Left-turning traffic without a protected left-turn signal is one of the major safety concerns at urban\nintersections. Though an average of only l0% - 15% of all approaching traffic turns left, significantly\na large proportion of left-turn crashes occur involving 21% of all intersection fatal crashes. Where\ntraditional safety countermeasures of signal timing-phasing and use of flashing yellow light have\nreportedly failed to significantly reduce the rate of crashes, an in-vehicle advance collision warning\nmessage can be helpful to reduce left-turn collisions at intersections. In this study, an in-vehicle\naudio warning application has been designed by providing two safety warning messages (Advance\nWarning Message and Safe Left-turn Maneuver Message) under the vehicle to vehicle (V2V)\ncommunication system, which is triggered based on the acceptable gaps of oncoming opposing vehicles\nfor a safe left-turn. A driving simulator test has been conducted with 30 participants to investigate\nthe impacts of warning messages on performance measures such as speed and acceleration\nprofiles, collision records, brake reaction distance, and intersection clearance time. Statistical\nresults showed that with the help of these messages, all participants were able to reduce speeds\nand accelerations and chose suitable gaps without potential conflicts. Moreover, the results of questionnaire\nanalysis provide a positive acceptability especially for the Safe Left-turn Maneuver Message.\nBased on the performance measurements, this type of safety warning messages can be recommended\nfor possible real-road tests for practical applications.
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