The train motive power system includes the motive power concentration system for pulling a locomotive and the motive power dispersion system by an electric train or diesel rail car and these systems have advantages and disadvantages. Therefore, it is necessary to select either system by synthetically considering the state, profitability, and maintainability of a line to be used.
(2) Reduction of car weight
The motive power performance of a car is determined by "output/weight". The reduction of car weight has the same effect as increase of car output and decreases energy consumption.
Moreover, the car weight reduction moderates an impact force to a track because the axle load decreases and moreover decreases the maintenance cost. Therefore, car weight reduction is indispensable to economically realize a high speed.
(3) Reduction of running resistance
Running resistance of a train is shown by the following expression in the case of a diesel rail car. Running resistance of a train which is not a problem at a low speed cannot be ignored as the train speed increases. At a speed 140 km/h, a resistance equal to the upgrade of 10 % is added. Therefore, it is necessary to decrease running resistance such as decrease of air resistance.
(4) Increase of output of motor
It is relatively easy to increase the output of an electric rolling stock because energy is supplied from the outside.
However, an internal-combustion-engine car such as a diesel rail car must cover driving motive power along with auxiliary motive power including cooling and illumination power supplies, and compressors by a mounted engine. The auxiliary motive power reaches 100 PS per car or more in the case of the above-described the 281-series rail car of JR Hokkaido, which tends to increase as the comfortableness for passengers is improved.
