Safety Evaluation of Directional Interchange with Semi-direct Ramp Connections and Loops

This article evaluates the safety of the Directional Interchange with Semi-Direct Ramp Connection with Loops (DI-SDRL). Toward this end, the Federal Highway Administration’s Interchange Safety Analysis Tool-Enhanced (ISATe) was utilized to predict the safety performance of this interchange under 30 different scenarios covering a wide range of traffic volumes. This interchange’s performance has also been compared to a conventional one, i.e., Directional with Loops Interchange (DLI), in terms of the percentage difference in predicted crash frequencies and using the paired t-Test. The results showed that DI-SDRL ramp segments witnessed a higher number of crashes than the DLI by an average of 36% and 37% for fatal-injury (FI) and property-damage-only (PDO) crashes, respectively. The statistical t-Test results showed that the differences between the two interchanges were statistically significant, except for the freeway segments. On the other hand, the differences reported by crash type were not as large as ramp segments. For example, the DI-SDRL reported a higher number of multiple-vehicle (MV) crashes than the DLI by an average of 4% and 2% for FI and PDO severity levels, respectively. As for the total single-vehicle (SV) crashes, the DI-SDRL reported a higher number of crashes than the DLI by an average of 2% for both FI and PDO severity levels. Nevertheless, the statistical t-Test indicated that the difference between the studied interchanges is statistically significant.