【正文】 long vertical curves, and otherdesirable design features that create a safe ， most of the nation’s freeways enjoy thisrelatively high level of design and safety, there are many opportunities for further ，但還是有很多地方需要進一步增強。Safety improvements on freeways can also result in substantial savings in life and property(生命和財產)because freeways carry 25 percent of the nation’s total ，還會節(jié)約大量的生命財產資源，因為高速公路流量占了全國的總流量的25﹪。Selecting the design speed for a freeway is an important safety element because most geometric criteria(準則，標準)related to or depend on In general, 110 kilometers per hour(km/h)should be the design speed for the mainline of a freeway , but it may need to be lower in areas of severe terrain or heavy ，110千米每小時應該作為高速公路主干道的設計速度，但是在崎嶇的地區(qū)或者施工難度大的地區(qū)可能需要降低。For reconstruction, rehabilitation, and resurfacing(3R)projects, the design speed should not be less than the original design speed or the current legal speed limit of that highway ，恢復鋪新路面工程，設計速度不應該低于平時設計速度或者那塊交通干線區(qū)域的目前規(guī)定的速度限制。Design speeds for interchange ramps（立交匝道）depend on the type of ramp selected, for example , loop，diamond, or direct, and the lowvolume（低交通量）, running speed（行駛速度）of the intersecting ，例如，環(huán)形、菱形、直線型以及低交通量，相交交通干線的運行速度。Usually, the design speed is established by the most restrictive element of the ramp, typically, the sharpest curve（小半徑曲線）.通常，這個設計速度被匝道的最限制的范圍，典型的是小半徑曲線。Whatever design speed is selected, adequate transitions（轉變、過渡）from the freeway proper and at the ramp terminal（末端、末尾）or merge point（合流點）should be ，都應該發(fā)展來自高速公路本身的和在匝道末尾或者合流點的合適的過渡。Safe and efficient traffic operations depend on adequate laneand shoulder widths as outlined in A Police on Geometric Design of Highways and 《道路的幾何尺寸的規(guī)定》設計的適當的行車線和路肩寬度。The need to acmodate more traffic within existing or limited additional rightofway on highvolume urban freeway has led some agencies to increase capacity by exchange fulllane or shoulder widths for additional travel lanes with reduced ，在已有的或者額外有限的公路用地條件下，容納更多的交通的需求，導致許多機構通過減小車道寬度或者路肩寬度來騰出額外的車道來提高通行能力。Any proposed use of lessthanfullstandard crosssection must be analyzed carefully on a sitebysite indicates that lane can operate safely if there are no other lessthanstandard features。however, bined with shoulderwidth reductions, substandard sight distance, and other features, lanes may not provide the same safe 。經驗表明，不考慮其他低于標準的因素，米得行車道寬足夠保證安全。但是結合路肩寬度的減少，視距不足及其他因素。Converting shoulder to travel lanes for additional capacity through a short bottleneck section has been shown to significantly reduce congestionrelated accidents on some shoulders for several kilometers, however, has not had the same ，在短程的瓶頸路段為了額外的通行能力，將路肩轉變成行車道能顯著減少由道路擁擠導致的交通事故。然而減少幾公里長的路肩寬度，得不到同樣的的結果。Pavement marking, such as lane lines, edge lines, channelizing lines at interchanges and ramps, and word symbol markings, provide important information to the ，像在立體交道和斜坡處的車道線，邊緣線，通道線以及文字和符號標記，為駕駛員提供重要信息Pavement markings define separate lanes of traffic traveling in the same direction, inform drivers of lane restrictions, and convey certain regulation and warnings that would not otherwise be clearly ，告訴駕駛員該車道限速，以及傳達某些規(guī)則和警告，否則，它們不會被駕駛員清楚的明白。Pavement markings are particularly important at night and during inclement weather, and,therefore, must be wellmaintained painted pavement markings are acceptable, thicker, longlife markings ,such as thermoplastic or performed tapes ,may perform better in wet weather and heavy ，厚的，長壽命的標記，像熱塑性塑料或預成行的條帶，可以在潮濕的空氣和交通繁忙時表現得更出色。Some studies have been made regarding the benefits of wider edge line markings(150 to 200 mm versus the standard 100 mm width).The wider markings may particularly benefit older （150到200毫米相對于100毫米的標準寬度）。更寬的標記對老司機尤為有利。