Study Details
Study Title: A National-Level Safety Evaluation of Diverging Diamond Interchanges
Authors: Nye et al.
Publication Date:JAN, 2019
Abstract: A national-level safety evaluation of Diverging Diamond Interchanges (DDIs) in the United States was completed. This study aimed to update previous evaluations and to expand the treatment group size of previous studies to provide a more robust and reliable safety assessment of DDI deployments. For this particular treatment, it was determined that, of the observational before-and-after evaluation methodologies, the comparison group approach yields the best evaluation results. The naïve method can be influenced by outside factors that cannot be accounted for (weather, crash reporting tendencies, etc.). The empirical Bayes methods is unnecessary as DDIs are installed for operational benefits, meaning that risk of selection bias and regression-to-the-mean is minimal. This study recommends a total crashes CMF of 0.633 based on the comparison group analysis of 26 DDIs in 11 states. The comparison group method was also applied to a variety of crash variables for this study. Angle, rear-end, and sideswipe crashes were found to have CMFs of 0.441, 0.549, and 1.139, respectively. Fatal-and-injury crashes provided a CMF of 0.461. Daytime and nighttime crashes provided CMFs of 0.648 and 0.638, respectively.
Study Citation: Nye, T. S., C. M. Cunningham, and E. Byrom. "A National-Level Safety Evaluation of Diverging Diamond Interchanges". Presented at the 98th Annual Meeting of the Transportation Research Board, Paper No. 19-01950, Washington, D.C., (2019).
CMFs Associated With This Study
Category: Interchange design
Countermeasure: Convert diamond interchange to Diverging Diamond Interchange (DDI) or Double Crossover Diamond (DCD)
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 0.633 | 36.7 |  | All | All | Not specified | Not specified |
| 0.549 | 45.1 | | Rear end | All | Not specified | Not specified |
| 0.572 | 42.8 |  | Rear end | All | Not specified | Not specified |
| 1.44 | -44 | | Sideswipe | All | Not specified | Not specified |
| 0.587 | 41.3 | | Rear end | All | Not specified | Not specified |
| 0.655 | 34.5 | | Sideswipe | All | Not specified | Not specified |
| 0.153 | | | Angle | All | Not specified | Not specified |
| 0.257 | 74.3 | | Rear end | All | Not specified | Not specified |
| 0.11 | 89 | | Angle | All | Not specified | Not specified |
| 0.576 | 42.4 | | Rear end | All | Not specified | Not specified |
| 0.714 | 28.6 | | Sideswipe | All | Not specified | Not specified |
| 0.461 | 53.9 | | All | K,A,B,C | Not specified | Not specified |
| 0.582 | | | All | K,A,B,C | Not specified | Not specified |
| 0.888 | | | All | O | Not specified | Not specified |
| 0.502 | 49.8 | | All | K,A,B,C | Not specified | Not specified |
| 0.6 | 40 | | All | O | Not specified | Not specified |
| 0.232 | 76.8 | | All | K,A,B,C | Not specified | Not specified |
| 0.36 | 64 | | All | O | Not specified | Not specified |
| 0.312 | 68.8 | | All | K,A,B,C | Not specified | Not specified |
| 0.919 | 8.1 | | All | All | Not specified | Not specified |
| 0.53 | 47 | | All | All | Not specified | Not specified |
| 0.5 | 50 | | All | All | Not specified | Not specified |
