An Update on Public Transportation's Impacts on Greenhouse Gas Emissions (2021)

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15   National Sustainability Benefits of Public Transportation Public Transportation’s GHG Savings Public transportation in the United States saved 63 million metric tons of carbon dioxide equivalent (MMT CO2e) emissions in 2018—the equivalent of taking 16 coal power plants offline for a year (U.S. EPA 2020c). This study examined public transportation’s impacts on GHG emissions by calculating the difference between transit vehicle GHG emissions (12 MMT of CO2e) and GHG reductions associated with transit. • Transportation Efficiency GHG Savings: The GHG emissions saved by passengers riding transit rather than using personal vehicles: 9 MMT CO2e saved in 2018. Transit passenger surveys show 33% of transit passenger miles would otherwise be replaced by personal vehicle miles (APTA 2020). • Land Use Efficiency GHG Savings: The GHG emissions saved by the broader impact of transit on VMT in the community: 66 MMT CO2e saved in 2018. Even residents who do not ride transit themselves save GHGs because transit creates land use efficiencies, such as through shorter driving trips, fewer driving trips, and more trips on foot or by bicycle. • Net impact: 12 MMT CO2e emitted − 75 MMT CO2e reduced = 63 MMT CO2e. Transit Vehicle GHG Emissions, 12 MMT CO2e Public transportation vehicles traveled 4.7 billion miles in 2018 using diesel fuel, gasoline, natural gas, hydrogen, liquefied petroleum gas, electricity, biodiesel, and ethanol. Public transportation consumed 837 million gallons of fossil fuels, 6.7 billion kilowatt hours (kWh) of electricity, and 137,559 gallons of hydrogen in 2018. Transit vehicle emissions include direct CO2e emissions that occurred at the vehicle, indirect CO2e emissions that occurred at power plants and during hydrogen production, and upstream CO2e emissions from production and distribution. C H A P T E R 3

16 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions Public transportation in the United States used 49 million gallons of biodiesel fuel and 47 thousand gallons of ethanol in 2018 (FTA 2020a). The CO2 emitted by these fuels is con­ sidered “biogenic” by major GHG accounting standards because it is sourced from plant matter and part of the natural carbon cycle, so it is tracked separately, while the CH4 and N2O emissions associated with these fuels is tracked as part of the overall vehicle GHG emissions (U.S. EPA 2016). Transit use of biodiesel and ethanol emitted 0.5 MMT biogenic carbon dioxide [CO2(b)] in 2018. Transit vehicle GHG emissions fell 19% from 2005 to 2008 even as transit passenger miles rose 9% over that period. The savings from 2005 to 2008 came from decreased fossil fuel use and an increased use of cleaner electricity. The average CO2 per kWh fell 47% from 2005 to 2018, making electricity a much lower­carbon choice (Davis and Hale 2007). Transportation Efficiency GHG Savings, 9 MMT CO2e Transportation efficiency GHG savings are from the avoided personal vehicle travel of transit passengers. Passengers rode public transportation 54 billion miles in 2018. Transit passenger surveys show 32.9% of transit passenger miles would otherwise be replaced by personal vehicle miles (APTA 2020). The term “personal vehicle” is used to indicate automobiles and light trucks and includes ridehailing and taxi vehicles for hire. The average personal vehicle on the road in 2018 had a fuel economy of 22.5 mpg. Land Use Efficiency GHG Savings, 66 MMT CO2e Even residents who do not ride transit themselves save GHGs because transit creates land use efficiencies, such as through shorter driving trips, fewer driving trips, and more trips on foot or by bicycle. In 2018, these efficiencies avoided 131 billion miles of personal vehicle travel in communities with transit. The combination of these three emissions impacts: transit vehicle GHG emissions (12 MMT CO2e) − transportation efficiency GHG savings (9 MMT CO2e) − land use efficiency GHG savings (66 MMT CO2e) = a net 63 MMT CO2e savings impact of public transportation in 2018. That net savings is equivalent to 3% of U.S. transportation GHG emissions in 2018 (U.S. EPA 2020c). More information about public transportation GHG impacts by individual transit agency can be found in Appendix B and in the spreadsheet tool for this project. Electric vehicles made up approximately 0.4% of all light­duty vehicles in 2018 [Edison Electric Institute (EEI) 2019 and FHWA 2019a]. The GHG savings here do not include electric personal vehicles due to lack of data about the location of electric vehicles and their limited prevalence in 2018. At the national average emissions factor for electricity and a presumed average efficiency of 30 kWh per 100 miles of travel, the inclusion of electric vehicles would have reduced the transportation efficiency GHG savings by 29,052 metric tons (MT) CO2e, or 0.3% of the 9 MMT CO2e total. The inclusion of electric vehicles would have reduced the land use efficiency GHG savings by 213,514 MT CO2e, or 0.3% of the 66 MMT CO2e total. This will become a more important element of public transportation’s GHG impact in the future as electric vehicles become more common for personal use. Figure 4 shows public transportation’s 2018 GHG impacts, with transit vehicle emissions on the left and the reductions associated with transit on the right. When the emissions and reductions are added together, the net savings is 63 MMT CO2e. This study takes into account the full life cycle of transportation fuels (see Figure 4), as follows: • Direct CO2e emissions at the vehicle. • Indirect CO2e from power plants and hydrogen production facilities. • Upstream CO2e from fuel production and distribution.

