Shelters at bus stops intended to provide relief from heat can actually result in higher temperatures, UTHealth Houston researchers discover

(Press-News.org) Some public transit shelter designs can actually do more harm than good when it comes to shielding from summer temperatures, according to a study led by UTHealth Houston.

The research was published in Transportation Research Part D: Transport and Environment.

Public transit can be more affordable, healthy, and safe than commuting by car. Research supports that public transportation is also better for the environment by limiting emissions and air pollution. According to the American Public Transportation Association, more than two-thirds of transit users in the U.S. walk to the transit stop or station. However, during extreme summer temperatures, transit riders may find taking public transport more difficult.

Shelters installed at transit stops and stations are designed to provide protection from extreme heat, high winds, solar radiation, rain, and snow. But according to Kevin Lanza, PhD, assistant professor in the Department of Environmental and Occupational Health Sciences at UTHealth Houston School of Public Health, no studies have taken ground measurements to determine how shelters and tree shade at bus stops influence heat stress.

“Heat stress is a combination of factors, not just the temperature you see on your phone’s weather app or your car dash,” Lanza said. “Imagine it’s 100 degrees out. If the sun is also strong and hitting you, that continues to heat you up.”

Prolonged exposure to high temperatures, such as when one is waiting for the bus, can lead to heat stroke, which can occur in minutes when the body’s core temperature reaches 104 degrees. The chances of heat stroke increase when high temperatures are accompanied with high humidity. 

The study focused on trees and shelters at 17 bus stops in Houston over 13 days when temperatures reached 95 to 103 degrees between July 20, 2023, and Aug. 7, 2023. Researchers used advanced sensors to record wet bulb globe temperature (WBGT), a measure of heat stress that combines air temperature, humidity, wind speed, and solar radiation, in shaded and unshaded areas at bus stops. Taking into account shelter design, tree canopy coverage, and time of day, they determined how shade impacts the heat stress of bus riders.

On average, unshaded areas at bus stops recorded a WBGT of 92.5 degrees, posing a significant heat stress risk. Results found that providing shade at bus stops significantly reduced WBGT. On average, trees lowered WBGT by 5.9 degrees.

Lanza and the team looked into four bus shelter designs. Of the four, a stainless steel frame with glass sides and roof provided the most cooling (5.9 degrees lower). Another design, with an aluminum frame, translucent acrylic walls, and a slightly domed roof, only cooled the air by 1.6 degrees. A third similar design with a larger dome but shallower depth and an overhanging roof cooled the air by 2.9 degrees. However, the team measured temperatures underneath that shelter, when unshaded, to actually be 5.2 degrees higher than unshaded areas outside of shelters. 

“Because the enclosed acrylic walls with metal trapped radiation inside the shelter, it was like an oven, making it hotter than outside the shelter,” Lanza said. “Study results can serve as evidence for planting trees at bus stops for maximum cooling, and if shelters are the only option, then being strategic in design.”  

Co-authors of the study include Baojiang Chen, PhD, an associate professor of biostatistics at UTHealth Houston School of Public Health, and Sara Ernst and Katie Walkins, former journalists at Houston Public Media.

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