建筑工程設(shè)計外文翻譯外文文獻(xiàn)英文文獻(xiàn)公路線形設(shè)計(參考版)
2024-11-08 14:31本頁面
【正文】 the condition of brakes, times, and roadway surface。 hence the decision regarding their use should be made before the final location survey. They point of beginning of an ordinary circular curve is usually labeled the PC (point of curve) or BC (beginning of curve). Its end is marked the PT (point of tangent) or EC (end of curve). For curves that include easements, the mon notation is, as stationing increases: TS (tangent to spiral), SC (spiral to circular curve), CS (circular curve to spiral), and ST (spiral go tangent). On twolane pavements provision of a wilder roadway is advisable on sharp curves. This will allow for such factors as (1) the tendency for drivers to shy away from the pavement edge, (2) increased effective transverse vehicle width because the front and rear wheels do not track, and (3) added width because of the slanted position of the front of the vehicle to the roadway centerline. For 24ft roadways, the added width is so small that it can be neglected. Only for 30mph design speeds and curves sharper than 22176。 otherwise, accident hazards will be created. Likewise, placing circular curves of different radii end to end (pound curves) or having a short tangent between two curves is poor practice unless suitable transitions between them are provided. Long, flat curves are preferable at all times, as they are pleasing in appearance and decrease possibility of future obsolescence. However, alignment without tangents is undesirable on twolane roads because some drivers hesitate to pass on curves. Long, flat curves should be used for small changes in direction, as short curves appear as “kink”. Also horizontal and vertical alignment must be considered together, not separately. For example, a sharp horizontal curve beginning near a crest can create a serious accident hazard. A vehicle traveling in a curved path is subject to centrifugal force. This is balanced by an equal and opposite force developed through cannot exceed certain maximums, and these controls place limits on the sharpness of curves that can be used with a design speed. Usually the sharpness of a given circular curve is indicated by its radius. However, for alignment design, sharpness is monly expressed in terms of degree of curve, which is the central angle subtended by a 100ft length of curve. Degree of curve is inversely proportional to the radius. Tangent sections of highways carry normal cross slope。 以上五項之和就是超車視 距。在超車過程中，超車在超車道上加速，其平均速度比被超車快 10mile/h。 3. 當(dāng)?shù)竭^超車區(qū)時，駕駛員需一短時間來觀察超車區(qū)，并開始超車。在 1938～ 1941年間，進(jìn)行了建立超車視距標(biāo)準(zhǔn)的基本調(diào)查。由于人與人的顯著差別，主要是人的判斷和動作而不是力學(xué)定理決定的超車行為隨著駕駛員的不同 而大不相同。 駕駛員在做出是否超車的決定時，必須將前方的能見距離與完成超車動作所需的距離對比考慮。 在雙車道公路上，每間隔一定距離，就應(yīng)該提供超越慢行車輛的機(jī)會。第一部分停車視距取決于車速及駕駛員的察覺時 間和制動時間。此外，認(rèn)為車輛通過離開所行駛的車道就可以躲避危險的想法是不安全的，因為這會導(dǎo)致車輛失控或與另一輛車相撞。同樣，轎車或卡車也可能會被一溜車輛阻在車道上。安全 視距具有兩方面含義：“停車視距”或“不超車視距”或“超車視距”。 C 視距 為保證行車安全，公路設(shè)計必須使得駕駛員視線前方有足夠的一段距離，使他們能夠避讓意外的障礙物，或者安全地超車。調(diào)整公路的最大縱坡為 9%只有當(dāng)路面排水成問題時，如水必須排至邊溝或排水溝，最小坡度標(biāo)準(zhǔn)才顯示其重要性。 持續(xù) 長坡的坡度必須小于公路任何一個斷面的最 大坡度，通常將長的持續(xù)單一縱坡斷開，設(shè)計成底部為一陡坡，而接近坡頂則讓坡度減小。 當(dāng)采用較長的 待續(xù) 爬坡時，在沒有為慢行車輛提供爬坡道時，坡長不能夠超過臨界坡長。 在不同的州，最大縱坡也相差懸殊， AASHTO 建議由設(shè)計車速和地形來選擇最大縱坡。一個較為經(jīng)濟(jì)的方案則可使坡度減小而增加的年度成本與坡度 不減而增加的車輛運行年度成本之間相平衡。 在坡度的分析和控制中，坡度對機(jī)動車運行費用的影響是最重要的考慮因素之一。 城市項目往往比農(nóng)村項目要求對控制要素進(jìn)行更詳盡的研究，對高程進(jìn)行更細(xì)致地調(diào)整。 由上坡向下坡變化的路段應(yīng)設(shè)在挖方路段，而由下坡向上坡變化的路段應(yīng)設(shè)在填方路段，這樣的線形設(shè)計較好，往往可
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