The California Air Resources Board last week unveiled a draft regulation that will require retrofits and engine replacements for the estimated 300,000 privately owned diesel trucks and buses transiting California roadways beginning in 2012.

The proposed regulation calls for truckers to retrofit pre-2007 model year trucks with soot filters and then requires a gradual modernization of trucks beginning in 2012, so that all trucks eventually will be 2010 or newer models.

The draft regulation addresses the largest unregulated source of diesel emissions in the state. Between 2010 and 2020, CARB estimates the regulation will prevent 11,000 premature deaths associated with exposure to diesel exhaust, and save about $500 million in health care costs during that period.

The regulation is projected to cost the trucking industry between $3.6 and $5.5 billion from 2010 to 2021.

CARB recently adopted regulations to limit diesel emissions from off-road construction equipment and truck idling as well as other sources.