New rider data shows how public transit reduces greenhouse gas and pollutant 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
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The current study looks at the bus and train fleet as they are now, with some UTA buses around 20 years old and FrontRunner trains whose engines are rated a Tier 0+ on a 0-4 scale of how clean a locomotive's emissions are (Tier 4 is the cleanest; UTA is scheduled to receive funds programmed through the Metropolitan Planning Organizations to upgrade FrontRunner locomotives to Tier 2+). So, Mendoza and his colleagues envisioned the future.
"What if we upgrade all these buses, some of them from 1996 or so?" Mendoza says. "They emit a significantly larger amount than the newer buses, which are 2013 and newer."
What if, they asked, UTA upgraded their buses to only 2010 models and newer, fueled by either natural gas or clean diesel? And what if the FrontRunner engines were upgraded to Tier 3?
Emissions of some pollutants would drop by 50%, and some by up to 75%, they found.
https://www.sciencedaily.com/releases/2019/08/190826143407.htm