Today the California Air Resources Board announced proposed changes to the state’s “off-road” diesel regulation.  Adopted in 2007 the rules affect approximately 150,000 construction, mining, and airport support vehicles.   The proposed new rules delay the start of the regulation until 2014 (rather than 2010), increase the number of exempted vehicles, and relax some requirements.

The San Francisco Chronicle reports that the revisions come after the Air Board staff admitted to miscalculations that led to the original regulation.  According to the Chronicle, regulators overestimated emissions from off-road diesel vehicles by 340% in a scientific analysis used to set the 2007 rule.