Speed Limit On Freeway At Night

Freeway is easy to lead traffic accidents as the high vehicle speed, at night is more prone to traffic accidents than during the day, according to statistics, freeway traffic accidents and death rate at night accounted for 65% and 72% of the total respectively. Therefore, on the premise of meeting the vehicles needs, carrying out the study of speed limit for freeway at night, is not only urgent but also meaningful.Compared driving at night with during the day, except for common factors, the main difference is the reduction of illumination condition at night, which causes vision limited and identification distance drop, and once prone to risk of high speed, besides the existence of dark environment will change the driver's perceptual speed, feel-safe speed is not necessarily a real safe speed. Therefore, identification distance and perceptual speed is indispensable for the study of nighttime speed limit.The paper adopt field test and take Changsong freeway as test object, according to horizontal radius and longitudinal slope difference, carry out identification distance and perceptual speed at different line shape and speed, which help quantitative grasp the driver's identification distance and perceptual speed, at the same time, through real-time inquiries record the safe feelings of the driver, add identification distance and perceptual speed during the day as a reference test.Analyze the collected data of identification distance from the field test, explore the relationship between speed, horizontal curve radius, the longitudinal slope and identification distance, and study the discipline of identification distance both day and night to establish identification distance model for the day and night; Based on the grasping of perceptual speed influencing factor, analyze the collected data from the field test, explore the influence of speed, horizontal curve radius, the longitudinal slope to perceptual speed, and study the discipline of perceptual speed to establish perceptual speed model during the day and night.According to the relationship between driver's response-braking distance and identification distance, establish discriminating conditions of safe driving at night based on response-braking distance and nighttime identification distance model, thus calculate theory theoretical speed limit under different combination of horizontal radius and longitudinal slope at night; Consider the driver's safety perception under different speed and linear conditions, use perceptual speed model to revise the theory data, get revised of the speed limits at night; Based on driving continuity, Determine the minimum length of the speed limit segment, and divide the speed limit section, give reasonable speed limit under the theory, using the method of probability and statistic, give the 95% confidence interval of night speed limit under different linear, which provide decision support and practical basis for management departments.