Research On The Prediction Of Operating Speed On Horizontal Curve Combined With Logitudinal Slope For Freeway

There are many kinds of factors that can induce the occurance of freewaytraffic accidents, among which poor road alignment condition is often one of themajor causes. Operating speed is one of the most important indices for evaluatingthe continuity, consistency and amenity of road geometric alignment, and it is thecomprehensive result of all alignment indices. Hence, it is necessary to furtureresearch of the operating speed and developing prediction models, which will haveimportant theoretical significance and application value of road construction andmanagement. Combining with practical project, this paper was to analyze theoperating speed characteristics and to develop the prediction models based onoperating speed on horizontal curve combined with longitudinal slope sections forfreeway, which design speed is100km/h.Firstly, Guangdong section of Yuegan freeway had been chosen as dataacquisition sites in this paper, and the data acquisition and extraction scheme wereformulated. As operating speed was calculated based on free flow traffic, it wasnecessary to determine the evaluation standards for free flow condition. Timeheadway had been chosen as the critetion for the evaluation of free flow conditionby investigating the relationship between time headway and measured-speed,combined with the related research results of domestic and foreign scholars. Andfree-flow speed could be defined as time headway between successive vehiclesequal to6s or more, which could be used to calculate operating speed on eachsection.After finished the calculation of operating speed on each investigating section,the relationship between operating speed and road alignment indices had beenanalyzed in this paper, and two conclusions were drawn. First, the operating speedsof passenger cars were significantly affected by horizontal curve radius; second, theoperating speeds of trucks were dramatically influenced by grades, especically inthe upgrade section.For developing operating speed prediction models based on horizontal curvecomibined with longitudinal slope of freeway based on road alignment indices,horizontal curve radius and grades had been chosen as influence variables in thispaper, which have great influence on operating speeds, the multiple regressionstatistical method was used to develop the operating speed prediction models ofpassenger cars and trucks, and the rationality of the models were analyzed.Thirdly, horizontal curve radius and grades had also been chosen to develop operating speed predictiobn models by applying fuzzy logic theory in this paper.Using horizontal curve radius, grades and horizontal curve deflection angel as inputvariables, the operating speeds of passenger cars and trucks as output variables, andthen the membership functions of each variables were obtained after the the fuzzysets and the clustering centers of each input and output variables were determinedby applying fuzzy statistical principles, finally developed the operating speedprediction models based on fuzzy logic, and then tested and analyzed the rationalityof the prediction models.Finally, the comparasion analysis of the prediction results based on regressionand fuzzy logic methods had been made in this paper based on the measuredoperating speeds which were not used in developing the prediction models,. Theresults showed that the proposed two operating speed prediction models havecomparable predict capability.