The Interpretation of Train Rolling Resistance from Fundamental Mechanics

Past efforts in railway improvement have focused on increased train stability and ride quality for safe and smooth operations at higher speed. The question of energy consumption has rarely been considered. In view of projections of higher fuel costs and increased rail traffic volume, energy effects caused by improved train resistance should be considered. First-order expressions for the rolling resistance of freight trains on level tangent track were derived from the basic principles of physics and engineering. The average power dissipated by the suspension system was obtained from a linear model of the track train system. Hysteresis in the soil is computed using basic principles of soil mechanics. Losses due to wheel rolling friction, imposed wheel sliding, and bearings were estimated from simple engineering and considerations. Rolling resistance as would be measured in coast down or drawbar pull tests on level tangent track is found to depend strongly on the quality of the track as well as weight and speed. On good track, most of the rolling resistance is due to bearing resistance, while on poor track, suspension losses predominate. Empirical expressions such as the Davis formula, which have been used in the past by the railroad industry, are unable to describe train rolling resistance adequately because of the way in which they are parameterized. Some of the parameter values obtained from fits to experimental data do not carry the physical meaning with which they were traditionally associated.