Crashes at isolated rural intersections, particularly those involving vehicles traveling perpendicularly to each other, are especially dangerous due to the high speeds involved. Consequently, transportation agencies are interested in reducing the occurrence of this crash type. Many engineering treatments exist to improve safety at isolated, high-speed, signalized intersections. Intuitively, it is critical to know which safety treatments are the most effective for a given set of selection criteria at a particular intersection. Without a well-defined decision making methodology, it is difficult to decide which safety countermeasure, or set of countermeasures, is the best option. Additionally, because of the large number of possible intersection configurations, traffic volumes, and vehicle types, it would be impossible to develop a set of guidelines that could be applied to all signalized intersections. Therefore, a methodology was developed in in this paper whereby common countermeasures could be modeled and analyzed prior to being implemented in the field. Due to the dynamic and stochastic nature of the problem, the choice was made to employ microsimulation tools, such as VISSIM, to analyze the studied countermeasures. A calibrated and validated microsimulation model of a signalized intersection was used to model two common safety countermeasures. The methodology was demonstrated on a test site located just outside of Lincoln, Nebraska. The model was calibrated to the distribution of observed speeds collected at the test site. It was concluded that the methodology could be used for the preliminary analysis of safety treatments based on select safety and operational measures of effectiveness.

Driver behavior within the dilemma zone can be a major safety concern at high-speed signalized intersections. The Nebraska Department of Roads (DOR) has developed and implemented an actuated advance warning dilemma zone protection system. This paper investigates the impact that system has had on safety at high-speed signalized intersections. The operating algorithm has been designed such that the system continually monitors an upstream detector, as well as traffic at the intersection, to predict the onset of the yellow signal indication. Flashing beacons are used to warn drivers of the impending end of the green indication. Although these systems have received positive reviews from the public—and commercial vehicle operators in particular—there has been no comprehensive analysis of their effect on safety. The focus of this research was to address this evaluative need and provide answers about the effectiveness of the Nebraska DOR system in improving safety. Crash records from before and after the implementation of the system at 26 intersections were compared. In addition, 29 control intersections were used to compare crash rates over time, and a fully Bayesian technique was employed to ensure that no exogenous variables affected the study. Results of the analysis were promising (an overall crash reduction rate of 8%) and suggested that the use of the system should be encouraged as an effective safety treatment for the dilemma zone problem at high-speed signalized intersections.

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This paper presents a calibration and validation procedure for microsimulation models, which used metrics (mean, variance, and mean absolute percentage error) with statistical tests (t-test, Shapiro-Wilk, KolmogorovSmirnov and Wilcoxon), to compare empirical and simulated data. A genetic algorithm was used to identify calibration parameters set. The paper justifies the approach using VISSIM microsimulations to analyze two safety countermeasures: Advance Detection System and Advance Warning System, which can be applied at signalized intersection. The end result was a calibrated and validated model, which could be used to compare different safety countermeasures at rural signalized intersections in the state of Nebraska (USA). The proposed approach could be utilized in similar studies.Keywords: signalized intersection, safety countermeasures, calibration, validation, simulation model Streszczenie W artykule przedstawiono procedurę kalibracji i walidacji modeli mikrosymulacji z użyciem mierników (średnia, wariancja i średni bezwzględny błąd procentowy), oraz testów statystycznych (studenta, ShapiroWilka, Kolmogorow-Smirnova oraz Wilcoxona) dla porównania danych empirycznych i z symulacji. Algorytm genetyczny wykorzystano do doboru parametrów kalibracyjnych. Metodologia została sprawdzona w programie VISSIM do analizy dwóch systemów poprawy BRD: Systemu Wczesnej Detekcji i Wczesnego Ostrzegania, które stosuje się na skrzyżowaniach z sygnalizacją świetlną. W wyniku uzyskano skalibrowany i zweryfikowany model, który można użyć do porównania środków poprawy BRD na zamiejskich skrzyżowaniach z sygnalizacją w stanie Nebraska (USA). To podejście można wykorzystać w podobnych analizach.Słowa kluczowe: skrzyżowanie z sygnalizacją, środki poprawy brd, kalibracja, walidacja, model symulacyjny 124