外文文献翻译
(含：英文原文及中文译文)
文献出处：Y Hassan. Geometric Design of Highways[J] Advances in Transportation Studies, 2016, 6(1):31-41.
英文原文
Geometric Design of Highways
Y Hassan
A. Alignment Design
The alignment of a road is shown on the plane view and is a series of straight lines called tangents connected by circular curves. In modern practice it is common to interpose transition or spiral curves between tangents and circular curves.
The line shape should be continuous, sudden changes from flat line to small radius curve or sudden ch
ange of long line end connected to small radius curve should be avoided, otherwise a traffic accident may occur. Similarly, arcs with different radii end-to-end (complex curves) or short straight lines between two arcs with different radii are bad lines unless an easing curve is inserted between arcs. The long, smooth curve is always a good line because it is beautifully lined and will not be abandoned in the future. However, it is not ideal that the two-way road line shape is composed entirely of curves, because some drivers always hesitate to pass through curved road segments. The long and slow curve is used in the
smaller corners. If you use a short curve, you will see "kinks." In addition, the design of the flat and vertical sections of the line should be considered comprehensively and should not be only one. No matter which, for example, when the starting point of the flat curve is near the vertex of the vertical curve, serious traffic accidents will occur.
V ehicles driving on curved sections are subjected to centrifugal force, and they need a force of the same magnitude in the opposite direction due to the height and lateral friction to offset it. From the viewpoint of highway design, the high or horizontal friction cannot exceed a certain value. The maximum, these control values for a certain design speed may limit the curvature of the curve. In general, the curvature of a circular curve is represented by its radius. For the linear design, the curva
ture is often described by the curvature, ie, the central angle corresponding to the 100-foot curve, which is inversely proportional to the radius of the curve.
A normal road arch is set in a straight section of the road, and the curve section is set to a super high, and an excessively gradual road section must be set between the normal section and the super high section. The usual practice is to maintain the design elevation of each midline of the road unchanged. By raising the outer edge and lowering the inner edge to form a super high, for the line shape where the straight line is directly connected with the circle curve, the super high should never start on the straight line before reaching the curve. At the other end of the curve at a
certain distance to reach all the ultra-high.
If the vehicle is driving at a high speed on a restricted section of road, such as a straight line connected with a small radius circle curve, driving will be extremely uncomfortable. When the car enters the curve section, the super high starts and the vehicle tilts inward, but the passenger must maintain the body because it is not subjected to centrifugal force at this time. When the car reaches the curve section, centrifugal force suddenly occurs, forcing passengers to make further posture adjustments. When the car leaves the curve, the above process is just the opposite. After inserting th
e relaxation curve, the radius gradually transitions from infinity to a certain fixed value on the circle curve, the centrifugal force gradually increases, and ultra-high levels are carefully set along the relaxation curve, and the centrifugal force is gradually increased, thereby avoiding driving bumps.
The easement curve has been used on railways for many years, but it has recently been applied on highways. This is understandable. The train must follow a precise orbit, and the uncomfortable feeling mentioned above can only be eliminated after the ease curve is used. However, the driver of a car can change the lateral position on the road at will, and he can provide a relaxation curve for himself by making a roundabout curve. But doing this in one lane (sometimes in other lanes) is very dangerous. A well-designed relaxation curve makes the above roundaboutness
unnecessary. Multi-cluster safety is a measure, and roads are widely used as transition curves.
For a circular curve with the same radius, adding an easing curve at the end will change the relative positions of the curve and the straight line. Therefore, whether or not to use an easing curve should be determined before final alignment survey. The starting point of the general curve is labeled PC or BC and the end point is labeled PT or EC. For curves with transition curves, the usual marker configurations are: TC, SC, CS, and ST.
For two-way roads, the road width should be increased at sharp bends. This is mainly based on the following factors: 1. The driver is afraid to get out of the edge of the road. 2. Due to the difference in the driving trajectory of the front and rear wheels of the vehicle, the effective lateral width of the vehicle increases; 3. The width of the front of the vehicle that is inclined relative to the centerline of the road. For roads that are 24 feet wide, the added width is negligible. Only if the design speed is 30 mil / h and the curvature is up to 2 ft. However, for narrow roads, widening is very important even on smooth curve sections. The recommended widening values and widened designs are shown in ". Highway linear design."
B. Longitudinal slope line
The vertical alignment of the highway and its impact on the safety and
economy of vehicle operation constitute one of the most important elements in highway design. V ertical lines consist of straight lines and vertical parabolas or circular lines called vertical slope lines. When a grade line rises gradually from a horizontal line, it is called an uphill, and vice versa, it is called a downhill slope. In the analysis of slope and slope control, designers usually have to study the effect of changes in slope on the midline profile. In determining the slope, the ideal situation is th
e balance of excavation and filling, and there is no large amount of borrowers and abandoned parties. All the earth moving is carried down as far as possible and the distance is not long. The slope should change with the terrain and be consistent with the direction of ascent and descent of the existing drainage system. In the mountains, the slopes should be balanced to minimize the total cost. In the plain or grassland areas, the slope is approximately parallel to the surface, but higher than the surface at a sufficient height to facilitate drainage of the surface. If necessary, winds can be used to remove surface snow. If the road is approaching or running along a river, the current height of the slope is determined by the expected flood level. In any case, the gentle slope should be set at the excavation section compared to the short vertical section connecting the short vertical curve due to the upslope downslope, and the section from the downslope upslope should be set at the fill. Road section. Such a good linear design can often avoid the formation of a mound or depression
>width的意思中文翻译

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