With the use of better rider tracking tools, a new report from the University of Utah and the Utah Transit Authority can better answer the question: How much does public transit reduce pollution emissions?
Researchers used tap-on tap-off rider data to quantify the emissions saved by buses and commuter rail lines, and also project how much additional emissions could be saved by upgrading the bus and rail fleet.
High-resolution rider data
A couple of recent technological advances have enabled University of Utah researchers Daniel Mendoza, Martin Buchert and John Lin to answer the question with a level of detail previously unparalleled.
The first is the advance of tap-on tap-off farecards that provide anonymized data on where those riders who have electronic passes enter and exit public transit. Approximately half of UTA’s passengers use an electronic fare medium. “Now we can truly quantify trips in both time and space,” Mendoza says. “We accounted for all of the 2016 passenger miles by scaling the farecard data, and we know which trips farecard holders make on buses, light rail and commuter rail.”
The second is the General Transit Feed Specification system. It’s the data source that supplies Google Maps with transit information to help users find the bus or train they need. With that data source, the researchers could track where and how often UTA’s buses and trains run.
So, with high-resolution data on the movement of both vehicles and passengers, the researchers could paint a nearly comprehensive picture of public transit along the Wasatch Front.
Balancing emissions
So, with that data, the researchers could quantify the emissions produced and miles traveled of the transit systems (TRAX light rail uses electricity produced outside the Wasatch Front, hence the emissions aren’t in Salt Lake’s air) and balance that with the miles traveled by passengers and the estimated amount of car travel avoided by riding transit.
On weekdays during rush hours, and in densely populated areas, the balance was clearly on the side of reduced emissions. “That tapers off significantly during the evening hours, on the outskirts of the city, and definitely during the weekends,” Mendoza says. In those situations, the number of passengers and how far they rode transit did not offset certain criteria pollutant emissions. (Criteria pollutants are six common air pollutants that the EPA sets standards for through the Clean Air Act.)
For transit to improve its regional reduction in emissions, particularly PM2.5 and NOx, the following strategies, alone or in combination, could be employed: more daily riders per trip, more clean-fuel buses and train cars and/or fewer low-ridership trips.
