One commenter questions whether 25 percent is demonstrated by DDC test results, because the baseline testing that DDC performed does not represent the typical emissions from currently rebuilt engines. The commenter cites testing it has done to show that current rebuilds are less that the baseline that DDC uses. The program requirement of reducing PM by 25 percent is based on the emission levels of the original engine configuration. While some rebuilds, as of yet uncertified under the urban bus program, may result in lower PM exhaust levels than the original engine configurations, this is not the case for rebuilds which return an engine to an original configuration. The urban bus program will make engine configurations having lower PM levels a requirement.
Certification is available for other rebuild kits which meet program requirements.
It was commented that the Agency should not certify the candidate equipment for high altitude regions of the country because no emissions data at high altitude have been provided. In a consistent manner, the urban bus program does not require demonstration of compliance with emissions standards at high-altitude. In its comments the catalyst manufacturer requests certification for the combination of the candidate rebuild kit and a catalyst previously certified for the urban bus program. Review of this matter will be handled independently of certification of the DDC equipment, and a separate Federal Register notice will announce Agency intentions, as necessary. Several questions were raised regarding the life cycle cost analysis provided by DDC in its notification in order to trigger program requirements.