The Clean Diesel Independent Review Panel, whose members have attempted to evaluate industry compliance with upcoming heavy-duty engine emission standards, concluded last week that more work is needed on emerging technologies to cut smog-forming emissions to government-mandated levels. Essentially, the panel's position underscores the challenge that lies ahead for engine manufacturers and trucking fleets: reducing heavy-duty diesel emissions of nitrogen oxides and particulate matter to negligible levels in 2007. The group, which EPA established to advise it on potential problems in meeting emissions regulations for 2006 and 2007, included public health groups, engine makers, motor carriers, refiners, and engineering interests.