The Educational Railroading Conference Leader Since 1994


2021 Rail Transit Session


Controlling Grinding-Induced Corrugation to Maintain Lower Wayside Train Noise Levels

Shankar Rajaram

Shankar Rajaram
Sound Transit

Rail surface condition plays a dominant role in influencing noise emissions from Light Rail Vehicles (LRV) at train speeds greater than 25 mph. Rail roughness data reported from transit properties in North America over the last decade indicate that Grinding-induced Corrugation (GIC) peaks tend to be at 30 mm. This wavelength corresponds to a grinding speed of 4 mph and a motor rate of 3600 rpm. Ensuring good rail surface condition would require an achievable grinding specification and a verification process. Rail roughness measurements at different Sound Transit rail sections over a 5-year period showed GIC peaks between 24 mm and 47 mm, indicating grinder speeds in range of 4 mph to 6 mph. To reduce noise emissions from trains and to improve rail life, a new rail grinding strategy was developed by Sound Transit that required two distinct steps: (a) Grinding and (b) Polishing. The Grinding step required a slower optimized grinding speed for removing metal and the Polishing step required a faster speed with a finer grit stone.

The roughness data during the grinding program was reviewed in 1/24th octave band to precisely identify the GIC peaks and verify grinding speeds. The final reporting of rail roughness was performed in 1/3 octave band wavelengths to verify compliance. The goal of realizing the primary roughness peak at 50 mm was achieved during this program. Overall, the measured Lmax noise showed that the peak 1/3 octave band noise frequency correlated reasonably well with noise predictions based on rail roughness. This presentation will also discuss the details of how the grinding strategy was adjusted for different track types: (1) embedded tracks that limits the maximum grinding speed to 4.5 mph and (2) floating slab track areas that tend to interact with the grinder at the track slab resonance frequency.

Source: Sound Transit noise and rail roughness data.

Relevance: Reduced noise mitigation cost and enhanced SGR strategy for transit agencies