National Sustainability Benefits of Public Transportation 17   Public Transportation’s VMT and Fuel Impacts Communities with public transportation avoided 148 billion miles of personal vehicle travel in 2018 through transportation efficiency and land use efficiency savings. That was 5% of the 3 trillion total U.S. vehicle miles that year, but in transit­rich areas, it can be a much larger share of total travel. The personal vehicle miles savings include vehicle trips avoided by transit passen­ gers and vehicle trips avoided in communities with transit due to location efficiency and other transportation and land use factors. This value was calculated using the methods identified in Chapter 2. Transit vehicles traveled 4.7 billion miles in 2018, and the average transit vehicle had 12 passengers. For comparison, average private vehicle occupancy for commute trips was 1.18 passengers, and for all trips was 1.67 passengers (FHWA 2018). Public transportation helped avoid 6.6 billion gallons of gasoline use in 2018 through trans­ portation efficiency and land use efficiency savings, and transit vehicles used significantly less energy than that—837 million gallons of fossil fuels, 49 million gallons of biodiesel and ethanol, and 6.7 billion kWh of electricity. Figure 4. Public transportation GHG impacts, 2018.

18 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions Transit’s Transportation Efficiency Impact, or the avoided personal vehicle travel of transit passengers, was 17.8 billion miles of vehicle travel and 790 million gallons of fuel use in 2018 based on 54 billion total transit passenger miles, a mode shift factor of 0.329 and an average personal vehicle fuel economy of 22.5 mpg. That represents $1.7 billion in annual fuel cost savings at current fuel prices, or $2.2 billion at 2018 fuel prices [Energy Information Administration (EIA) n.d.]. Transit’s Land Use Efficiency Impact, or the avoided vehicle miles in the communities where transit operates, was 131 billion miles of vehicle travel and 5.8 billion gallons of fuel use in 2018 based on 17.8 billion avoided personal vehicle miles among transit passengers and a transit multiplier of 8.35 across all transit agencies (17.8 billion × 8.35 − 17.8 billion = 131 billion). That represents $12.2 billion in annual fuel cost savings at current fuel prices, or $15.8 billion at 2018 fuel prices (EIA n.d.). Importance of Equity and Health The transportation and land use efficiency enabled by public transit and the resulting fuel savings create many other sustainability benefits that were outside of the scope of this

