California Highway Patrol
The CHP maintains a statewide database of all accident data. There are several tools that consume this data to provide maps, graphs etc. The incident data presented throughout this site is obtained from the CHP source data available here
Caltrans utilizes traffic flow analysis software for longitudinal data analysis. Rather than the more primitive point-in-time studies, this software allows real-time modeling over multi-year, to assess traffic flow across a corridor. Data is continuously gathered from vehicles using in-road detectors, Bluetooth, Fasktrak and other devices, creating a large database which can be analyzed at any time. This is the type of analysis that should be used in preference over point-in-time counts which do not present seasonal, weather variations, and cannot detect how changes such as road-diets change the flow to other neighborhoods. The software used by Caltrans is here.