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This paper discusses a well-known tool for calculating train resistance to motion and its suitability for describing operations at high speed. The tool, originally developed by Armstrong and Swift 1, also permits the estimation of the contribution to aerodynamic resistance of various features of the architecture of a train. They compare this approach with the results of other formulae for calculating train resistance, as well as published measurements taken during experimental work. It is concluded that Armstrong and Swift's expressions can be considered to provide good estimates for the coefficients to the Davis equation for both high-speed and suburban trains that fit the British loading gauge and have a power car-trailer ratio of 1:3 or less without the need for run-down testing. However, the expressions are not suitable for trains with a predominance of powered axles.
Rochard et al. (2000) studied this question.