Diesel particle filters (DPFs) are standard equipment on heavy-duty diesel trucks with 2007 and newer engines in the U.S. This study evaluates the performance and durability of these filters. Black carbon (BC) emission rates from several thousand heavy-duty trucks were measured at the Port of Oakland and Caldecott Tunnel over multiple years as California regulations accelerated the adoption of DPFs. As DPF use increased, fleet-average BC emissions decreased, and emission factor distributions became more skewed. Relative to 2004−2006 engines without filters, DPFs reduced BC emission rates by 65−70% for 2007−2009 engines and by >90% for 2010+ engines. Average BC emission rates for 2007−2009 engines increased by 50− 67% in 2015 relative to measurements made 1−2 years earlier. Some trucks in this cohort have become high-emitters, indicating that some DPFs are no longer working well. At the Port, where DPFs were universal in 2015, high-emitting 2007−2009 engines (defined here as emitting >1 g BC kg⁻¹) comprised 7% of the fleet but were responsible for 65% of the total BC emitted. These observations raise concerns about DPF durability and the prospects for fully mitigating adverse effects of diesel particulate matter on human health and the environment.