| Highway long tangent sections can easily cause driving fatigue problems.The social hazard is serious because of the bad traffic accident caused by this problem,so the maximum length of the tangent of the road should be limited.In China,20 times the design speed is often used as the maximum length of long tangent sections.However,the situation in China cannot be set as a unified standard as a result of the vast territory of China.How to determine the maximum length of tangent according to the existing conditions of the project is an urgent problem to be solved.The maximum length of tangent should be limited from the perspective of avoiding driving fatigue and ensuring safe driving.The safe tangent should be determined according to the driver’s psychological reaction and visual effect.Therefore,so as to determine the maximum length of a safe tangent for the existing situation of a project,this paper relies on the National Natural Science Foundation of China Youth Science Fund Project “Research on the Maximum Tangent Length Flexibility Design of Highway Based on Road Environment”(51508033).From the perspective of highway visual environment,this paper systematically quantifies the visual environmental that influence the maximum length of tangent sections and studies the influence of visual environmental on the design of maximum length of tangent sections.Based on the research on the movement law and characteristics of the highway environment in the driver’s vision on the tangent sections,this paper drawed on the relevant literature research results at home and abroad,and five visual cues were extracted: the lateral distance of the visual object and the driver,the height of the visual object from the ground,the size of the visual object,the color contrast of the visual object,and the edge rate of the visual object.Then,we used the driver’s questionnaire to study the subjective fatigue of the driver’s visual cues from the extracted.The results of the analysis of variance clearly shows that the visual cues that influence the driver’s subjective fatigue perception are: the size of the visual object,the height of the visual object from the ground,and the interaction between the two.In order to further verify the impact of the extracted visual cues on the driver,this paper designed and implemented the driving fatigue experience experiment based on the driver’s questionnaire results.Two-way analysis of variance for repeated measurements shows that dimensional visual cues perpendicular to the driver’s gaze direction(hereinafter referred to as the vertical dimensions of visual objects)significantly affect the time of driver fatigue.The paper further discussed the influence of vertical dimension cues of visual objects on the maximum length design of highway tangent.The study found that when the vertical size of visual object is too large or small,the maximum tangent length for ensuring driving safety is relatively shorts,because of driving fatigue;when the vertical size of the visual object is in the middle level(about 10 m),the driver has a late driving fatigue time,which can ensure that maximum tangent length of safe driving is longer.According to this result,this paper puts forward the idea of designing the maximum length of highways for safety based on the existing situation of an engineering project: determing the maximum design tangent length to visual cues of in different places;if a long tangent is needed,in order to driving safety,slight inducing facilities should be introduced and be designed in such a way that the visual cues reach the medium level.The results of this study can be applied to the design of the maximum length of tangent in the existing situation of the project,as well as to the design and evaluation of line of sight guidance facilities in long tangent sections.It conforms to the development direction of encouraging and advocating flexible route design in norms and standards,and helps to alleviate the driver’s fatigue sense in long tangent sections and improve driver’s driving safety. |
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