01590044

Component

https://doi.org/10.3141/2583-04

Diverging diamond interchanges (DDIs) are increasingly popular because they provide improved traffic operations and cost savings. On the basis of theory, DDIs should be safer than conventional diamonds, but previous empirical safety studies have been limited. The objectives of this work were, therefore, to conduct a broader safety evaluation of DDIs and to recommend a crash modification factor (CMF) for the conversion of a conventional diamond to a DDI. The team analyzed seven of the earliest DDIs in the United States. Four were in Missouri and other sites were in Kentucky, New York, and Tennessee. The team collected more than 28 site years of crash and other data before intersection conversion and more than 19 site years of data after their conversion. The primary analysis was before and after with comparison sites to account for trends and potential simultaneous event biases. The results showed that crashes were reduced at most of the sites, and the team recommended a CMF of 0.67, meaning that installation of a DDI to replace a diamond should reduce all crashes by 33%. The reduction in injury crashes was even larger, with the team recommending a CMF of 0.59. Other analyses indicated that DDI installation should mean a substantial reduction of angle and turning crashes, with some reduction in rear-end crashes as well, although rear-end crashes will still be the dominant crash types after DDI installation. Clearly, DDIs offer potential safety benefits, and agencies should consider them strongly as replacements for conventional diamonds.

01595167

16-5481

English

pp 25–33

2016

Transportation Research Record: Journal of the Transportation Research Board

9780309441179

Print

Figures (1) ; Photos; References (9) ; Tables (6)

Crash causes; Crash injuries; Diamond interchanges; Evaluation; Highway safety

Diverging diamond interchanges

Kentucky; Missouri; New York (State); Tennessee

Design; Highways; Safety and Human Factors

PRP, TRIS, TRB, ATRI

Jan 12 2016 6:23PM

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