Previous studies have shown that regenerating particulate filters are very effective at reducing particulate matter emissions from diesel engines. Some particulate filters are passive devices that can be installed in place of the muffler on both new and older model diesel engines. These passive devices could potentially be used to retrofit large numbers of trucks and buses already in service, to substantially reduce particulate matter emissions. Catalyst-type particulate filters must be used with diesel fuels having low sulfur content to avoid poisoning the catalyst.A project has been launched to evaluate a truck fleet retrofitted with two types of passive particulate filter systems and operating on diesel fuel having ultra-low sulfur content. The objective of this project is to evaluate new particulate filter and fuel technology in service, using a fleet of twenty Class 8 grocery store trucks.This paper summarizes the truck fleet start-up experience. The test vehicles, retrofit issues, and refueling considerations are discussed. Maintenance, mileage accumulation, fuel economy and operating cost data from the retrofitted trucks are compared to control trucks operated on California diesel fuel. Exhaust temperature and back pressure data from on-road operations are discussed. Lessons learned from the fleet start-up experience are presented.The trucks retrofitted with particulate filters have operated reliably for over five months of service and after accumulating approximately 50,000 miles per truck. The average fuel economy for the retrofitted trucks was essentially the same as the control trucks operated on California diesel fuel. A companion paper, SAE Technical Paper 2000-01-2815, reports on testing and exhaust emissions for these same grocery trucks.