National Sustainability Benefits of Public Transportation 19   analysis but are extremely important for communities. These include a reduction in criteria air pollutant emissions that have an impact on health, traffic safety improvements as fewer residents drive, and health benefits as more residents walk and bicycle to transit and in place of driving for shorter trips in location­efficient areas. The health impacts of our trans­ portation choices are also important to consider. Studies show that air pollution and living near busy roads contribute to respiratory and cardiovascular health problems, including asthma in children (Health Effects Institute 2010, Chen et al. 2015). Investment in public transportation can reduce air pollutants in addition to GHGs and make the air safer for those at risk. Public transportation serves many essential community needs, so while its role as a climate solution is important, GHGs are not the only metric that should be used to measure transit success. Every transit passenger is traveling for a reason, and equity and transportation access require that transit service be available to meet the needs of seniors, shift workers, students, and others who may not ride the highest­occupancy routes or at peak commute times. Measured by CO2e per passenger mile alone, these routes may look like they perform less well, but incorpo­ rating metrics like access to jobs or travel time to low­cost grocery stores may show these to be high­priority routes. Sustainability is not a one­dimensional concept, and public transportation contributes to community resilience in multiple ways beyond its carbon savings, such as by reducing house­ hold transportation costs (CNT n.d.). As communities look to public transit investment as a climate solution, the full spectrum of equity and resilience impacts of transit should be part of that decision making. Planning for a sustainable, resilient future must include public transpor­ tation that serves community needs. Reduced Carbon Footprint of Individuals Using Public Transit Public transportation helps passengers reduce their carbon footprint. Passengers contributed 55% fewer GHGs per mile by riding transit in 2018 than those driving or ridehailing alone. Public Transportation Emissions averaged 0.23 kg CO2e per passenger mile across all transit modes in 2018 including direct, indirect, and upstream GHG emissions.

20 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions The Average Light-Duty Personal Vehicle Emissions—a weighted average of passenger cars, pickup trucks, vans, and sport utility vehicles—was 0.51 kg CO2e per mile of direct, indirect, and upstream GHG emissions at 22.5 mpg (FHWA 2019a). What about carpooling? A two­person carpool cuts vehicle emissions per person in half to 0.25 kg CO2e per mile each, which remains slightly higher than the public transportation average of 0.23 kg CO2e per passenger mile. The 2017 National Household Travel Survey found that the typical commute trip in a personal vehicle had 1.18 passengers, and the average trip of any purpose, including shopping, recreation, or errands, had 1.67 passengers (0.43 kg CO2e per passenger mile and 0.30 kg CO2e per passenger mile, respectively) (FHWA 2018). By those measures, typical personal vehicle trips had higher emissions per person per mile than riding transit. The average light­duty vehicle traveled 11,556 miles in 2018. A person driving that distance alone would have had a transportation GHG footprint of 5.9 metric tons of CO2e per year as compared to 2.6 metric tons of CO2e if transit had been used. An average U.S. household would have to cut its electricity use in half to achieve those same GHG savings at home (U.S. EPA 2020c). These figures are for a gasoline­powered personal vehicle. Depending on the source of electricity, the emissions profile of an electric car can be significantly lower. In 2018, there were an estimated 1 million electric vehicles on the road—approximately 0.4% of all light­ duty vehicles (EEI 2019 and FHWA 2019a). An electric car emitted 0.14 kg CO2e per mile in 2018 at the U.S. average emissions factor for electricity and a fuel efficiency of 30 kWh per 100 miles. Depending on the electricity grid subregion supplying the electric vehicle, emissions per mile could have ranged from 0.04 to 0.24 kg CO2e per mile. This range is similar to the per­passenger emissions of a battery electric bus in 2018. Of note, fuel economy improvement in personal vehicles can have a mixed effect on overall emissions if it induces more automobile travel (Munyon et al. 2018). Emissions per Passenger Mile by Transit Mode Public transportation is a low­carbon solution for passengers, and it has gotten better over time. Compared against two previous studies, emissions per passenger mile in 2018 were 26% lower than in 2005 (Davis and Hale 2007) and 10% lower than 2008 (FTA 2010). Slight differences in research methodology between those studies make those two values not directly comparable, but both indicate that today’s transit is lower carbon than it was in the past. Figure 5 shows that rail modes have seen the largest savings in GHG per passenger mile, but the carbon efficiency of bus ridership has improved as well as transit agencies have adopted new technologies, fuels, operations, and practices. All in all, transit kept pace with private auto efficiency improvements over the decade of 2008 to 2018.

