Modeling net effects of transit operations on vehicle miles traveled, fuel consumption, carbon dioxide, and criteria air pollutant emissions in a mid-size US metro area: findings from Salt Lake City, UT

• Published in: Environmental Research Communications 2019-10, Vol.1 (9), p.91002
• Main Authors: Mendoza, Daniel L, Buchert, Martin P, Lin, John C
• Format: Article
• Language: English
• Subjects: Air pollution; Air quality; Buses; Carbon dioxide; carbon emissions; Commuter transport; Compressed gas; criteria air pollutants; Diesel fuels; electronic fare collection; Emissions; Fuel consumption; Gasoline; Infrared analysis; Light rail transportation; Locomotives; Metropolitan areas; Modelling; Natural gas; Nitrogen oxides; Particulate emissions; Particulate matter; Passengers; Photochemicals; Pollutants; Pollution control; public transit; Ridership; Schedules; Sulfur; Sulfur oxides; transportation; Travel demand; urban development; Urban rail
• ISSN: 2515-7620; 2515-7620
• DOI: 10.1088/2515-7620/ab3ca7

The Utah Transit Authority (UTA) serves Utah's Wasatch Front, a rapidly growing conurbation with a current population of ∼1.8 M people. UTA uses an electronic fare collection (EFC) system that requires riders to tap on as they enter a bus or train and tap off as they exit, as well as an automated passenger counter (APC) system that counts interruptions of infrared beams across vehicle doorways as riders board and alight. We analyzed EFC and APC data for 2016, along with service schedules and routes from General Transit Feed Specification (GTFS) data, to estimate the impact of UTA on the air quality in its service region by accounting for vehicle miles traveled, gasoline gallons equivalent of fuel consumed, and multiple pollutant species emitted. Buses, light rail, and commuter rail were found to collectively offset approximately 1.5% of the onroad emissions from the counties served by UTA due to transit use replacing single passenger vehicle use. These offsets are not homogeneous; ridership drops significantly (∼20%-50% depending on the mode) during the summer months as some of the largest users are educational institutions with noticeable seasonal cycles. Low transit use during the weekend negates some of the air quality benefits as buses and trains travel at lower capacity. Central routes, particularly during peak travel hours provide noticeable congestion, fuel consumption, and pollutant emissions reduction due to trips taken by transit replacing personal vehicles but off-peak, and non-central routes, show lower benefits. Because the light rail is electric, its local air quality benefits are significant due to the electricity being produced primarily outside the airshed. Upgrading the bus fleet to 2010 model, and newer, diesel and compressed natural gas (CNG) buses, as well as modeling an envisioned change to Tier 3 locomotives for the commuter rail system, was found to significantly reduce regional nitrogen oxides (NOx), fine particulate matter (PM2.5), and sulfur oxides (SOx) emissions.