Table 15. Summary of Propulsion-Related Maintenance Cost Comparisons*
Exhaust Fuel Engine
Non-Lighting Air Intake Cooling Transmission
Hybrid vs. CNG 9% (higher) 111% (higher)
2% (lower or same) N/A
13% (lower) N/A
The cost comparisons are provided as hybrid compared to CNG as the baseline.
((Hybrid cost per mile/CNG cost per mile) – 1) * 100% = Percent comparison For example, the total propulsion related entry is 9% higher, this is hybrid costs being 9% higher than CNG for this category.
Figure 17 shows the monthly propulsion-related maintenance cost per mile for the CNG and hybrid buses. Each study group’s maintenance cost per mile is shown as an average for the month and cumulative average for the evaluation period. The cumulative average propulsion- related maintenance cost per mile for the hybrid and CNG buses have been tracking together for the last three or four months of the evaluation period and end up with the hybrid buses being 9% higher (as mentioned above).
Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05
Figure 17. Propulsion-Related Maintenance Cost per Mile for CNG and Hybrid Buses
The maintenance costs of the CNG bus group have generally been decreasing for the propulsion- related systems. There was one peak in the monthly average cost per mile around April 2005, which was caused by several isolated repair actions on different buses. These repair actions