Canopy Cover Linked to Lower Risk of Pedestrian Falls

Higher levels of tree canopy cover may help prevent injurious pedestrian falls, according to a new study led by researchers at Columbia University Mailman School of Public Health. The research found that during summer months, locations on streets and sidewalks where pedestrians fell and suffered an injury were less likely to be shaded by trees than matched control locations. The protective effect of tree canopy cover is potentially due to the cooling effects of shade from trees. The results are published in the American Journal of Epidemiology.

While indoor falls have been well studied, outdoor pedestrian falls have received far less attention, despite accounting for about half a million injurious incidents in the U.S. each year. Walking has multiple health benefits and the findings provide new evidence that urban greenery, perhaps through cooling the local ambient environment, contributes to pedestrian safety.

“Many cities have tree planting campaigns, particularly street trees, but these campaigns are controversial because street trees can cause sidewalk damage, and building owners worry that this damage will put people at risk of falls,” said lead author Katie Burford, PhD, a postdoctoral research scientist in the Department of Epidemiology at the Columbia Mailman School of Public Health and a postdoctoral research scholar in the Department of Parks, Recreation and Tourism Management at North Carolina State University. “And in many areas home/building owners are responsible for sidewalk maintenance and are liable if someone falls on the sidewalk in front of their building.”

Researchers analyzed data on tree canopy cover at 497 locations where Emergency Medical Services attended to pedestrians injured in a fall between April and September 2019 and at 994 carefully matched control locations. Tree canopy cover at each location where an injurious fall occurred and at matched control locations was measured using the 2019 National Land Cover Database—the national gold standard for canopy assessment.

Average tree canopy cover at fall locations was 8 percent, compared with 14 percent at control sites. Higher tree canopy cover was strongly inversely associated with locations where a pedestrian fall occurred after controlling for neighborhood socioeconomic factors and proxy measures for pedestrian volume.

“Sidewalk-related injuries represent a substantial public health burden,” said Andrew Rundle, DrPH, professor of Epidemiology at Columbia Mailman Public Health and senior author. “Unlike indoor falls, which are often linked to personal health factors, outdoor falls are shaped by environmental conditions. Our findings suggest that tree cover, by lowering ambient temperatures, may help reduce fall risk.”

The researchers note that while outdoor fall risk is well known to be associated with snow and ice, emerging data suggest that high temperatures can increase fall risk.  High temperatures can increase fall risk by adversely affect human physiology and by degrading road and sidewalk surfaces. High heat softens asphalt and causes sidewalk pavers to pop out of alignment creating trip and fall hazards.

“Our work demonstrates how emergency medical services data can be leveraged to study pedestrian falls on a large scale,” said Rundle. “Future studies should examine how the cooling effects of tree canopy directly influence fall risk.”

Co-authors are Alexander X. Lo, Northwestern University Feinberg School of Medicine; James W. Quinn, Columbia Mailman School of Public Health; Remle P. Crowe, ESO Solutions LLC, Austin; Allan C. Just, Brown University; Michelle C. Kondo, United States Department of Agriculture; and John R. Beard, Columbia Mailman School and Butler Columbia Aging Center.

The study was supported by the National Institute of Environmental Health Sciences (5T32ES007322-21, R01 ES031295), the National Institute on Alcohol Abuse and Alcoholism (R01AA028552), the Columbia Center for Injury Science and Prevention (CDC R49CE003094), and the National Institute on Aging (P20 AG089308).

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