Proposed regulations by the state Air Resources Board aimed at reducing emissions from diesel engines, including those used in agriculture, will impact about 400,000 California, on-road diesel vehicles and about another 1.2 million from outside the state, the California Farm Bureau Association’s Ag Alert reports.

The proposed rules call for the highest level of particulate matter control technology available and NOx emissions from every diesel-powered vehicle to be equal to or less than exhaust emissions from a 2007 model-year engine. Because so many agricultural vehicles are highly customized, are operated seasonally and often remain within a limited geographic range, farm equipment usually is older than that of commercial transport fleets.

It is common for agricultural vehicles to be kept in operation for several years--sometimes decades longer than fleet-operated, long-haul trucks. As proposed, for pre-2004 engine models, NOx exhaust emissions must be reduced by at least 70 percent to be equivalent to an engine that meets the 2007 federal emissions standards for heavy-duty diesel-fueled engines.

For 2004 to 2006 engines, NOx exhaust emissions must be reduced by at least 40 percent to be equivalent to an engine that meets the 2007 federal standards. No economic analysis has been conducted, but preliminary estimates put the cost of this rule at more than $50 billion.

Some say the ARB's proposed regulations, as currently drafted, are too costly and changes to the proposal are necessary to provide for low-use exemptions, one-time replacements and incentives. According to the Ag Alert, the ARB proposal currently sets an exemption threshold of 1,000 miles and 100 hours, which agricultural associations, including CFBF and county Farm Bureaus, say is unreasonable.

They stressed that it's not cost-effective to replace or retrofit trucks used infrequently or for short periods of time during the year. To fill out a diesel truck survey online, click here.