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data was accessed prior to an injury severity update, the agency retrieving the data may unknowingly be working with an outdated version.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.

Geographic Information Systems (GIS) are frequently used to analyze collision data. In order to utilize GIS, the data must be geocoded, or assigned a latitude and longitude coordinate by translating a descriptive location onto street network data. However, the ability for accurate spatial analysis can be limited by geocoding errors that may occur due to limitations in data collection technologies, incorrect data entry due to human error, or inaccurate street reference data. In the state of California there is an increased opportunity for data entry errors, given the long sequence of events and resulting paper trail that is required prior to finalizing each collision record. Data entry errors can occur during the initial traffic collision report completion, statewide database entry, state highway reference location input, or during a separate process to geocode fatal collisions. These data entry errors are incorporated into any geocoding process and frequently cause geocoding errors; but even in the absence of data entry errors, discrepancies in street network data can also result in geocoding inaccuracies. The objective of this paper is to summarize the sources of geocoding errors that occur before and after collision data is compiled into the California state database and the federal database of fatal collisions. Consideration is also given to the potential errors that can arise from the use of Global Positioning System coordinates as an alternative to geocoding. Finally, the impact of geocoding errors on traffic safety analysis is discussed in the context of specific applications currently available in California.

Traffic collision reports typically provide descriptive locations indicating where a collision occurred and referencing the nearest intersection. Global Positioning System (GPS) technology can be used to provide latitude and longitude coordinates in addition to the descriptive location and many states now include GPS coordinates in collision reports. However, research has shown that there is potential for numerous errors when police agencies use GPS to complete traffic collision reports. In California, GPS coordinates have been included in the statewide collision database since 2006, but their overall accuracy has never been evaluated. The objective of this paper was to review the status of GPS coordinates in California collision data from 2009 to 2011 and to categorize types of errors or discrepancies that were exhibited, investigate error trends, and develop recommendations for use of the GPS coordinates. Instead of just classifying a GPS coordinate location as correct or incorrect, eleven categorizations were developed to better assess the breadth of differences between the GPS coordinate and descriptive location. Overall, 43% of GPS coordinates were categorized as correct, 2.5% were unknown, and the other 54.5% exhibited some type of discrepancy with the descriptive location. GPS coordinates located off the roadway were the most frequent error type, comprising nearly 20% of the sample, while systematic GPS errors such as truncated coordinates occurred 7% of the time. Accuracy appears to be improving over time, but it is recommended to thoroughly review the coordinate locations prior to conducting any spatial analyses. 

There is a disproportional risk of motor vehicle death and injury among American Indian/Alaska Native (AI/AN) populations in the United States. As home to the nation’s largest population of AI individuals, it is vital that California develop a better understanding of the factors contributing to this risk to guide the development and implementation of interventions to improve traffic safety for this population on the nearly 100 Rancherias and reservations in the state. However, there is very little data about the numbers and types of collisions, and driver and environmental factors contributing to the collisions that occur on tribal lands. As a first step toward better understanding the scope of the risk disparity, and the shortcomings in data collection, SafeTREC conducted a literature review and crash analysis using data from the Statewide Integrated Traffic Record System (SWITRS) and tribal area base maps targeting these communities. As a result of presentations and discussions at a California Tribal Safety conference where these analyses were presented, a number of procedural and institutional challenges were identified. Addressing these issues will not only help policymakers identify interventions to improve traffic safety on tribal lands, but it will give tribal jurisdictions tools to compete for scarce safety funding through the use of data documenting the need for safety improvements. Future research efforts should be aimed at refining these and other initiatives to address both the dire conditions of traffic safety on California’s tribal lands, and the limitations of the data.