Reacting to a proposal by California and 13 other states to put their own regulations into effect, Caterpillar and Cummins proposed an alternate plan to the U.S. Environmental Protection Agency.
The plan would have challenged engine manufacturers to voluntarily meet more stringent engine emission testing requirements in 2005 -- rather than in 2007 as EPA has proposed -- in exchange for revised emission levels in 2007 and beyond.

However, after meeting with EPA Administrator Carol Browner, Caterpillar Chairman Glen Barton said the companies "were disappointed that the EPA is unwilling to consider this plan. Unlike a proposal supported by the California Air Resources Board and two pollution program agencies, the option we presented is a national, rather than a state-by-state solution.
"It also provides the certainty that we and other engine manufacturers require as we continue to invest heavily to create the nation's next generation of clean diesels."
The California Air Resources Board is expected to approve a plan next month that will plug what state officials see as a gap in federal regulations between 2004 and 2007.
Under a legal settlement with the federal government that resulted from a lawsuit claiming electronic engines were "defeat devices" to cheat on emissions regulations, engine manufacturers agreed to meet new emissions standards in 2002, two years ahead of EPA's original 2004 timetable. However, the EPA's new rules have been delayed, and are expected to go into effect in 2007 rather than 2004. Environmentalists believe engine manufacturers will go back to producing dirtier engines during this two-year gap between the end of the consent decree terms and when the new regulations go into effect.
Thirteen other states plan to follow California's lead. California is the only state allowed to set stricter environmental regulations than the federal government; other states can abide by the federal rules or adopt California's.
The EPA's new 2007 standards are expected to be released in December.