平均日交通量

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Chapter 3. Volume, Density & Speed Studies and Characteristics,Volume (rate of flow) - intensity of traffic movement,Speed - motion condition,Density - distribution of traffic flow over space,Relationship among three parameters - mathematical equations,1,1. Volume,Volume - is defined as the number of vehicles that pass a point on a highway, or a given lane or direction of a highway, during a specified time interval, generally a day or an hour.,2,Some useful volumes,AADT (Average Annual Daily Traffic,年平均日交通量,),AAWT (Average Annual Weekday Traffic,年平均工作日交通量,),ADT (Average Daily Traffic,平均日交通量,),AWT (Average Weekday Traffic,平均工作日交通量,),These four volumes remain at macroscopic level,3,4,5,Daily variation factor (DF),- is defined as ratio of AADT over yearly average volume for particular day of week (Monday, Tuesday etc.),Calibration of Daily Variation Factors,6,Monthly variation factor (MF),- is defined as ratio of AADT over ADT for particular month of the year,Calibration of Monthly Variation Factors,Month,Total Traffic,(vehs),ADT for Month,(veh/day),Monthly Variation Factor (MF),January,19,840,/31=640,797/640=1.25,February,16,660,/28=595,797/595=1.34,March,21,235,/31=685,797/685=1.16,April,24,300,/30=810,797/810=0.98,May,25,885,/31=835,797/835=0.95,June,26,280,/30=876,797/876=0.91,July,27,652,/31=892,797/892=0.89,August,30,008,/31=968,797/968=0.82,September,28,620,/30=954,797/954=0.84,October,26,350,/31=850,797/850=0.94,November,22,290,/30=743,797/743=1.07,December,21,731,/31=701,797/701=1.14,Total,290,851,AADT=290,851/365=797veh/day,7,Hourly volumes and peak hour volume,（小时流量，高峰小时流量）,Hourly volumes are used to reflect variation (fluctuation) of traffic volume in a day,Peak hour volume is defined as the volume in the single hour that has the highest hourly volume,8,Rate of flow,(流率）,- defined as an equivalent hourly volume for a given interval (interval can be 5, 10, 15 minutes),used in design to reflect the worst scenario,used in modeling mathematical relationship among parameters in research,generally the shorter the interval the higher the rate of flow,9,Interval Volume Interval Volume,7:00 7:05 15 7:30 7:35 17,7:05 7:10 25 7:35 7:40 35,7:10 7:15 18 7:40 7:45 28,7:15 7:20 42 7:45 7:50 32,7:20 7:25 31 7:50 7:55 26,7:25 7:30 18 7:55 8:00 20,V5 = (180, 300, 216, 504, 372, 216, 204, 420, 336, 384, 312, 240),V10=(240, 360, 294, 312, 360, 276),V15=(232, 364, 320, 312),Max V5 = 504; Max V10 = 360; Max V15 = 364,Hourly volume = 307,10,Peak hour factor,（高峰小时系数）,- is defined as the ratio of hourly volume divided by maximum rate of flow,PHF is used to reflect the fluctuation of,volume distribution in an hour!,PHF5 = 307/504 = 0.61;,PHF10 = 307/360 = 0.85;,PHF15 = 307/364 = 0.84;,11,Peak-Hour-Factor (PHF),12,The 30th hourly volume,(第30位小时交通量),- defined as an hourly volume at which its ranking on yearly-counting curve counts 30th among 8760 hourly volumes in a year,DDHV,(Directional Design Hourly Volume,设计小时流量),- DDHV = AADTK D where: K is proportion of daily traffic occurring during the peak hour, expressed as a decimal; D is proportion of peak-hour traffic traveling in the peak direction, expressed as a decimal,13,D= ratio of design hour volume in the major direction to the total,(,方向性系数）,K=ratio of design hour volume to the 24 hour volume,（,设计小时系数）,Relationship Between DDHV and AADT,In general D and K is,constant!,14,15,VMT (Vehicle Miles Traveled=,车英里,) or VKT(Vehicle Kilometers Traveled,车公里,) - defined as a product of number of vehicles and miles (or kilometer) traveled by these vehicles,Estimation of Vehicle-Miles Traveled on a Limited Network: An Example,16,PCE and PCU,（小汽车当量）,- defined as the number of passenger cars displaced by one truck, bus, or RV in a given traffic stream,Traffic intensity,can be used as criterion to determine passenger car equivalent,17,2. Speed,Time mean speed (TMS，,时间平均车速,) -,defined as the average speed of all vehicles passing a point on a highway over some specified time period,Space mean speed (SMS，,空间平均车速,) -,defined as the average speed of all vehicles occupying a given section of a highway over some specified time period,18,TMS is a point