"Currently no new diesel passenger vehicles can be sold in the five
states that adhere to the more stringent California requirements:
California, Massachusetts, Maine, New York and Vermont. The EPA,
however, is tightening its diesel emissions requirements, and moving
them more into alignment with the California requirements. The point
at which the two map exactly for passenger cars is called Tier 2 Bin 5
(T2B5).

For a 2007 or later model year diesel passenger car to be sold in all
50 states, it must meet the T2B5 emissions requirements. Currently,
there are no T2B5-compliant, 50-state diesel cars. One is on the
horizon--the new Mercedes E320 BLUETEC, to be introduced in 2007.
BLUETEC refers to the emissions after treatment system that enables
the vehicle to meet the T2B5 standard. The 2007 E320 BLUETEC has NOx
emissions that are more than eight times lower than the outgoing 2006
E320 CDI."

Mercedes hopes to get EPA approval for the urea-addition system for
2008, which would make its diesel 50-state legal.