East Link EIS Noise Mitigation Requirements

 

A previous post detailed Sound Transit Board’s latest approach to mitigating light rail noise was to pass the following resolution:

 

 R2023-15: Adopting a Noise and Vibration policy and superseding Motion. No. M2004-08.  The resolution included the following excerpts:

 

Revising the existing Link Noise Mitigation Policy (Motion No. M2004-08) is appropriate because it is out of date, applies only to Link light rail noise and can be improved to reflect lessons learned from implementing Sound Move and ST2 projects.

 

The chief executive officer (CEO) has discretion to assess and mitigate impacts to new development that are built after this date. 

Key policy points in the existing policy have been retained, such as the need for mitigation to be reasonable and feasible. 

 

It's not clear what makes the commitment to  M2004-08 "out of date" or "can be improved". The post also pointed out the motion did not include any mention of “the need for mitigation to be reasonable and feasible”.  Sound Transit committed to Link light rail noise mitigation in Chapter 4 in the July 2011 East Link Project Final EIS, “Affected Environment and Environmental Consequences.”

 

Section 4.7.5 Potential Mitigation Measures included subsection 4.7.5.1 “Noise Mitigation During Operation” with the following excerpts regarding limiting light rail noise and noise mitigation:

 

Sound Transit is committed to minimizing noise levels at the source. 

 

It included details as how they will limit the noise with “state of the art vehicles”, maintenance program” and “operator training”.  However, it also included the following commitment: 

 

For all noise impacts that still exist after these source noise treatments, noise mitigation measures would be provided that are consistent with Sound Transit’s Light Rail Noise Mitigation Policy (Motion No M2004-08)

 

 Again, it's not clear what makes the commitment to  M2004-08 "out of date" or "can be improved". Subsection “Transit Noise Mitigation" included the options for mitigating the noise:  

 

The potential mitigation options available for noise from transit operations on the East Link Project are primarily sound walls, special trackwork lubricated curves, and residential building sound insulation.

 

Sound Transit chose to use “residential building sound insulation” to mitigate noise levels along Central Link route in Seattle.  They chose to use sound walls along route into Bellevue to shield homes from East Link train noise. 

However, they’ve made no attempt to shield those along the light rail route from Bellevue to Redmond.  Thus, to comply with the 60dB limit in Bellevue Commercial Noise Code and Chapter 4 in East Link Project EIS Sound Transit is required to “minimize noise levels at the source”.

 

Light rail noise is do irregularities on the wheel and rail surface that excite the rail and cause it to vibrate.  Small flat spots (1-2mm) on wheels and small gaps (7mm) between rails with steps (1-3mm) or dips (5-10 mm) cause up and and down wheel movements that vibrate the rail. Rounding the ends of the flat spots and limited rail roughness "softens" the up and down movement, vibration, and noise. Vibration and Noise levels increase with the number of wheels, weight on the wheels, and the train velocity.  

 

It's unlikely anything can be done about wheel flat spots, joints between rails, number of wheels or weight.  The only viable way for Sound Transit to comply with East Link Project Final EIS Noise Level is to limit light rail train velocity. Thus, the Sound Transit CEO shall be required to include as “Operator Training” the limiting of Starter Line velocity to meet 60dB noise level as “Reasonable and Feasible” in R2023-15.