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Motorised transport is the fastest-rising cause of energy-related greenhouse gas emissions and there’s a strong imperative to address this by moving towards a low-carbon transport system. Moreover, as Woodcock, from the Centre for Diet and Activity Research, explained: “It’s possible to benefit public health at the same time.”

But which approaches to achieving a low-carbon transport system would provide the biggest health benefits?

“We can think about the problem in two ways,” he said. “We can evaluate the impacts of an intervention such as new cycling infrastructure, or we can develop scenarios around what a healthy, low-carbon future transport system would look like, and then we think about how to achieve major changes in how people travel. We often see quite small effects from the interventions happening now, whereas potentially large things are possible.”

“Cycling could have a big role to play,” he said. “But to achieve this you’d have to start thinking about changes in land use to reduce trip distances, and cultural and infrastructural changes to make cycling an everyday mass activity for short- and medium-length trips.”

��Woodcock has led the development of an Integrated Transport and Health Impact Modelling (ITHIM) tool, which models the health impacts of travel behaviours on both population health and greenhouse gas emissions.

“We’re seeing different effects in different populations,” said Woodcock. “In health terms, switching from driving to cycling consistently shows a net benefit, and the greatest benefit comes from getting older people more active. However, a complicated web of other problems arises. In some contexts, such as inner London, cyclists seem to face notably higher injury risk than users of other travel modes,” he said. “They also breathe harder so are inhaling more air pollution, which is bad for health.But on the other hand, they are not in a car putting other road users at injury risk or producing pollution for everyone else. We need this model to tell us which is the more important effect.”

There are also rebound effects to consider. “If I sell my car and buy a bike, I’ll have money left over, and where do I then spend that money?” he asked. “I may end up causing greenhouse gas emissions somewhere else, and it’s complicated to account for these second-order factors.”

ITHIM has now been taken up in California to evaluate transport plans in the San Francisco Bay area. It showed that a shift from driving to walking and cycling on short trips reduced the burden of cardiovascular disease and diabetes by 14% and reduced emissions by around 14%. By contrast, low-carbon driving reduced emissions by 33.5% but cardiorespiratory disease burden by less than 1%.

̽��ֱ��results are feeding into new policy in which a combination of active transport and low-carbon driving could meet legislative emissions mandates. Meanwhile, working with the Greater London Authority, Woodcock is also evaluating the impact of achieving the Mayor’s cycling targets and has also separately modelled the impacts��of the Barclay’s Cycle Hire Scheme.

With funding from the Economic and Social Research Council and the Medical Research Council, Woodcock is leading two additional projects to address the problem of how to achieve the necessary behaviour change. By focusing on the development of cycling cultures through social learning and social influence, and��by understanding the unintended outcomes that policies might bring about, these projects are attempting a different approach from those used in traditional transport modelling.

“Our research brings out a potential good news story,” he added. “Health benefits link transport and environment problems, and we need to be sure of the best route to achieving the biggest benefits.”

CEDAR is a partnership between the ̽��ֱ�� of Cambridge, the ̽��ֱ�� of East Anglia and Medical Research Council Units in Cambridge. Visit for more information.