The LRT (Light Rapid Transport) system in Porto was opened in 2002. After four years, the system already exceeded a length of 70 km. The system was designed and is operated according to modern standards. However, one problem has occurred in the recent past: The noise emissions produced from the interface between wheels and rails are higher than expected and sometimes exceeding legally established values. Pöyry was asked to conduct a technical study on how these noise emissions could be reduced.
In the course of this project the profiles of wheels and rails have been carefully investigated, taking into account different stages of wear. In addition, noise emission measurements have been carried out in different locations of the network. These measurements provided valuable data on noise levels and frequencies of emissions.
On the side of the vehicle, the resonant frequency of the wheels has been measured to understand the mechanisms of noise generation in this specific case.
On the basis of these results it was possible to develop suitable mitigation measures. A rail surface conditioner which modifies the adhesion between wheel and rails has been successfully tested in selected locations of the network. It is possible to modify the vehicles in a way that the noise level can be significantly reduced in the whole system.