Commuting by car remains a significant health concern, according to new commentary by Lawrence Frank, professor of urban studies and planning at UC San Diego. Frank revisited his influential 2004 study, which found that every additional hour spent in a car increased the likelihood of obesity by 6%, while each kilometer walked decreased it by 5%. This research helped establish the connection between city design and public health.
Frank’s original work used GPS-based travel data alongside health information to demonstrate a clear link between community design, time spent in cars, and obesity risk. The findings have since been replicated globally and contributed to the development of walkability assessment tools like Walk Score.
In his latest commentary published in the American Journal of Preventive Medicine, co-authored with Jacob Carson, a student at the UC San Diego Herbert Wertheim School of Public Health and Human Longevity Science-San Diego State University Joint Doctoral Program in Public Health, Frank emphasized that technological improvements such as electric vehicles do not address sedentary behavior.
“You can spend just as much time sitting in an electric vehicle as you can in a gas one,” said Frank. “Every hour in a car will still be a 6% increase in the likelihood of obesity.”
The commentary reviews two decades of evidence showing that built-environment design affects not only obesity but also heart disease, diabetes, and mental health. According to Frank, walkable streets and accessible transit offer substantial health benefits, especially for those most at risk. However, he notes that transportation budgets often overlook the health costs associated with car dependence.
“We are still driving blind,” said Frank. “We’re acting like these things don’t exist, but they’re so huge.”
Carson added: “The last 20 years of technological progress haven’t changed the original findings of this paper, and neither will the electrification or autonomization of cars. Robust public transportation and safe cycling and walking infrastructure are still relevant solutions to the challenge of creating healthy and sustainable communities.”
Frank’s team is developing models such as the National Public Health Assessment Model to help cities evaluate investments in streets, sidewalks, and transit using cost-benefit frameworks similar to those applied for congestion or emissions analysis.
“Most people do not find the time to be physically active to counter the adverse effects of sedentary driving time,” Frank said. “You have to reduce car dependence — and integrate active transportation into daily life.”
A related study led by Frank shows that small-scale features like sidewalks, trees, benches, shade, and safe street crossings can significantly improve public health outcomes—particularly for older adults. He advocates focusing investment on these features in low-income neighborhoods where residents face higher risks for chronic disease.
“Investing in those small features is fairly easy to do; it’s fairly inexpensive. That’s going to give you the biggest return on investment of anything you can do to improve public health through transportation investment,” he said.
Frank concluded: “We’ve learned exactly how the built environment shapes behavior. Now it’s time to put that knowledge to work — because every mile we walk instead of driving matters.”
