Research On Raising Speed Limit Of Freeway Based On Geometric Alignment

With the development of China's social economy,people are increasingly demanding for the speed limit increase of expressways,while developed countries gradually implement the management measures to increase speed limits on expressways,and the speed limit increase of expressways has become a hot issue in current traffic research.Using field survey data,theoretical analysis,mathematical statistics,and model simulation methods,an in-depth study on the speed increase of a certain section of the Beijing-Hong Kong-Macao expressway Hebei section was conducted.By studying the relationship between speed limit and design speed,running speed,desired speed and other speeds,it is pointed out that the design speed is an important factor in the speed limit of the current highway,and the relationship between speed and safety after the speed limit increase is analyzed.It also pointed out that control the different speed between vhicle will guanrantee the safety.According to the speed limit principle and the experience of speed limit in foreign countries,the current speed limit target based on safety and high efficiency is determined.In depth analysis of China's expressway design specification system,studies the relationship between different design speeds and linear indicators,and proposes the practical significance and calculation methods of the corresponding line indicators for highways,longitudinal sections,and cross-sections,and further proposes that the specific linear indicators of higher design speeds of expressways.This paper introduces the current German highway design system for the first time,analyzes the differences between the German highway design and our country's design system,and points out it is lower that the requirements of the German regulations for the maximum circular,vertical curve radius and longitudinal control index.It points out the linear indicators of higher design speed that German highway design system proposed.According to the higher design speed linear indicators proposed by China regulatory system and the alignment requirements of the German system,the linear elements in the Hebei section of Beijing-Hong Kong-Macao expressway are analyzed.It is proposed that the section of expressway basically meets the higher design speed under the national regulatory system in China.The road section has the possibility to raise speed limit,,but the section does not meet the requirements of German standard.Through the study of the calculation method of running speed,the calculation method of the theoretical running speed of car and bus under higher design speed is proposed.It is pointed out that the car running speed of the Beijing-Hong Kong-Macao expressway is well coordinated,but the coordination of the bus running speed is poor,and the speed control method for the section after increasing the speed limit.By analyzing the visual characteristics and reflection process of the driver recognition of road signs,a Chinese character height calculation model and the sign front distance model are proposed.It pointed out that the range of Chinese character height and the minimum sign front distance for the Beijing-Hong Kong-Macao expressway that in higher speed limit condition.Based on the traffic characteristics of a Beijing-Hong Kong-Macao expressway,the VISSIM simulation software was used to simulate the capacity of the road section under different speed limit conditions.Taking the relationship between the input traffic volume,average speed,density,and output traffic volume as the evaluation index,the basic capacity of the Beijing-Hong Kong-Macao expressway in higher speed limit is proposed,and the accuracy of the simulation model is verified.