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10 CHAPTER THREE ROLE OF TRANSIT IN REDUCING GREENHOUSE GAS EMISSIONS Transit agencies can both reduce GHG emissions from the Figure 5 diagrams the impacts of transit on GHG emis- transportation sector and reduce their own GHG emis- sions, including emissions displaced by and emitted by tran- sions. Transit reduces, or displaces, emissions from other sit agencies. The following sections explain in more detail modes of transportation in three ways. First, buses, vans, the role of transit agencies in reducing their own emissions trains, and ferries can move more people with less fuel and displacing GHG emissions through travel mode shift, compared with private cars. By shifting passengers from mitigation of congestion, and compact development. private to public modes, transit saves energy and reduces GHG emissions. Second, transit service can reduce con- gestion on roadways and thus reduce emissions from vehi- TRAVEL MODE SHIFT cles idling in congested conditions. Third, transit service facilitates compact development patterns that allow people Shifting trips from private cars to transit vehicles is the most to walk and bike instead of drive, thereby saving energy direct way that transit service reduces GHG emissions. Each and reducing emissions. In addition to displacing emis- time someone decides to take an existing bus or train and sions from other modes of transportation, transit agencies leave his/her car at home, GHG emissions from that trip are also produce some GHG emissions of their own from their reduced immediately. Most Americans drive alone to work, use of electricity and vehicle fuels. Furthermore, transit an average distance of 10 mi each way. The average commuter agencies can also reduce and minimize their own GHG driving this distance can reduce GHG emissions from her car emissions by using efficient vehicles and alternative fuels, by 20 lb a day, or 4,800 lb per year, by switching to public and decreasing the impact of their auxiliary functions such transit (4). The more people transit agencies can lure out of as construction and maintenance. their cars and onto more efficient trains, buses, and other tran- sit vehicles, the more GHG emissions are reduced. FIGURE 5 Components of transit's impact on GHG emissions (Source : Recommended Practice for Quantifying Greenhouse Gas Emissions from Transit: Draft, APTA Climate Change Standards Working Group, Mar. 2008, p. 12).
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11 FIGURE 6 Per passenger GHG emissions of transportation options (Source : Hodges, Public Transportation's Role in Responding to Climate Change, Federal Transit Administration, U.S. Department of Transportation, Jan. 2009). (Note : Average vehicle occupancy for commute trips is 1.14. Average occupancy for all trips is 1.63. As reported by the National Household Travel Survey (NHTS) (2001). Passenger loads on transit vehicles, or load factors, are an are not the only benefit, or even the main benefit, that transit important determinant of transit's net impact on GHG emis- systems provide (6 ). For example, CARTA provides travel sions. If a transit vehicle is largely empty, its efficiency is choices for those who cannot or choose not to drive, includ- eroded. Since most transit vehicles release GHG emissions ing people of low income, children, and seniors. CARTA from their own tailpipes, a bus with only a few passengers can should not be viewed as a failure just because it increases net actually emit more GHGs per mile than those passengers would GHG emissions. CARTA may have opportunities to reduce emit traveling in their own cars. Figure 6 shows the effect of GHG emissions by increasing ridership on its existing ser- vehicle occupancy on the GHG efficiency of various passenger vice or by restructuring its service to focus on more heavily transportation modes. A bus, train, or vanpool with average used routes, but the agency must consider impacts on the occupancy is more GHG efficient per passenger mile than an local community in addition to impacts on GHG emissions. average auto trip to work. On the other hand, a carpool of four people rivals or exceeds the GHG efficiency of an average bus, U.S. transit agencies can directly reduce GHG emissions train, or vanpool, but when transit vehicles fill all their seats, by increasing ridership on their existing services, so that more they are more efficient than a four-person carpool. A typical people leave their cars at home on a daily basis. Currently, the 40-seat diesel bus must carry around seven passengers at a time United States falls far short of other industrial countries in to be more efficient than the alternative of SOVs. The average transit ridership. A 2002 study found that the net impact of heavy-rail car must fill 19% of its seats to be more efficient than the travel mode shift induced by U.S. transit, weighed against an automobile carrying an average passenger load of 1.63 (3). emissions from transit, is a savings of 7.4 million metric tons of carbon dioxide (MMtCO2) per year, or about as much emit- Some transit systems in the United States have relatively ted by the transportation sector in the state of New Hampshire. low load factors; that is, vehicles typically carry few pas- If Americans increased their transit mode share to the level sengers at a time. These systems are inefficient in their GHG of Canadians, that reduction would increase to 50 MMtCO2, emissions. For example, a 2003 study of the Chattanooga about the amount emitted by transportation in Louisiana Area Regional Transportation Authority (CARTA) found annually. If U.S. transit mode share increased to the level of that the transit agency produces a net increase in GHG emis- Europeans, the annual reduction would be 74 MMtCO2, as sions. Low ridership means that emissions from the agen- much as all transportation in Pennsylvania emits each year cies' buses outweigh savings in GHG emissions from mode (7,8). Although historical development patterns have facili- shift. GHG emissions in Chattanooga actually would fall if tated higher transit mode share in Canada and Europe than in bus service were discontinued and riders switched to driving the United States, the comparison demonstrates the scale of instead. The study also noted that reducing GHG emissions transit ridership achievable in industrial countries.