National Sustainability Benefits of Public Transportation 21   Note: Values in are in CO2 not CO2e in this chart only for consistency with previous analysis; private auto value in terms of single occupancy vehicle (SOV). Figure 5. Change in transit GHG emissions per passenger mile 2008 to 2018. In 2018, the most carbon­efficient modes on a per­passenger­mile basis were rail transit modes, which also transported 60% of passenger miles (Figure 6). Buses varied in emissions efficiency depending on fuel, technology, operations, and occupancy. Electric and biodiesel buses had the lowest GHG emissions per passenger mile in 2018 among all buses. Passengers on ferries and vans had higher emissions profiles, but those modes only accounted for 5% of passenger travel in 2018. The lowest­emitting transit mode on a per­passenger­mile basis was heavy rail at 0.08 kg CO2e per passenger mile. Heavy rail’s emissions profile was driven by its high average occu­ pancy (48% of revenue seat miles) and all­electric power source. The electricity powering heavy rail had average GHG emissions of 0.32 kg CO2e per kWh, which was less than the national average of 0.43 kgCO2e per kWh but similar to other transit averages. Vans had high emissions on a per­passenger­mile basis, but much of that is a factor of their small number of seats compared to other transit vehicles and their relatively low occupancy. The typology for this study classifies transit vehicles from automobiles to cutaways as “vans.” The average van in 2018 carried just two passengers per vehicle, as compared to over eight for a bus. Vans often provide essential accessibility services, so their efficiency should not be judged without considering their purpose. Ferryboats were the highest emission mode per passenger mile at 1.0 kg CO2e per passenger mile in 2018; however, ferryboats are not a large source of transit emissions overall—just 4% of the total in 2018. Only 27 transit agencies operated ferryboats in 2018. Transit passengers took 4.7 billion trips on buses in 2018, the most of any public transporta­ tion mode. The emissions profile of those trips varied with the fuel and technology of the bus. A typical passenger bus trip in 2018 was 4 miles. The emissions for that trip were 1.4 kg CO2e per passenger in an average transit bus, but just 0.5 kg CO2e per passenger in an average battery electric bus, although that trip could have ranged from 0.1 to 0.9 kg CO2e per passenger based on

22 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions the electricity sources in their area (Figure 6). Emissions per passenger mile broken out by indi­ vidual transit agency and mode can be found in Appendix B and this project’s spreadsheet tool. Transit Agency Contributions to GHG Emission Reduction and Sustainability Figure 6. Average GHG emissions per passenger mile by mode.

National Sustainability Benefits of Public Transportation 23   Transit agencies are taking climate actions. Transit GHG emissions have fallen over the past 15 years on both an overall basis and a per­passenger­mile basis. Even those that are not setting specific GHG targets are pursuing fuel efficiency and cost savings that can bring GHG saving along with them. Transit agencies are adopting lower­carbon vehicle technologies and fuels, such as hybrids, regenerative braking, biofuels, and electric vehicles. The growth of electric buses in recent years has been notable and especially beneficial as more carbon­intensive grid electric power sources like coal have been replaced by renewable solar and wind. TCRP Research Report 219: Guidebook for Deploying Zero-Emission Transit Buses provides detailed information for transit agencies looking to pursue this option (Linscott and Posner 2020). Looking forward, a continuation of these trends will ensure that transit continues to be a low­carbon solution to meeting transportation needs. This will be even truer if ridership and occupancy increase over time. However, decreases in ridership, whether due to COVID­19 creating lasting disruptions in our travel patterns or scaling back of transit service, will shrink transit’s GHG benefits. TCRP Research Report 209: Analysis of Recent Ridership Trends presents a detailed description of factors that can increase ridership, including increased service in transit­oriented areas (Watkins et al. 2020). Nevertheless, transit will continue to provide other resilience benefits in terms of essential mobility and access to communities that are otherwise made vulnerable by age, income, disability, neighborhood disinvestment, or other forces that may also put them on the front lines of climate disruption. Bus Fleets Are Moving to Lower-Carbon Fuels and Technologies In recent years, a significant share of the transit bus fleet has shifted away from traditional diesel technology, and this is contributing to emissions reductions. Figure 7 from the Alter native Source: U.S. Department of Energy 2020. Notes: 2018 NTD data used elsewhere in this report include 628 electric propulsion buses not represented in the Figure 7 dataset. *Biodiesel counted as other in 2008. **2012 data estimated. Figure 7. Transit bus fleet by fuel type, 2007–2018.

