Analysis on Reasonable Value of Highway Transition Curve Length
To provide a reasonable length for vehicles to move from a straight line(circular curve)to circular curve(straight line),and ensure drivers driving into the target curve at a safe,comfortable and natural state,the study analyzes the rationality of specification values of transition curve length in the current route specification.It is found that the length distribution among curve units is uniform,the length is too long,and it is not easy to coordinate with terrain and features.Combining with the relevant provisions of AASHTO on the value of transition curve,the value of transition curve length is theoretically analyzed and studied from the aspects of driving track,offset value of transition curve,and superelevation transition.The result indicates that the transition curve length decreases with the increase of circular curve radius when the design speed is fixed.With the increase of design speed,the transition curve length should also increase,but the increase value is small and can be ignored.When the design speed and circular curve radius are the same,with the increase of transition curve length,drivers would judge that the curvature radius of flat curve ahead is small.It is easy to enter the adjacent lane,which is not conducive to traffic safety.In addition,according to the study on offset value of transition curve and the length required for superelevation transition,it is found that by controlling the offset value of relaxation curve to 1 m and the length of relaxation curve to 200 m,the changing relationship between circular curve radius and transition curve is relatively stable,which is in line with the driving trajectory,and basically meets the requirements for setting superelevation transition segments.When the circular curve radius is greater than 1 666 m,the length of relaxation curve should be shortened with the increase of circular curve radius.
road engineeringtransition curve lengththeoretical analysisdriving trackoffset value of cycloidlength of superelevation transition section
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