Truck and engine manufacturers planning to use selective catalytic reduction (SCR) technology in 2010 have dismissed Navistar Inc.'s most recent court move as "of no relevance at this early stage" in a federal court challenge to Environmental Protection Agency actions governing SCR use to meet upcoming diesel emissions requirements.

Navistar originally challenged the EPA's SCR actions in late March, asking the U.S. Court of Appeals for the District of Columbia to review those actions, which it said violated federal rulemaking requirements and the Clean Air Act. Navistar is the sole U.S. heavy-duty manufacturer to reject the SCR approach, and instead has committed to meeting the rule's standards using high levels of EGR (exhaust gas recirculation).

Subsequently, Cummins Inc., Detroit Diesel Corp., Daimler Trucks North America LLC (DTNA), Volvo Group North America Inc. and Mack Trucks Inc. as a group asked the court that they be allowed to participate in the case as amici curiae, or friend of the court. The group members, along with Paccar and its Peterbilt and Kenworth subsidiaries, have all committed to using SCR to meet the federal emissions requirement that NOx emissions from diesel engines be at or below 0.2 g/bhp-hr. beginning Jan. 1, 2010.

Last week, Navistar opposed the amici curiae with a strongly worded brief charging that the SCR group had essentially written EPA's "illegal guidance" and could offer the court no important new information as "the SCR Manufacturers support EPA's position because it is, literally, their position."

On Friday, the amici group responded with its own reply to the court, complaining that Navistar "devoted the better part of its nine-page opposition to arguing the merits of its case. Those arguments are of no relevance at this early stage."

The only relevant opposition offered by Navistar "is limited to the unadorned suggestion that Amici Curiae will not meaningfully contribute to the case," the group's filing said, adding "That is quite wrong."

As Navistar is not intending to use SCR, the SCR manufacturers are the only ones "in a position to assist the Court in understanding and elaborating upon the technology," the Amici response argued.

"Amici, and not EPA or Navistar, have developed, tested, and used SCR technology. Accordingly, Amici are in the best position to provide the Court with a complete and accurate understanding of the SCR technology that will be necessary to demonstrate why Navistar's assertions regarding their technology are simply incorrect."

There has still been no official response to the court from EPA, nor has the court released a schedule of hearings on the various motions.