الفهرس 
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Abstract
The Operating costs represent an effective share of the total costs of city bus tlect. The management of the maintenance. as a cost center is the focus that enables the optimization or operating costs. The study presents a new methodology to optimize the operating costs of city bus !lcct. The study was carried out on the fleet of Greater Cairo
13us Company in order to cstabli::;h a new system lo optimize the operating costs.
The analysis is based upon actual data collected lor the chosen sample of 143 buses during four years. The data proved that there were inaccuracy in the expenditure spare
parts system or the replacement stores let! to discrepancies in values oftotal operating
costs of the bus. A new suggested system was applied to reanalyze the data. The new
analysis proved that the average total operating costs of city bus increase sharply after ten years or operation. Further, the main components of operating costs in a descending
order arc: Tyrcs, engine and gearbox. The costs of these coniponcnts were studied in details.
The mcU10dology of reliability and hazard rate were applied on engine and gearbox data
to calculate the optimal service life for new or renewed engine or gearbox.
- The analysis of engine data showed that the mean time to failure (MTIF) of air-cooled engine, which is mounted on NASR 811 bus is 580364 km and its unit cost is 0.16093
L.E/km. The MTTF of water-cooled engine which is mounted on NASR 871 bus is
682859 km and its unit cost is 0.099 L.E /km. The analysis proved that water-cooled engine is more suitable lOr city bus especially in dusty environments.
- The analysis of gearbox data showed that MTTF of gearbox, which is mounted on
NASA 811, is 414016 km and its unit cost is 0.0837 L.E/km. The MTfF of gearbox, which is mounted on NASR 871 bus, is 735619 km. and its unit cost is 0.1025 L.E/km
- Relationships between service life of new units and their subsequent overhaul service
liJC were developed.
- The study recommended performing the preventive maintenance for engine or gcm•box before lirst natural failure. The timing of the first preventive maintenance for both the tv•/0 engines and gearboxes \vas calculated according to the ha arcl rates methodology.
- For the lyres, which arc the main costly item, a survey was done to get the real
statistical distributions ror number of passengers and speeds. The survey was applied on a sample of the ncet representing the operation conditions. The main parameters aiTccting the service life of the tyrc were discussed. A ge•ncral JOnnula for service life ortyrc based on inllation pressure, applied load and speed of bus has been established.
- A guideline to adjust the inflation pressure was given with a nc\V formula and charts. A
calculatcc.l case study on one route of the company llcetprovcd that incorrect inllation
pressure decreases {he tyrc service lire by about 30% of its normal service life.