24 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions Fuels Data Center shows counts of public transportation buses by fuel and technology from 2007 to 2018 using data from APTA’s 2019 Public Transportation Fact Book (APTA 2019). These data show that the adoption of hybrid vehicles has been growing in recent years. Hybrid buses may still use diesel fuel but use it more efficiently. The adoption of natural gas and biodiesel fuel alternatives are also notable. The recent rise in electric bus technology is still small compared to the overall fleet but was starting to be noticeable in 2018. Figure 7 is included because it has a useful temporal perspective on the public transportation bus fleet, but it should be noted that it uses a slightly different dataset than that used for the analysis in this report. The NTD data used for this study show 363 electric battery buses being used by 44 transit agencies over 4 million miles in 2018; an initial examination of 2019 NTD data show this grew to 547 electric battery buses traveling 7 million miles. That is a striking increase from 2015 NTD data, which show 114 electric battery buses. Transit agencies have indicated success with electric battery bus adoption, citing the lower energy cost and reduced maintenance needs as particularly beneficial, although the up­front capital cost of electric vehicles and charging infrastructure remains a barrier to broader adoption. Electricity pricing structures also affect cost effectiveness, and high demand charges or time of use variability mismatched to transit agency needs may need to be addressed to make electri­ fication viable in some communities. Battery electric buses have many co­benefits, including noise reduction, zero tailpipe criteria air pollutant emissions, and an association with innovation that are appealing to many stake­ holders. Cold weather performance is a limitation of battery electric buses today, but operational solutions can extend vehicle range, including preheating vehicles at the garage and deploying charging stations along routes. Electric transit vehicle technology is improving rapidly and may become an even better choice for communities in coming years. Electricity Is Getting Cleaner The rise in electricity as a public transportation fuel is reducing GHG emissions because, on average, electricity in the U.S. is becoming less carbon intensive. As fossil fuel power production is retired and new renewable sources come online, the average CO2e per kWh of electricity used in the U.S. is going down. Figure 8 shows the relevant electricity emissions factors. (Black dots are average; gray dots are ranges for all grid subregions.) The two values on the left outlined in the blue rectangle are the U.S. average for all electricity in 2005 and 2018. In 2005, electricity use in the United States contributed 0.61 kg CO2e per kWh (excluding upstream emissions). In 2018, that fell to 0.43 kg CO2e per kWh, a 29% reduction. Not only is electricity getting cleaner, but transit service is often powered by lower­carbon electricity. Comparing the two values outlined by the green dashed rectangle in Figure 8 shows that transit vehicles in 2018 used electricity that emitted 0.32 kg CO2e per kWh on average. This is 26% better than the U.S. average electricity emissions rate in 2018. Battery electric buses had a slightly higher average emissions rate at 0.40 kg CO2e per kWh. Electric propulsion buses had a rate of 0.27 kg CO2e per kWh. On average, rail vehicles had an emissions rate of 0.32 kg CO2e per kWh. This cleaner­than­average electricity contributes to transit’s climate benefits. Some transit agencies are also generating renewable power to lower their emissions even further, or making clean power purchases, but this study uses U.S. EPA Emissions and Generation Resource Integrated Database (eGRID) subregion electricity emissions factors (U.S. EPA. 2020a) for all transit agencies because there is no national data source on transit agency clean power procurement.

