Driving in London has been falling since 1990. Has the city passed "peak car"?

Which lane is the future? Image: Getty.

Cars are one of the biggest threats to the planet. The transport sector accounts for more than 60 per cent of global oil consumption and about a quarter of energy-related carbon emissions.

It's also seen as harder to decarbonise than other parts of the economy. Typical forecasts of future world vehicle ownership point to substantial increases, particularly in the developing economies.

But the problem of transport-related greenhouse gases may be less than generally thought. There is emerging evidence that individual car use, as measured by the average annual distance travelled, has ceased to grow in most of the developed economies – a phenomenon that started well before the recent recession. In some countries, it may already be declining, a phenomenon known as “peak car”.

A number of factors could could contribute to this trend. Suggestions have included a decline in the number of younger people holding driver’s licences, changes to company car taxation and the technological constraints that stop us travelling faster on roads. It may also be that we have simply sufficient daily travel to meet our needs.

There has also been a shift away from car use in urban areas. This could be particularly important in a world where future population growth will be mainly urban, and where densely populated cities are seen as a driver for economic growth.

For example, over the past 20 years the population of London has been growing and incomes have been rising – yet car use has held steady at about 10m trips a day. This is mainly because the city has not increased road capacity but instead has invested in public transport.

Most importantly, rail offers speedy and reliable travel for work journeys compared with the car on congested roads. This gets business and professional people out of their cars, which makes the city a less congested and more agreeable place to be.

With a growing population but static car use, London has seen a marked decline in the share of journeys by car, from 50 per cent of all trips in 1990 to 37 per cent currently. With continued population growth projected and more investment in rail planned, the share of trips by car could fall to 27 per cent by mid-century. There is every reason to suppose that London will continue to thrive as car use declines – and perhaps because car use declines.

This decrease in car use from 1990 was preceded by a 40-year period of growth from 1950. That was the result of rising incomes, leading to increased car ownership – and, at the same time, a falling population, as people left an overcrowded damaged city for new towns, garden cities and greener surroundings. So we see a marked peak in car use at around 1990, the time when the population of London was at a minimum, which was when attitudes to city living began to change.

Screenshot from David Metz's 2015 paper, "Peak Car in the Big City: Reducing London's transport greenhouse gas emissions".

This phenomenon of peak car in big cities is not unique to London, although this is the city for which we have the best data. There is evidence for something similar happening in Birmingham, Manchester and other British cities, as well as those in other developed countries. The shift in economies from manufacturing to services is an important driver, as is the growth of higher education located in city centres, attracting young people for whom the car is not part of their lifestyle.

If car use has really peaked, both in the sense of national per capita figures and the share of trips in cities, it should help mitigate greenhouse gas emissions from transport. I have estimated that these changes in behaviour, taken together with expected developments of low-emission vehicles, could by 2050 reduce UK surface transport greenhouse gas emissions by 60 per cent of their 1990 level. This falls short of the overall target of an 80 per cent reduction, but it's a good deal better than conventional projections.

Peak car is not just an emerging phenomenon to be investigated. It is a helpful trend to be encouraged, to achieve both successful, sustainable cities and national reduction of transport greenhouse gas emissions. The Conversation

David Metz is a visiting professor in transport studies at University College London.

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Green roofs improve cities – so why don’t all buildings have them?

The green roof at the Kennedy Centre, Washington DC. Image: Getty.

Rooftops covered with grass, vegetable gardens and lush foliage are now a common sight in many cities around the world. More and more private companies and city authorities are investing in green roofs, drawn to their wide-ranging benefits which include savings on energy costs, mitigating the risk from floods, creating habitats for urban wildlife, tackling air pollution and urban heat and even producing food.

A recent report in the UK suggested that the green roof market there is expanding at a rate of 17 per cent each year. The world’s largest rooftop farm will open in Paris in 2020, superseding similar schemes in New York City and Chicago. Stuttgart, in Germany, is thought of as “the green roof capital of Europe”, while Singapore is even installing green roofs on buses.

These increasingly radical urban designs can help cities adapt to the monumental challenges they face, such as access to resources and a lack of green space due to development. But buy-in from city authorities, businesses and other institutions is crucial to ensuring their success – as is research investigating different options to suit the variety of rooftop spaces found in cities.

A growing trend

The UK is relatively new to developing green roofs, and governments and institutions are playing a major role in spreading the practice. London is home to much of the UK’s green roof market, mainly due to forward-thinking policies such as the 2008 London Plan, which paved the way to more than double the area of green roofs in the capital.

Although London has led the way, there are now “living labs” at the Universities of Sheffield and Salford which are helping to establish the precedent elsewhere. The IGNITION project – led by the Greater Manchester Combined Authority – involves the development of a living lab at the University of Salford, with the aim of uncovering ways to convince developers and investors to adopt green roofs.

Ongoing research is showcasing how green roofs can integrate with living walls and sustainable drainage systems on the ground, such as street trees, to better manage water and make the built environment more sustainable.

Research is also demonstrating the social value of green roofs. Doctors are increasingly prescribing time spent gardening outdoors for patients dealiong with anxiety and depression. And research has found that access to even the most basic green spaces can provide a better quality of life for dementia sufferers and help prevent obesity.

An edible roof at Fenway Park, stadium of the Boston Red Sox. Image: Michael Hardman/author provided.

In North America, green roofs have become mainstream, with a wide array of expansive, accessible and food-producing roofs installed in buildings. Again, city leaders and authorities have helped push the movement forward – only recently, San Francisco created a policy requiring new buildings to have green roofs. Toronto has policies dating from the 1990s, encouraging the development of urban farms on rooftops.

These countries also benefit from having newer buildings, which make it easier to install green roofs. Being able to store and distribute water right across the rooftop is crucial to maintaining the plants on any green roof – especially on “edible roofs” which farm fruit and vegetables. And it’s much easier to create this capacity in newer buildings, which can typically hold greater weight, than retro-fit old ones. Having a stronger roof also makes it easier to grow a greater variety of plants, since the soil can be deeper.


The new normal?

For green roofs to become the norm for new developments, there needs to be buy-in from public authorities and private actors. Those responsible for maintaining buildings may have to acquire new skills, such as landscaping, and in some cases volunteers may be needed to help out. Other considerations include installing drainage paths, meeting health and safety requirements and perhaps allowing access for the public, as well as planning restrictions and disruption from regular ativities in and around the buildings during installation.

To convince investors and developers that installing green roofs is worthwhile, economic arguments are still the most important. The term “natural capital” has been developed to explain the economic value of nature; for example, measuring the money saved by installing natural solutions to protect against flood damage, adapt to climate change or help people lead healthier and happier lives.

As the expertise about green roofs grows, official standards have been developed to ensure that they are designed, built and maintained properly, and function well. Improvements in the science and technology underpinning green roof development have also led to new variations on the concept.

For example, “blue roofs” increase the capacity of buildings to hold water over longer periods of time, rather than drain away quickly – crucial in times of heavier rainfall. There are also combinations of green roofs with solar panels, and “brown roofs” which are wilder in nature and maximise biodiversity.

If the trend continues, it could create new jobs and a more vibrant and sustainable local food economy – alongside many other benefits. There are still barriers to overcome, but the evidence so far indicates that green roofs have the potential to transform cities and help them function sustainably long into the future. The success stories need to be studied and replicated elsewhere, to make green, blue, brown and food-producing roofs the norm in cities around the world.

Michael Hardman, Senior Lecturer in Urban Geography, University of Salford and Nick Davies, Research Fellow, University of Salford.

This article is republished from The Conversation under a Creative Commons license. Read the original article.