Particulate matter (PM) pollution presents one of the greatest threats to human health, decreasing average life expectancy by nearly two years globally, and disproportionally impacting low-income communities. In California, the problem is especially severe with seven of the nation’s ten cities with the greatest PM pollution. Heavy-duty diesel trucks are the largest source of PM in the U.S., and California has implemented stringent emissions standards for these trucks. However, enforcing truck regulations has proven prohibitively costly, and non-compliance and evasion are rampant. While one million heavy-duty trucks operate in California each year, only 1% are inspected.  

Advances in technology offer the potential to drastically, and cost-effectively, improve the enforcement of emissions regulations and air quality, allowing regulators to measure emissions in real time as trucks pass by. The E&E Lab has partnered with the California Air Resources Board (CARB) to test the effectiveness of this real-time monitoring technology on reducing truck emissions and improving regulatory compliance in two different interventions.  

In the first intervention, some trucks identified as likely high emitters will be randomly and automatically sent a letter requesting documentation to show they are in compliance. In the second, some fleets with many high-emitting trucks will be randomly selected to receive a comprehensive audit.  As policymakers around the world often look to California for guidance on environmental enforcement, large-scale evaluation of these enforcement mechanisms has the potential to affect regulatory decision-making across the U.S. and around the world.