城市交通规划外文翻译-交通线路(编辑修改稿)

城市交通规划外文翻译-交通线路(编辑修改稿)内容摘要：

cost and that they can be interconnected and coordinated to vehicles to move through a series of intersections with a minimum of stops and other delays. Also, their operation is unaffected by conditions brought on by unusual vehicle behavior such as forced stops， which， with some trafficactuated signal installations may bring a traffic jam. Their disadvantage is that they cannot adjust to shorttime variations in traffic flow and often hold vehicles from one direction when there is no traffic in the other. This results in inconvenience, and sometimes a decrease in capacity. ‘ Cycle length’ the time required for a plete sequence of indications, ordinarily falls between 30 and 120s. Short cycle lengths are to be preferred, as the delay to standing vehicles is reduced. With short cycles, however a relatively high percentage of the total time is consumed in clearing the intersection and starting each succeeding movement. As cycle length increases, the percentage of time lost from these causes decreases. With high volumes of traffic, it may be necessary to increase the cycle length to gain added capacity. Each traffic lane of a normal signalized intersection can pass roughly one vehicle each of green light. The yellow (caution) interval following each green period is usually between 3 and 6s， depending on street width， the needs of pedestrians, and vehicle approach speed. To determine an approximate cycle division, it is mon practice to make short traffic counts during the peak period. Simple putations give the number of vehicles to be acmodated during each signal indication and the minimum green time required to pass 河南理工大学本科毕业设计（论文） 外文翻译 9 them. With modern control equipment, it is possible to change the cycle length and division several times a day, or go to flashing indications to fit the traffic pattern better. At many intersections， signals must be timed to acmodate pedestrian movements. The Manual remends that the minimum total time allowed be an initial interval of 4 to 7s for pedestrians to start plus walking time puted at 4 ft/s (1. 2m/s). With separate pedestrian indicators， the WALK indication(lunar white) covers the first of these intervals, and flashing DON39。 T WALK (Portland orange ) the remainder. The WALK signal flashes when there are possible conflicts with vehicles and is steady when there are none. Steady DON39。 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 (0. 76km)to more than a mile (1. 6km) are very effective in producing a smooth flow of traffic. On the other hand， when a street is loaded to capacity， coordination of signals is generally ineffective in producing smooth traffic flow. Four systems of coordinationsimultaneous, alternate， limited progressive, and flexible progressivehave developed over time. The simultaneous system made all color indications on a given street alike at the same time .It produced high vehicle speeds between stops but low overall speed. Because of this and other faults， it is seldom used today. The alternate system has all signals change their indication at the same time， but adjacent signals or adjacent groups of signals on a given street show opposite colors. The alternate system works fairly well on a single street that has approximately equal block spacing. It also has been effective for controlling traffic in business districts several blocks on a said, but only 河南理工大学本科毕业设计（论文） 外文翻译 10 when block lengths are approximately equal in both directions. With an areawide alternate system， green and red indications must be of approximately equal length. This cycle division is satisfactory where two major streets intersect but gives too much green time to minor streets crossing major arteries. Other criticisms are that at heavy traffic volumes the later section of the platoon of vehicles is forced to make additional stops， and that adjustments to changing traffic conditions are difficult. The simple progressive system retains a mon cycle length but provides 39。 go39。 indications separately at each intersection to match traffic progression. This permits continuous or nearly continuous flow of vehicle groups at a planned speed in at least one direction and discourages speeding between signals. Flashing lights may be substituted for normal signal indications when traffic bees light. The flexible progressive system has a master controller mechanism that directs the controllers for the individual signals. This arrangement not only gives positive coordination between signals， but also makes predetermined changes in cycle length， cycle split， and offsets at intervals during the day. For example， the cycle length of the entire system can be lengthened at peak hours to increase capacity and shortened at other times to decrease delays. Flashing indications can be substituted when normal signal control is not needed. Also the offsets in the timing of successive signals can be adjusted to f。