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32 historical and real-time flight performance data.12 However, regional initiatives to promote other modes as alternatives for less-experienced air travelers, who constitute the majority the shorter distance markets could do the following: in most air markets, do not necessarily apply similar knowl- edge when choosing among alternative travel itineraries. Few Cause some diversion of air trips to other modes. Esti- of the major consumer-oriented online booking sites pro- mates of changes in GHG emissions from diversion to vide on-time performance information for the flight itiner- other modes range from a factor of three or more reduc- aries that they create.13 As a result, a flight during a peak period tion for diversions to rail or intercity bus (12) to a much with very low on-time performance will, in advance, appear more modest 1520%, depending on assumptions about undifferentiated from other flights with higher on-time vehicle types, occupancies, and other factors that affect the performance. relative fuel efficiencies (11). Result in net changes in trip patterns. Alternative modes such as rail and bus are most competitive for shorter dis- 1.6.2 Environmental Effects of tance trips for which air is generally the least efficient, for Doing Nothing a given aircraft type. For a given type of aircraft, there is As noted in the Senate JEC report (8), airport delays cur- almost a factor of two difference in GHG emissions per rently result in an additional 7.1 million metric tons per passenger-mile between short-haul and the most energy- year of CO2 emissions in the United States, with 1.3 million efficient medium-haul flights (11). This is largely a result tons from the major coastal mega-regions airports alone. of the take-off and landing stages, which represent rela- On the basis of aviation data published by the FAA (11), tively large energy expenditures that are approximately the these represent approximately 3.6% of the total greenhouse same regardless of the flight length. gas (GHG) emissions in the aviation sector. However, future Affect aircraft mix. The shorter trips that are the most increases in delays could substantially increase the total likely to be diverted to alternative modes are also those delay-related emissions and their fraction of total aviation that are most likely to be served by smaller regional jets emissions. As described previously, increases in delays as a and propjets. The effects of shifting shorter trips to alter- result of growth in air traffic could result in delay-related native modes depend on the types of aircraft that are emissions growing to 17 million metric tons per year across being reduced in the airports' mix. Figure 1.8 describes the United States. This translates to over 3.2 million per year the relative fuel consumption levels for different aircraft in the major coastal mega-region airports--more than dou- types and trip (stage) lengths, derived from Smirti and bling that impact. Hansen (13). In this example, which compares a stan- The 2025 projections of GHG emissions (which are in dard 137-seat narrow body jet, a 72-seat turboprop, and turn based on the air traffic forecasts in the FACT 2 report) a 42-seat regional jet, the fuel consumption rates per assume that mega-region airports will continue to function seat-mile are lowest for the turboprop and highest by a in much the same way as they do now, that air travel patterns factor of up to five for the regional jets. Reductions in will remain similar to the current ones, and that the fleet mix smaller regional jet aircraft trips at an airport most likely does not change substantially. Of course, any or all of these will result in significant fuel--and thus GHG--reductions. assumptions could be affected by deliberate policy changes On the other hand, reductions in relatively fuel-efficient or by unanticipated events with resulting impacts on GHG turboprop trips would have more modest effects on GHG emissions. emissions. The coastal mega-region airports may well be able to reduce delays or at least prevent them from increasing to the extent Overall, there are clearly significant opportunities for that would be indicted by the simple extrapolation to the reducing GHG emissions both as a direct result of reducing FACT 2 traffic levels. Any such improvements would obviously delays and indirectly as a result of shifts that could occur from have a direct effect on the delay-related emissions. However, changed air traffic patterns. the changes could also affect the ways that the airports serve travelers, patterns of air travel, and fleet mixes in ways that 1.7 Conclusion could either amplify or diminish these effects. For example, Chapter 1 concludes with a concern that the amount of 2025 aviation capacity assumed by leaders in the aviation 12 For example, DOT's BTS maintains monthly online flight performance data community and reflected in the FACT 2 study (1) may be and dedicated sites such as offer detailed ratings of flights by OD based, as least in part, on the working assumption that, as pair, carrier, and even flight number along with real-time tracking of flights. 13 When this report was written, most of the available websites did not offer online demand increases, a voluntary program of aircraft up-gauging performance data for each alternative itinerary presented in flight searches. can be expected to take place. Given the overall decrease in

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33 Figure 1.8. Fuel consumption rates for representative aircraft (14). the average number of passengers per plane over the past better use of procedures developed for highway planning. decade, the research team believes that this assumption needs Chapter 2 explores both. more analytic attention. The research team addresses this in A lack of immediate answers for how to get more capacity Chapter 5 after presenting a review of both multimodal and from the overcrowded airports should lend support for local multijurisdictional issues facing the industry. and regionally based initiatives to find more usable capacity The concern that more help may be needed in finding at underused airports in the two study areas. This need for long-distance trip-making capacity merely increases the need greater multijurisdictional planning to solve the air capacity of forging a better level of integration with HSR planning and problem is discussed in Chapter 3.