Caltrans measures this indicator continuously using automated counters placed in the roadway at the intersection of Park Avenue and U.S. Highway 50 in South Lake Tahoe, including on the Saturday of Presidents’ Day weekend from 4 p.m. and midnight, coinciding with the historical period of the most frequent exceedance of California’s carbon monoxide (CO) standards. Data are summarized by Caltrans and subsequently accessed by TRPA for reporting purposes.