Analysis of the Error on Fitting Highway Alignment Based on the Cubic Spline Function

To meet the demand of traffic growth and guarantee road operation security, reconstruction and extension projects are carried on high-level highways and the partial local roads of the national investment construction in earlier period, which needs to know road design principle and some parameters before they are put in practice. But in concrete implementation, it doesn´t agree with the fact that it lies in the lack of road design and completion information, settlement and deformation of subgrade, slope collapse, pavement breakage and vehicle bumping at bridgehead and so on, which brings about great differences in the actual highway alignment from the original design situation. Consequently, surveying and fitting alignment parameters are necessary in the process of reconstruction and extension to meet the original design. The accuracy will directly affect smooth alignment, comfortable driving and driver´s behavior. The paper puts forward the basic principles of fitting highway horizontal alignment based on cubic spline function, analyzes the sources of errors and discusses the step influence on the calculating results. Combined with one practical engineering, the affecting errors of fitting results on the different sampling step are worked out, and a appropriate sampling step scope of fitting highway alignment based on the cubic spline function is educed, that is to say, in order to minimize the error, choosing sampling step values of 50m at line and 20m at curve is suitable while measuring.