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Condition monitoring of track geometry from sensors mounted on an in-service vehicle offers continual monitoring of track geometry that can aid track maintenance strategies. Mounting and maintaining a full track geometry recording system on an in-service vehicle is an expensive proposition as the commonly used optical sensors are difficult to keep working in the dirty railway environment. A simpler and more cost-effective alternative is to estimate track geometry using a small number of robust sensors such as accelerometers and rate gyroscopes, from which a worthwhile proportion of geometric quality measures and specific irregularities can be identified. This paper describes the theory and practical results of using a bogie-mounted pitchrate gyro to obtain mean vertical alignment, conditional on the secondary vertical damper geometry. Left and right axlebox-mounted accelerometers can be added to provide short wavelength irregularity, if required. Results from trials on Tyne and Wear Metro vehicles and on a Class 175 mainline vehicle demonstrate effective vertical irregularity monitoring, in particular the ability to monitor vertical irregularity over a wide range of vehicle speeds down to about 1 ms-1, where vertically sensing accelerometers combined with displacement transducers are unable to function correctly.

Maintaining the alignment of railway track is vitally important for the smooth and safe passage of railway vehicles. Poor track alignment can result in poor ride quality, flange contact, or even flange climb. Accurate horizontal track geometry can be measured using a dedicated track recording vehicle or from a full track geometry recording system mounted on an in-service vehicle. This paper describes the use of sensors mounted on the bogie of an in-service vehicle to estimate the mean track alignment without the use of optical or contact sensors. In principle, either bogie lateral acceleration or yaw rate can be processed to give an estimate of mean lateral track irregularity, but a yaw rate gyro provides consistent estimates down to lower vehicle speeds than does an accelerometer and does not require compensation for the effects of bogie roll. An improved estimate can be obtained by inverting the dynamic relationship between the mean track alignment and the bogie yaw motion. This is demonstrated with results from a Class 175 vehicle. Continually monitoring the lateral response of a bogie on an in-service vehicle, using only a yaw rate gyro, can provide data enabling the prioritization of maintenance operations.

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