This is a guest post by Andrew Price. It originally appeared on his blog.
I love narrow streets, they are an essential part of making a city feel warm, inviting, and most importantly, human-scale.
American traffic engineers will hate me. Most of them believe in building cities around cars and that every street should be a highway. Here is downtown Fort Smith, Arkansas — the closest thing they have to a street in the city, yet cars still flow freely at 45 miles per hour, as if this is a highway.
A city planner or traffic engineer that does not know the difference between a street and a road should be one that does not have a job. They are killing our cities.
Streets are the living room of cities. A city without any real streets (not roads or highways) is akin to a house without a living room. If the whole house has been designed to get you from bedroom to bedroom, without any living room or other common space, then no matter how nice the bedrooms are, living in that house is going to be pretty lonely and isolating and probably inhumane (I stole this analogy from this podcast.) Allowing traffic engineers — whose job is ‘to achieve the safe and efficient movement of people and goods’ — to design your city will result in a city that has been designed solely to move big metal machines around (cars) — not one designed for people to live in.
A place designed to move machines around everywhere sounds more like a factory than a livable city — it would not be a pleasant place to immerse yourself in all day long.
A lot of what our cities are designed around has to do with the scale at which we build our cities. Just by looking at a simple street level photo, we can infer if a place looks like it has been built at a scale designed around driving; (suburbia)
Or at a scale designed around transit; (hypertrophic cities)
Or designed around walking. (traditional cities)
There are many factors that affect the perceived scale of a place — block size, how fine-grained your destinations are, and one of the most important elements is the street width.
Some people only measure the publicly-owned right of way as the street.
However, I like to measure the entire space between building fronts as the street width;
because the entire space between building fronts is what determines how the place is framed.
Street width is important for our perception of scale, but there are also practical implications. Given the same block size and development pattern, wider streets result in less developable land, less tax revenue, and greater infrastructure costs overall than narrower streets. Imagine this is a square 300 by 300 foot block surrounded by a 15 foot street.
Here is the same block surrounded by an 80 foot street.
We can see how much more area is taken up by having a wider street. The bottom image (460×460) is about 94% larger than the top image (330×330).
Now let’s imagine this on a large scale. Imagine that we have an area of land (a square mile) and we divide it up into square 300 by 300 foot blocks. The wider the streets are (horizontal axis), the less land we have that can be developed on, put to productive use, and ultimately generate tax revenue;
And the fewer blocks that we can fit into our square mile of land.
Let’s assume that the developable land generates about $10,000 per acre in tax revenue. I took this graph from Joe Minicozzi at Urban-Three showing average property tax revenue.
For the purpose of this example, we will assume that we have low-rise buildings that generate approximately $10,000 per acre (of developable land) in tax revenue. As we widen our streets, we have less developable land within our square mile generating tax revenue (so our tax revenue falls) while we have a greater area of streets to maintain (so our expenses go up).
Let’s combine these two figures together to see how much tax revenue we have supporting each square foot of street.
This is still an over simplified model, but replace ‘square foot of street’ with water pipes, electrical lines, mail routes, fire/police protection, or transit service, and you can see why most American cities are broke. You can download my calculations here.
We have spread our tax base so thin, and built more infrastructure to support it, that the return we are getting on the infrastructure we invest in exponentially decreases.
Sometimes I feel that I am the only one who sees it.
Not only are narrow streets human-oriented with a great sense of place, they make sense financially.
Of course you still need wide arterial roads to get you across large distances – which traffic engineers should be allowed to go crazy with, because that is their job – to move vehicles across large distances efficiently.
But these wide arterial roads should make up around 15%, definitely no more than 25% of your street network.
The remaining 75-85% of your streets should be very narrow. 15 feet is a really good width for a quiet street lined with low rise buildings.
Once you start going above 25 feet, things start to feel a little barren;
To make wide streets feel inviting and humane, we need to spend money decorating it. Trees are popular.
But, if your street is already narrow and cozy, you can save a lot of money on decorating.
Designing streets around cars is a bad idea. Even if you drive, you spend most of your trip driving across town on the arterial roads (or on the highways and freeways between towns.) It does not make much of a difference if you have to spend 2 minutes at the start and end of your trip navigating narrow streets (and because everything is closer together, chances are that your overall trip will be shorter.)
Would you want to live in a crappy place just to shave an extra 4 minutes off a long drive?
Andrew Price is a programmer, urbanist, and blogger at andrewalexanderprice.com.