measure, while SMS is a measure relating to a length of highway or lane,SMS is often used in traffic flow theory study at macroscopic level while TMS is used for engineering study,TMS SMS,19,Average travel speed and average running speed,（平均行程，行驶速度),-,Average travel speed = distance /travel time,Average running speed = distance/running time,Running time = travel time - stopped delays,20,Operating speed,（运营速度）,-,defined as the maximum safe speed at which a vehicle can be conducted in a given traffic stream, without exceeding the design speed of the highway segment.,Critical speed or Optimal speed,(临界车速),-,defined as the speed at which maximum flow rate (capacity,通行能力,) can be achieved (or at which gas consumption of vehicles is at the lowest),21,Percentile speeds,（百分位速度）,- is a speed below which the stated percent of vehicles in the traffic stream travel,22,23,In traffic engineering, 85th percentile speed is often used as a measure of the maximum reasonable speed for the traffic stream (upper limit), while the 15th percentile speed may be used as a measure of the minimum reasonable speed for the traffic stream. The 50th percentile or median speed is used to describe the midpoint of the speed distribution.,24,3.Density,It is defined as the number of vehicles occupying a given length of highway or lane and is generally expressed as vehicles per kilometer per lane.,Difficult to obtain from the field - using occupancy,(占用率）,which is defined as the proportion of time that a detector is covered by a vehicle in the specified period of time,25,26,Closely related to traffic demand,It is easy for drivers to perceive,Spacing (,车头间距）,and headway,（车头时距）,spacing is defined as the distance between successive vehicles in a traffic lane; headway is defined as the time interval between successive vehicles as they pass a point along the lane,27,Different density on both directions of freeway, USA,28,Freeway of I-15 in San Diego, USA,29,Different density on each direction of expressway, Beijing,30,Different density on both directions of main street, Beijing,31,It should be noted that density and volume are different. The former represents,distribution,of vehicles in terms of space occupying the roadway; whereas the later expresses the,frequency,of vehicles passing a point of roadway.,32,4. Relationship among volume, speed and density,This equation is valid for uninterrupted flow only!,33,The Greenshields linear model,34,Graphical Relationship Among Three Parameters,Congestion Zone,35,Greenbergs logarithmic model,36,Underwoods exponential model,37,Northwestern University Model,38,Summary,Name of model,Must known Parameter,Notes,Greenshields,u,f, k,j,u,f,between speed limi u,f, and design speed,kj is hard to estimate,Greenberg,u,0, k,j,u,f,is infinite,Underwood,u,f, k,0,ko is hard to observe,u never reaches zero,kj is infinite,Northwestern,u,f, k,j,kj is infinite,u will be never zero,39,40,Derivation of flow-speed and flow-density relationships under Greenshields,Capacity,Capacity is defined as the maximum rate of flow that can,be achieved on roadway facilities under prevailing roadway,traffic, and control conditions.,41,Similarly we can get:,42,Three important traffic states,Free flow (u,f, q=0, k=0),Optima state (q,max,u,o, k,o,),Traffic jam (k,m, q=0,u=0),43,Flow-Speed Curve Under Different Conditions,44,Flow-Speed Curve For,Major Arterial of Beijing,Flow-Speed Curve For,Minor Arterial of Beijing,45,Some conclusions,When density less than 20, Greenberg and Underwood models overestimate speed,When density between 20 to 60, all models underestimate speed and flow that may lead to underestimate capacity,When density bigger than 90, Greenshields model starts to deviate from the data, at density 125, Greenshields model has zero speed and flow rate,46,Discussion of the models,Greenberg and Underwood models have higher free flow speed than the observed,Greenberg underestimates optimal (critical ) speed,Greenshields mode underestimates jam density,Underwood and Northwestern models predict jam density infinite,Greenberg model slightly over estimates optimal density,47,本章要点,流量与流率的定义及其不同,高峰小时流量与高峰小时系数,标准小汽车当量,第30位小时交通量,流量，速度和密度三者关系,百分位速度的概念和在交通工程中的应用,48,