National Sustainability Benefits of Public Transportation 25   Transit Vehicle Emissions by Fuel Heavy rail and light rail systems were all powered by electricity in 2018 and had GHG emissions per vehicle mile of 1.85 and 2.92 kg CO2e per vehicle mile, respectively, including both direct and upstream emissions. Commuter rail systems used several different fuels in 2018. Biodiesel commuter rail emitted 2.32 kg CO2e per mile plus 5.89 kg of CO2(b), diesel commuter rail emitted 6.28 kg CO2e per mile, and electric commuter rail emitted 2.71 kg CO2e per mile on average. Emissions per vehicle mile metrics across modes are not apples­to­apples comparisons because the vehicles have varying occupancy. Commuter rail averaged 92 seats per vehicle, while heavy rail averaged 49, and light rail averaged 58. The average bus had 35 seats in 2018. To enable a comparative look at fuel performance within a single mode, the fuel discussion in the remainder of this section focuses on buses. Diesel fuel remained the most common bus fuel in 2018, and diesel buses emitted 3.05 kg CO2e per mile. The next most common fuel was compressed natural gas (CNG), which emitted 3.46 kg CO2e per mile—a metric affected by the life­cycle emissions properties of the fuel and the fuel economy of the vehicles it is used in. On a per­energy­unit basis, CNG has a lower carbon footprint than diesel, but the energy use and vehicle mileage metrics reported in the NTD indicate a lower vehicle fuel efficiency for CNG buses. This may be influenced by the growing use of hybrid diesel technology. In 2018, the average biodiesel bus had lower GHG emissions per mile than any other fuel type, at 0.92  kg CO2e per mile (see Figure  9); however, biodiesel direct CO2 emissions are considered biogenic so are tallied separately in most GHG assessments, which added another 2.32 kg CO2(b) per mile to those buses. The average battery electric bus emitted 0.97 kg CO2e per mile. Electric propulsion was also efficient at 1.90 kg CO2e per mile on average. The ranges of reported efficiency for these fuels in the NTD are significant, however, and the varying emissions rates of electricity by region contributed to a wide variability of CO2e per mile seen in the electric­powered buses. Note: Ranges indicate highest and lowest eGRID (U.S. EPA. 2020a) subregion GHG values. Figure 8. Electricity emissions factors kg CO2e per kWh.

26 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions Hydrogen was used as a fuel by only four transit agencies in the 2018 NTD dataset. The emissions value used here is for hydrogen produced from natural gas. Hydrogen produced from renewable electricity has a much lower emissions rate, but the NTD data do not indicate hydrogen sources, so the most common source was used in this analysis. Gasoline, liquefied petroleum gas (LPG), and liquefied natural gas (LNG) were all rarely used for transit buses, and buses using these fuels had higher emissions per mile than other fuels. Many factors contribute to the CO2e per mile of buses beyond the carbon content of the fuel. Vehicle size, occupancy, traffic congestion, state of good repair, wait times, driving speeds, and even weather can have an impact on fuel economy and thus GHG emissions. Transit agencies are making significant investments in these operations factors that affect GHG emissions and should continue to do so. Right­sizing transit vehicles to the community’s needs is also important. While high­ occupancy routes in dense areas may fill up an extra­long articulated bus at rush hour, that may not be the right vehicle for other routes, and in small communities, a van may meet passenger needs. The average gasoline van in this study had a fuel efficiency of 9.1 miles per gallon in 2018 as compared to 4.1 miles per gallon for the average diesel bus. However, improving carbon efficiency is not just a matter of reducing bus size—increasing ridership along with occupancy has the added benefit of reducing net emissions in the community. As more people ride transit, more personal vehicle miles are saved. *Biodiesel also generates CO2(b) of 2.32 kg per bus mile. Figure 9. Average transit bus GHG per mile by fuel.

National Sustainability Benefits of Public Transportation 27   National Sustainability Benefits of Public Transportation by Mode Adding together the three categories of GHG impacts (transit vehicle emissions + trans­ portation efficiency + land use efficiency), heavy rail has the largest net GHG savings overall at 30 MMT CO2e (see Figure 10). The GHG benefits of heavy rail come in part because of its electric fuel and in part because of its relatively high average occupancy (48%), but also because of its strong ridership at 17 billion passenger miles. Heavy rail is located in communities with high transit multipliers on average; heavy rail strongly affects the land use patterns in the communities in which it operates and is located in denser places. Transit buses had the largest share of passenger miles of any mode in 2018, with 19 billion passenger miles, and the second largest net GHG impact at 16 MMT CO2e. Buses saved somewhat fewer emissions than heavy rail because buses are a different technology; they had lower occu­ pancy, at 24%, so more vehicles were needed to carry passengers; many buses in 2018 were diesel fueled, a more carbon­intensive fuel than electricity; and buses operate in more places with a lower average transit multiplier than heavy rail. The other modes had GHG impacts in line with the passenger share in 2018: commuter rail saved a net 13 MMT CO2e in 2018, light rail saved 3 MMT CO2e, vans saved 1 MMT CO2e, and ferryboats saved just 0.03 MMT CO2e. Emissions by Transit System Size There were 31 transit agencies in 2018 that had ridership between 250 million and 12 billion passenger miles. These largest transit agencies represented 78% of transit passenger ridership in 2018 (Table 1, column 2) but only 58% of the GHG emissions from transit vehicles. Figure 10. GHG impacts of public transportation by mode, 2018.

