Cars and suburbia: urban density, the compact city, sustainability …

“One of the chief contributing factors to traffic congestion is crowds of pedestrians interrupting the flow of traffic at intersections.” Dallas planner Vincent Ponte, quoted in W. Whyte, ‘City: Rediscovering the Center’ [p.198]

“The present relationship between cities and automobiles represents … one of those jokes that history sometimes plays on progress. The interval of the automobile’s development as everyday transportation has corresponded precisely with the interval during which the ideal of the suburbanised anti-city was developed architecturally, sociologically, legislatively and financially. But automobiles are hardly inherent destroyers of cities … We went awry by replacing, in effect, each horse on the crowded city streets with half a dozen or so mechanised vehicles, instead of using each … vehicle to replace half a dozen or so horses.” [J. Jacobs, ‘The Death and Life of Great American Cities, pp.446-7]

Since photos of freeways and parking lots are not very exciting, let's illustrate with the help of a few car movies!

 

We ended the last post by quoting Hans Blumenfeld: “High density requires transit, and transit makes high density possible. Low density requires individual car driving, and universal use of the car requires low density.” Both he and Jacobs were writing in around 1960, during the early stages of the build-out of the freeway system and suburban sprawl in North America. However, while Blumenfeld clearly identified the degree to which lower residential densities erode, and finally eliminate, public transit options by making feeder networks uneconomic, he nevertheless implies that there is a more or less stable trade-off, and hence choice, between the high-density/public transit and low-density car systems. In this respect, and with the advantage of 50 years’ hindsight, Jacobs was in my opinion more prescient insofar as she very clearly recognised that a central aspect of this trade-off was that it was certainly not stable, but rather highly dynamic and subject to severe feedback loops – in other words, that once a society began the process of moving from a high-density to a low-density model of organisation, that this process would feed upon itself and therefore was unlikely to reach a stable equilibrium at any meaningful level of density. It could be argued, from a 21^st century perspective, that there may be no straightforward and stable “choice” between car-based suburban sprawl on the one hand and high-density cities on the other, but that rather the complex positive feedbacks involved in car-based low-density living mean that the urban environment will be subject to wild and unstable fluctuations (or, more accurately, decreases) in density – effectively a “chaotic” system rather than a linear system. (Many modern “behaviouralist” economists, such as Robert Shiller who has also focused on the American housing market, are moving in this direction).

How does Jacobs make her argument? It is worth laying out the logic at some length: “Too much dependence on private automobiles and city concentration of use are incompatible. One or the other has to give. In real life, this is what happens. Depending on which pressure wins most of the victories, one of two processes occurs: erosion of cities by automobiles, or attrition of automobiles by cities … We also have to be aware that surface traffic in cities exerts pressures upon itself. Vehicles compete with each other for space and for convenience of their arrangements. They also compete with other uses for space and convenience.” [pp.454-5]. The urban planner Victor Gruen did an analysis of Fort Worth’s downtown traffic requirements in 1955: “Gruen, in order to understand the size of the problem … began by calculating the potential business that Fort Worth’s currently underdeveloped and stagnating – but traffic jammed – downtown ought to be doing by 1970, based upon its projected population and trading area. He then translated this quantity of economic activity into numbers of users [shoppers, workers etc] … [He then] translated the putative future users into numbers of vehicles [and] calculated how much street space would be required to accommodate [them]… He got an outlandish figure of roadbed needed: sixteen million square feet, not including parking [compared with five million in 1955]. But the instant Gruen had calculated his sixteen million square feet, the figure was already out of date and much too small. To obtain that much roadbed space, the downtown would have to spread out physically to an enormous extent. A given quantity of economic uses would thereby be spread relatively thin. To use its different elements, people would have to depend much less on walking and much more on driving. This would further increase the need for still more street space … Differing uses … would be so far from one another that it would become necessary to duplicate parking spaces themselves … This would mean spreading the downtown even thinner… As Gruen pointed out …, the more space that is provided cars in cities, the greater becomes the need for use of cars, and hence for still more space for them … Swiftly or slowly, greater accessibility by car is inexorably accompanied both by less convenience and efficiency of public transportation [because of uneconomic feeder networks], and by thinning-down and smearing-out of uses, and hence by more need for cars.” [pp.456-7] “When a city has become a sufficiently homogeneous and thin smear, it should have the traffic problem, at any rate, in hand. Such a state of equilibrium is the only possible solution to a positive feedback process like city erosion. This point of equilibrium has not yet been approached in any American city.” [p.461]

Can it be said in 2013 that such a point of equilibrium has been reached in any American urban environment? I leave that judgement to those better qualified, but the figures are quite striking: “between one third and one half of urban America’s land is typically dedicated to the driving and parking of vehicles. In Los Angeles, that ratio jumps to two thirds. Houston provides the equivalent of 30 asphalt parking spaces per resident.” [J. H. Kay, ‘Asphalt Nation’, p.64].

The critics of suburban sprawl, and particularly of the car suburb, are legion (books such as ‘Suburban Nation’, ‘Asphalt Nation’, ‘The Geography of Nowhere’, and much of Lewis Mumford’s writings) and there is no point trying to summarise their analyses in any detail here.

