Safety evaluation of diverging diamond interchanges in Missouri.

Details

• Creators:
  Edara, Praveen ; Sun, Carlos ; Claros, Boris R. ; Brown, Henry
• Corporate Creators:
  University of Missouri--Columbia. Department of Civil and Environmental Engineering
• Corporate Contributors:
  Mid America Transportation Center
• Subject/TRT Terms:
  • Diamond interchanges
  • Diverging traffic
  • Traffic safety
  • Evaluation
  • Before and after studies
  • Crash rates
• Publication/ Report Number:
  cmr 15-006
• Resource Type:
  Tech Report
• Geographical Coverage:
  Missouri
• Corporate Publisher:
  Missouri. Department 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.
  More +
• Format:
  PDF
• Funding:
  TR201406
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/28522/dot_28522_DS1.pdf
• File Type:
  [PDF - 1.42 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:41681caa2d4470d6d57d3608ea13937df24d3b4c6e1217ed6085cde75c3b16ebbb3cad80768a1a249357ad8d23c15b64bb39a83e4f2660da1cf98440dd824b22