Let violations of speed limits and intersection signals be matters for your vehicle warranty or insurance company, not decisions of human drivers to take reckless risks or not.]
  • Legalizing small cars and golf carts on public streets. [I’m mostly for this. Vehicles designed for highway travel are the wrong way to get around inside cities. The problem is that you put these lighter vehicles on the public streets, and human beings in them are going to be hurt and killed by other human beings choosing to irresponsibly operate highway vehicles inside cities. They will also hurt and kill pedestrians on occasion. You need to either have separate infrastructure for the light vehicles, or have vehicles regulated or controlled by computers or passive means (see above). Advances in street design, construction and maintenance in the U.S. are so slow I find it hard to hold out hope that there will be big changes in the course of a single generation of humans. But technology is moving much faster so I am going to put more of my hopes for near-term progress in the technology basket.]

So there it is. I don’t have much hope for seeing widespread progress in subway, light rail, and modern street design and construction (with separate infrastructure and signals for pedestrians, light vehicles, and highway vehicles) in U.S. cities in the next few years. We can hope for slow, incremental progress on congestion pricing, parking pricing and policy, and passive speed controls for some vehicles. The rollout of automated, electric vehicles has been slower than I might have predicted 5-10 years ago, but it is happening. It is uneven because the barriers seem to be more legal/institutional/cultural/political than technological and this varies by location. And it’s not a straight-up red/blue divide because pro-big-business forces on the right are favoring automated vehicles at the same time reactionary cultural/political forces on the right and pro-labor forces on the left are opposing them. So this tension will just play out state-by-state and city-by-city for some time to come. Very slowly, we may realize that the demand to devote so much of our urban space to parking and maneuvering inefficient vehicles has decreased. This feels like it might take a decade or more and be obvious to most people only in retrospect. Overall, when Americans travel I think we will increasingly get the sense that urban conditions in our country are continuing to stagnate while European and Asian cities march into the future. Those of us Americans who don’t travel will be cocooned in reactionary cultural/political propaganda and will not realize life is improving elsewhere while transportation in our cities is stuck at a 1970s technology and safety level.

May the streets of our cities be soaked with less blood in 2026 and beyond!

medieval French towns

This (paywalled) Financial Times article has eye-popping pictures of French towns built in the 1200s and 1300s. Many of these still exist and are going strong today, and people love them. They were small (around a thousand people) and densely populated. They were generally built around a public square with a weekly market. At the time, the article says, feudal lords created the towns as a way of concentrating, controlling, and taxing people, in exchange for greater safety and quality of life. The feudal lord generally owned the commercial and industrial real estate, of course, but the article says this can be a model for development corporations today, with master planning and long-term ownership of business districts. Housing developers in theory can do their short-term thing but pay into these development corporations which are then set up in perpetuity to operate and maintain the commons. Sounds good in theory. Clearly the private markets don’t create the kind of green spaces, schools, etc. that people say they want but then vote against with their actual dollars and housing and transportation choices.

Lussan, Département Gard – aerial view

the problem with sprawl

This article from Strong Towns has a good explanation of why low-density development is not the answer to the housing supply issue.

this style of development works extremely well for a specific type of private developer… developers like Ross Perot Jr. are masters of the assembly-line approach: secure cheap land on the fringe, install infrastructure, and build tract housing as quickly as possible. At this scale, the profits are enormous, and the risks are low. The federal government provides generous support through mortgage guarantees, tax preferences, and highway spending, and buyers keep lining up for new homes.

But while the private sector gets the cash, local governments get the bill. Sprawling developments create long-term infrastructure liabilities—roads, water lines, sewer systems, schools, fire protection—that far exceed the revenue they generate. Local governments, which are really just collections of us acting together, are left trying to maintain and operate systems that are fundamentally unaffordable.

As Mayor Eugene Escobar of Princeton, Texas, put it, his town boomed with affordable homes, but now it’s struggling with traffic, overburdened infrastructure, and a lack of basic amenities. The city’s leadership is trying to build a real downtown, attract jobs, and create public spaces—but they’re doing it after the fact. That’s not planning. That’s triage.

Some suburbs seem to persist for long periods of time. But they are ones located within commuting distance of urban centers with high-paying professional jobs, and the zoning serves to keep the median income in those successful suburbs very high, and therefore able to support the very high infrastructure costs per resident or per square mile. There aren’t enough of these highly affluent people for all suburbs to work like this, so for every successful one there are many turning into slums.

