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L NKPart One —Define the following termsHeadway （车头时距）：is defined as the time interval between successive vehicles as they pass a point along the lane ， also measured between common reference points on the vehicles.Peak Hour Factor （高峰小时系数）：The relationship between the hourly volume and the maximum rate of flow within the hour is defined by the peak hour factor(PHF).PHF=错误！未找到引用源。
Flow of Rate Max Volume HourlyPerception-reaction time(PRT)(反应时间): from start of perception to the end of reaction (2.5 second is very common);it varies greatly from person to person ，from situation to situation.Capacity: Maximum Hourly Rate at which persons or vehicles can traverse a point or a uniform section of a lane or roadway during a given time period under prevailing roadway ，traffic and control conditions.Gap acceptance: is defined as the distance between the pedestrian and the approaching vehicle at the time the pedestrian begin his or her crossing.Spacing(车头间距)：is defined as the distance between successive vehicles in a traffic lane ， measured from some common reference point on the vehicles ，such as the front bumper or front wheels.Level of service(服务水平): is a quality measure describing operational conditions within a traffic stream ，generally in terms of such service measures as speed and travel time ，freedom tomaneuver ，traffic interruptions ，and comfort and convenience.PCU(passenger car units)：a unit of measure whereby large trucks and turning movements are converted to passenger cars using multiplication factors.T otal stopping distance ：The sum of the reaction distance and the braking distance.TDM:is the application of strategies and policies to reduce travel demand (specifically that of single-occupancy private vehicles), or to redistribute this demand in space or in time.TSM ：is a process for planning and operating a unitary system of urban transportation.Delay ：is defined as “the addiional travel time experienced by a driver,passenger or pedestrian”and with respect to field measurements,it’s the d ifference in travel time when a vehicle is unaffected by the controlled intersection or traffic incidents and when a vehicle is affected by the controlled intersection or traffic incidents.动视力 ：汽车运动时驾驶人的视力设计小时交通量：将一年中所有8760（365*24）小时的小时交通量按由大到小的顺序排列时其第30位的那个小时的交通量，又称为设计小时交通量(Design Hourly V olume ，DHV ， 30HV)。
