This is an important chart from a recent study commissioned by Greater Wellington, New Zealand. The study looks at the cost benefits of urban intensification and the above chart shows the relationship been density and infrastructure costs. For this study, they specifically looked at the costs that local governments face in providing road, public bus transport, and "three-waters infrastructure." I hadn't heard this latter term before, but it refers to drinking water, wastewater, and stormwater.

What they obviously found was that there are real economies to higher densities. More density lowers the per dwelling cost of delivering infrastructure. In the case of three-waters infrastructure, it doesn't even really matter if you're proximate to reservoirs or treatment plants. The bulk of the cost lies in the local connection pipes. So what matters most is how many dwellings you can service off of the main lines -- even if these lines need to be upsized.

The goal of this study is to enable more support for smart growth within the Wellington region:

Regional councillor Thomas Nash says the report should give councils confidence to press on with plans that support compact mixed-use development in and around city centres and connected by high quality public transport. 

“Regional growth needs to be smart growth. This report clearly shows that the best bang for our buck is to focus on upgrading existing water, public transport and local roading infrastructure so that we can build better quality, compact residential form, with improved amenities within our cities and towns,” Cr Nash says.

Of course, this doesn't just apply to Wellington. Every city should read the study.

As a follow-up to yesterday's post about infill housing and overall urban densities, let's look at some basic math.

The City of Toronto has an estimated population of 3,025,647 (as of June 2023) and a land area of 630 square meters. That means that its average population density is about 4,803 people per km2. Obviously this number will be higher in some locations, and lower in others. But overall, this is the average.

Now let's consider how many people we could actually fit within the existing boundaries of the city (city proper not the metro area) if we were to simply match the average population densities of some other global cities around the world.

Again, what this chart is saying is that if we took the same physical area (Toronto's 630 square meters) and just increased the population density to that of, say, Paris, we would then have a total population of over 13 million people and we'd be housing an additional 10,011,573 humans on the same footprint.

I am not suggesting that this is exactly what should be done. (Though, you all know how much I love Paris.) What I'm suggesting is that calling a place "full" isn't exactly accurate. How would you even measure that? What someone is really saying is that they are content with the status quo in terms of built form and density.

Note: The above population densities were all taken from Wikipedia, except for Toronto's figures, which were taken from here.

I tweeted this out last week:

Not surprisingly, the responses were divided. Some responded saying that beauty is more important than density, and a lot of people were quick to point out that there's good density and there's bad density. And because I can appreciate both of these comments, it made me think that I should probably elaborate on my glib tweet.

The points I was trying to vaguely imply are the following.

More often than not (at least for North American cities), I think our problem is not too much density, it's too little. This translates into cities that aren't walkable, aren't conducive to transit, and that are overall less sustainable. Right now, every mayoral candidate in Toronto is promising to fix our crippling traffic congestion. I don't know how they're going to do it, but they're promising it because they know it's something people are pissed off about.

But here's my take: counterintuitively, the problem is not enough density. The problem is that too many people in our region have no reasonable way to get around without a car. So they're forced to drive. The way you fix this not as simple as more traffic enforcement or better signal timing. Good luck! You fix it through density, because density is what makes other forms of mobility suddenly possible.

All of this is not to say that density alone will render you a great city. Obviously things like beauty also matter a great deal. But in my opinion, density is a fundamental component. Because what good is beauty if you don't have any urban vibrancy? The answer is that you probably don't have a real city.

The other point I was trying to make is that space and density are both relative and oftentimes difficult to understand. We think building height and density are correlated, but that's not always the case. Look at Paris or Barcelona. We also like to make a lot of spatial rules that we think are right and make our cities better: streets should be at least this wide, buildings should be no taller than the width of the street, and so on.

But here (pictured above) is a street that narrows to around 6 meters and has buildings that are probably 2.5-3x the width of the right-of-way. Sure, it also happens to be beautiful, historic, and Italian. But what would happen if you maintained this same beauty and made the street 5x as wide and lined up parking in front of the stores?

Somehow it wouldn't be as enjoyable as what you see here.