What seems to be suggested instead is a gradual process of intensification from the middle out, so that populations, incomes, and tax revenues can keep rising over time as value is continuously created. This makes sense to me. I think there may be a more linear model though that could work for U.S. suburbs, where the intensification happens along a transportation corridor with progressively less dense development as you move back from highway. This way, you get a long linear downtown with access to transportation and other infrastructure at a low unit cost. People could live in relatively low-density neighborhoods if they want to and still not be too far from work, school, and inter-city public transportation. And these commercial corridors already exist in the form of arterial highways, water and power lines, big box stores and car dealerships separated by oceans of parking.

April 2025 in Review

Most frightening and/or depressing story: Maybe an irreversible methane tipping point is happening. This could be the scariest thing out there short of nuclear war.

Most hopeful story: 3-30-300 is a nice, simple idea. “you can see 3 trees from your window, your neighborhood has 30% tree canopy cover, and you are within 300 m of a half-hectare park.” Sure, you have to figure out some details and make some sustained effort over time to implement simple ideas. Still, not rocket science. Combined with the “15 minute city”, this is a pretty good urban planning philosophy that should be communicable.

Most interesting story, that was not particularly frightening or hopeful, or perhaps was a mixture of both: I made what I would consider a “common sense” trade policy proposal. “I generally support…free trade. But if we are going to trade freely, we need a safety net for people who are hurt. We could do this with generous unemployment benefits and retraining programs. We could help people relocate to places with jobs. We could provide much better communication and transportation infrastructure allowing them to commute regionally to places with jobs. We could educate their children so they are prepared for the jobs of tomorrow. We could institute a value added tax on our productive, growing economy and use it to provide services or cash to workers. We could invest even more in research and development to make our economy even more productive and growing. We could invest in neighboring countries to help them be more productive and growing, import cheap stuff from them, and reduce some of the migration pressure on our borders.”

https://homertree.com/blog/the-3-30-300-rule/

Planetizen’s top posts of 2024

There are a lot here. Quite a few have to do with housing, a topic I would be interested in brushing up on. A lot have to do with transportation, a topic I have just feeling complete and utter despair about, at least in the context of the United States and my particular city and state. One possible bright spot is congestion pricing in New York City. Congestion pricing just works, even though it is politically unpopular and counter-intuitive to many people’s “common sense”. Maybe people will notice that it solves some of the congestion and parking issues they like to complain about, and maybe it will slowly spread to other cities and states.

top urban planning books of 2024

I always enjoy Planetizen’s list of top urban planning books. My training is in engineering, but like almost everyone I am a citizen of an urban area, and besides urban planning is an umbrella that touches on many aspects of engineering, infrastructure, housing, the economy and the environment. Anyway, here are a handful of books that caught my eye. My commentary below doesn’t really have much to do with the books (which I haven’t read), but rather my off-the-cuff thoughts on the topics each book is nominally about.

