Tag Archives: urban design

exponential decay and park visits

Leave a reply

Exponential decay applies to a lot of physical phenomena, such as dissipation of sound for example, and interestingly the evidence suggests it is also a good model of human behavior in the aggregate. For example, people are more likely to visit a park near home, which makes sense, and they become less likely with increasing distance. And that likelihood doesn’t decline in a straight line but exponentially, which suggests to me it is better for urban quality of life to have many small decent parks rather than a few large great ones.

Exponential distance decay in urban park visitation: A comparative analysis of recreational mobility across 20 U.S. metropolitan areas

Urban parks are essential infrastructure for public health and environmental resilience, yet systematic comparative evidence on how distance constrains recreational access across metropolitan areas remains scarce. This study analyzes 60 million park visits across 20 U.S. metropolitan areas to establish mathematical relationships governing park visitation and their determinants. Park visitation universally follows exponential decay (V = αe-βd) rather than power law scaling, with exceptional model fits (R2 > 0.95) across diverse urban contexts. However, decay parameters vary substantially, from β = 0.090 (Minneapolis) to β = 0.211 (Detroit), creating a 2.34-fold difference in distance sensitivity. This variation produces markedly different accessibility patterns: residents in high-constraint cities experience 50% visitation decay within 3.3 km, while those in low-constraint cities maintain equivalent access to 7.7 km. Regression analysis reveals that transportation infrastructure, built environment characteristics, and sociodemographic factors collectively explain 56.3% of variation in median travel distance to parks. Transit proximity, street network design, and regional employment accessibility emerge as primary associations, while minority-predominant and car-free neighborhoods face compound disadvantages through both restricted mobility ranges and heightened distance sensitivity. These findings establish exponential decay as a consistent mathematical relationship for recreational mobility while demonstrating how local context shapes its parameters. For planning practice, uniform park service area standards may inadequately reflect actual visitation patterns, as the empirically measured half-distance at which visitation drops by 50% varies more than twofold across metropolitan areas. Calibrating park spacing to locally measured decay rates and coordinating green space provision with transportation investment could improve both the efficiency and equity of urban park systems.

I have one quibble, and I would be surprised if the authors didn’t think of it and control for it somehow. And that is the idea that car-free neighborhoods would be at a disadvantage in terms of park access. Now maybe this is true, but it seems to me the decay should be measured in travel time or cost (in the difficulty sense) rather than absolute distance. People who get around a neighborhood mostly by walking aren’t going to travel to a park three miles away, which is no big deal by car (if there is ample free parking on both ends, which is one reason the park has to be so far away!). But the people walking to a smaller nearby park might have an equally pleasant subjective experience than the ones driving. Or they might not. But my point is I can’t tell, at least just from this abstract.

Random Creative Commons licensed image that is loosely related to my post

e-scooter hate

Leave a reply

Here’s a Canadian e-scooter hit-piece. You definitely won’t find me on an e-scooter in Philadelphia, because both the outdated infrastructure and driver behavior make it much more risky than I could ever accept. But that suggests the solution: rethinking and modernizing infrastructure. E-scooters belong in the “bike lanes”, and bike lanes need to be modernized to accommodate all sorts of light personal vehicles. They need to be separated and physically protected from high-momentum vehicles designed for inter-city highway travel, and if they are combined with infrastructure for these high-momentum vehicles at all, they need their own signals at intersections so that the two are never, ever in conflict.

You need some enforcement, but we should remember that the core reason for all the traffic rules, licensing, registration, insurance, sobriety checkpoints, search and seizure, personal injury litigation, etc. is that cars are just so deadly. Yes, there are anecdotes of bikes and scooters running into each other and running into pedestrians and causing the occasional injury, but most of those are not going to be serious. So there is a question of how much we want to constrain personal freedom (as we do very significantly and appropriately with private cars) when it comes to much less dangerous forms of transportation (now, about those aggressive jogging strollers…)

