Research On The Key Elements Of Exit Forenotice Sign Setting To Urban Expressway

The urban expressway is the main artery of the urban road,carrying a considerable part of the traffic demand.With the rapid development of social economy,the traffic congestion on the expressway is becoming more and more serious.And its entrances and exits have been the main accident black points.Expressway exit forenotice sign is an important traffic safety facility.And the exit can be easily missed for the excessive information of exit sign,or some unsafety driving behaviors are taken,such as decelerating,parking,and even reversing.All of the phenomenon above are resulted from the improper location of exit forenotice sign.Therefore,the setting of expressway exit forenotice sign is urgently needed to be optimized through research and analysis so as to improve the visibility and consistency of the exit sign,and to induce drivers to enter the exit ramps smoothly and safely.Firstly,this paper aimed at the improper problems of the setting of the expressway exit forenotice sign,and three key elements,including the amount of sign information,the advance distance of sign and the spacing of sign were determined to be the major research contents.From the dynamic perspective of driver,the process from receiving signal information to responding to take actions was analyzed.And the driver's process of processing information,the short-term memory law and the vehicle lane-changing process were introduced.Secondly,based on the psychological e-prime experiment,a positive correlation between the recognition reaction time of exit sign and the number of road name was found.And according to the curve changing rate,the information threshold of expressway exit forenotice sign was determined.The difference in reaction time of visual recognition of three kinds of exit forenotice signs was analyzed by multiple comparisons afterwards.The test results showed that it was more advantageous for drivers to recognize and search for road names by using two forenotice signs when there was a high amount of information.Thirdly,the existing simulation lane changing model was optimized and improved.First,the delay time was employed instead of the travel time to represent the waiting time for the vehicle to search for the insertion gap,reducing the time error.Second,the vehicle lane changing distance was added to the model,more consistent with the whole process of vehicle lane changing.Based on the lane changing distance,the model for calculating the advance distance of the expressway exit forenotice sign was established and the advance distances of exit sign under various conditions were calculated.The advance distances of two-way eight-lane or more and the designed speed of 80km/h or above should be increased appropriately.Then,the concept "memory interval of signs" was proposed.Based on the short-term memory,a model of spacing setting of the exit forenotice sign was constructed And the intervals of the exit sign under multi-lane expressway were calculated.The sign should be installed repeatedly if the interval is more than 500 meters and suggestions for the setting of expressway exit forenotice sign were put forward.Finally,this paper took the northern second ring road of Changsha city as an example to analyze the setting of expressway exit forenotice sign,by applying the relevant conclusions of the previous study.