The California Air Resources Board implemented tighter diesel truck regulations aimed at cutting emissions 50% from current levels by 2014 and 70% by 2020.

New rules include amendments to the Transport Refrigeration Unit (TRU) Airborne Toxic Control Measure that make it easier for some engines to meet new emission standards. The amendments were added after produce industry earlier this year disputed the board’s data.

The amendments complement earlier emission control measures that “aggressively” target diesel pollution, which is associated with ailments including cancer, the board said in a Dec. 17 statement. The board agreed to adopt the amendments last month.

“The changes we set in place today will continue those public health benefits while reducing the cost of compliance by more than 60%,” board chairwoman Mary D. Nichols said in the statement. “No other state… has such an extensive set of rules to slash pollution from diesel engines.”

One amendment grants less-stringent performance standards for 2003 model year TRU engines, allowing for all 2003 engines to comply with the low-emission TRU in-use standard instead of the ultra-low-emission standard.

Additionally, the board agreed to exempt about 150,000 lighter trucks from having to retrofit with particulate filters and to delay the initial compliance date for the retrofitting of heavier trucks, allowing them to operate another eight years before being required to use trucks that meet 2010 emissions standards.

Western Growers, Irvine, Calif., has been at odds with the board, saying controversies over the emissions and public health data on which the regulations are based undermine the credibility of the regulations.