I might allow autonomous golf carts traveling at low speeds (5-15 mph maybe) in the bike lanes, although today’s bike lanes are not wide enough for that. I might just ban private high-momentum human-driven vehicles from most streets and let the golf carts use them. Cities need this if forms other than cars are going to be viable forms of transportation in all kinds of weather for all kinds of people, and not just a from of recreation for the young and healthy. Of course, at this point the cyclists and e-scootists might decide they want to use the street too, and that might end up being okay. And then, especially if we don’t need so much space for parking as shared autonomous vehicles and human-powered transportation modes become more practical, we can turn part of what used to be the bike lane and sidewalk into gardens, affordable housing, or whatever a city needs. It’s a nice vision, and anything in the urban U.S. public infrastructure context has just taken much, much longer to progress than I would have thought in my youth. But I hold out some hope the breakthrough of autonomous electric vehicles, which is inevitable, could catalyze some faster change.

Culdesac Tempe

This is basically just a real estate development with no parking. It’s on a light rail line, and the main idea seems to be to embrace micromobility (bikes, scooters, autonomous taxis) for people to get around. It doesn’t seem hugely pathbreaking to me, but I think what might make it seem pathbreaking to suburban Americans is that the bikes, scooters, human beings, and cars are not in conflict with each other. This is so simple, and yet so pathbreaking. It’s also pathbreaking because it’s in greater Phoenix. We assume this can’t be done in American cities because when we choose to devote most of our space to car maneuvering and car storage, there is not also room for the bikes, scooters, and human beings.

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.

why parking is the enemy of affordable housing

This article has a clear explanation of why parking mandates push up housing costs in cities.

Off-street parking mandates add hundreds of dollars a month to people’s rent, even for tenants who don’t drive, who then have to subsidize their neighbors’ parking in the building’s garage. One reason for this is that off-street parking is incredibly expensive to build, especially now that building material costs keep rising, and are expected to rise even more with President Trump’s tariffs.

But the other reason is that parking just takes up a lot of space in a building. All the space devoted to a garage and all the related internal building infrastructure takes up room that can’t be devoted to more homes and living space. Not surprisingly, when cities remove parking mandates, builders add more housing and less parking to projects.

In some cases, the cost of building an underground garage for the required parking spaces ends up being the real limit on how tall a building can be. On paper a builder might be legally allowed to add more units than proposed, but if providing the parking for them is too unaffordable, they’ll opt for a smaller building.

I still think self-driving (and self-parking) vehicles will solve this particular problem in the long term, because vehicles will be able to park themselves in very tight spaces. The technology has arrived in the world’s most advanced countries (not the U.S. sorry, we are behind and falling more behind.). But it might take a generation for laws to catch up, and we are going to be stuck with a lot of wasted space for a long time to come.

3-30-300

The idea is 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.

Parks Please! Implementing the 3–30-300 green space rule in developing countries − The case of Surakarta, Indonesia

Interest in the 3–30–300 green space rule has recently emerged in urban forest scholarship, but its applicability in developing country contexts, especially in intermediate cities, remains largely unexplored. This study assesses the feasibility of the rule’s three components—visibility of three trees from every building, achieving 30 % neighborhood canopy cover, and ensuring 300-meter walking access to 0.5-hectare parks—using geospatial analysis. We employ a combination of remote sensing data, local administrative records, and open-source global datasets to evaluate tree canopy cover, greenspace distribution, and accessibility under different scenarios. Our case study focuses on Surakarta, an intermediate city recognized as Indonesia’s most livable city. Results show that only 29 % of buildings meet the visibility requirement, 2 % are in neighborhoods with 30 % canopy cover, and 25 % are within 300 m of a greenspace. However, accessibility could increase to 79 % if all greenspaces were fenceless and high quality. Our findings highlight disparities in urban greening, as smaller residential buildings tend to have lower scores than larger office buildings. These results underscore the role of park governance in shaping access to green spaces and the persistent challenges of achieving the 3–30–300 targets. We propose place-based recommendations tailored for each urban commune and advocate for the adoption of the 3–30–300 rule as a target for national and local development planning to enhance urban green space accessibility and equity. This framework has the potential to be used in participatory planning processes for consensus-based siting of green infrastructure and nature-based solutions in cities in developing countries.

