Lexus: The hybrid debate blog

It is said that a city's skyline can be viewed as a four-dimensional graph of evolving land prices. Skyscrapers point to expensive business districts; clusters of cranes point to upcoming areas of commercial development; and high-rise dormitories built by local authorities point to cheap labour and "key workers".

However, this traditional view is predicated on the idea that all forms of transport must operate on one plane, at or near ground level. Hybrid cars, especially if they represent a stepping stone to emission-free transport, remove several major constraints to urban planning, and therefore make multi-layered cities more viable.

For example, in a hybrid future, tunnelling would be much easier and cheaper, since there would be a reduced need for large-scale ventilation. Indeed, it would be less problematic to

allow cars into any enclosed space. Roads could therefore extend upward more easily, with highways running through towers and across gantries.

In this context, hybrid cars or emission-free cars would act as elevators. And as the city began to develop on a vertical axis, so it would take on a kind of braided aesthetic, as nodes of activity were connected by a complex but ecologically more stable series of high-level routes.

Population density around these nodes would be high but, as many recent studies on urbanisation have shown, this would facilitate the provision of services as well as economic growth. Healthy cities are ones where people live, work and educate their children in close proximity, yet still benefit from efficient communication and travel networks across the city as a whole.

Nodal areas would include railway stations (both underground and overground), schools, libraries, homes and workplaces. And hybrid or emission-free cars would be used to circulate between nodes in a non-linear fashion.

Meanwhile, the areas in between nodes would be used to develop more green areas such as parks or even woodland. As the nodal structures gleamed in the sunlight, so the green interstitial spaces would act as lungs, mitigating the environmental damage already caused by the pollutants of previous inefficient and unecological designs.

Cities could indeed sprawl -- sympathetically -- into the countryside. It's a dream that architects and planners have had since the 19th Century: the Arcadian city, co-joining the benefits of the pastoral with the metropolitan and cosmopolitan.

In any case, we would expect to see a more "distributed" approach to business.

Today, the centre of a city such as London, with its inflated property prices, excludes all but the rich. This is due to businesses competing for central accommodation because: (a) it provides a geographical proximity to other businesses and services; and (b) they feel it connotes the success and longevity of their services and brands. To occupy positions on the periphery of the city is to be subject to infrastructural disruption and a consequent loss of efficiency.

Equally, most large cities currently have to accommodate a massive influx of commuters in the morning and a massive exit of commuters in the evening. In our highly networked world, "rush hour" is a hectic, stressful and frenetic anachronism, yet people still prefer to meet face-to-face whenever possible.

In this context, the multi-layered city offers more options for communications. Nodes would specialise, of course, but they would have many more exits and entrances. And clusters of expertise could spread out more easily.

Similar visions have been outlined before. In the 1950s and 1960s, for example, there was great optimism over the emancipating effects of technology developed during the Second World War. Ubiquitous, cheap power seemed a real possibility. But the oil crisis of the 1970s ended such hopes, and with them the hopes of innovative architects for denser (and smarter) cities.

Now that optimism is returning in a new guise. Society has a new ecological mission that is giving architects more reasons to embrace and develop the visions of their professional mid-20th Century ancestors. Hybrid technology, as a stepping stone to emission-free driving, might indeed herald a contemporary Renaissance in urban planning.