Rockridge Soundwalls

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

The Noise Study examined ten soundwalls, five along each side of Highway 24. While all ten soundwalls appear on the Settlement Agreement Final Project List, the Noise Study found that only four were considered to "achieve the criteria of the ACCMA freeway soundwall policy and are also considered cost-effective". These are:

- Eastbound between 40th Street and 52nd Street (EB#1)
- Eastbound between Vincent Way and Broadway (EB#3)
- Westbound between Claremont Avenue and M.L. King Jr. Way (WB#2)
- Westbound between Ross Street and Ayala Avenue (WB#3)

The soundwalls "above the line" on the Project List are:

- EB#3 Eastbound between Vicente Way and Broadway (#7 on Final Project List)
- WB#3 Westbound between Ross Street and Telegraph Avenue (#8 on Final Project List)
- WB#4 Westbound between Patton Street and Ross Street (#18 on Final Project List but not considered cost-effective in the Noise Report).

Here are the key points:

- The Alameda County Traffic Commission (ACTC, formerly ACCMA) applies a noise threshold for soundwalls that is lower than the Federal and State of California Department of Transportation (DOT) noise threshold.
- Of the Study's 25 short-term noise measurements, 13 were below the ACTC noise threshold and 19 were at or below the State/Federal noise threshold, even when corrected for the time of day.
- Of the Study's 5 long-term sound measurements, 3 were below the State/Federal noise threshold.
- Some assumptions made in calculating present and future predicted noise levels are incorrect.
- A reasonable assumption regarding future noise levels was not made which might have lowered the predicted future noise levels.

Soundwalls could be justified by the Noise Study long-term noise measurements on the north side of Highway 24 near Claremont Middle School (a middle section of WB#3) and also around Hardy Park (the southern ends of WB#3 and EB#3). All short-term noise measurements (corrected for time of day) along EB#3 and WB#3 were below the State/Federal noise threshold and all but one were below the ACTC noise threshold. EB#3 is proposed to be 4,852 feet long and WB#3 3,083 feet long.

The Noise Study justifies soundwall construction based not on these measured noise levels but on "predicted" noise levels calculated by means of a computer using the Federal Highway Administration (FHWA) Traffic Noise Model software. Two sets of results are provided: predictions for current noise and for noise in the year 2030. However, some of the assumptions fed into this computer model do not reflect actual conditions. For example, for EB#3 and WB#3:

- Peak traffic hour volumes were used, not peak noise hour volumes.
- 65 MPH traffic was assumed for peak traffic, a condition which rarely exists.
(Another questionable assumption that was stated in the Noise Study may not have actually been applied. See the section "Calculated Noise" under Noise study III for details.)

One could say that these assumptions were close enough; that this methodology is the way that ACTC works; that the Noise Study was accepted by Caltrans; and that the public should leave this kind of technical analysis to the experts. But - the effect of these assumptions was to create a prediction of current noise that is significantly higher than that which was actually measured. And a small shift one way or the other due to some questionable assumptions is apparently enough to move the result above or below the threshold which is required to permit soundwalls to be constructed. The scenario that the Noise Study labels as "worst case" actually appears to be "worse than worst case".

Groucho Marx said, "Who are you going to believe, me or your own eyes?" In this version, which should be believed: a computer model based on inaccurate assumptions or the actual noise measurements?

Since the current noise predictions do not match the current measured noise levels, one can also question whether the predicted future noise levels would be accurate. But in the case of the future predictions, another questionable assumption was made.

Highway noise results from a loss of energy coming from each vehicle, whether from engine noise, wind noise, tires flexing, etc. As more vehicles embody higher Federal fuel efficiency standards, one would expect less wasted energy in the form of emitted noise. Electric vehicles emit no engine noise at all (although their predominant noise is from tires). This was not taken into account in the predicted future noise level calculations.


The Pre-NBSSR Noise Study shows that the soundwall noise thresholds are not exceeded by the measured noise levels throughout most of the proposed routes of soundwalls EB#3 and WB#3. The predictions of current and future noise levels by calculation are questionable. Therefore, there is a serious question as to whether soundwalls EB#3 and WB#3 are justified outside of two specific locations.

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