Safety Evaluation of Seven of the Earliest Diverging Diamond Interchanges Installed in the United States

Abstract

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.

Safety Effect of Diverging Diamond Interchanges on Adjacent Roadway Facilities

“…The crash reductions reported through use of the empirical Bayes (EB) method were 62.6% for fatal and injury (FI) crashes, 35.1% for property damage only (PDO) crashes, and 47.9% for total crashes (6). Similar results were reported later in a national study conducted by Hummer et al, which included DDI sites in Missouri, Kentucky, New York, and Tennessee (7). They reported that the DDI design effected a 33% reduction in total crashes and a 41% reduction in FI crashes.…”

Sustainable Design of Diverging Diamond Interchange: Development of Warrants for Improving Operational Performance

“…In the present study, a 60 s cycle length was found as the A lower delay period will not only save the user time and associated fuel cost (i.e., socio-economic benefits), it will also reduce the vehicular emissions (i.e., environmental impact), particularly carbon monoxide (CO) and hydrocarbons (HC), which are produced at a much higher rate during idling in comparison to the cruising condition [31]. Past studies compared the pre-and post-installation conditions for DDI at seven locations in the USA based on several years of traffic data analysis [32,33]. The main findings were, (i) a 33% reduction in the number of crashes for DDI, and (ii) around 60% reduction in the severity of the crashes, i.e., injuries and fatalities.…”

Framework for Considering a Diverging Diamond Interchange to Improve Operations and Safety

“…Several researchers have studied and evaluated the effectiveness of DDI's on safety while taking crash data of existing DDI's into consideration [4][5] [6]. Safety evaluation methods, including the Comparison Group Method and the Empirical Bayes Method, among others, have been applied to compare and evaluate DDI safety improvements.…”

“…Several studies have researched driver behavior in DDIs, one of which was done by Joe Bared [4]. He explains that some drivers may still be confused about DDIs because they are unfamiliar with this new design.…”