Long distance car commutes to work produces significant greenhouse gas emissions (GHG). While that fact is established, a new study — using tens of millions of mobility data — “was able to reveal direct links between urban structure and car commuting with unprecedented detail, beyond mere correlations”.
The study, conducted by researchers from Potsdam Institute for Climate Impact Research (PIK) in collaboration with the University of California, Berkeley, the University of Sussex and other partners, finds that the distance between homes and workplaces is the primary driver of car commuting.
Earlier, the usual discussion around city planning was based on overall city density and transport connectivity but according to the researchers, these factors are secondary.
“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,” Felix Wagner, the lead author of the study said.
The observation is based on millions of mobility data points from six cities: Berlin, Boston, Los Angeles, the San Francisco Bay Area, Rio de Janeiro and Bogotá.
While the main crux of the study revolves around ensuring homes are located close to city centres, leading to less commute and reduction in GHG emissions, the researchers also argue their solution implementation might vary from city to city.
“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,” Wagner argued.
The study divides the cities into two broad classifications: monocentric cities — jobs and economic activity are concentrated in or around one main centre — like Berlin and Boston and polycentric cities with multiple city centres, like Bogota and Los Angeles.
Based on the classification, the study argues, the approaches are very different.
In Berlin’s case, a monocentric city, the study argues for building more homes in areas that are already reasonably well-connected to that centre but are not yet densely built-up. The area stretches to a 26 kilometre radius from the city centre. For areas outside that stretch, building new homes nearby won’t solve the problem as they are simply too far from jobs for that to make a meaningful difference. Hence, having better public transport is the way forward so that people don’t have the need to commute by car.
For a polycentric city like Los Angeles, which has no one dominant city centre, simply building homes won’t suffice. What matters more in Los Angeles is how close people live to wherever their jobs are. Since those jobs could be anywhere across the city, the strategy should be to strengthen the local job clusters and build more homes near them, wherever they happen to be.
The zone where this approach can make a meaningful difference extends up to 36 km from any given employment hub. But even within that zone, the maximum reduction in car travel the study could measure was 2 km per trip — the smallest gain of any city in the study.
For people living beyond those employment clusters — in the outer areas where jobs are sparse and distances are long — building new homes nearby won't help. The same supplementary measures apply as in other cities: better public transport, stopping construction of new housing even further out into open land, carpooling, and working from home, the study argues.