We left off my series about zoning with Car Dependent By Design, and in this post I will be talking about density without zoning. My goal of this series is to open a mature discussion into urban planning in the post-zoning, bottom-up driven world of tomorrow.
Controlling density is often an argument used by zoning advocates - whether it is by smart growth advocates to encourage density or by suburban conservatives todiscourage it. It seems tempting to use zoning to control what can be built and where, and while zoning can work to enforce density, you also inherit many of thenegative qualities of zoning. In this post I will be discussing alternative ways cities can plan for density without zoning.
Density, or more specifically - population density, is the measurement of how many people reside in a given area. Density is often measured in units such as People Per Square Mile (replacing mile with kilometre if you are metric). The equation for population density is very simple;
If you had a town of 1000 residents, the population density would decrease as you add more land;
If our town of 1000 residents occupied two square miles, it would have a population density of 500 people per square mile. At 500 people per square mile, the town will feel very exurban, regardless of absolute population;
If our town of 1000 residents only occupied 0.1 square miles (64 acres), it would have a population density of 10,000 people per square mile. At 10,000 people per square mile, the small town would probably feel very urban, and the town would also feel highly walkable, as at 64 acres it would take approximately 3 minutes to walk anywhere in the town. Population densities even greater than this in even smaller towns are not unusual around the world, as is often the case in small towns and villages;
The relationship is also inverse. If your town has a fixed area - imagine it being located on an island that has only 2 square miles of developable land - our town's density would increase along with population;
This relationship is very simple - it is just a ratio that a child could easily understand. Take away land, and your town becomes more dense. Take away people, and your town becomes less dense, and vice versa. But, many people do not seem to understand that there are two sides (population and area) to this ratio and they consider 'density' is a taboo word in small town setting. There is no natural law that says small towns must not be dense, and that words like density, walkability, human-scale do not apply in small towns, because there are a near infinite number of counter examples around the world that prove the opposite;
If we look into art - a reflection of how we see the world - villages typically tend to be small but dense, surrounded by untouched country side;
There is also no natural law that says large cities, even those with millions of residents, must be dense;
Why would a city want to control density?
One reason is preference - some people may want to live somewhere that feels very secluded, while other people may want to live somewhere that is very convenient and walkable. Some people want a huge lot with a private yard, while for others their town is their living room and their home is just a place to sleep. The elderly, disabled, and people that prefer not to drive may want to live somewhere relatively dense where all their needed amenities are within walking distance.
There are practical reasons why you would want to control density. A common theme on Strong Towns is the financial productivity of cities. The less dense a city is, the less tax revenue you are collecting (on a per acre basis), so your property and/or land is considered 'less productive'. However, the less dense a city is, the greater the service area is for your infrastructure is - your fire trucks have greater coverage area to cover the same number of people, your utilities need to cover a greater area, you need to build a more extensive road network - and so these greater costs combined with less tax revenue become a double whammy to the city's budget.
How do we control density without going so far as to implement zoning and regulate what can be built where?
Urban Growth Boundaries
A very easy way to control density is by explicitly controlling the supply of land that can be developed on. When you set up a border that defines the edge of town (and nothing can be built outside of that edge), it is typically called an urban growth boundary. An urban growth boundary is a form of zoning - a very simple binary zoning system in which there are two zones; urban, and rural. You could imagine if a town with an urban growth boundary released a zoning map, it would look something like this; (Green - urban, grey - rural, black lines - streets, thick black lines - highways.)
You could refer to these two zones as zone A/zone B, urban/rural, city/country, or even simply as build-here/don't-build-here.
Because we limit the supply of land, as population increases, density increases. Let's look at that chart again;
If the population density becomes greater than what is desirable, we expand the urban growth boundaries, increasing the supply of land. If the population density becomes too low (people move out and we cannot continue supporting all of that infrastructure), we can contract the urban growth boundaries (and make many people mad because they will loose city services!), decreasing the supply of land.
Urban growth boundaries are still a form of zoning, because we are explicitly placing boundaries on what can be built where.
Without explicitly stating what land can and cannot be built on, there are still some natural constraints that control the supply of land. Some of these natural constraints may be related to infrastructure (a homeowner may not wish to live where there is no mains electricity). A large factor that controls the supply and desirability of land is the accessibility to said land. I am going to define the accessibility of a plot of land as the time it takes to the reach the surrounding amenities (which may be your job, nearby retail stores, parks, entertainment, and other everyday needs) from the plot of land.
When I was writing my blog post on optimizing the street grid, I discovered that what is reachable within a fixed distance forms a diamond shape along a street grid;
If we assume that the typical person does not wish to travel more x minutes away, whether it be for commuting to work every day, travelling to the store for groceries, or to their child's baseball game, we can chart out how much of the surrounding area we can reach in x minutes at different travel speeds. I say 'x' because the maximum amount of time a person is willing to travel largely depends on the individual's tolerance, so I mapped out the amount of accessible land for 3 different travel time tolerance levels - 5 minutes, 15 minutes, and 30 minutes;
I did a quick Internet search for some common travel speeds, and here they are in table form;
Average Travel Speed (Miles Per Hour)
5 Minutes (Square Miles)
15 Minutes (Square Miles)
30 Minutes (Square Miles)
30 (City Streets)
For visual comparison;
With this, we can come up with a fuzzy supply of accessible land to plug into our population density equation. I say 'fuzzy' because this chart largely depends on individuals' thresholds for travel times, therefore it is not an absolute chart but an approximation of the minimum population density within a town. This time our example town houses 20,000 residents;
The chart shows that as we increase our travel speeds - the ability to travel farther, faster - we increase our supply of land, and if we increase our supply of land (without increasing population, and without any zoning or land use regulations) we lower our population density. Logically, this makes sense - the faster you can get around your town, the more spread out your town can be.
Density Without Zoning
We can influence density without zoning by controlling the amount of accessible land, which we can do so by the way in which we design our streets and transportation systems. A city can decrease the amount of accessible land by lowering travelling speeds - building streets at a human-scale that encourage walking and cycling, and incorporating traffic calming measures and shared spaces. Not only do these create more livable, safer, and healthier neighbourhoods, they focus on creating destinations rather than simply places people pass through. On the other hand, by widening roads and building highways and freeways, we increase our travel speeds, which in turn increases the amount of accessible land, which encourages sprawl and lowers our density.
One example of this is the city of Houston. Despite having no zoning, Houston has a vast freeway network (aswell as minimum-lot requirements) that encourage a low-density form;
This may seem counter intuitive at first - trading efficiency for density and livability - but there is a critical difference between connecting productive places together, such as two towns, in which both towns find a benefit in being connected together, and increasing the efficiency at which people can travel through productive places, which can have unproductive consequences such as thinning out the tax base and increasing the town's infrastructure obligations.
The purpose of this blog post was to demonstrate how zoning is not necessary for controlling density. Density is result of a ratio between population and land area, and by controlling the scale of our streets and transportation infrastructure, cities can influence their population density without resort to zoning or regulating land use.
I am going to be continuing this series on zoning, and in the future I will be discussing zoning and traffic. Zoning has the potential to be unintentionally abused with many bad side effects, and by offering alternatives to how we can accomplish the same goals without all of the nasty side effects, I am hoping that we can largely eliminate the need for zoning and return to building great, human-centric towns and cities.