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28 CHAPTER SIX CONCLUSIONS AND FURTHER RESEARCH This report summarizes results from an online survey of 33 airports and phone interviews with 16 airports on their experi- ence with using alternative fuels in airport fleet vehicles. As previously stated, airports differ in their mix of vehicles, mix of fuels, geography, and ultimate goalsâall of which contribute to great diversity among their experiences with these fuels. The following are observations and considerations to support other airports in moving forward with alternative fuel programs. GENERAL OBSERVATIONS â¢ Rationale for alternative fuels. Airports purchase alternative fuel vehicles for a variety of reasons, most notably to reinforce an environmentally conscious image and to reduce greenhouse gas (GHG) emissions. â¢ Compressed natural gas (CNG) and electricity are the two most common fuels. The use of alternative fuels has steadily risen in airport vehicle fleets since the early 1990s, in both the total number of airports using alternative fuels and the diversity of fuel types used. Among the fuels considered in this synthesis report, CNG is used at the most airports (71% of airports surveyed). However, the fastest growing fuel type in the past 5 years is electricity, used at 64% of airports surveyed. â¢ Increasing availability of low-cost alternative fuels. The use of certain low-carbon fuels, such as renewable natural gas and renewable diesel, is limited in airport fleets, but the fuels are promising because of their competitive costs and their potential to dramatically reduce GHG emissions. â¢ Role of airport administrative structure. Airports tend to be either bureaucratic or hierarchical in how they make decisions related to alternative fuel adoption. According to Sperling and Nesbitt (2001), a hierarchical structure is espe- cially conducive to the adoption of alternative fuels because it has relatively few decision makers and because cross- cutting initiatives that involve multiple divisions or departments at the airport can be centrally planned and delegated. â¢ Advantages of bi-fuel vehicles. Airports reported receiving great value in bi-fuel vehicles, such as vehicles that can use CNG or diesel/gasoline. A primary advantage of bi-fuel powertrains is the vehicleâs reliability when one of the fuels has an inoperable refueling station. â¢ Possible infrastructure modifications. Most alternative fuel dispensing stations are owned by private firms, operating both on- and off-airport. CNG stations are an exception; they are mostly airport-owned. Of the airports interviewed, 83% reported needing to construct new alternative fuel infrastructure when introducing a new alternative fuel, rather than being able to leverage existing infrastructure in the region. OBSERVATIONS BY FUEL TYPE â¢ Biodiesel. Eighty-nine percent of airports reported being âsatisfiedâ or âextremely satisfiedâ with biodiesel. Airports use biodiesel in most vehicle applications that also use diesel. The main challenges expressed with biodiesel include fuel filter fouling in lower temperatures (however, this challenge was overcome by either adding solvents or changing the fuel supplier). â¢ Renewable diesel. Renewable diesel is currently used at San Francisco International Airport. Airport managers expressed extreme satisfaction with the fuelâs cost competitiveness and operating characteristics. â¢ Compressed natural gas. CNG is the most commonly used alternative fuel in airport-owned and airport-operated vehicles. The U.S. Department of Energy (DOE) estimates that GHG emissions resulting from CNG are 11% lower than those emitted by diesel, in addition to important reductions in nitrogen oxides and particulate matter emissions (ANL 2016a). â¢ Renewable natural gas. RNG is a renewable substitute for fossil-based natural gas. Limited environmental assess- ments of RNG have been performed, but the current literature suggests that the fuel can achieve promising reductions in GHGs.
29 â¢ Liquefied natural gas (LNG). LNG is rarely used in airport fleets; it is typically reserved for specialized equipment. The main barriers to using LNG are the higher cost compared with CNG (DOE 2016a) and the need for special storage tanks capable of maintaining the cryogenically cooled fuel in liquid form. Additionally, life-cycle emissions and petro- leum consumption of LNG are higher than for CNG because of the compression stage. â¢ Hydrogen. Hydrogen fuel has zero tailpipe emissions and the potential for zero life-cycle emissions if the hydrogen is created from renewable energy. Although itâs in the early stages of development, hydrogen fuel has potential to support a long-term strategy for mitigating emissions and petroleum use. â¢ Electricity. Electricity is the fastest-growing alternative fuel among survey respondents in the past 5 years. Two key advantages of these powertrains over petroleum-fueled vehicles are the low fuel costs and stable fuel prices. OBSERVATIONS BY VEHICLE TYPE â¢ Shuttles. These vehicles are often the first vehicle type that an airport considers for alternative fuels and are good can- didates for alternative fuels because (1) they operate near pedestrians and could limit negative health and environmental impacts; (2) they tend to have highly predictable duty cycles, which helps in planning the refueling events; and (3) they are publicly visible, creating an opportunity for airports to present an environmentally friendly image. Airports often use grant funding to help finance the refueling stations. A key concern expressed by airports regarding the use of alternative fuels in buses, shuttle buses, and vans is the potential for negative publicity in the case of a failed vehicle deployment. â¢ Emergency response and security vehicles. Emergency response and security vehicles are less frequently powered by alternative fuels. Barriers to alternative fuel adoption in these vehicles include the need for them to be âready,â and the structure of oversight required for them. At many airports, the vehicle procurement, operation, and refueling are overseen by the security and police department, rather than by the general airport fleet, which typically oversees other vehicles. â¢ Facility and maintenance vehicles. Few clear, overarching themes emerged for this class of vehicles, due primarily to the variation among the individual vehicles and the resulting usage needs. To address these unique challenges, airports relied on their historically innovative abilities, such as using goats for vegetation management in hard-to-reach areas. KEY CONSIDERATIONS â¢ Fuel and vehicle availability. Rapid growth in the alternative fuel industry in recent years means airports have an increasing ability to adopt alternative fuels. Figure 9 shows the fuel-vehicle combinations that are currently available on the market or in the demonstration phase. â¢ Barriers to alternative fuel adoption. Airports vary in their willingness to try new fuels. Phone interviews revealed the following key barriers: (1) higher fuel, vehicle, or infrastructure costs for certain alternative fuels; (2) unavailability of fuel or vehicles in the airportâs geographic region; (3) inadequate refueling infrastructure as a result of the airport spatial footprint; (4) failure to meet the necessary fuel requirements of the vehicle duty cycle; (5) tunnels prohibit the use of certain gaseous fuels; and (6) equipment reliability concerns owing to the frequency of extreme weather. â¢ Funding opportunities. The primary external funding source for alternative fuels in airport fleets is such federal grants as Voluntary Airport Low Emissions grants. Airports also rely on state grants. To a lesser degree, airports use publicâ private partnerships and federal and state vehicle rebates. â¢ Procurement restrictions. At some airports, a major barrier to alternative fuel use is the limited selection of vehicles in the procurement system as a result of (1) Buy America requirements, or (2) requirements to procure vehicles only from a given automaker (e.g., Ford). FUTURE RESEARCH NEEDS â¢ Synthesize literature on the lifetime durability of alternative fuel vehicles compared with conventionally powered vehi- cles. Survey respondents noted the lack of information on alternative fuels at the middle and end of the life of vehicles. â¢ Conduct a market assessment of certain emerging fuels associated with deep reductions in GHG emissions, such as electricity, RNG, renewable diesel, and hydrogen. â¢ Develop a handbook that helps airports conduct costâbenefit analyses on alternative fuel vehicles at their airports. Such a handbook would include the environmental, social, and economic costs and benefits associated with vehicle procurement, maintenance, operation, and disposal. Additionally, the handbook could provide guidance on innovative financing models that would enable airport fleets to take advantage of federal and state tax incentives for the purchase of alternative fuel vehicles.