Evaluation of Injury Severity Updates in California Collision Data

Fatal or injury collisions in California must be reported to the California Highway Patrol (CHP) for inclusion in the Statewide Integrated Traffic Records System (SWITRS). After records have been entered into SWITRS they are made publicly available and are accessible through the CHP’s report and data retrieval site called I-SWITRS. However, records accessed in SWITRS are considered provisional and can be updated several years after initial entry. This includes the injury severity level of collisions. If the collision data was accessed prior to an injury severity update, the agency retrieving the data may unknowingly be working with an outdated version. This can have an impact on government agencies use of data driven safety analyses to apply for safety improvement funding in order to achieve key safety goals in reducing fatal and serious injury collisions. This paper evaluated the frequency and level of injury severity changes for severe injury and fatal collisions that occurred in 2016 and which were retrieved at four different times between March 2017 and June 2018. In total, 94 injury collisions were upgraded to fatal collisions (2.653%) and 2 fatal collisions were downgraded to severe injury collisions (0.056%) out of the 3,543 total fatal collisions that occurred in 2016. The authors concluded that government agencies need to perform regular checks of their data to ensure that fatal and severe injury collisions are properly accounted for to maximize their ability to achieve safety performance targets.