I have just finished reading your article on the 2007 EPA regulations and the proposed California air regulations (Diesel Doldrums, July, p. 13). In all the previous changes made by the EPA, older equipment has been grandfathered in accordance to the applicable regulations of the year made. The retrofitting or elimination of said equipment would be impractical, since it was not imposed on trucks or other equipment in past changes. Further, no data has been obtained on the performance of older equipment with ultra-low-sulfur diesel and the amount of emission improvement with this supposed cleaner fuel. It would be great if we could just scrap these machines, but completely absurd, since many small business could not burden the cost.