On-board measurement of the acoustic performance of railway tracks is nowadays necessary to qualify networks on a large scale. The issue concerns not only the supply of prediction models for strategic noise mapping, but also the optimization of track maintenance. One of the key parameters to be measured is the rail acoustic roughness. Unlike direct measurements where sensors are directly applied to the rail surface, indirect measurements of rail roughness focus on quantities that result from wheel/rail interaction, such as noise or vibrations of axle-boxes or rail, and from which the effective wheel/rail combined roughness are estimated. In particular, on-board measurements make the qualification of long track lengths possible without major constraints on traffic. A number of improvements can be made to the existing methods, especially in estimating the transfer functions between the effective roughness and the signals provided by the sensors. This study is part of the MEEQUAI French project aiming to combine modelling and measurements to optimize the estimation of the transfer functions and the location of sensors while taking into account the variability of tracks. This paper concerns the measurement performed on a static vehicle/track configuration in order to validate and calibrate the numerical simulations.