Research Of Possible Velocity And Highway Alignment Design Method

Highway alignment must accord with the properties of automobile driving. Alignment design should attach to the rational combination of cross and vertical section and conform to the continuity equilibrium and harmony of the principle of alignment design in order to guarantee safe driving. At present, there is still no scientific and reasonable alignment design evaluating method and examining basis and judging standard of the design quality and driving safety at home, which makes alignment design a hidden problem of safety. In the sight of present situation of highway alignment design, the thesis, aiming at examining the design quality of cross and vertical section, directing the taking of alignment design indexes, controlling automobile speeding and reducing traffic accident, put forward a research topic on attainable speed and the applying of attainable speed to highway alignment design so as to realize the basic requirements of safe driving.The concept of attainable speed and its application in highway alignment design are put forward according to the limitation of speed designing in highway alignment design. Attainable speed refers to speed attainable by skillful drivers along a certain highway under good weather and traffic conditions and without any influence other than geometric one brought about by the highway itself. On the basis of the present designingmethod, the design of attainable speed alignment, by increasing the steps of the speed calculation, is to examine and modify the preliminary indexes of the cross and vertical section so as to get a graph of continual and balanced changing attainable speed which becomes the foundation of getting other technical indexes and setting equipment along the highway.The model of attainable speed calculation is set up on the basis of preliminary technical indexes of cross and vertical section and the transverse and axial curve .Suppose the transverse, axial and vertical acceleration is continual, the respective acceleration modal and index model are set up to attain the formula of the transverse permissible speed, axial driving speed and vertical permissible speed. The axial driving speed and is decided by the motive power of the automobile itself, but it is also influenced by both the transverse and vertical permissible speed; therefore, the minimum speed among the three is taken as the calculating value of the attainable speedThe method of attainable speed application is proved reliable through experiment on the sections of highway. The graph of attainable speed can be drawn from the data of section design experiment, whereas the actual speed can be obtained by observing the highest speed attained along the highway; on all the mile posts along the experimental sections it is larger than the actual speed, and is also larger than the running speed of the same class. Most high-frequency accident spots have to do with the alignment. Three accident spots in the experimental section can be accurately shown on the graph of attainable speed; which is continual, direct and changeable, and reliable in examining evaluating and modifying the alignment. Besides, it is simple in method, strict in theory and easy in spreading.The application of attainable speed is a brand new method in alignment design. The thesis put forward the speed difference as the evaluating standard in alignment design and the difference measurement to establish the evaluating index of different classes of highway. It also sets up steps of drawing graphs of attainable speed, judgingdesign quality and safety, and deciding on modifying spots. It gets the maximum ratio between the concurrent and reverse curve radius and the thesis also points out two methods of modifying the alignment design, i.e., modifying the key elements as to change the attainable speed and deciding on the modifying elements through attainable speed and deciding on the modifying elements through attainable speed. Safety facilities must be set in those spots that can not be changed. The theory of attainable speed is put into use through the application in examining, evaluating and modifying the highway alignment design.The thesis further discusses the application of attainable speed in other relevant designs. For instance, the shortage of superelevation problem can be solved to some extent by getting the superelevation value on the basis of attainable speed; the problem of shortage of sight distance can be avoided by getting the driving sight distance and the problem of shortage of width can be prevented by selecting the key width elements of sections, based on the attainable speed in different sections. What 's more, the position, length in the transitional section of the climbing lane can be directly reflected on the graph of attainable speed, which can be used to study the construction of emergency escape lane. It is safer and more reasonable to decide on the length of speed change lane on the basis of attainable speed, and more scientific to decide the position and boundary of limiting speed signs. The thesis also provides a method of safety evaluation by applying attainable speed in such spots as at-grade intersections, mainline toll stations as well as villages and towns alongside. Furthermore, four safety evaluating indexes namely salt ation quantity, maximum speed difference amount, relative speed difference value and surplus lateral force, are obtained by applying attainable speed in alignment design evaluation.