【正文】 峰時段可以延長來提升通行能力或者在其他時間縮短來減少延遲。關(guān)于此裝置，當(dāng)它們變回原來的顏色，指示經(jīng)過一個適當(dāng)?shù)臅r間間隔變得相反。 Level F indicates forced flow. The two best measures for level of service for uninterrupted flow conditions are operating or travel speed and the radio of volume to capacity 達(dá)到最大限度的廣播， called the v/c ratio. For two and threelane roads sight distance is also important. Abbreviated descriptions of operating conditions for the various levels of service are as follows: Level A— Free flow。 flow unstable。 如果司機(jī)駕駛一輛汽車一直自由的以設(shè)計(jì)時速獨(dú)自行駛在一個行車道上，這種情形在左上角的圖 中以適當(dāng)?shù)那€表示出來。 基本高速公路和多車道公路路段 速度，車流量和通行能力的關(guān)系 速度，車流量和通行能力之間關(guān)系是了解某一地方公路設(shè)計(jì)和運(yùn)行能力的基礎(chǔ)。 tolerable speeds can be maintained but temporary restrictions to flow cause substantial drops in speed. Little freedom to maneuver，fort and convenience low. Level E— Volumes near capacity。s feeling of freedom or constraint more than any other factor. Studies of drivers as they follow other vehicles indicate that the time required to reach a potential collision point， rather than vehicle separation， seems to control behavior. However， this time varies widely among drivers and situations. Field observations have recorded headways (time between vehicles) ranging from 0. 5 to 2 sec, with an average of 河南理工大學(xué)本科畢業(yè)設(shè)計(jì)（論文） 外文翻譯 16 about 1. ， the calculated capacity of a traffic lane based on this 1. 5 s average, regardless of speed， will be 2400 vehicles per hour. But even under the best of conditions, occasional gaps in the traffic stream can be expected， so that such high flows are not mon. Rather, as noted， they are nearer to 2020 passenger cars per hour. The ‘Level of Service’ Concept As indicated in the discussion of the relationships of speed, volume or density, and vehicle spacing, operating speed goes down and driver restrictions bee greater as traffic volume increase. ?Level of service? is monly accepted as a measure of the restrictive effects of increased volume. Each segment of roadway can be rated at an appropriate level，A to F inclusive， to reflect its condition at the given demand or service volume. Level A represents almost ideal conditions。對于它們，探測器僅被布置在次要街道。 彈性連續(xù)前進(jìn)信號系統(tǒng)有一種主控制器裝置來指導(dǎo)個別信號控制器。交互式系統(tǒng)在大約相等的街區(qū)間隔的信號街上能相當(dāng)好的工作。在正常的交通量下，適當(dāng)?shù)恼{(diào)整從 2500 英尺（ 千米）到超過一英里（ 千米）的各種信號間隔對于形成流暢的交通是非常有效的。對于單獨(dú)的行人指示，步行指示（淺白色）包括最開始的時間間隔，禁止通行閃光燈（橘黃色）包括了剩余的時間間隔。對于高流量的交通，可能需要增加循環(huán)周期來獲得更大的通行能力。它們有這些優(yōu)勢，包括有低生產(chǎn)成本的控制器，可以聯(lián)系和協(xié)調(diào)使 車輛 以最少的停靠和其他的延遲 通過 一系列的 交叉口 。Pretimed39。于此同時，特別是自 第二次世界大戰(zhàn)結(jié)束以來，私人汽車使用的增長，一般來說已顯著的使公共交通的使用縮減。有軌電車的出現(xiàn) 使 城市地區(qū) 超出了 之前運(yùn)輸技術(shù)（例如走 路、騎馬、馬車） 所限定的界限進(jìn)行了擴(kuò)展。這個關(guān)系還暗示可供與交通問題打交道的政府官員多采用的選擇方案。 當(dāng)提供這些出行機(jī)會的 公共設(shè)施和服務(wù) 集合起來 ,使從一個地點(diǎn)到另一個地點(diǎn)的運(yùn)動成為可能時就會形成網(wǎng)絡(luò)。這樣，為了發(fā)展和維護(hù)城市交通系統(tǒng)而制定的規(guī)劃是一項(xiàng)重要的活動，既是為了促進(jìn)人和貨物在市區(qū)的有效運(yùn)轉(zhuǎn)，同時也是為了保持交通在實(shí)現(xiàn)其他社團(tuán)目標(biāo)方而所能起到的強(qiáng)有力的支援作用。 the transportation technologies that provide the means of moving over these distances。 