What is the test for driving under the influence of alcohol?

People v. Wells, supra, 38 Cal.4th 1078 is instructive. There, the officer received a dispatch report of a possibly intoxicated driver "weaving all over the roadway." The record did not identify the caller or circumstances of the report, but the court inferred the report was based on an anonymous phoned-in tip. The vehicle was described as a 1980's model blue van traveling northbound on Highway 99 at Airport Drive. The officer positioned himself on the shoulder of the highway and watched for the vehicle. Two or three minutes later, he saw a blue van traveling approximately 50 miles per hour. He activated his patrol car lights and stopped the van to investigate whether the driver was impaired. He did not observe the van weaving, speeding, or otherwise violating any

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