Research On The Method Of Setting Speed Limits On Mountainous Expressway

The rapid development of mountain expressway brings conveniece to traffic of mountain, however, high traffic accidents of expressway result in great damage for nation and people. Speeding is one of the main factors that cause traffic accidents. Therefore, to explore effective management strategies and methods of speed, well balanced motorization and traffic safety is the current public attention and the problems to be solved. Setting speed limit is the most commonly used speed management method, practice has proved that reasonable speed limit can promote safety level and service level of freeway. Currently there is no uniform standard and methods of setting speed limit in china, on the basis of deeply analyzing domestic and international research results of speed limits, the paper research the method of setting speed limit based on efficiency and safety for mountain expressway, which provides gist for speed management of expressway.Through analyzing the relationship between speed and safety and the relationship among speed, speed limit and safety, combining domestic and international research results of setting speed limit on expressway, the paper put forward the method of setting speed limit to control the average speed, speed variance and to satisfy drivers speed expectation as the main basis for determining reasonable speed limit. According to the driver's visual recognition and psychological reaction characteristics for information of speed limit signs, taking into account the minimum stable travel time of vehicle, proposing the minimum standard length of speed limit section.On the basis of analyzing the limitations of design speed and operating speed in determining the speed limit value, the concept of critical speed of road supply is put forward. Critical speed of road supply refers to the highest speed of road geometric dimensioning can provide under good weather and traffic conditions and ensuring the safety and stability of the vehicle operating. According to the combination of road alignment, under the condition of the comprehensive consideration of the plan, longitudinal, cross and sight distance, the calculation model of critical speed of road supply is determined.Using the ideas of multi-objective optimization, the paper brought forward the method of determining the maximum speed limit for expressway based on safety and efficiency. According to the critical speed of road supply to determine the possible speed limit value, by deadly accidents, speed variance, time of operating and meet drivers speed expectation as the goal, using multi-attribute decision-making method-the TOPSIS method evaluates the possible speed limit value, and gets the optimal values of the maximum speed limit. With the speed discrete degree as the control indicators, the minimum speed limit is concluded.After analyzing the safety of expressway tunnel and long and steep down hill road, put forward the method on setting the maximum speed limit of expressway tunnel based upon operating speed and visual adaptation, and the method on setting the maximum speed limit of long and steep down hill road based upon brake failure. Finally, relying on the Lan- Shang expressway already built, speed limit theory and method is applied in engineering practice.