A UO researcher's examination of urban mobility and climate change offers perhaps the most comprehensive insights to date on extreme weather events and public transit ridership.
Nicole Ngo, associate professor with the UO's School of Planning Public Policy and Management, hopes the results will help city planners and transportation officials address the challenges of climate change.
"A growing number of studies demonstrate the impact of climate change on travel behavior," Ngo said. "But those tend to focus on one city over a narrow time period. It's useful to quantify these trends and confirm they apply nationwide. This will have ramifications for transit agencies down the line."
Ngo gathered data spanning 17 years from the 48 U.S. cities with the highest public transit ridership, covering diverse geographic regions. Her paper in the December edition of Transportation Research Part D also looks at how population and income factor in.
Shahinur Bashar, a doctoral candidate in the UO's School of Planning, Public Policy and Management, was co-author of the paper.
As climate change brings longer, more intense heat waves and heavier precipitation, understanding how weather affects public transit will become more important.
Severe weather events affect our daily lives in ways that have demonstrable financial, health and social welfare costs, Ngo said. Those often affect lower income populations disproportionally, for example those without air conditioning or vehicles.
Policy makers also point to public transportation as an important tool for reducing greenhouse gas emissions. However, Ngo's research demonstrates how extreme weather caused by climate change correlates with a decline in public transit use, especially for buses.
Ngo looked at instances of at least four consecutive days with extreme heat, cold or precipitation. But "extreme" in Phoenix is different than Seattle. The study accounted for those geographical differences.
The project starts with data from 2002, the earliest year with publicly available statistics from the National Transit Database. It ends in 2019, just before the coronavirus pandemic threw a wrench in ridership numbers.
According to Ngo's study, national ridership decreases during periods with extreme heat, cold or precipitation. That decrease was greatest for bus ridership, but only for extremely hot and cold events. Precipitation affected bus and rail equally.
Trains are popular among commuters, Ngo said, whereas bus trips tend to be more diverse. More riders take the bus for recreational and personal trips, as well as commuting to work, and that may account for the differences.
It could also explain why other studies show weekends are more sensitive to weather than weekdays.
On an extremely hot day, Ngo said, you're probably still going to work. But you might skip a trip to a friend's house or a movie if walking to the bus stop and waiting 30 minutes could be excruciating (or, in some cases, potentially dangerous).
You might also opt for a ride hailing service, despite the added cost.
The growth of businesses like Uber and Lyft, as well as bicycle and e-scooter sharing programs, could be the cause of another national trend Ngo discovered. Extreme heat has affected bus ridership from 2016 to 2019 more than in the earlier years of the study.
The prevalence of ride-hailing and micromobility programs could offer attractive alternatives to the bus on hot days, Ngo speculated.
The study also revealed that the impact of extreme cold on ridership has declined over the years. That could be the result of fewer extremely cold spans, another result of climate change. The effect of precipitation, however, was constant throughout the time period.
Also, areas with lower median income demonstrated a pronounced decrease in public transit ridership on very cold days. Finally, for more populated cities, precipitation decreased ridership in some cases.
Ngo hopes the national view covering nearly two decades will help researchers and planners zoom in on distinct challenges and opportunities for their cities. Ultimately, she said, the best solutions will be developed at the local level. But Ngo has some ideas.
Adding bus stops, expanding transportation networks and increasing the frequency of routes could help. Better shade and rain coverage at bus stops also could encourage riders.
Ngo's research indicates lower-income cities are more sensitive to cold than higher-income cities. Bus shelters with insulation or heating could work for those areas. Cities with higher populations tend to be more sensitive to precipitation, so protection from rain, sleet and snow may be more effective for them.
For some cities, infrastructure updates might help. For example, on extremely hot days Portland's Max trains must slow down because of expanding rails and overhead electrical wires.
The same solutions won't work for every city, Ngo said. But her examination of public transportation across the nation could help get everyone on board.
