Research On Relationship Between Speed Limits And Operating Speed For Freeway

The speed limit is a reasonable measure which is necessary to insure traffic safety and improve operational efficiency .However, there is still no comprehensive and detail guide or standard for posted speed limit according to all kinds of road in China, making the roads speed limit set in a chaotic situation. The relationship between posted speed limit, operating speed and design speed is the prerequisite and basis to set posted speed limit. This paper focused on the interactive relationship between the speed limit and operating speed for freeway which is the research object. And the corresponding theoretical model is established, providing a basis for initial speed limit. The related research will provide some references and relevant proposals for the road design and traffic management.This thesis based on the large number of traffic investigation, by means of statistical methods, such as frequency distribution histograms, Q-Q probability distribution histograms and the K-S test in order to test whether the research speed data frequency distribution is in accordance with normal distribution. The test results showed that the speed distribution for all sizes of the vehicles is in line with normal distribution. Followed by curve fitting using direct rendering normal size frequency distribution of vehicle speed, the influence of speed limits on speed distribution is analyzed which the road type is divided into straight segments, the slope section, curve and slope section,curve section. The results show that speed limit is an important factor which influenced operating speed. As the speed limit value increases, the average speed and speed dispersion of car and truck increases to a certain extent. But in different road sections the influence differed. On the slope section, curve and slope section and curve section where the conditions are poor, linear conditions such as gradient and curve radius are also a direct factor impact on operating speed. Under the same speed limit, the installations of speed- limit sign and speed control humps can better play the role of the speed limit.Then according to survey data, from the qualitative point of view, the relationship between speed limit and design speed ,speed limit and operating speed indicators which includes 85th speed, average speed and standard deviation of the speed characteristics. The results showed that the quantitative relationship between speed limit and operating speed under different sections of freeway is similar. That is with the speed limit value increases, the operating speed is also in an increasing trend; and on most surveyed freeway section 85th speed is greater than speed limits. At the same time, by means of regression analysis, from a quantitative point of view, the relationship model between speed limit and 85th speed for straight section, the slope section, curved section and curved and slope section is established. And the statistical methods used to test regression model significance. Finally, based on the above analysis, the car/truck speed limit proposals is tabled for the straight section, the slope section, curved section and curved and slope section.