Study On Methods For Freeway Speed Limitation

With the rapid social and economic development in China, the freeways in China are playing a more and more important role in the transportation system. The demands of passengers and freights transportation by highways are constantly rising in recent years. Speed-limits have been widely used as a way to balance between the safety and operational efficiency of freeways all over the world. At present, the main problem of speed-limits on freeways is how to set the standards, the methods and the related facilities for speed-limits on freeways and the research on this field has not been adequately done. Based on the analysis of freeways in China and the research on speed-limits for freeways at home and abroad, combining with the state of the art in speed-limit on freeways in China and over the world, the outcomes of this research are concluded as follows:(1)The concepts of the designed speed, the expected speed, the operating speed and the speed-limit are discussed. The relationships among the design speed, the expected speed, the operating speed and the speed-limit are studied in detail. It is unscientific and unreasonable to use the designed speed as the standard of the actual speed-limit for freeways. The operating speed plays the most important role in the research of speed-limits for freeways. Based on the impact of the relationship studies between the operating speed and the traffic accidents, this thesis points out that the higher diserepancy of operating speeds would lead to a higher rate of traffic accidents, and the absolute higher operating speed would lead to more serious accidents.(2) The methods for determining the operating speed on the freeway are studied in detail, including the method of field observation, the method of determining the operating speed based on the HIGHWAY Specifications,the relational model Between operating speed and CCRs,and the Highway Safety Project Evaluation Guide.(3) Take Changzhang Freeway as an example.The relationship models between operating speed and CCRs for small car and large car are established.The models for operating speed of Highway Safety Project Evaluation Guide are modified.(4) The principles of formulate speed-limit standards for freeway are proposed.Changzhang freeway's speed-limit standards is formulated based on the principles and operating speed of calculation results.(5) The adaptability of the speed-limit standards are analysed by using the microscopic traffic simulation software VISSIM.