|►◄ Reverse Zone|
Complete List of Posts
Wed, 16 Sep 2009
Based on a book review of Green Metropolis by David Owen and an earlier New Yorker article by the same author, there is still a great deal of confusion about the effect of localized density on energy use. Everyone should live in Manhattan says the author, who apparently lives in Manhattan. New Yorkers use the least energy of anyone. Did you notice the old switcheroo? Manhattan and New York briefly became synonymous.
Let's sort out the fact from the fiction. The book claims that living in highrises in Manhattan makes you use less heat, because of shared walls. Is that true? No. Heating and cooling highrises in fact uses a lot more energy per square metre and per person than heating and cooling any other sort of building including single family homes, and the total energy requirement is also greater. The average household in Manhattan is much smaller than the average household elsewhere, so Manhattan apartments tend to be a lot smaller than houses elsewhere. To its credit, Manhattan has a wonderfully efficient community heating system where steam produced in part as a byproduct of electricity generation is piped to buildings to be used for heat.
The book's specious argument about elevators is a bit silly. They say it take less energy to move people horizontally than vertically. Per metre when doing it mechanically, perhaps. But when you want to move people 15 metres away vertically you build an elevator. To do this horizontally you expend no energy at all, you expect them to walk, and more often than not you will not provide them with a lit, heated, cooled, maintained, stainless steel construction within concrete. Unless they take the subway, which probably requires even less energy.
New Yorkers in general use a lot of public transit. This proves in part that people are more likely to take a subway when there is a subway than when there is none. New York is different from most other cities in the US. In research I did a few years back when I tried to see the relation between density, household type and transit use, New York City was off the charts for just about everything. Everyone there takes the subway whether they are in high or low density. You have to remember that Manhattan is only a small part of New York City. Most of the city is not highrises, a lot of the area of New York City is made up of medium density single family houses. I lived in one in Queens and commuted to Manhattan every day. People in medium density in New York take the subway practically as much as people who live in Manhattan highrises. You have to be careful in your assumptions. A large proportion of Manhattan is not highrises and outside Manhattan the vast majority of residential buildings are ground-oriented. But New York has great public transit even in densities where other cities would not have a subway, so lower-density New Yorkers use it.
To me, it is the transit use by lower-density family-oriented areas outside Manhattan that is the great success of New York City. The two populations are very different. Take a typical apartment dweller in a highrise in Manhattan and move him to a lower-density area still in roughly the same size apartment. Is he driving more? Probably not very much. Now take a family of four or five in Queens and move them to lower density. How much will they drive then? A whole lot more. The lower-density area they have moved to will probably not be walkable at all and with 2 jobs and a few kids, that family has very high transportation needs.
It happens that in New York City, the highest population density areas are made up of highrises. But that is not the case in other cities. So, for instance, while Manhattan with its highrises has a population density of 27,000 people/km2, the Eixample area of Barcelona has a density of over 35,000 people/km2, and it does it almost entirely with attractive 5-6 storey buildings (see picture). Many areas of San Francisco do the same thing. Plateau Mont-Royal in Montreal is over 12,000 people/km2 with mostly 2-storey and some 3-4 storey buildings. You really don't need highrises to get population density. What you do need is units that appeal to households with children; that way you get a lot more people for the same number of units.
New York and other cities with dense cores and a high gradient between high-density centres and lower-density rings have polarized their population between the small households who are in the high density and the larger households who go further and further away. Having a Manhattan means that you will also have an extended metropolitan area of commuters spread across several states. When you count the total area and the total population density of this tentacled monster, the Greater New York area, which is a direct result of Manhattan's land use, doesn't look so good. This is a general rule in North America. The denser the core the greater the sprawl, and it gets worse every year. New York's population has not been growing, but its area has. Within New York City, population suddenly stopped growing in 1961 when zoning was changed to allow high density just about everywhere. Then earlier this decade in the "downzoning uprising", with Green Party people behind the movement, zoning was changed downward and lo and behold the population and population density started growing again for the first time in over 40 years.
Whether in Manhattan or in Portland, you can't just look at localized density and think you're making progress. When you change the distribution of the demographics you don't improve energy use as a whole. If you build up a small area you could get very good stats in that one area, as people who are already prone to taking transit move there and continue taking transit. But what happens to the other demographics who get displaced? What about the ones that don't want to live within a few blocks of a high-density hub and who see the area becoming less family-friendly. You may have just moved them away from a transit route to an area where their energy use will skyrocket.
It's a complex topic and the easy answers, like why can't everyone do what I do, simply don't work. It's a shame that people spend their time promoting simplistic solutions and attacking the simplistic solutions of other, rather than simply pricing carbon and letting our economic system minimize total emissions using the price signal.