Marchetti Constant, just another God of the Copybook Headings

Excellent piece.  From How Transportation Technologies Shape Cities by Tomas Pueyo.  The subheading is Part 3 of How to Understand Cities. 

We don’t realize it, but the shape of our cities—from how big they are to what services they have—is mainly driven by one thing: transport technologies.

1. Marchetti

The size of cities is determined by transportation technologies, whether it’s Ancient Rome, Medieval Paris, Industrial London, turn-of-the-century Chicago, or Highway Atlanta.

People live within 30 min of their work. This is the Marchetti Constant. 

For millennia, most cities were limited in size because people moved by foot. Even big cities like Ancient Rome or Medieval Paris didn’t grow beyond 3 km in diameter. Indeed, since people walk at a speed of about 5 km/h, and they are only willing to walk up to 30 min to commute, they were only willing to walk for ~3 km. 

Then, in the early 1800s, London (orange) built the first urban railway. Suddenly, you could live much farther, close to a station, take the train, and in 30 min reach your work. The city grew accordingly. But not uniformly. 

Marchetti notes in the original paper:

Cars make all the difference. As they have a speed of 6 to 7 times greater than a pedestrian, they expand daily connected space 6 or 7 times in linear terms, or about 50 times in area.—Marchetti, Anthropological Invariants in Travel Behavior.

The time budget for travel is a universal and narrow constraint.  

Click to enlarge.

I vaguely recollect that there is a related law to the effect that commuting speeds in cities are pretty invariant as well.  I don't recall the name of the phenomenon but the effect is that regardless of traffic design and technology speed, traffic congestion will always cluster around 10-15 mph in cities.  

You add road lanes, you improve light sequencing, you improve flows, etc. and you will gain brief relief from congestion before the system reverts to the mean.  Higher speed conditions invite more people to commute pushing the average speed back down to the norm.

Which raises an interesting point.  It is quite the fad now, and for several years, to focus on walkable cities when designing the built urban environment.  There are also related efforts to reduce or remove parking in order to discourage vehicular traffic.  Further, Vision Zero, also related, wants to reduce the speed of traffic in order to reduce traffic related deaths, principally in cities.  And let's not forget another clerisy obsession, repurposing scarce road space from cars to bicycle lanes, no matter how few people bicycle.  Finally, both the clerisy and City Planners are deeply enamored of the millions and billions of dollars available through the federal government for mass transit.  Which ever fewer people choose to ride.  

No matter how much is spent on mass transit though, its role in labor transportation is increasingly de minimis.  For example, see US Public Transit Has Struggled to Retain Riders over the Past Half Century. Reversing This Trend Could Advance Equity and Sustainability by Yonah Freemark.  Independent of the clerisy obsession with undefined equity and misunderstood sustainability, Public Transit can't get Americans to take a ride.  

Since 1970, the number of US workers roughly doubled, increasing from 77 million to more than 150 million. But over the same period, the number of transit commuters increased by only about 1 million. Just 5 percent of workers now get to work by bus or train nationwide, compared with almost 9 percent a half century ago. Most people are driving instead.

All these fads are popular among the clerisy and advocacy groups and reasonably unpopular among the public.  People want to get from A to B quickly, cheaply, safely, and reliably.  As long as the utopianism of the clerisy, and their pet City Planning Departments, don't interfere with those objectives, people don't object.  In recent years though, the clerisy, advocacy groups and Planning Departments are becoming increasingly insistent that there should be fewer cars, less parking, less roadway for cars, more mass transit, and fewer labor transportation choices. 

Fundamentally, they want to force their vision on the public even though that vision means that labor transportation will take longer, despite what the residents actually want.  The clerisy proceed blithely, without taking into account that longer commute times changes the configuration of the city, making it smaller and more condense.  The clerisy assumption, to the extent that they think about it explicitly, is that because they want people to live in small, dense, walkable cities, then everyone must want that.  

An assumption we are seeing tested in real time.  It would appear that over the past three years, people are exiting the big cities with the greatest manifestation of Clerisy thinking and planning.  The San Franciscos, Seattles, Los Angeles, Portlands, Chicagos, etc.  

My suspicion is that we are seeing fragmentation of most these cities as well.  All metropolitan areas are made up of multiple jurisdictions with a core City government but then massive areas of the functional city which are actually under the jurisdiction of counties or smaller independent city governments.  As an example, the City of Atlanta is a jurisdiction of about 500,000 people under a very progressive, clerisy dominated governance.  The metropolitan city is 6,500,000 people with the balance of 6,000,000 under county and other governance structures.  They do not experience the clerisy vision of bad public services and slow commutes.  93% of Atlantans do not live under the governance of the clerisy vision.  

Over the past fifty years, City of Atlanta has managed to attract perhaps 75,000 people to live within the city while the suburbs and exurbs have attracted some 5.5-6 million.  Not a particularly ringing endorsement of the vision of the clerisy and the City Planners.  

In the past five years, the clerisy vision for city centers seems to have come to the fore and I suspect we will see, over the next five years or decade, a further exodus from city centers as people seek the efficiencies, productivity and benefits of large city living without the harassment and functional failure arising from the vision of the clerisy.  

The Marchetti Constant was way after Kipling's time but it would seem to qualify as a Copybook Heading.  Labor transportation speed determines the size of the city and when you deliberately slow down the labor transportation speed you make the city smaller and you drive people out to jurisdictions with a focus on making labor transportation fast, cheap, safe, and reliable.  

Until then, as the clerisy pursue their vision in sacrificial city centers, you still have the Gods of the Copybook Headings defying the vision of the clerisy.

And that after this is accomplished, and the brave new world begins

When all men are paid for existing and no man must pay for his sins, 

As surely as Water will wet us, as surely as Fire will burn, 

The Gods of the Copybook Headings with terror and slaughter return!

UPDATE:  I came across what I had been recollecting in a Thingfinder post from December 2016, London Traffic.  Smeed's Law.

The Wikipedia post is here.