historically, has been an important determinant of urban form. Because of the relation between transportation and urban activities， many of the methods used by transportation planners depend on estimates of trips generated by specific land uses. The relation also suggests that the options available to public officials dealing with transportation problems should include not only those related directly to the transportation system, but also actions such as zoning that affect the distribution of land use, and thus influence the performance of the transportation system. The foregoing considerations point to two important principles for transportation planning: The transportation system should be Considered as an integral part of the social and economic system in an urban area. Viewed as a set of interconnected facilities and services designed to provide opportunities for travel from one location to another. The Technology of Urban Transportation The technology of urban transportation is closely related to the spatial configuration of the transportation system in that the design transportation works reflects the speed, operating , and cost characteristics of the vehicle or mode of transportation being used. Technology includes the means of propulsion, type of support， means of guidance， and control technique. The development and widespread use of electric streetcars in urban areas during the late nieenth century was a technological innovation that initiated the transformation of most 河南理工大學(xué)本科畢業(yè)設(shè)計(jì)（論文） 外文翻譯 3 North American cities. The advent of the electric streetcar permitted urban areas to expand beyond the boundaries that had been dictated by previous transportation technologies (e. g.，walking， horse， horsecar)， spawning `streetcar suburbs39。鑒于這種認(rèn)識 ,城市交通系統(tǒng)可以進(jìn)一步分解為 以下三個部分 :空間布 置 ,可使一點(diǎn)到另一點(diǎn)的出行成為可能；交通技術(shù) ,提供兩地區(qū) 運(yùn)轉(zhuǎn)的手段；機(jī)構(gòu)的機(jī)制 ， 提供交通系統(tǒng)設(shè)施的規(guī)劃、建設(shè)、運(yùn)營和維護(hù) 。 城市交通系統(tǒng)將會影響到 城市的社會和經(jīng)濟(jì)結(jié)構(gòu) （ 通常被稱為城市活動系統(tǒng) ） 的發(fā)展方式 。 被視為目的在于提供從一個地點(diǎn)到另一個地點(diǎn)出行機(jī)會的一套互相結(jié)合的交通設(shè)施和服務(wù)。 在電車提供由經(jīng)過挑選的郊區(qū)到中心商業(yè)區(qū)的道路取得成功后，接著是公眾對于第二個重大技術(shù)革新，即對內(nèi)燃機(jī)為動力的汽車的歡迎。應(yīng)當(dāng)注意到，某些交通方式較其他方式更適合于承擔(dān)不同類型的城市出行。T WALK tells the pedestrian not to proceed. If pedestrian control is solely by the vehicle signals， problems develop if the intersection is wide, since the yellow clearance interval will have to be considerably longer than the 3 to 5s needed by vehicles. This will reduce intersection capacity and may call for a longer cycle time. On wide streets having a median at least 6 ft (1. 8m)wide， pedestrians may be stopped there. A separate pedestrian signal activator must be placed on this median if pedestrian push buttons are incorporated into the overall control system. Coordinated Movement Fixedtime traffic signals along a street or within an area usually are coordinated to permit pact groups of vehicles called `platoons’ to move along together without stopping. Under normal traffic volumes， properly coordinated signals at intervals variously estimated from 2500 ft