This summer, Puget Sound area residents experienced high temperatures like never before — heat waves made worse by impacts of climate change, experts say.

While many people fled in air-conditioned cars to lakes and water parks to cool off, others, including transit-dependent essential workers, still relied on buses and trains to get to work. In some cases, that means standing outside on hot pavement in 90-plus degree temperatures to wait for a ride.

Of the approximately 7,500 Metro bus stops across King County, 1,700 have bus shelters, agency spokesperson Jeff Switzer said.

How does transit fare in extreme weather?

Researchers Kevin Lanza and Casey P. Durand studied this question by analyzing ridership data in Austin, Texas, between April and September of 2019. Their findings, which review whether bus stop shelters and trees can moderate the impacts of extreme heat, were published earlier this year.

Lanza earned his Ph.D. in city and regional planning from the Georgia Institute of Technology and studied the public health implications of heat intensified in urban environments.

In our latest Traffic Lab Ask An Expert Q&A, we spoke with Lanza about his report and what transit systems should understand about serving riders during high temperatures and extreme weather conditions.

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This interview has been lightly edited for length and clarity.

How did you get interested in this topic?

Hurricane Charlie hit Central Florida 2004 when I was in high school. I’m an avid runner, and I noticed after the hurricane, which took down many of the large Oak trees on my favorite running routes, that these routes became less appealing. Not only were they less attractive because of the trees no longer being there, but it was also hotter because there was less shade. That was my introduction into what is called the urban heat island effect, an area of a city that is warmer than its surroundings because of human activity.

What do you think cities around the U.S. should take away from the findings of your study?

High temperatures are reducing transit ridership. Trees have been shown to modestly reduce the effect of extreme heat on ridership or reduce the losses of ridership from extreme heat. Bus stop shelters don’t have that same association but both bus stop shelters and trees are proven heat management strategies that can in some specific instances be used exclusively or together to assist with climate adaptation of transportation networks.

Were any findings surprising?

We didn’t see bus stop shelters preventing losses of ridership when it was extremely hot. But we also understand that most of the population who uses transit, at least in Austin’s public transit system, is low-income. It may be that these communities have transit dependency. They may not have another mode of transportation accessible, such as a car. Therefore even when it is hot outside, they’re still using public transit.

Are these findings applicable to other cities?

This study took place in Austin, a humid subtropical climate that’s found in the Southeastern United States. Parts of the arid Southwest could also find this study relevant. Cities like Seattle, Portland and San Diego are just as threatened by heat but in a different way. These populations aren’t used to these types of temperatures and therefore might not have the infrastructure available and may not be climatized as individuals in other hot regions could be.

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Are bus stop shelters effective and a good use of investment by transit agencies to protect riders from heat?

That’s a tough one. Bus stop shelters and trees — considering those as two strategies to moderate temperatures — both have pros and cons.

A pro of a bus stop shelter is that there is relatively less maintenance involved. You build it and it doesn’t require much upkeep. You don’t water it. A bus stop shelter also gives you immediate shading and protection from incoming solar radiation that your body then absorbs and heats up with.

With trees, the largest cost is the upkeep. Who’s going to water it? Who’s going to trim it? Who’s going to handle the soil and infiltration? The benefit of a tree is that it provides aesthetics. It is noise reducing. And it has been shown to make walks feel shorter. They are storm water management, and they provide a habitat for a potential biodiversity. It takes time to receive those co-benefits.

Given the limited resources within public transit agencies, should officials and planners incorporate bus shelters or trees as part of bus project planning?

Transportation systems need to be resilient to climate change. There needs to be greater accessibility to public transit. That will reduce potential exposure to heat by allowing people to get to and from their station or bus stop quicker and minimize the amount of time they’re waiting or traveling in high temperature conditions. It also includes programmatic changes like increasing the headway of how often different transit vehicles come and go to ensure that individuals are not being unduly subjected to high temperature conditions.

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Are riders more likely to tolerate the heat if frequency and reliability of the service is met?

Yes. One hundred percent. How do we make transit the easy choice, for those who have the ability to choose their option? For those who don’t have the ability to choose, how do we make transit as comfortable and convenient as possible? Disproportionately some populations, like low-income communities and communities of color, are more affected by heat than others because of different exposure levels through past racist policies and ongoing disinvestment.

What is the impact of extreme weather in general, whether heat, rain, or snow, on transportation systems and what agencies can do to mitigate it?

Heat is drawing attention right now, but what the Pacific Northwest should refrain from doing is forgetting. Soon, it’s not going to be a summer anymore, and it may be a mild summer next summer, but even if you have an off year, your transit system has to be prepared.

Bus stop shelters are dual purpose. In Seattle, the bus stop shelter and even a heavily leafed mature tree will reduce the amount of rain droplets onto a person. Even if there are people that do not necessarily believe in climate change, I think they believe in the beauty of a tree.