28 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions Emissions among larger transit agencies are lower, in part, because these agencies are more likely to operate rail modes than are smaller transit agencies. For example, 11 heavy rail systems are operated by the largest transit agencies and have a median emissions of 0.10 kg CO2e per passenger mile. Small and mid­sized transit agencies operated four heavy rail systems that had a median of 0.16 kg CO2e per passenger mile, a metric that is affected by electricity emissions rates and transit vehicle occupancy. Comparing on an apples­to­apples vehicle basis of bus performance, the largest agencies also had lower average GHG emissions per bus passenger mile (Table 1, column 4), but they had the highest average CO2e per vehicle mile (Table 1, column 6). What are the reasons for these differences? Factors affecting efficiency include fuel type, technology, operating conditions, and ridership. Among buses using the same fuel, GHG performance per vehicle mile is directly linked to fuel economy. Looking at diesel­fueled transit buses in particular, large transit agency diesel buses had lower fuel economy and higher GHG emissions per mile on average (Table 1, columns 7 and 8). Some elements of this fuel economy difference include: • Vehicle Size. Buses operated by larger transit agencies are bigger—41 seats per bus as compared to 38 among mid­sized transit agencies and 29 among smaller transit agencies. • Vehicle Speed. Fewer data are available on operating conditions, but larger transit agencies typically operated in denser areas, had more passengers boarding, and had slower average bus speeds than mid­sized and smaller transit agencies. • Vehicle Technology. The larger transit agencies operated hybrid diesel buses more frequently in 2018 (24% of diesel bus miles as hybrid among the largest transit agencies, compared to 10% and 14% among mid­sized and small transit agencies), which is a countervailing element to the previous two described. The use of hybrid technology and regenerative braking improve fuel efficiency. Without the adoption of hybrid technology, many larger transit agencies would have had less­efficient diesel buses on average and higher GHG emissions. Passenger mile data are not available by fuel type in the NTD, but when ridership and occupancy are taken into account, buses that carry more passengers create CO2e efficiencies per passenger mile. This is multiplied when one takes into account the transportation efficiency and land use efficiency GHG savings discussed elsewhere in this report. What this means for communities and transit agencies working to design climate solutions is that public transportation is a climate solution, but its climate benefits can be strengthened by increasing ridership and occupancy, using vehicles efficiently, improving fuel economy, Column # 1 2 3 4 5 6 7 8 All Modes All Buses Diesel Buses 2018 Passenger Miles Count of Transit Agencies Share of Passenger Miles CO2e per Passenger Mile CO2e per Passenger Mile Median Bus Occupancy CO2e per Vehicle Mile Fuel Economy (mpg) CO2e per Vehicle Mile 250 million to 12 billion 31 78% 0.16 0.30 27% 3.2 3.6 3.4 50 million to 249.9 million 67 13% 0.39 0.39 21% 2.8 4.5 2.8 4,000 to 49.9 million 809 9% 0.56 0.49 14% 2.8 4.4 2.9 Table 1. Transit average GHG metrics by transit agency size, 2018.

