Adaptive Signal System Safety Impacts

US Transportation Collection2021PDFTech ReportChowdhury, MashrurHuynh, NathanGerard, PatrickJin, WeiminSalek, M SabbirTorkjazi, MohammadKhan, Sakib MahmudBrunk, KatherineClemson University. Department of Civil EngineeringSouth Carolina. Dept. of Transportation. Office of Materials and ResearchUnited States. Department of Transportation. Federal Highway AdministrationSouth Carolina. Dept. of Transportation. Office of Materials and ResearchSouth CarolinaUnited StatesAdaptive controlBayes' theoremCrash avoidance systemsHighway safetyLogistic regression analysisSafety analysisSignalized intersectionsSurveysTraffic signal control systemsTravel timeOperationsFully BayesianOrdered Regression ModelLogistic Regression ModelFHWA-SC-21-02SPR No. 737Final ReportThe research team conducted a literature review and a nation-wide survey at the beginning of the research. The literature review revealed that Adaptive Signal Control System (ASCS) was effective in reducing crashes in some studies, while in other studies, the crash reduction due to ASCS was not statistically significant. Twenty-eight states participated in the nation-wide survey and helped the research team identify corridor characteristics, such as the design speed and Annual Average Daily Traffic (AADT) of an ASCS corridor, which would allow for the best operational and safety outcomes. Then, to determine the safety effects of ASCS, the research team evaluated the safety effectiveness of ASCS in terms of reducing the crash frequency at 11 ASCS corridors with a total of 109 signalized intersections located throughout South Carolina. This analysis showed that ASCS reduced the number of crashes for most ASCS corridors and intersections. ASCS also reduced the severity level of crashes. Additionally, it was found that ASCS deployed on a corridor parallel to a freeway reduced the likelihood of secondary crashes on the freeway by 47%. To determine the operational effectiveness of ASCS in travel time reduction and travel time reliability improvement, the research team evaluated 11 ASCS corridors with a total of 102 signalized intersections. The results indicated that when ASCS was operational, it reduced the travel time by 6.4% on average and improved the travel time reliability by 31.4% on average compared to the case when the ASCS was not operational.125