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New York City Transit Hybrid and CNG Transit Buses: Interim Evaluation Results - page 41 / 64

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1

Cab, Body, and

Cab, Body, and

Accessories

Accessories

2

Propulsion-related

Propulsion-related

3

Brakes

PMI

4

PMI

HVAC

5

HVAC

Frame, Steering,

and Suspension

Table 13. Top 5 Maintenance

Cost Categories

Rank

CNG West Farms

Hybrid Mother Clara Hale

Propulsion-Related Maintenance Costs The propulsion-related vehicle systems include the exhaust, fuel, engine, electric propulsion, air intake, cooling, non-lighting electrical, and transmission systems. Table 14 shows the total propulsion-related maintenance costs and lists the costs for the two study groups. Table 15 summarizes the cost comparisons between the study groups. All comparison calculations are hybrid compared to CNG as the baseline.

Total propulsion-related systems maintenance costs for the CNG buses was 9% lower costs than the hybrid buses.

A breakdown of the propulsion-related maintenance costs included:

  • Exhaust system maintenance—The hybrid bus group had five work orders related to a DPF backpressure issue during the evaluation period. This problem was a result of a software problem in the active monitoring of the DPF in the hybrid buses. When the DPF was removed and cleaned or replaced, the system would recognize that there was a significant change in the backpressure and give a warning indicator light; however, there was no problem. A few exhaust backpressure sensors were replaced before this situation was properly resolved. A software change has been made and this is no longer an issue, but has shown up in the evaluation period. The hybrid buses had exhaust maintenance costs more than twice those of the CNG buses. The CNG buses have had a problem with the thermal blanket on the exhaust wear out from vibration. Five of the ten CNG buses had the thermal blanket replaced during the evaluation period. This issue has not yet been permanently resolved.

  • Fuel system maintenance— The CNG buses had fuel system maintenance costs 77% higher than the hybrid buses. This difference was mostly due to the extra fuel filter costs for the CNG buses and a few problems with the CNG fuel leak sensors.

  • Engine system maintenance costs—The CNG buses had engine system maintenance costs 2% higher than the hybrid buses. The CNG buses were reported to have high engine oil consumption. This extra cost was not captured here. The CNG engines are in the process of being rebuilt as a campaign with new cylinder kits along with new spark plugs.

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