公路幾何設(shè)計外文翻譯-公路隧道-資料下載頁
2025-05-12 16:06本頁面
【導讀】現(xiàn)代設(shè)計時常在直線與圓曲線之間插入緩和曲線。半徑曲線相連接的突然變化，否則會發(fā)生交通事故。長而平緩的曲線總是良好的線形，因為這種曲線線形優(yōu)美，然而，雙向道路線形全由曲線構(gòu)成也是不理想的，因為一些駕。駛員通過曲線路段時總是猶豫。短曲線，則會出現(xiàn)“扭結(jié)”。另外，線路的平、縱斷面設(shè)計應綜合考慮，而不應。嚴重的交通事故。通常情況下，某一圓曲線的曲率是由其半徑來體現(xiàn)的?？晚毦S持身體的垂直狀態(tài)，因為此時未受到離心力的作用。緩和曲線在鐵路上已經(jīng)使用多年，但在公路上最近才得以應用，這可以理解。設(shè)計合理的緩和曲線使得上述迂迴沒有必要。部門廣泛采用了緩和曲線。關(guān)位置，因此應在最終定線勘測之前應決定是否采用緩和曲線。豎向線形由直線和豎向拋物線或圓曲線組成，稱為縱坡線。縱坡線從水平線逐漸上升時稱為坡度變化的影響。臨界坡長可從3％縱坡的1700ft變化至8%縱坡的500ft。致車輛失控或與另一輛車相撞。第二部分停車視距取決于
【正文】 out danger. Sight distance is the length of highway visible ahead to the driver of a vehicle. The concept of safe sight distance has two facets: “stopping” (or “no passing”) and “passing”. At times large objects may drop into a roadway and will do serious damage to a motor vehicle that strikes them. Again a car or truck may be forced to stop in the traffic lane in the path of following vehicles. In dither instance, proper design requires that such hazards bee visible at distances great enough that drivers can stop before hitting them. Further more, it is unsafe to assume that one oning vehicle may avoid trouble by leaving the lane in which it is traveling, for this might result in loss of control or collision with another vehicle. Stopping sight distance is made up of two elements. The first is the distance traveled after the obstruction es into view but before the driver applies his brakes. During this period of perception and reaction, the vehicle travels at its initial velocity. The second distance is consumed while the driver brakes the vehicle to a stop. The first of these two distances is dependent on the speed of the vehicle and the perception time and brakereaction time of the operator. The second distance depends on the speed of the vehicle。 the condition of brakes, times, and roadway surface。 and the alignment and grade of the highway. On twolane highways, opportunity to pass slowmoving vehicles must be provided at intervals. Otherwise capacity decreases and accidents increase as impatient drivers risk headon collisions by passing when it is unsafe to do so. The minimum distance ahead that must be clear to permit safe passing is called the passing sight distance. In deciding whether or not to pass another vehicle, the driver must weigh the clear distance available to him against the distance required to carry out the sequence of events that make up the passing maneuver. Among the factors that will influence his decision are the degree of caution that he exercises and the accelerating ability of his vehicle. Because humans differ markedly, passing practices, which depend largely on human judgment and behavior rather than on the laws of mechanics, vary considerably among drivers. To establish design values for passing sight distances, engineers observed the passing practices of many drivers. Basic observations on which passing sight distance standards are based were made during the period 19381941. Assumed operating conditions are as follows: 1. The overtaken vehicle travels at a uniform speed. 2. The passing vehicle has reduced speed and trails the overtaken one as it enters the passing section. 3. When the passing section is reached, the driver requires a short period of time to perceive the clear passing section and to react to start his maneuver. 4. Passing is acplished under what may be termed a delayed start and a hurried return in the face of opposing traffic. The passing vehicle accelerates during the maneuver and its average speed during occupancy of the left lane is 10 mph higher than that of the overtaken vehicle. 5. When the passing vehicle returns to its lane there is a suitable clearance length between it and an oning vehicle in the other lane. The five distances, in sum, make up passing sight distance.
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