The California Air Resources Board (CARB) has announced plans to extend requirements limiting nitrogen oxide emissions from 2002-2004 big-rig diesel truck engines to include 2005-model year and later diesel engines. A coalition of 13 other states, including New York and Texas, is expected to adhere to the new California diesel engine requirements if CARB adopts them, making the rules de facto national regulations. To settle charges that their trucks were circumventing emission standards, six heavy-duty truck-makers had earlier agreed to use specific engine tests to ensure emission compliance during 2002-2004. These engine tests were adopted federally for the 2007-model year and later. But because those requirements were never adopted for 2005-2006, those firms could revert back to weaker require-ments between 2004-2007. The proposed CARB rules would prevent such an action.