1.5 meters is the new unit for smart city designers.

Urbanisation in the US is undergoing major changes. The image of a central city surrounded by sprawling suburbs therefore needs to be updated. The question is what place does the 15-minute city have in it? That is what this somewhat longer post is about
 
From the 1950s, residents of US cities began moving en masse to the suburbs. A detached house in the green came within reach for the middle and upper classes, and the car made it possible to commute daily to factories and offices. These were initially still located in and around the cities. The government stimulated this development by investing billions in the road network.
From the 1980s, offices also started to move away from the big cities. They moved to attractive locations, often near motorway junctions. Sometimes large shopping and entertainment centres also settled there, and flats were built on a small scale for supporting staff. Garreau called such cities 'edge cities'.
Investors built new suburbs called 'urban villages' in the vicinity of the new office locations, significantly reducing the distance to the offices. This did not reduce congestion on congested highways.
 
However, more and more younger workers had no desire to live in suburbs. The progressive board of Arlington, near Washington DC, took the decision in the 1980s to develop a total of seven walkable, inclusive, attractive and densely built-up cores in circles of up to 800 metres around metro stations. In each was a wide range of employment, flats, shops and other amenities . In the process, the Rosslyn-Balston Corridor emerged and experienced rapid growth. The population of the seven cores now stands at 71,000 out of a total of 136,000 jobs. 36% of all residents use the metro or bus for commuting, which is unprecedentedly high for the US. The Rosslyn-Balston Corridor is a model for many other medium-sized cities in the US, such as New Rochelle near new York.
 
Moreover, to meet the desire to live within walking distance of all daily amenities, there is a strong movement to also regenerate the suburbs themselves. This is done by building new centres in the suburbs and densifying part of the suburbs.
The new centres have a wide range of flats, shopping facilities, restaurants and entertainment centres.  Dublin Bridge Park, 30 minutes from Columbus (Ohio) is one of many examples.
It is a walkable residential and commercial area and an easily accessible centre for residents from the surrounding suburbs. It is located on the site of a former mall.
 
Densification of the suburbs is necessary because of the high demand for (affordable) housing, but also to create sufficient support for the new centres.
Space is plentiful. In the suburbs, there are thousands of (semi-)detached houses that are too large for the mostly older couples who occupy them. An obvious solution is to split the houses, make them energy-positive and turn them into two or three starter homes. There are many examples how this can be done in a way that does not affect the identity of the suburbs (image).
New construction in suburbs
 
This kind of solution is difficult to realise because the municipal authorities concerned are bound by decades-old zoning plans, which prescribe in detail what can be built somewhere. Some of the residents fiercely oppose changing the laws. Especially in California, the NIMBYs (not in my backyard) and the YIMBYs (yes in my backyard) have a stranglehold on each other and housing construction is completely stalled.
 
But even without changing zoning laws, there are incremental changes.  Here and there, for instance, garages, usually intended for two or three cars, are being converted into 'assessor flats' for grandma and grandpa or for children who cannot buy a house of their own.  But garden houses are also being added and souterrains constructed. Along the path of gradualness, this adds thousands of housing units, without causing much fuss.
 
It is also worth noting that small, sometimes sleepy towns seem to be at the beginning of a period of boom.  They are particularly popular with millennials. These towns are eminently 'walkable' , the houses are not expensive and there is a wide range of amenities. The distance to the city is long, but you can work well from home and that is increasingly the pattern. The pandemic and the homeworking it has initiated has greatly increased the popularity of this kind of residential location.
 
All in all, urbanisation in the US can be typified by the creation of giant metropolitan areas, across old municipal boundaries. These areas are a conglomeration of new cities, rivalling the old mostly shrinking and poverty-stricken cities in terms of amenities, and where much of employment is in offices and laboratories. In between are the suburbs, with a growing variety of housing. The aim is to create higher densities around railway stations. Besides the older suburbs, 'urban villages' have emerged in attractive locations. More and more suburbs are getting their own walkable centres, with a wide range of flats and facilities. Green space has been severely restricted by these developments.
 
According to Christopher Leinberger, professor of real estate and urban analysis at George Washington University, there is no doubt that in the US, walkable, attractive cores with a mixed population and a varied housing supply following the example of the Rosslyn-Ballston corridor are the future. In addition, walkable car-free neighbourhoods, with attractive housing and ample amenities are in high demand in the US. Some of the 'urban villages' are developing as such.  The objection is that these are 'walkable islands', rising in an environment that is anything but walkable. So residents always have one or two cars in the car park for when they leave the neighbourhood, as good metro or train connections are scarce. Nor are these kinds of neighbourhoods paragons of a mixed population; rents tend to be well above the already unaffordable average.
 
The answer of the question in the header therefore is: locally and slowly

A previous post made it clear that a 15-minute city ideally consists of a 5-minute walking zone, a 15-minute walking zone, also a 5-minute cycling zone and a the 15-minute cycling zone. These three types of neighbourhoods and districts should be developed in conjunction, with employment accessibility also playing an important role.
 
In the plans for 15-minute cities in many places around the world, these types of zones intertwine, and often it is not even clear which type of zone is meant.  In Paris too, I miss clear choices in this regard.
 
The city of Melbourne aims to give a local lifestyle a dominant place among all residents. Therefore, everyone should live within at most 10 minutes' walking distance to and from all daily amenities.  For this reason, it is referred to as a 20-minute city, whereas in most examples of a 15-minute city, such as Paris, it is only about <strong>the round trip</strong>. The policy in Melbourne has received strong support from the health sector, which highlights the negative effects of traffic and air pollution.
 
In Vancouver, there is talk of a 5-minute city. The idea is for neighbourhoods to become more distinct parts of the city. Each neighbourhood should have several locally owned shops as well as public facilities such as parks, schools, community centres, childcare and libraries. High on the agenda is the push for greater diversity of residents and housing types. Especially in inner-city neighbourhoods, this is accompanied by high densities and high-rise buildings. Confronting this idea with reality yields a pattern of about 120 such geographical units (see map above).
 
Many other cities picked up the idea of the 15-minute city.  Among them: Barcelona, London, Milan, Ottawa, Detroit and Portland. The organisation of world cities C40 (now consisting of 96 cities) elevated the idea to the main policy goal in the post-Covid period.
 
All these cities advocate a reversal of mainstream urbanisation policies. In recent decades, many billions have been invested in building roads with the aim of improving accessibility. This means increasing the distance you can travel in a given time. As a result, facilities were scaled up and concentrated in increasingly distant places. This in turn led to increased congestion that negated improvements in accessibility. The response was further expansion of the road network.  This phenomenon is known as the 'mobility trap' or the Marchetti constant.
 
Instead of increasing accessibility, the 15-minute city aims to expand the number of urban functions you can access within a certain amount of time. This includes employment opportunities. The possibility of working from home has reduced the relevance of the distance between home and workplace. In contrast, the importance of a pleasant living environment has increased. A modified version of the 15-minute city, the 'walkable city' then throws high hopes. That, among other things, is the subject of my next post.

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