  • Key to the City: How Zoning Shapes Our World by Sara Bronin – The tide of opinion seems to be against zoning at the moment, but it is just such a basic and important tool to try to shape the types of human settlements we want to live in, and that could be different for different groups of people. I think of private zoning and building codes as one half of the coin, and public infrastructure as the other, but I haven’t really seen a book that gives them an even treatment. Someone should write that book – maybe me, some day somehow?
  • Free the Land: How We Can Fight Poverty and Climate Chaos by Audrea Lim. “No piece of ground goes untouched, whether it’s private property, a public right of way, or government-owned open space.” Okay, maybe this one actually attempts something along the lines of what I mention above.
  • A Paradise of Small Houses: The Evolution, Devolution, and Potential Rebirth of Urban Housing by Max Podemski. Because I don’t really have a coherent personal theory of what is wrong with housing and the housing market in the U.S., but there is obviously a lot wrong and I would like to smarten up on this some day. But it pretty much seems to come down to needing more supply of housing whose market value matches the economic means of the majority of households, whereas there is a mismatch currently. Zoning is part of the problem. High rise living and public transportation could solve the problem if we wanted it to, but we just don’t seem to want that. Row houses and town houses with small porches, backyards, roof decks, and corner stores are a compromise in my view – these offer people more privacy and private outdoor space while allowing a pretty dense urban fabric to develop. But you just can’t mix this with universal private car ownership people, because geometry. Maybe autonomous vehicles will be the killer app that could eventually break this logjam, because they can move around in a more space-efficient way and go store themselves in out of the way places when they are not in use, which is most of them most of the time.
  • The 15-Minute City: A Solution to Save Our Time and Our Planet and Shrink The City: The 15-Minute Urban Experiment and the Cities of the Future. Relevant to the above. Basically a new(ish) way of explaining some of the concepts I mention above. I don’t think these ideas have penetrated the endlessly ignorant public discourse on “traffic” and “parking” just yet. Or is the problem just that geometry is not taught in a way that people relate to the actual physical universe?
  • On the Move: The Overheating Earth and the Uprooting of America by Abrahm Lustgarten. Right, so where are we supposed to live again? Of course, I want to sell my coastal property just before the real estate market wakes up to the fact that it is doomed – when is this? It also occurs to me that we better consider “the Americas” here and not just “the United States of”.
  • Radical Adaptation: Transforming Cities for a Climate Changed World by Brian Stone, Jr. Sounds a bit more technical than the one above. Please, let’s not turn everywhere into Singapore, which is essentially a network of air conditioned malls, offices and high rise housing connected by subway tubes. But you could pretty much build Singapore on Mars, or wherever, as long as you have some plan to get food and water to the people there (but this might be tricky in a “climate changed world”, eh?)
  • The Stadium: An American History of Politics, Protest, and Play by Frank Andre Guridy. The only reason I would read this one is that Philadelphia has been embroiled in a debate about whether to build a downtown basketball and hockey arena, and I would like to be a bit more informed on the issue. I walked by the one in Washington, D.C. the other week and it seemed to fit into the city fabric okay to me. Then again, what New York and Washington do well, Philadelphia has a tendency to do in a half-assed amateurish less good way about a decade later. And when we fail to implement proven solutions competently, we conclude that the solutions themselves were unworkable from the start.
  • Lost Subways of North America: A Cartographic Guide to the Past, Present, and What Might Have Been by Jake Berman. Speaking of Philadelphia, we have such a phantom system, including some stations that were built in anticipation of train lines that never actually got built. Thinking big is also no longer a thing, which is sad.
  • Human Transit: How Clearer Thinking about Public Transit Can Enrich Our Communities and Our Lives by Jarrett Walker. This is an update to an earlier book I haven’t read but would like to. Is this the book that all high school students or at least all undergraduate engineering and architecture students should read to have some basic literacy about transportation? Otherwise our mistaken ideas about how a functional transportation system could actually work will allow the auto-oil-highway-suburban sprawl propaganda machine uncontested dominance over our society and our land forever.
  • Killed by a Traffic Engineer: Shattering the Delusion that Science Underlies our Transportation System by Wes Marshall. Slightly unfair to blame the engineering profession alone for the evil auto-oil-highway-suburban sprawl monster I mention above, but some fair points here nonetheless. If you read the American Society of Civil Engineers code of ethics for example, you might think we would stand up to some of this rather than be the nails the monster uses to hammer the lid on our society. But we would have to wake up to the fact that the propaganda exists and is controlling our minds first, then pull the tubes out of our asses and get flushed out of the matrix before we could go to work.

If I sound a little bit salty when I think about transportation design, (lack of) maintenance and enforcement, and reckless driving and lack of respect for human life up and down our society, yeah I’m a bit salty!

why “free-flow” car sharing isn’t working in the U.S.

This article describes several attempts to create “free flow” car sharing services, where you can pick up and leave a car anywhere within a certain zone. This is in contrast to Zipcar’s “fixed model” where you have to leave the car where you found it. The article says the free flow model isn’t working well because the people it benefits most are lower-income people who do not otherwise have easy access to private or public transportation. But this market just does not have enough demand to cover the cost. This model is working well outside the U.S., and the article suggests one reason it does not work in the U.S. is the massive subsidies we have in place for private vehicle ownership with massive public funding for roads and parking. The car-highway-oil-sprawl industry propaganda is so entrenched that we can’t see these massive subsidies hidden in plain site. Take your red pills, people!

In October I passed the “car ownership free for 20 years” mark, which I am very proud of. I made it to the milestone through the stroller and car seat years, which was sometimes difficult. But I will say I have a Zipcar membership which I rarely use, and there are really two reasons. First is living in a walkable, public transportation oriented community. I simply don’t need a car most of the time, and I suspect the people who might currently be interested in car sharing are also the ones who value public transportation. But second, ride hailing has just gotten so convenient and it is much cheaper compared to Zipcar, so I really only use Zipcar if I am hauling something. It occurs to me that once cars can drive themselves (okay, they can now, but once the various institutional/legal/policy barriers are sorted) there will be less distinction between the two models, and car sharing will eventually go away. Public agencies can subsidize ride hailing if they want to, and I am actually concerned this will put downward pressure on the demand for traditional public transportation (buses, trains) and lead to doubling down on our poor low-density land use choices.