Brake and wheel design can cut train noise

The European Union's programme to develop technical specifications for interoperability includes setting noise limits for new trains under both static and running conditions. Rolling noise is the dominant source of noise at speeds below 300 km/h. Rolling noise can be reduced by reducing roughness and redesigning the wheels. The main feature affecting the wheel roughness is the braking system. Disc brakes, which are used on modern passenger rolling stock, are quieter than tread brakes with cast iron brake blocks, which are used in freight vehicles. There is a move to replace cast iron with composite materials. Multi-resonant absorbers and constrained layer damping have been developed to dampen wheel noise. Reductions in the wheel component of radiated noise can be achieved by modifying the cross-sectional shape and diameter of the wheel or by using perforated wheels. Bogie shrouds and trackside barriers can also be used to reduce sound radiation. Wheels can also produce curve squeal. This can be solved by lubrication.