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aged by the system modeling studies published recently by MIT and ANL (Weiss et al., 2000; Santini et al., 2001; An et al., 2001). These studies dealt strictly with fuel economies, greenhouse gases, and costs associated with various PNGV technologies, and not Tier 2 emission standards. Nevertheless, the committee believes that, with these studies as examples, the regulated emissions also can be dealt with in a useful, if rudimentary, manner. Even rudimentary modeling with engine steady-state emission maps and estimates of transient emissions (including cold starts and accelerations) would help to answer the question of whether hybridization controls can be adjusted away from the optimum fuel economy and toward reduced emissions.

Recommendation 8 called for a major study to determine how well lightweight PNGV vehicles would fare in collisions with the heavier vehicles that constitute the majority of the vehicle population entering service since 1995. As a partial response to safety issues, the Safety Working Group has been formed to identify and prioritize safety issues for PNGV-type vehicles. The committee believes that the formation of the Safety Working Group is a large step in the right direction. The Safety Working Group also recognized the high priority of the weight versus safety issue and has initiated statistical studies using existing accident databases to identify facts and trends pertaining to how vehicle size affects safety. However, the absence of PNGV-type vehicles in the database limits the ability to predict the safety of lightweight vehicles that are not small in size as well. The committee notes that no progress has been made on the fleet modeling study intended to complement the statistical analysis. In view of the difficulty of funding a study of the proposed magnitude, it is suggested that creativity be exercised by the Safety Working Group in defining and initiating affordable studies that would provide the most critically needed information that is lacking from the statistical study.

The issue of having an appropriate fuel for advanced PNGV vehicles has been a continuing issue that the committee has commented on in previous reviews. The committee recommended that the PNGV strengthen and expand its cooperative efforts with the petroleum industry. PNGV is exploring the possibility of having a joint symposium with the petroleum industry. It appears that relatively little progress has been made in response to this recommendation, but the committee understands that the petroleum and fuels industry is complex and that developing a good working relationship will take time and much effort on the part of the PNGV and the petroleum industry.

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