Wagner Researcher Examines Transit Patterns in Variety of Weather

By Robert Polner

Every transit commuter has war stories related to the weather, whether it was that rain storm that drowned their hopes of getting home on the subway, the blizzard that stopped bus service dead in its tracks, or withering heat that made them wish they were sitting in a cooled car, even one wedged in traffic.
     But plumb the research literature on weather and travel, and the studies focus almost entirely on driving and traffic volumes. Zhan Guo, an assistant professor of urban planning and transportation at the Robert F. Wagner Graduate School of Public Service, was surprised that, in the context of transit, Mark Twain was right when he said, “Everybody talks about weather, but nobody does anything about it.”
    To break the ice, Guo set out to discover how operators of mass transit systems could think more systematically about weather to fine-tune service, save money, and increase ridership.  His paper on the topic—co-written by Nigel H. M Wilson of MIT, and Adam Rahbee, a manager at the Chicago Transit Authority—focuses on transit ridership in Chicago and was published recently in the Journal of Transportation Research Board.
    Guo grew up in a coastal Chinese province where the bicycle was the most prominent mode of travel, contributing to his interest and expertise in sustainable transportation policy. His research illuminates that weather’s impact on ridership is not as straightforward as one might guess. To some transit experts, good weather is good and bad weather is bad. But that is not always true, says Guo. In inclement weather such as heavy rain or big snow, ridership might increase, especially on weekdays because motorists might opt for public transportation. The same is true on very foggy days, when driving is slow or even risky.
    Weather can also change the ridership pattern inside the transit system. Bus ridership is more responsive to weather than rail because the latter is better protected from weather. Bad weather on a Saturday normally increases ridership on Sunday because people may postpone their Saturday trips. Different bus routes also respond to weather differently depending on their locations and the served population. For example, routes along the Chicago lakeshore and subway corridors tend to be more affected by weather than other routes. The ridership response to this indicates how captive or flexible the passengers are on each bus route.        
    Knowledge of these sorts of patterns can help planners prepare, says Guo. It also helps them tease out whether they’re doing a good job retaining or increasing ridership, whether additional resources are needed or can be pulled back, and when investment in bus shelters and air conditioning can be helpful. The weather-transit relationship, properly modeled, tells planners many things, adds Guo. He notes that in Chicago, the bus ridership in July fell by about 1 million from 2002 to 2003, but after controlling for the impact of weather (inclement days kept people away in sizeable numbers), there was actually a small underlying ridership increase of 93,000.  
    “Weather matters—this is not new,” says Guo. “But through systematic research, we can go beyond just thinking about the weather and we can do something with it.”