industry experience with hybrid propulsion technology. However, NYCT operated the hybrid buses with the intent that they be treated just like any other diesel bus for reliability and operations.
Data for this evaluation were taken from NYCT’s data system, MIDAS. Data parameters included the following:
Diesel fuel consumption by vehicle
CNG fuel consumption by vehicle
Mileage data from every vehicle
Preventive maintenance action work orders, parts lists, labor records, and related documents
Records of unscheduled maintenance, including roadcalls and warranty actions by vendors (when available in the data system)
The data collection was designed to cause as little disruption as possible for NYCT. Data were sent from NYCT to Battelle electronically for analysis.
The study design included tracking of safety incidents that affected the vehicles or occurred at NYCT facilities. However, no safety incidents were reported during the data collection period.
Vehicle System Descriptions
Table 3 shows a summary of vehicle system descriptions for the CNG, hybrid, and two baseline diesel study groups of buses. The following discussion includes descriptions of each of the four study groups of buses and detailed differences between the CNG and hybrid buses versus their respective diesel baseline groups of buses.
CNG Buses at West Farms Ten CNG buses operating at West Farms Depot were selected from the order of 260 Orion VII low floor, model year 2002, CNG buses. The CNG buses use the DDC Series 50G engine. NYCT did not select the optional catalyst for emissions aftertreatment for these buses.
Diesel Baseline Buses at West Farms Although West Farms Depot is intended to be an all-CNG bus operating depot, some diesel buses have been operating at West Farms. The number of diesel buses operating at the depot decreased as the newer CNG buses were brought into service. The evaluation in this report used 10 Orion V high floor diesel buses as a baseline for the CNG bus evaluation of mileage usage, fuel economy, and roadcall rate results.
The diesel buses are model year 1994 and close to the end of their useful life. These diesel buses have DDC Series 50 diesel engines. One bus (number 416) had been repowered with a newer DDC Series 50 EGR engine as part of a test program. This bus was removed from the evaluation due to its significant difference in operation; however, some comments on this vehicle are provided in this evaluation.