Study And Disucss On The Minimum Spacing In Mountains Highway Interchange

The minimum interchange spacing,a design controlling index,affects the service level ,operation efficiency ,stability of the traffic and safety of the traffic of the highway directly . After 10 years peak construction of the western mountainous area highway, more and more examples of the works appeared,whose minimum spacing is less than the current specification. Because of terrain restrictions and regional economic development demand,the limits about the minimum interchange spacing is increasingly becoming the biggest trouble for designers when they design a highway in the western mountainous area. This paper mainly discussed and studied the minimum interchange spacing in mountainous highway, so as to provide a reference for revising relevant specification.Firstly, stated the concept of the minimum interchange spacing and analysed the special factors which influence it ,such as needs of regional economic development, constraints of bridges and tunnels'position,topography,geology,main linear, ramp form and so on. So that the author pointed out that the deficiencies of standards related to spacing in current specification of our country.Secondly, based on the collection of 140 interchange on Chongqing highway, analyzed the freeway's linear index quantitatively and qualitatively,summarized several main linear combination patterns on the mountains highway interchange and calculated the average operation speed accordingly. Based on automobile driving dynamics theory and using probability and differential method,gained the length of acceleration and deceleration lane under different road traffic conditions.This paper mainly studied the minimum distance between acceleration and deceleration lane.Firstly, based on lane-change theory,established the calculation model for the minimum distance between acceleration and deceleration lane;then,analyzed the traffic conditions under mountainous highway interchange , considered the demands of lowest speed limit at the same time , identified vehicles'opration speed on different lane under different conditions. On the results, figured out the minimum distance between acceleration and deceleration lane that meet the requirements for lane-change.Secondly, analyzed the disturbtion among split-flow, interflow and straight traffic flow, with the impact length, identified the minimum distance between acceleration and deceleration lane under which the main traffic flow can keep basic stability.After comprehensive analysis ,the author gived the suggested minimum length between acceleration and deceleration lane.Lastly, the author put forward the suggested length of minimum interchange spacing and proposedsome countermeasures and measures to shorten minimum spacing.After consulting a number of data, research achievements aiming at minimum spacing in mountains highway interchange do not have been found. The conclusion provides a new idea for designing mountainous interchange and useful information to solve the problem of small spacing. The thesis has certain practical significance.