Roughness of the running surface is the main cause of noise radiated by rail traffic systems in the velocity range of 60 km/h to 250 km/h. Therefore, for reliable sound measurements on rail vehicles dependable roughness measurements of the running surfaces of the rail are required. European standards EN ISO 3095 and 3381 for internal and external track noise ask for the roughness level of the test track to be determined and compared with the limiting curves. The new European technical specifications (TSI-HS and TSI-CR) are defining trans-European rail network limiting noise values. For the test sites the running line of the rail has to be determined.

In the late eighties, Müller-BBM developed a first device to measure the roughness of the running surface of rails (RM1200E) in cooperation with Deutsche Bahn AG. For the development of its successor, which is presented here, we contributed our experience from measurements with the RM1200E gained over more than 15 years. Effective features were kept, others were improved and the application was distinctly simplified.

The measuring length of 1200 mm was kept as well as the discretisation of 0.5 mm. The measuring device is fixed on the rail at two points and is aligned with the second rail by means of an outrigger. The positioning of the measuring head on the running surface is facilitated by a line-laser and the shifting on the rail in longitudinal direction by a fold-out tail wheel and moveable, ergonomic handles. For measurements at night, the measuring head can be illuminated.

The battery operated device can measure automatically 20 traces in about 7 minutes in one measurement position. During this process, the measurement routines and all functions of the device are controlled and monitored by the integrated microcontroller. A tablet PC with a display suitable for daylight use is utilized as control panel, to which the measuring data is transferred wirelessly during the measurement via WLAN. The data can be viewed as roughness graph during the measurement, and once all tracks are measured, it can be represented graphically as 1/3 octave spectra.