The Longitudinal Design Research In Highway Reconstruction

With the development of transportation industry and the increasement of the vehicle holding rate, some roads have already can’t adapt the needs of the growing traffic. The traffic congestion has become more and more serious. Road reconstruction is the trend of the highway construction in our contry. The profile design of the reconstruction is more complicated than that of the new roads construction. And it involves more problem.So it makes a lot of sense to study the profile design of the roads reconstruction.Based on the background,this paper determine the the emphasis by collating relevant informations about the reconstruction.First of all,this paper presents the content and steps of the profile design in reconstrucion,lists the restricting factors in the profile design, and how to consider these factors in design. Secondly, this paper presents a curve fitting model by comparing many methods and the actual situation of our country. This model fits the longitudinal slope to find the parameters of the vertical curve by using the least-squares method. Proved that fitting the slope by using least-squares is superior to that by traditional method. Finally,this paper summarizes some form of vertical curves which can be used in alignment design, including traditional unsymmetrical vertical curve, equal-arc unsymmetrical vertical curve and the new and single unsymmetrical vertical curve. Derivates the traditional unsymmetrical vertical curve and equal-arc unsymmetrical vertical curve ‘s equations according to their geometric properties, and calculates the minimum length of the vertical curves by using the impact and sight distance. This paper analyses the application situations in the road reconstruction by analyzing the engineering example. In crest vertical curve design, when the excavation need to be reduced, and the alignment is not asked to be too smooth, the traditional unsymmetrical vertical curve can be used. The alignment of the equal-arc unsymmetrical vertical curve is better than that of the traditional vertical curve, but the elevation is higher. So it can be used in increasing the pavement’s height. The cubic parabolic vertical curve can be used where the elevation need to be reduced in the sag type vertical curve. This paper presents some thoughts and methods in longitudinal design of the road reconstrution. It is helpful to standardize the profile design in the road reconstruction.