I will continue the theme of looking at the underlying structures and dynamics of transport networks at an abstract level, as well as at their underlying cost structures, in order to establish some sort of a basis for comparison and maybe some tentative conclusions about re-configuring urban environments and their transport networks. We have made the assumption that the raison d’etre of a city was physical communication – that is ease of movement for its inhabitants as a corollary of the division of labour and multiplicity of choice in work and living. In simple terms that was of course exactly the radical promise made for the car and the truck – they would liberate individuals and industry by providing the convenience and efficiency of universal door-to-door communication. This would be the case both for interurban (via the freeway network) and intraurban traffic. The complexity, redundancy, inefficiencies and costs of the multiple modes of transport that constitute public transit systems, and the need to transfer between them to achieve a door-to-door service, would be thereby be eliminated.

Let’s get back to our concept of “Los Angeles”, an abstract and simplified city of 15 million people which is fully dependent on the car and truck for personal and goods transport, as a comparator to “Paris”. At 7,500 people per sq mile “Los Angeles” will extend over 2,000 square miles; i.e. it will fit into a square with approximately 45-mile sides. In order to facilitate the efficient movement of cars the city will be served by a number of high capacity intraurban freeways, so that any door-to-door journey outside the immediate neighbourhood will involve driving to the nearest freeway, driving on the freeway network to as close to the final destination as possible, and exiting to use the “feeder network” of smaller roads to get to the final destination. The longest possible drive within this city is clearly dependent on the positioning and number of freeways, and there’s not much point in being excessively detailed, but as an indication the distance from one corner of the square city to the opposite corner will involve a drive of around 64 miles.

But as with underground rail, the freeway system needs to be built to cope not with the average daily number of car and truck journeys evenly distributed, but rather to cope as far as possible with the two daily rush hour spikes of traffic. The various engineering and human behavioural aspects of traffic management are extremely complex, but the basic reality is that it is (to say the least) much harder to build sufficient capacity into a freeway system than into an underground rail system. It may well be that there are now technologies in the pipeline (such as automatic steering for cars in convoy) that will substantially improve the efficiency of use of road space; but the historical experience to-date has been that all attempts to add capacity by building new freeways or adding lanes to existing freeways have been negated within a short period of time by increased traffic. “A recent University of California at Berkeley study covering 30 California counties between 1973 and 1990 found that, for every 10% increase in roadway capacity, traffic increased 9% within four years’ time” [quoted in Duany et. al., Suburban Nation, p.88].

This reflects a general and worldwide phenomenon, which is due to the fact that the reasons for it reflect the interaction of fundamental human behaviour and the feedback loops of car suburbia – induced traffic and latent demand. “The mechanism at work behind induced traffic [can be described by the aphorism]: ‘Trying to cure traffic congestion by adding more capacity is like trying to cure obesity by loosening your belt’. Increased traffic capacity makes longer commutes less burdensome, and as a result, people are willing to live farther and farther from their workplace. As increasing numbers of people make similar decisions, the long-distance commute grows as crowded as the inner city, commuters clamour for additional lanes, and the cycle repeats itself.” [Suburban Nation, p.88]. Latent demand refers to the fact that, “since the real constraint on driving is traffic, not cost [an issue we will look at below], people are always ready to make more trips when the traffic goes away.” [p.91] The level of traffic on any road reflects the aggregate of drivers’ individual choices: “How crowded a roadway is at any given moment represents a condition of equilibrium between people’s desire to drive and their reluctance to fight traffic. Because people are willing to suffer inordinately before seeking alternatives … the state of equilibrium of all busy roads is to have stop-and-go traffic. The question is not how many lanes must be built to ease congestion but how many lanes of congestion do you want?” [pp.91-2]

There are a couple of points that I think are worth addressing before closing this post: first, that there are ways of mitigating traffic congestion – primarily by pricing; and second, that to some extent you might find similar dynamics with regard to passenger traffic on underground rail systems in large cities. Governments can always reduce demand for a service by charging for its use – specifically by making it more expensive to drive by charging tolls either in general or focused on high congestion times of day. London for example has instituted a “congestion charge” on car commuters. This is certainly do-able when congestion becomes unbearable, but it has tended in practice to be politically difficult and is perceived as discriminatory in favour of the wealthy against the poor. With respect to the second question, many underground systems (London for example) suffer with serious under-capacity and overcrowding, and there may be elements of induced traffic and latent demand creation. However, as we saw in the previous post, while it is expensive there is no meaningful limit to the additional capacity one can add to an underground line because of the inherent efficiency of fitting people rather than cars into a given amount of space and time.

But the basic point to bear in mind is that these sorts of questions are really aimed at dealing with symptoms rather than the underlying disease. The disease is the one Jane Jacobs identified, the inexorable and self-reinforcing dynamic between car use and urban form over time. To repeat and emphasise an earlier quote: “the more space that is provided cars in cities, the greater becomes the need for use of cars, and hence for still more space for them … Swiftly or slowly, greater accessibility by car is inexorably accompanied both by less convenience and efficiency of public transportation [because of uneconomic feeder networks], and by thinning-down and smearing-out of uses, and hence by more need for cars.”