My city (Philadelphia, USA) has set the 30% canopy goal in the past and failed to implement it. Not only failed, but failed to maintain the inadequate tree canopy we already have. Part of the reason is dysfunctional and uncoordinated government agencies, and part of the problem is the “sidewalks are private property” farce.

R.I.P Donald Shoup

Donald Shoup explained why parking is so scarce in walkable, livable cities. Basically, you can have walkable, livable cities, or you can have free parking. You can’t have both. This is a matter of geometry. Pricing parking is one answer. Progress on this issue is a dog fight every inch of the way. Most people are not interested in waking up from the auto-oil-highway propaganda matrix and seeing the world for what it is. The fight is worth it. Thank you Donald Shoup for opening my eyes to reality.

sidewalks

Sidewalks are important. Besides being (obviously?) part of the transportation system (because the purpose of a transportation system is to move people and goods from point A to point B, NOT to move your private motor vehicle from point A to point B), we can put trees in them, manage water and pollution in them, move water/electricity/gas/communications under them and over them, conduct business and engage in social interactions in them. In engineering lingo, they are part of the “public right of way” along with the street. This is why most U.S. cities recognize that they are a critical part of the urban public infrastructure…wait, what? They don’t? They pretend they are private property and put the onus on private property owners to keep them in a state that provides all these public amenities. The article I link to here compares sidewalk policy in U.S. cities and concludes that some are better than others.

closing streets to cars raised business sales by 68%

This was during four Sundays of “open streets” (which means open to humans and closed to big, heavy motor vehicles) in a portion of Center City Philadelphia. But this works because people live nearby. People don’t really have to “walk to” the event because they live there. When cars are the only practical way to get around, most of the space has to be reserved for cars to maneuver and park (relatively) safely so you can’t have space for people too. It’s obvious, sure, but 100 years of oil-highway-car industry propaganda has brainwashed us to be blind to the realities of geometry. Take your red pills, people!

electric vehicle charging in Philadelphia

Here’s an article on the woes of electric vehicle charging in my home city of Philadelphia. On the plus side, electric vehicles are becoming more common.

As of January, there were 6,615 all-electric vehicles and 3,149 plug-in hybrids registered in Philadelphia, according to data from the state Department of Transportation (PennDOT). Combined, those represent 1.3% of the city’s nearly 767,000 registered vehicles. That doesn’t include cars used by the many commuters and visitors who drive into Philly every day.

To fully charge a typical EV on a standard Level 2 charger, the owner may have to leave their car parked there eight hours, which means there need to be more chargers per EV than gas pumps per gas car. 

Yet Philly has only 145 publicly accessible charging stations with 378 charging ports, according to U.S. Department of Energy data. Most of the stations have Level 2 chargers, but 13 of them have Level 3 or DC Fast chargers, which typically charge a car in an hour or less, depending on the vehicle’s battery capacity and other factors. Pennsylvania as a whole has 1,785 public stations with 4,598 ports.

Philadelphia is a large city with many neighborhoods, some quite car-dependent. That is where chargers belong, not in the walkable urban core. What we need there are safe, separated, protected lanes for bicycles and light electric vehicles, like e-bikes and scooters and even light-weight golf carts. These need their own signals and they need to never, ever, ever be in conflict with highway vehicles, whether those are electric or not. So I wouldn’t prioritize chargers there, but on the other hand we should be thinking about air pollution. Replacing fossil-fueled vehicles with electric ones is certainly a win for all the lungs of all the people walking and using those light-weight electric vehicles, so that is one argument in their favor, even in urban cores.

I still autonomous vehicles will eventually solve the charging problem, even in urban cores. Because your vehicle will be able to drop you off at your home or another walkable location, then go park itself somewhere it will not be in the way, then come pick you up again when you need it. So ideally we will be able to have walkable urban cores not ruined by private vehicles, and the ability to take trips to car-dependent locations when we need to. I want to believe this is a decade or less in the future, but it seems to be coming along very slowly.