That shady street you like to walk along might be doing more than keeping you cool—it might be keeping you from a nasty fall. A new study published in the American Journal of Epidemiology found that the streets with more tree coverage had substantially fewer falls among pedestrians requiring emergency medical service.
Scientists at Columbia University’s Mailman School of Public Health, along with colleagues at Northwestern, Brown, and the USDA Forest Service, compared nearly 500 sites in 44 large US cities. Their discovery was simple but persuasive: the greener the street, the safer the stairs.
There are about half a million Americans treated for falls each year after falling down while walking outside. The most fall-prevention studies have been done indoors, however, with little known about what makes people trip while walking outside. This is what the Columbia-led team set out to fix.
They examined Emergency Medical Services (EMS) reports from April to September of 2019—months when tree canopies are thickest and heat is most severe. All of the fall locations were compared with two control locations nearby with no injuries. From satellite imagery, scientists approximated how much forest canopy surrounded each location within a 100-meter radius.
The results were stark. Streets where the residents did trip had a median canopy cover of just 8 percent, while the control sites had 14 percent. Statistically, every category up through the interquartile range of tree canopy was associated with a 43 percent lower chance of a fall. In plain terms, shaded streets were safer streets.
Outdoor slipping and falling are not just a case of clumsiness—weather conditions like surface heat, lighting, and road surface quality enter the picture. Hot weather, for example, can warm asphalt, loosen pavers on sidewalks, and cause people to feel lightheaded or exhausted, all of which multiply tripping hazards. Trees counteract the effects by cooling the air and hardening the walking surface.
Street trees could have a pivotal role in lessening heat-related fall dangers in summer, according to the lead author, Dr. Kathryn Burford, a postdoctoral researcher at Columbia and North Carolina State University. She further noted that in addition to shading pedestrians on sidewalks, trees lower surface temperatures, increasing comfort as well as possibly offsetting balance for walkers.
Dr. Andrew Rundle, a senior author and professor of epidemiology at Columbia University, further added that the research points out the impact urban design has on public health. “In contrast to indoor falls, which are frequently attributed to individual-level factors of health, outdoor falls are influenced by environmental factors,” he said. “Our results imply that tree cover, by decreasing ambient temperature, could lead to a decrease in fall risk.”
The team analyzed information from ESO Solutions, Inc., that monitors millions of emergency response reports nationwide. Of 8.3 million EMS activations in 2019, about 15,000 were falls by a pedestrian on a street or sidewalk. After the incidents involving alcohol or drugs were excluded, researchers randomly selected 500 cases and mapped their exact coordinates.
They determined that more than half of the falls occurred in the South, where summer heat can be extreme. The average victim was 54 years old, and approximately 61 percent were age 50 or older. Even after they adjusted for income, poverty rates, and neighborhood walkability, tree canopy remained strongly linked with lower fall risk.
When the researchers divided the data into four quartiles, the pattern was obvious. Neighborhoods in the densest canopy quartile experienced 68 percent lower odds of a pedestrian fall compared to the sparsest quartile. The pattern persisted even when the group extended the analysis to broader surrounding neighborhoods.
The study also sheds light on an ancient controversy over city trees. The majority of homeowners worry that roots damage sidewalks and pose a hazard to trip over. But the statistics show that, overall, trees might even be rendering streets safer by offsetting the danger of heat.
Some cities have tree-planting programs, but it’s a contentious process,” Burford said. “Building owners are typically responsible for upkeep of sidewalks and don’t want to take on liability if someone falls.” Research suggests that tree canopy may, overall, reduce such risks.
The authors propose that urban planners consider trees as public safety infrastructure, not beautification. Urban canopy expansion can actually be a low-cost solution to reducing fall injury, particularly in low-income neighborhoods with poor shade and healthcare access.
The researchers acknowledge some limitations. The EMS data did not capture all details of each fall, and canopy measurements came from a big national database rather than counts at the street level. Any flaws, however, would likely have made the results more conservative. That is, the trees could be having a bigger impact than the study suggests.
Upcoming studies will investigate how pedestrian walking patterns and temperature gradients combine with canopy cover to influence the risk of falling. EMS data usage provides “a powerful tool for seeing how urban environments shape health and injury risk,” Rundle said, with possible extension to other conditions, including heatstroke and dehydration.
The research offers a new argument for urban tree planting and canopy conservation. As climate-change fueled heat waves become more common, shaded streets might save lives, lower healthcare costs, and make cities more livable.
For the oldest, most prone to falls, tree-shaded sidewalks could offer a simple protection. For city planners, the message is clear: trees are not just ornaments—also preventive care.
Integrating canopy objectives into city street safety and climate resilience plans could cool urban heat, improve health, and keep residents on their feet.
Research findings are available online in the American Journal of Epidemiology.
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