National Sustainability Benefits of Public Transportation 29   choosing low­carbon fuels and technologies, and supporting efficient transit operations. Some other efficiency improvements may include public on­demand service where route­based service is not a good match to community needs and low­carbon microtransit options such as providing shared electric bicycles and scooters as part of transit service. A high­level set of scenarios for public transportation’s potential future were created to high­ light the elements of climate impact for transit agencies (see Figure 11). These scenarios are not meant to be predictive but rather serve as hypotheticals for consideration and to provide more information to conversations about public transportation climate action. Public Transportation Scenarios for 2030 and 2050 Business as Usual Base Case As a business­as­usual base case looking to 2030 and 2050, it is expected that transit vehicle technologies will continue to improve, and fuel economy will increase. Given current trends in technology and fuel adoption, it is anticipated that electrification will continue (0.5% per year), and that the use of hydrogen and biofuels will increase to a small degree (0.2% per year). The base case assumes a 2% annual decarbonization of electricity based on recent trends (U.S. EPA 2020a). The base case assumes a ridership recovery from the COVID­19 period and a slight increase in ridership from 2018 to 2030 and beyond. Passenger ridership and fuel economy assumptions for transit vehicles and personal vehicles follow the assumptions in the EIA’s Annual Energy Outlook 2020 (EIA 2020). The net result of this future­year analysis of current trends is that public transportation continues to have significant GHG benefits under business as usual. Ridership Increases GHG Benefits A hypothetical set of scenarios was created that included three types of climate action: electrification, zero­carbon electricity, and increased ridership. The largest GHG change under the scenarios is avoided personal vehicle travel as ridership doubles and triples. Avoided personal Figure 11. Public transportation scenarios for 2030 and 2050 (hypothetical for consideration).

30 An Update on Public Transportation’s Impacts on Greenhouse Gas Emissions vehicle travel creates net savings of 120 MMT CO2e via transportation and land use efficiency in 2050. As passenger levels grow, land use efficiency is expected to grow as well, so a large share of these savings comes from avoided travel among community members who may not be transit passengers. Even with the gradual uptake of personal electric vehicles and cleaner electricity sources, transit provides significant savings to communities into the future. Transit Vehicle Emissions Fall Significantly The combined scenario of electrification, zero­carbon electricity, and increased ridership eliminates 83% of transit vehicle emissions by 2050 even as ridership triples. Emissions from transit vehicles fall from just over 12 MMT CO2e in 2018 to 2 MMT CO2e in 2050 (see Figure 12). The scenario elements creating these changes are explained further in the following. Strong Electrification of Transit As a first future hypothetical, the scenarios apply a significant uptick in electrification to the base case—the assumptions include 50% of buses becoming electric by 2030, 80% of buses becoming electric by 2050, and rail becoming fully electric by 2050. This would reduce the direct and indirect emissions associated with transit vehicles from 10 MMT CO2e in 2018 to just over 6 MMT CO2e in 2030 and about 2 MMT CO2e in 2050. Clean Power The second hypothetical assumption made in the scenarios is that all electricity used for public transportation vehicles comes from zero GHG emissions sources. This change is applied on top of the strong electrification assumption. With clean power, the two steps together would reduce the direct and indirect emissions associated with transit vehicles from 10 MMT CO2e in 2018 to 4 MMT CO2e in 2030 and just over 1 MMT CO2e in 2050. The electrification and clean power scenario elements can also be considered proxies for other zero­carbon fuels and technologies, including the adoption of fuel cells using zero­carbon hydrogen. Figure 12. Transit vehicle direct and indirect GHG emissions, 2030 and 2050 scenarios.

National Sustainability Benefits of Public Transportation 31   Doubling and Tripling Ridership Increasing ridership is the strongest way to increase public transportation’s GHG impacts in communities (Figure 11). Increasing ridership will require additional transit service, which can increase transit vehicle GHG emissions, but this is more than offset by the GHG savings of passengers who avoid personal vehicle use and the larger land use impacts of transit. In this scenario, ridership is doubled over 2018 levels by 2030 and tripled by 2050; at the same time, average occupancy rises above 50% so that some of the additional ridership is absorbed on base­case transit vehicle trips. These assumptions are applied on top of the strong electrification and clean power assumptions. This assumption increases transit vehicle emissions slightly, but that is more than offset by the GHG benefits generated. Scenario Tool The spreadsheet tool produced along with this report allows users to apply these scenarios to 2018 data for individual transit systems to give transit agency staff, decision makers, and researchers a sense of the potential scale of the actions described here.