Details:

Creators:
Edara, Praveen ; Sun, Carlos ; Claros, Boris R. ; Brown, Henry
Edara, Praveen ; Sun, Carlos ; Claros, Boris R. ; Brown, Henry Less -
Corporate Creators:
University of Missouri--Columbia. Dept. of Civil and Environmental Engineering
Corporate Contributors:
Mid America Transportation Center
Subject/TRT Terms:
[+]
Accident Rates Before And After Studies Diamond Interchanges Diverging Traffic Evaluation Traffic Safety
Publication/ Report Number:
cmr 15-006
Resource Type:
Tech Report
Geographical Coverage:
Missouri
Corporate Publisher:
Missouri. Dept. of Transportation
Abstract:
The Diverging Diamond Interchange (DDI) has gained in popularity in the United States during the last decade. The

operational benefits and lower costs of retrofitting a conventional diamond with a DDI have contributed to its increased use.

Existing research on DDIs has focused primarily on the assessment of operational benefits. Unfortunately, formal safety

evaluations of DDIs are lacking. This study filled the knowledge gap by conducting a safety evaluation at the project-level

(interchange) and the site-specific level (ramp terminals) of DDIs using three types of before-after evaluation methods: Naïve,

Empirical Bayes (EB), and Comparison Group (CG). Three evaluation methods were used since the methods involved

different trade-offs, such as data requirements, complexity, and regression-to-the-mean. The safety evaluation at the project-level accounts for the influence of the DDI treatment in the entire footprint of the interchange. On the other hand, the site-specific approach focused on the influence at the ramp terminals only. All three methods showed that a DDI replacing a

conventional diamond decreased crash frequency for all severities. At the project-level, the highest crash reduction was

observed for fatal and injury (FI) crashes – 63.2% (Naïve), 62.6% (EB), and 60.6% (CG). Property damage only crashes were

reduced by 33.9% (Naïve), 35.1% (EB), and 49.0% (CG). Total crash frequency also decreased by 41.7% (Naïve), 40.8%

(EB), and 52.9% (CG). Similarly, in the site-specific analysis, the highest crash reduction was observed for fatal and injury

(FI) crashes – 64.3% (Naïve), 67.8% (EB), and 67.7% (CG). Property damage only crashes were reduced by 35.6% (Naïve),

53.4% (EB), and 47.0% (CG). Total crash frequency also decreased by 43.2% (Naïve), 56.6% (EB), and 53.3% (CG). A

collision type analysis revealed that the DDI, as compared to a diamond, traded high severity for lower severity crashes. While

34.3% of ramp terminal-related FI crashes in a diamond occurred due to the left turn angle crashes with oncoming traffic, the

DDI eliminated this crash type. In summary, the DDI offers significant crash reduction benefits over conventional diamond

interchanges.


Format:
PDF
Funding:
TR201406
Collection(s):
US Transportation Collection
Main Document Checksum:
[+]
urn:sha256:ece44b3854abbc9e98ac39dccc0c5baf37a892c81050e051483679978e9d97b7
Download URL:
https://rosap.ntl.bts.gov/view/dot/28522/dot_28522_DS1.pdf
File Type:

Supporting Files

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