Conflict Analysis using SSAM
After the 10 simulations for each intersection were completed in VISSIM, their respective outputs were imported in SSAM. The analysis in SSAM resulted in possible conflicts generated at each intersection. As mentioned earlier, the results from the SSAM analysis were filtered to remove any uncertainties, including possible conflicts of pedestrians. The filters used are explained in Table 3 (Section 2.5.3).
Per Saleem (2012), the principal reason for removing the pedestrian conflicts is that in his study only vehicle-to-vehicle crashes are modeled. In the same way, this study only focuses on evaluating safety of signalized intersections with the presence of automated vehicles without including pedestrians due to…show more content…
The CMF was calculated for each crash prediction model applied at both scenarios: 50%AV and 100%AV. Using the method studied by Shahdah, Saccomanno, & Persaud (2014) to predict the CMF based on simulated conflicts, the total predicted crashes after the countermeasure was applied (crashes at 100% AV and crashes at 50%AV) were divided by the total predicted crashes before the countermeasure was applied (crashes at 0%AV). This provided crash modification factors for the two AV penetration levels investigated in this study.
Finally, to have a better perspective with regards to simulated conflicts and crashes, an average was calculated for each element used to calculate the CMFs for the four prediction models (crashes at 0%AV, crashes at 100%AV, crashes at 50%AV). With these new values, new CMFs were calculated for 100%AV and 50%AV with respect to the untreated site scenario of 0%AV.
3.5 Evaluation of Safety Treatments for Signalized Intersections
After analyzing the safety of the 78 signalized intersections when introducing automated vehicles, this part of the research explored and evaluated the safety effects on crashes when hypothetical treatments were applied to selected intersections.
The first safety treatment consisted of changing left turn operation from permissive to permissive-protected. Permissive left turns can raise safety concerns since drivers take a higher risk in crossing the