Study Details

Study Title: Safety Performance Analysis of Roundabout Interchanges in Missouri

Authors:

Publication Date: JAN, 2018

Abstract: There is significant knowledge about the safety performance of roundabout intersections with a large body of literature from all around the world, including the United States. Even though the roundabout interchange terminal shares many similarities and design principles with the roundabout intersection, it differs in many important ways, such as in traffic patterns, operations, and geometry. There is limited knowledge about roundabout terminals due to its newness. Also, the crash data for interchanges is usually problematic because the reporting agency often does not locate crashes precisely within an interchange. This paper describes a safety performance study of roundabout terminals using three related methods: Empirical Bayes before and after study, collision diagramming, and vehicle conflicts microsimulation. A significant data undertaking involved the review of 1,681 individual crash reports for 13 roundabout terminals. The Empirical Bayes study showed single-lane roundabouts replacing stop-controlled ramp terminals reduced crashes by 32.8%, 23.1%, and 24.4% for Fatal and Injury (FI), Property Damage Only(PDO), and Total (TOT) crashes, respectively. The results were not as high as the safety benefits of roundabout intersections. Dual-lane roundabout ramp terminals, as an aggregate, showed an increase in crashes of 28.8% in FI, 33.6% in PDO, and 33.3% in TOT crashes; although, a few individual terminals experienced decreases in crashes. The collision diagrams showed that exit-ramp-related-crashes accounted for 49.2% (single-lane) and 43.1% (dual-lane) of roundabout crashes. Conflict analysis showed that unbalanced demand conditions had fewer conflicts for single-lane roundabouts, but dual-lane roundabouts showed similar increasing conflict trends under balanced or unbalanced demand conditions.

Study Citation: Claros, B., J. Berry., C. Sun., and P. Edara. "Safety Performance Analysis of Roundabout Interchanges in Missouri". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-008337, Washington, D.C., (2018).


CMFs Associated With This Study

Category: Interchange design

Countermeasure: Convert to roundabout interchanges

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.047 -4.7 3 Stars All K,A,B,C All All
1.067 -6.7 3 Stars All O All All
1.066 -6.6 3 Stars All All All All
0.756 24.4 3 Stars All All All All
0.769 23.1 3 Stars All O All All
0.672 32.8 2 Stars All K,A,B,C All All
1.288 -28.8 2 Stars All K,A,B,C All All
1.336 -33.6 3 Stars All O All All
1.333 -33.3 3 Stars All All All All