A new approach to urban planning with less car traffic and lower carbon emissions

Urban planning needs to tackle greenhouse gas emissions – and an important way to achieve this is by reducing the number and length of car commutes. This can be achieved primarily by ensuring that homes are located close to city centres and workplaces, so well-targeted building densification becomes a critical lever. City-wide population density and transport links are of secondary importance. These are the findings of a new study in Environmental Research Letters, led by the Potsdam Institute for Climate Impact Research (PIK) in collaboration with the University of California, Berkeley, the University of Sussex and other partners.

Using ten million mobility data points from Berlin, Boston, Los Angeles, the San Francisco Bay Area, Rio de Janeiro and Bogotá, the research team was able to reveal direct links between urban structure and car commuting with unprecedented detail, beyond mere correlations. The newly developed approach shows how planners can use GPS data, travel patterns and artificial intelligence to determine where in a metropolitan region a particular measure will have the greatest impact.

“Our model reveals the actual interdependencies between various urban factors even before we determine their specific effects,” explains Felix Wagner, who completed his PhD at PIK in 2025 and led the study as part of his doctoral research. “This fundamentally changes the recommendations that can be responsibly given to planners. Distances to city centres and working places are key. And urban densification cannot be viewed in isolation: one must understand how urban density relates to secondary factors such as connectivity, accessibility and the choice of residential location.”

A ring-shaped corridor around the city centre

One of the study’s key findings is that, in more monocentric metropolitan regions such as Berlin and Boston, the most valuable sites for infill development are neighbourhoods arranged in a ring around the centre. The area here is less densely built-up, yet the city centre remains easily accessible. In Boston, densification would ideally extend between 10 and 21 kilometres from the city centre; in Rio de Janeiro, the respective ring-shaped corridor would stretch up to 40 kilometres outwards from the centre. In polycentric cities such as Los Angeles and the San Francisco Bay Area, emissions could be reduced by further densification of areas with a high concentration of job opportunities.

The study also challenges the common practice in urban research of treating urban structural variables as independent of one another: using a causal analysis, the research team demonstrates that they are, in some cases, closely interlinked. For instance, population density and road connectivity are strongly coupled. In contrast, income only has an indirect influence on driving behaviour, mainly through the choice of residential location. This research builds on a study from 2023 published in Nature Communications, which highlights the significance of the built environment for carbon emissions: an aspect that has so far been missing from many economic studies on this topic.

Look at local conditions

“Urban planning experts often discuss densification as a one-size-fits-all policy that is either implemented or not,” says PIK researcher Felix Creutzig, a co-author of the study. “However, our data show that a single measure can significantly shorten commuting distances in one neighbourhood, yet have little effect two kilometres away. This spatial specificity has been missing until now.” In Berlin, for example, emissions per journey vary between minus 0.8 and plus 2.9 kilograms of CO₂ relative to the city average, depending on the neighbourhood – an indication of the potential for targeted climate policy measures tailored to local conditions.

For neighbourhoods further away from employment centres, the study finds that urban planning measures alone are not sufficient. Supplementary strategies such as transit-oriented urban development, restrictions on new developments in greenfield areas, carpooling and home-working arrangements could be helpful here.

The study was produced as part of the CircEUlar project, funded by the European Union’s Horizon Europe programme. The source code, which enables other researchers to build on the methodology, is available at https://github.com/wagnerfe/xml4uf.