Rockridge Soundwalls

State Route 24 Oakland, CA Pre-NBSSR Noise Study: Introduction

There are issues concerning the methodology that was used to produce the State Route 24 Oakland, CA Pre-NBSSR Noise Study. The Study's justification for the construction of the two soundwalls that are highest on the Caldecott Tunnel Settlement Agreement Final Project List is questionable. In fact, this Study shows that, along most of the route of these two soundwalls, measured noise levels are below the required threshold. And predicted noise levels which were above this threshold were calculated using invalid assumptions.

The Noise Study is a technical report. Critiquing it is also a technical exercise, one that may not be easy for the general public to understand. But the ramifications of the Study for the public are real. This analysis approaches the issues in a general way and then goes into more detail for those who are interested.

According to the Proposed Alameda County Congestion Management Agency (ACCMA) Freeway Soundwall Policy, "an existing or future exterior noise level of at least 65 decibels" must exist in order for a soundwall project to proceed. In order to demonstrate that this requirement was met, Acoustical and Vibration Consultants Wilson, Ihrig, and Associates, Inc. issued the Pre-NBSSR Noise Study. As described in this Study, measurements of noise levels on streets close to Highway 24 were made. In addition, predictions of noise levels based upon current and estimated future traffic volumes were made. According to ACCMA and CalTrans policy, either measured or predicted noise levels must exceed a threshold in order to justify soundwall construction.

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