Much of the debate about urban development and sustainability relates to transportation, a sector that has done less than any other to decrease its carbon dioxide emissions. One need only look at the projections for future car use to see that current private vehicles are unsustainable in energy use, pollution, and road capacity.
It is therefore inevitable that car use will be constrained in the future, if not by taxation or regulation then by sheer congestion. As car use becomes more difficult, low density, car-dependent locations will become less attractive. This may be key to challenging society's deeply ingrained attachment to the car, which is the result of policies of dispersal and ease of access to private mobility.
Energy-efficient, single-family housing design concentrates on demand reduction. Autonomous housing goes further by seeking to supply its needs from available renewable resources. This is difficult because the limitation of resources tends to mean that autonomous housing can only work if the dwelling is incredibly efficient. As part of our research, we asked whether autonomy becomes easier at the neighborhood level because of economies of scale. For example:
• Waste recycling in higher densities improves the potential to develop markets for recycled materials.
• Sharing of infrastructure costs makes more feasible communal gray-water restoration, renewable energy, and combined heat and power (CHP) systems.
• Systems integration can link energy, water, and waste treatment systems, recovering heat, for example, from gray water or sewers as is common in Sweden.
• Mixed-use development can even out demand fluctuations, making systems less wasteful and more economical. In our climate, for example, workplaces require energy during the day in summer for cooling while housing requires energy in the evenings and in winter.
• Unit efficiency. A single-person household will consume less than a five-person household, but not five times less. Urban sustainability looks beyond the individual house with, for example, multifamily housing with fewer heat-loss walls.
• Capital investment at the urban scale can link revenue from utility bills and service charges to capital investment in resource-saving measures.
Our work suggests that such "best practice" measures to improve the efficiency of housing could halve the current energy consumption in urban residential areas. It is also possible to go beyond this with efficiency measures, but the costs and technical difficulties start to outweigh the marginal benefits of further improvements.
Local Energy Supply
At the neighborhood scale a range of energy solutions become possible. Key to this are combined heat, power, and cooling networks that supply energy needs more efficiently. If individual boilers are installed in a property, the technology is ossified. With district heating, by contrast, the neighborhood level infrastructure can be upgraded as new technology becomes available, as has been demonstrated in Danish cities.
Neighborhood-scale infrastructure also makes possible future technologies when they become viable. These include groundwater heat pumps, fuel cells, solar thermal and photovoltaic panels, new fuels such as hydrogen, biomass, biogas, or bio-oil, and shared energy storage systems.
Entry-level technologies in the United Kingdom would be gas-fired CHP and back-up boilers. In addition, neighborhood electricity networks can be installed to overcome regulatory and market barriers. Cooling networks can use waste heat and groundwater for chilling, as demonstrated by European Union CHP specialists Utilicom and Thameswey.
Our work on the autonomous urban block demonstrates that even in the cloudy north of England there is sufficient solar and wind power available over the year to meet the region's energy needs. The problem is that, even with a mix of uses, the greatest energy demand is in winter and the greatest availability in summer. The issue of energy storage therefore becomes crucial to full autonomy. This is where the costs escalate and system efficiency plummets.
Water and Waste
Despite the scarcity of water in some parts of the country and the energy used to purify water and treat sewage, existing UK bylaws limit our ability to reduce water use in the home. Viable measures could include low-flush toilets, low-flow showers, and spray taps.
Individual autonomous houses can use reed beds to treat wastewater — something rarely practical in urban areas (though a UK water company is currently testing a roof based system) — as well as rainwater storage tanks and systems for home gray-water reuse.
Again, the possibilities are greater at the neighborhood level. We calculated that in Manchester (admittedly, the so-called "rainy city"), the annual rainfall on a dense urban neighborhood is greater than its annual water requirement. Given proper treatment and storage, a centralized water supply would theoretically not be needed.
It is also possible to use a "living machine" — an intensive ecological system, to treat the area's sewage, to support aquaculture and horticulture, and to supply the area's gray-water needs. This system forms part of urban blocks in Kolding, Denmark and the Beddington Zero Energy Development at Sutton in London.
Our experience is that such water management is not viable in urban areas unless managed as a whole system. These systems can be attractive in areas where there is no sewage capacity, and developers must pay for new infrastructure. Research also suggests that byproducts from ecological treatment systems, such as aquaculture, could make such systems even more viable.
Urban Car-Sharing Schemes
Car use is another good example of incremental change that could occur in urban areas. The cost of owning a car — fuel, taxes, insurance, parking — is likely to increase in the future. While the cost of parking in city centers has become astronomical, this is where it is probably more convenient to walk or use public transportation for most trips anyway.
In these circumstances it becomes economically sensible to join a car club and drive on a pay-per-use basis. This transforms the economics of car use by making the real cost of each trip more apparent. Clubs such as Smart Moves in the United Kingdom, Stattauto in Germany, and Zip Cars in the United States have proved effective at encouraging people to give up their private cars.
Car clubs potentially have the same implications as district heating in that they create early upgrade paths for more efficient technologies such as electric or fuel cell vehicles. The more limited range of electric vehicles is less problematic when most trips are within the urban area. Honda is promoting this concept with their Intelligent Community Vehicle System, which aims to provide city-wide access to electric vehicles.
By broadening our horizon from the home to the neighborhood, a new dimension can be added to the sustainability debate. All the lessons about reducing resource use in housing are still relevant but to this can be added urban economies of scale.
It may never be possible to make an urban neighborhood entirely autonomous. But it should be possible in the near future to create neighborhoods where resource flows are circular rather than linear, and where the net environmental impact is neutral or even positive.
David Rudlin is the northern director of the Urban and Economic Development Group (URBED) and is responsible for the Sustainable Urban Neighborhood Initiative. He is the author with Nicholas Falk of Building the 21st Century Home from the Architectural Press. Nick Dodd is an environmental consultant at URBED. He carried out the research for the Autonomous Urban Development Project which was funded by BRECSU (the United Kingdom's Energy Efficiency Best Practice Programme) and the European ALTENER renewable energy program.