ARCO has developed diesel fuel called Emission Control Diesel (EC-D) that results in substantially lower exhaust emissions compared to a typical California diesel fuel. EC-D has ultra-low sulfur content, low aromatics, and has a high cetane number. EC-D is produced from typical crude oil using a conventional refining process.Initial engine laboratory tests and vehicle tests indicated that EC-D reduced regulated emissions while maintaining fuel economy, compared to a typical California diesel fuel.Ultra-low sulfur diesel fuels such as EC-D may enable the widespread use of passive catalyzed particulate filters for both new and existing diesel engines. The use of catalyzed particulate filters could allow large reductions of particulate matter emitted from vehicles.A one-year technology validation program is being run to evaluate EC-D and catalyzed particulate filters using diesel vehicles operating in Southern California. The fuel's performance, impact on engine durability and vehicle performance, and emission characteristics are being evaluated in several fleets in various vocations. This interim report outlines the validation program and provides new results from vehicle emissions tests conducted to date. Based on these interim results, vehicles retrofitted with catalyzed particulate filters and fueled with EC-D emitted 91% to 99% less particulate matter compared to the CARB-fueled vehicles having no exhaust filter equipment.