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71 3.1 Conclusions Published studies have shown that HEB offer cleaner and more fuel-efficient performance than conventional diesel buses. Concurrently, new stoichiometric CNG buses being deployed are likely to represent a substantial emissions ad- vance over legacy lean-burn CNG buses in real-world opera- tion, and all CNG buses have traditionally offered very low PM emissions. Advanced engine after-treatment devices and engine technologies will enhance emissions from both diesel and diesel HEB in the future. However, it is expected that a 14% to 48% HEB FE advantage would remain in real-world operation depending on different operation situations, pri- marily related to the average route speed, or degree of stop- and-go operation. Bus capital and operation cost data were acquired for this study from four transit fleets (NYCT, KC Metro, LBT, and WMATA) with additional information gathered from litera- ture reviews. Data from NYCT and KC Metro were obtained from a DOE/NREL study.(3, 4) Additional cost data were collected through a survey of bus and hybrid drive OEMs, and from the fuel industry. The study team gathered future fuel pricing data from various agencies and government sources. Based on these data and projections from the re- search team, the LCCM was built in spreadsheet format to calculate costs including vehicle purchase, insurance, war- ranty, personnel training, infrastructure, facility maintenance, fuel, major component replacement, and vehicle mainte- nance. A detailed model for FE was constructed, using field and chassis dynamometer data, for inclusion in the LCC. This FE model was essential, because route speed impacts the FE of all bus types substantially. The LCC also considered the FE impact of climate control, including air conditioning and fuel burner heating. These auxiliary loads can account for FE changes of fuel consumption at 4% to 9% from season to season. The model provides users with default values and with upper and lower limits for all cost items. Users are permitted and encouraged to input their individual assumptions and known data for a specific transit operation. In particular, the user may have a bus purchase cost that reflects additional equipment, or is reduced through volume-purchase negotia- tion. Several test runs were performed to investigate typical operations and some special cases. LCCM predictions are summarized as follows: ⢠The LCCM demonstrates that conventional drive diesel buses are nearly always least expensive to operate, with or without subsidy. ⢠Transient behavior of buses increases as bus average speed decreases, and average speed has a substantial impact on fuel economy, in general, and the difference in fuel econ- omy between technologies, in particular. HEB regenerative braking benefits HEB relative to diesel at low speeds. Hotel loads (particularly climate control) impact fuel consump- tion measurably. ⢠For low-speed operation (tested at 6 mph average speed) with a subsidy of 80% of bus purchase price, diesel HEB ex- cels in terms of low overall cost. ⢠Gasoline HEB usually cost 5% to 10% higher than diesel HEB in 12-year overall expense. ⢠CNG proved to be the next-best cost option after conven- tional drive diesel for mid- and high-speed operation (12.7 and 20 mph each) without subsidy; with an 80% subsidy, the diesel HEB offers similar, or slightly higher, cost bene- fit to CNG. ⢠The C-15 researchers considered the important scenario of high liquid fuel prices ($5/g diesel fuel price), which bene- fits HEB in comparative LCC performance against conven- tional diesel buses. ⢠CNG buses would gain advantages from a low and stable CNG price. For an extreme case with diesel at $5/g and C H A P T E R 3 Conclusions and Suggested Research
CNG at $2/DEG, the low CNG price makes CNG bus operation lowest in total cost with or without subsidy. However, fuel costs tend to track one another in the U.S. economy. ⢠The study also found that CNG buses are most suited to mid-size or large bus fleets (operating over 50 CNG buses) because of the costs of CNG infrastructure (primarily the compressor station), unless infrastructure costs are not borne by the transit agency. Lack of existing CNG fueling infrastructure would adversely impact a decision to pur- chase CNG buses. ⢠The model was demonstrated on data from four transit agencies. The projected results are close to real operation data, and the model reasonably reflects comparative differ- ences among technologies in real-world operation. ⢠Uncertainties in future fuel prices, and the relationship between HEB capital cost and market penetration, add uncertainty to the model conclusions. 3.2 Suggested Future Research Extended data collection is suggested to study the impact of after-warranty bus operation in greater detail, and to under- stand the reliability and longevity of advanced engines and propulsion systems. Data are lacking on stoichiometric CNG buses, which are entering service only at the time of this writing. The lack of complete data merits further study of FE, emissions, and maintenance cost. Other advanced propul- sion technologies such as fuel cells or electric buses could be considered in the model, and the model could be extended to include other bus sizes, particularly 30- or 35-ft 12-year-life buses. In addition, the present LCCM has not considered the possibility of improved technology rebuilds for middle-aged 12-year or extended-life buses, or the effect of operating terrain (gradient) on bus FE. Climate change concerns may spawn carbon trading in the future, and this would require future examination as a cost impact. 72
