It appears the first eco towns will be announced later today. I have to confess that my reaction is mostly one of indifference (I don't live near one).
It is clear that the scheme as it stands will not make a huge difference to housing supply. Because it doesn't do a lot for housing supply it can't do much for the environment (only a small % of the population will live there). The direct differential benefits (i.e. due to the house itself) of "eco-town-new-build" over "standard-building-regs-new-build" will be positive but not huge. Overall, the new build will only make up a tiny proportion of existing stock. If you want to seriously tackle the carbon footprint of homes you need to tackle problems relating to the latter.
If the savings aren't large on housing, then most of the benefits need to come from transport via changing travel patterns (shorter journeys) and mode choices (fewer cars). At face value it seems like these might be easy to influence, but in practice the relationship between built environment and transport decisions is uncertain on many dimensions.
To get some perspective, new towns accommodate about 2 million people (4% of the population). Are they the "balanced self contained communities" they were planned to be? They are reasonably self-contained in the sense that a lot of people live and work in the town. Of course, this is true of most towns new or not. They may be less geographically self-contained than intended . They also tend to be more auto-orientated . More growth in new towns is likely to reinforce the dependency on auto leaving journey times unchanged .
So, overall, a small benefit from housing. Small populations mean any potential benefits from transport are small (and because there is lots of uncertainty there could end up being large costs). The brownfield/greenfield debate is the usual red-herring. Finally, they might act as examples, but for what? The huge number of new towns we are going to build next decade? They are an interesting experiment, but a marginal story compared to the major questions of housing supply and climate change.
: R. Cervero, Urban Studies, 1994
: Those numbers not peer-reviewed
: Titheridge and Hall, Journal of Transport Geography, 2006.