01658306

Component

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.

This paper was sponsored by TRB committee ANB75 Standing Committee on Roundabouts.

18-00837

English

2018

Transportation Research Board 97th Annual Meeting

Digital/other

Figures; Photos; References; Tables

Crash data; Highway safety; Highway traffic control; Interchanges; Roundabouts

Missouri

Design; Highways; Operations and Traffic Management; Safety and Human Factors

Transportation Research Board Annual Meeting 2018 Paper #18-00837

TRIS, TRB, ATRI

Jan 8 2018 10:12AM