When using radar the posted speed limit must be in accordance with the speed limit indicated by the survey. In other words, if the survey recommends a speed limit of 40 MPH, and the local jurisdiction posts "30 MPH" signs, any ticket written should be thrown out of court, irrespective of the transgressor's speed, since the police would be enforcing a speed limit not legally set. Unless extenuating safety circumstances such as an excess of accidents indicate a lower speed is needed.
Additionally, the appropriate standard for determining the proper speed limit is based on the 85th percentile of the surveyed speeds. the survey must set forth ANY justification for reduction of the recommended speed from the 85th percentile of the survey data.
I find it hard to believe the the 85th percentile on the Atherton stretch of the Alameda is 30mps - unless they did the north and southbound surveys during the morning rush hour southbound and the afternoon rush hour northbound. During which time the traffic within 200 ft of Atherton Ave moves at 5mph.