Average daily traffic counts on arterial roadways are collected from each of the 34 cities and the county on an annual basis to create the Traffic Flow Map. OCTA reviews the traffic volumes and adjusts the data, as necessary, to reflect weekday traffic for the year of the published map. Not all cities update their counts on an annual basis. For these cities, previously provided counts are adjusted based on traffic growth in the surrounding area. Annual average daily freeway volumes are collected by CalTrans and adjusted for the map to reflect a 5-Day (weekday) count. The map is used for transportation planning and to compare and validate the results of travel demand forecasting models.

Zoomable traffic volume maps