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.

Recent experience with the operation of high-speed railways in the UK and elsewhere has revealed the phenomenon, termed ‘ballast flight’, of ballast particles becoming airborne during the passage of trains, potentially causing damage to both the railhead and the vehicle. This article reports the results of an investigation into the mechanical and aerodynamic forces acting on ballast particles that are generated during the passage of a high-speed train and addresses the question whether these might offer a possible explanation for the initiation of ballast flight. As the high-speed trains passed, measurements were made of the air pressure and velocity at various locations across the track, and of the velocity and acceleration of the track system (sleeper and rails) and the ballast itself. The aerodynamic forces exerted on a suspended ballast particle were also measured. An analytical model of the behaviour of small ballast particles was constructed to assist in the interpretation of the measured data. Analysis of the data and modelling suggest that neither mechanical forces nor aerodynamic forces in isolation are likely to be sufficient to initiate ballast flight under the conditions investigated, but that the phenomenon could arise from a combination of the two effects. It appears that the process is stochastic in nature: further work, with an increased number of measurements, is required to explore this.