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California relaxes in-use diesel emission rules

18 December 2010

The California Air Resources Board (ARB) adopted amendments to its emission rules for in-use diesel vehicles that relax the emission requirements for diesel trucks and buses and for diesel off-road machinery such as construction equipment.

A review process of the rules was started over a year ago, in response to concerns voiced by California construction contractors represented by the Associated General Contractors of America and other affected diesel engine operators that would have to cope with the financial burdens to comply with the new emission rules while their business suffered from the economic recession. ARB staff held 20 public workshops throughout the state to solicit stakeholder input.

It also became apparent in the review process that the original off-road rule was based on a grossly miscalculated diesel emission inventory. According to new calculations, the ARB overestimated the inventory of off-road diesel PM emissions that was the basis for the off-road rule by 340%, more than could be explained by the economic slowdown. This large miscalculation—widely publicized by California and US media—cast doubts on the methods used by the ARB in the development of this and other air quality regulations.

On-Road Truck and Bus Regulation: Approved in December 2008, this regulation affects nearly one million heavy-duty diesel trucks that operate in California. The approved amendments are estimated to reduce overall compliance costs by about 60%. The key amendments will:

In addition, the ARB voted to require all school buses greater than 14,000 lbs. GVWR to be retrofit with diesel filters by 2014. If no retrofit is available, the buses have until 2018 to be replaced by vehicles with a 2010 model year engine or emissions equivalent.

Off-Road Regulation: First approved in July 2007, this regulation is aimed at reducing diesel emissions from the state’s estimated 150,000 off-road vehicles used in construction, mining, airport ground support and other industries. The amendments, which reduce compliance costs in next 5 years by 97%, will:

Source: California ARB