In a further field evaluation of diesel particulate trap oxidizer systems the New York City Transit Authority (NYCTA) and ORTECH International have expanded their evaluation to include three more buses. The expansion of this program was two fold: 1) To further evaluate the ORTECH burner based trap system. 2) To evaluate a Donaldson Company Inc. (DCI) dual trap system utilizing an electric heater. 3) To evaluate a Webasto burner based trap system. Four additional revenue buses #4511, #4512, #4513 and #4517 were chosen for this evaluation, in addition to bus #1698 which was equipped with an ORTECH trap system, and has been in revenue service since April 1989. All four buses were retrofitted with new Detroit Diesel Corp. (DDC) DDEC controlled 6V92-TA California rated low NOx engines, with ATEC Allison transmissions.Buses #4511 and #4512 were each retrofitted by ORTECH International of Mississauga, Canada with an ORTECH burner based system. This system consists of two catalyzed trap monolithic exhaust filters and a Webasto burner to promote regeneration. This system has proven to reduce emissions by 80 to 90 percent and is also effective in reducing hydrocarbon and carbon monoxide emissions. Both of these buses have been in service since October 1989.Bus #4517 was retrofitted by ORTECH with a DCI electric trap system. This system utilizes two non-catalyzed traps to collect particulate and an electric resistance heater to initiate regeneration. This system also reduces particulate 80 percent while having only minor effects to the operation of the vehicle. This bus has been in revenue service since February of 1990. A Campbell Scientific Datalogger was installed on this bus in May of 1990, further expanding the information database.The NYCTA has operated these vehicles on the M-15 route in midtown Manhattan. Their performance has been monitored and compared to a control fleet running on the same route to verify the durability and deterioration of the trap systems. Exhaust emissions levels were taken at the New York City Department of Environmental Protection (NYC DEP), on a chassis dynamometer allowing for data in gr/mile.All problems with these systems were carefully recorded and the resolution to the problems fully explained.The Webasto burner system was tested for 450 hours using a test cell dynamometer over the NYC bus cycle. The system utilizes a single non-catalyzed trap and a diesel burner to heat the bus exhaust for regeneration. Emission test results show efficiency of particulate removal over 85% with a weighted fuel penalty of 2-3%.