Tag Archives: green infrastructure

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

what is green infrastructure

Here’s a paper that goes into the many definitions of green infrastructure across different disciplines, along with related concepts. I’ve certainly seen narrow definitions used in my own discipline of water resources engineering. Defining clearly what you mean by a term and sticking to that definition is actually a good thing, because it takes the power out of the words in the definition itself, and you are now defining the actual structure and/or function of something, and you can now have a conversation with someone else once they understand the definition you are using. Using words without a clear definition, or not being aware of alternate definitions or broader perspectives that are out there, is a problem, and unfortunately not an uncommon one.

March 2021 in Review

Most frightening and/or depressing story: In the U.S. upper Midwest (I don’t know if this region is better or worse than the country as a whole, or why they picked it), electric blackouts average 92 minutes per year, versus 4 minutes per year in Japan.

Most hopeful story: I officially released my infrastructure plan for America, a few weeks before Joe Biden released his. None of the Sunday morning talk shows has called me to discuss so far. Unfortunately, I do not have the resources of the U.S. Treasury or Federal Reserve available to me. Of course, neither does he unless he can convince Congress to go along with at least some portion of his plans. Looking at his proposal, I think he is proposing to direct the fire hoses at the right fires (children, education, research, water, the electric grid and electric vehicles, maintenance of highways and roads, housing, and ecosystems. There is still no real planning involved, because planning needs to be done in between crises and it never is. Still, I think it is a good proposal that will pay off economically while helping real people, and I hope a substantial portion of it survives.

Most interesting story, that was not particularly frightening or hopeful, or perhaps was a mixture of both: One study says 1-2 days per week is a sweet spot for working from home in terms of a positive economic contribution at the national scale. I think it is about right psychologically for many people too. However, this was a very theoretical simulation, and other studies attempting to measure this at the individual or firm scale have come up with a 20-50% loss in productivity. I think the jury is still out on this one, but I know from personal experience that people need to interact and communicate regularly for teams to be productive, and some people require more supervision than others, and I don’t think technology is a perfect substitute for doing these things in person so far.

June 2020 in Review

In current events, the coronavirus crisis in the U.S. is spinning out of control as I write this in early July. I made a list of trackers and simulation tools that I have looked at. Asian countries, even developing countries, pretty much have it under control, Europe is getting it under control, and the U.S. and a few other countries are melting down. Some voices are very pessimistic on the U.S. economy’s chances to come back. So of course I’m thinking about that, but I don’t have all that many novel or brilliant ideas on it so I’m choosing to write about other things below. Most frightening and/or depressing story:
  • The UN just seems to be declining into irrelevancy. I have a few ideas: (1) Add Japan, Germany, India, Brazil, and Indonesia to the Security Council, (2) transform part of the UN into something like a corporate risk management board, but focused on the issues that cause the most suffering and existential risk globally, and (3) have the General Assembly focus on writing model legislation that can be debated and adopted by national legislatures around the world.
Most hopeful story:
  • Like many people, I was terrified that the massive street demonstrations that broke out in June would repeat the tragedy of the 1918 Philadelphia war bond parade, which accelerated the spread of the flu pandemic that year. Not only does it appear that was not the case, it is now a source of great hope that Covid-19 just does not spread that easily outdoors. I hope the protests lead to some meaningful progress for our country. Meaningful progress to me would mean an end to the “war on drugs”, which I believe is the immediate root cause of much of the violence at issue in these protests, and working on the “long-term project of providing cradle-to-grave (at least cradle-to-retirement) childcare, education, and job training to people so they have the ability to earn a living, and providing generous unemployment and disability benefits to all citizens if they can’t earn a living through no fault of their own.”
Most interesting story, that was not particularly frightening or hopeful, or perhaps was a mixture of both:
  • Here’s a recipe for planting soil using reclaimed urban construction waste: 20% “excavated deep horizons” (in layman’s terms, I think this is just dirt from construction sites), 70% crushed concrete, and 10% compost

Technosols

A technosol is an artificially created planting/structural medium from manmade materials, such as construction debris and compost. This article from Ecological Engineering journal says a mix of 20% “excavated deep horizons” (in layman’s terms, I think this is just dirt from construction sites), 70% crushed concrete, and 10% compost might work. If we truly want green cities, and we don’t want to reduce natural habitats to wastelands by harvesting materials from them to green our cities, this could be a good approach.

“supporting” ecosystem services in cities

This long article makes a distinction between services provided by natural and semi-natural areas in cities, and a concept of a city as a whole as an ecosystem that provides services. What it reminded me of, though, is the distinction between the UN’s definition of “regulating” ecosystem services and “supporting” ecosystem services.

• Regulating ecosystem services, such as control of stormwater discharge, mitigation of heat in urban areas, mitigation of noise, etc.

• Supporting ecosystem services, such as provision of habitats for urban biodiversity, provision of pollinators for urban farms, etc.

Journal of Landscape and Urban Planning

In the engineering world I inhabit, we have the regulating services reasonably well figured out. We don’t always do a great job of implementing and enforcing, and we exempt too many projects, but basically we have cost-effective standards and best practices for things like flood management and water pollution reduction.

The supporting ecosystem services are mostly not even on our radar. And that means that when we are designing for flood or water quality objectives, our designs are not as green as they might be if we took biodiversity and habitat into account. It might not even cost more to do that, but it would require a more expansive way of thinking. To do that, we would need to communicate effectively to the decision makers and then the rank and file just why they should care.

May 2019 in Review

This wasn’t my most prolific writing (or reading) month ever. In fact, it my have been my worst. But here are a few highlights of what I did get around to.

Most frightening and/or depressing story:

  • Without improvements in battery design, the demand for materials needed to make the batteries might negate the environmental benefits of the batteries. I’m not really all that frightened or depressed about this because I assume designs will improve. Like I said, it was slim pickings this month.

Most hopeful story:

  • Planting native plants in your garden really can make a difference for biodiversity.

Most interesting story, that was not particularly frightening or hopeful, or perhaps was a mixture of both:

  • Joseph Stiglitz suggested an idea for a “free college” program where college is funded by a progressive tax on post-graduation earnings.

 

August 2018 in Review

Most frightening stories:

  • In certain provinces with insurgent activity, the Chinese government is reportedly combining surveillance and social media technologies to score people and send those with low scores to re-education camps, from which it is unclear if anyone returns.
  • Noam Chomsky doesn’t love Trump, but points out that climate change and/or nuclear weapons are still existential threats and that more mainstream leaders and media outlets have failed just as miserably to address them as Trump has. In related news, the climate may be headed for a catastrophic tipping point and while attention is mostly elsewhere, a fundamentalist takeover of Pakistan’s nuclear arsenal is still one of the more serious risks out there.
  • The U.S. government is apparently very worried about a severe cyber attack. Also, a talented 11-year-old can hack a voting machine.

Most hopeful stories:

Most interesting stories, that were not particularly frightening or hopeful, or perhaps were a mixture of both: