Assessing the Safety Impacts of Roundabouts in California and the San Joaquin Valley

Abstract: Roundabouts are designed to reduce traffic congestion, minimize accidents, and
promote more efficient vehicle movement compared to traditional signalized
intersections. Despite these advantages, public perceptions of roundabouts in California
remain mixed, with concerns often raised regarding their safety, usability, and
effectiveness. This work presents a quantitative methodology to assess the safety
impacts of roundabouts.

This project compared different safety measures – e.g. fatalities, injuries and crashes –
at intersections before and after the implementation of roundabouts. Our geographic
focus is divided into two components: the entirety of California and the San Joaquin
Valley. The scope of the analysis examines the effects within a 100ft, 250ft, 500ft, and
1000ft buffer zones around the intersections. Our crash data covered the years 2012 to
2019. We excluded the 2020 crash data and beyond from our analysis due to the
pandemic’s impact on driving behavior.

Using ArcGIS, we employed geoprocessing tools to prepare the data for extraction,
which was then further analyzed using MS Excel.

The quantitative findings evaluate the effectiveness of roundabouts in California post-
construction, specifically their impact on reducing crashes, injuries, and fatalities. The
results identify the safety benefits of implementing roundabouts, where quantifying
these benefits serves as an effective strategy for evidence-based decision making
moving forward.

Keywords: Roundabouts, Crash Analysis, Road Safety, Public Education, California,
Signalized Intersections, Crash Reduction, Multi-Lane Roundabouts, Accident Severity.