Chapter 4 Traffic Engineering Studies

26/10/1433Chapter 4Traffic Engineering StudiesTraffic Engineering Studies Trafficstudies may be groupedinto three main categories: (1)Inventories, (2) Administrative studies, and (3) Dynamic studies.1

26/10/1433Traffic Engineering Studies(1) Inventories:provide a list or graphic display ofexisting information, such as: street widths,parking spaces,transit routes,traffic regulations.Traffic Engineering Studies(2) Administrative studies use existing engineering records,available in government agencies anddepartments. include the results of surveys, which mayinvolve:field measurements and/or aerial photography. 2

26/10/1433Traffic Engineering Studies(3) Dynamic traffic studies involve the collection of data underoperational conditions and include studies of: speed,traffic volume,travel time and delay,parking, andcrashes.They are described in detail in this chapter.Traffic Engineering Studies 4.1 SPOT SPEED STUDIESSpot speed studies are conducted toestimate the distribution of speeds ofvehicles in a stream of traffic at a particularlocation on a highway. carried out by recording the speeds of asample of vehicles at a specified location. 3

26/10/1433Traffic Engineering Studies SPOT SPEED STUDIESUsed to: Establish parameters fortraffic operation and control, such as:speed zones, speed limits (85th-percentile speed) Traffic Engineering Studies 44.1.1 Locations for Spot Speed Studies Represent different traffic conditions on ahighway for basic data collection. Mid-blocks of urban highways and straight,level sections of rural highways for speedtrend analyses. Any location may be used for solution of aspecific traffic engineering problem.

26/10/1433Traffic Engineering Studies 4.1.1 Locations for Spot Speed StudiesShould be selected to achieve the following:Unbiased data Drivers be unaware Equipment concealed from the driver, Observers inconspicuous. Traffic Engineering Studies 54.1.1 Locations for Spot Speed Studies statistical analysis, statistically adequate number of vehiclespeeds be recorded.

26/10/1433Traffic Engineering Studies 4.1.2 Time of Day and Duration ofSpot Speed Studiesdepends on the purpose of the study. recommended when traffic is free-flowing, during off-peak hours. typically: the duration is at least 1 hour and the sample size is at least 30 vehicles. Traffic Engineering Studies 4.1.3 Sample Size for Spot Speed Studies The larger the sample size, will give anestimated mean within acceptable errorlimits.Average SpeedMedian Speed Modal Speed The ith-percentile Spot Speed Pace Standard Deviation of Speeds 6

26/10/1433Traffic Engineering Studies 4.1.4 Methods for Conducting SpotSpeed Studies manual and automaticmanual method is seldom usedautomatic devices1.2.3.road detectorsradar-basedthe principles of electronics.Traffic Engineering Studies Road Detectors pneumatic road tubes & induction loopscollect data on speeds & volume at thesame timeAdvantage: Disadvantages: 7Human errors are considerably reducedexpensivemay, affect driver behavior,

26/10/1433Traffic Engineering Studies Pneumatic road tubes laid across the lane in which data are tobe collected.When moving vehicle passes over, an airimpulse is transmitted to the counter.two tubes are placed across the lane, 2 mapart.An impulse is recorded when the frontwheels of a moving vehicle pass over thefirst tube;Traffic Engineering Studies Pneumatic road tubes 8a second impulse is recorded when thefront wheels pass over the second tube.The time elapsed between the twoimpulses and the distance between thetubes are used to compute the speed ofthe vehicle.

26/10/1433Traffic Engineering Studies inductive loop a rectangular wire loop buried under theroadway surface.It operates on the principle that adisturbance in the electrical field is createdwhen a motor vehicle passes across it.Traffic Engineering Studies Radar-Based Traffic SensorsElectronic-Principle Detectors 9traffic characteristics, such as speed,volume, queues, and headways arecomputed.Using video image processing

26/10/1433Traffic Engineering Studies(a) RTMS Deployed in the Forward Looking ModeTraffic Engineering Studies(b) RTMS Deployed in the Side-fire Mode10

26/10/1433Traffic Engineering Studies(a) Schematic Illustrationof the Auto scopeTraffic Engineering Studies(b) The Auto scope Deployed11

26/10/1433Traffic Engineering Studies 4.1.5 Presentation and Analysis ofSpot Speed Data Statistical methodsAnalyzing datafrequency histogramcumulative frequency distribution curveTraffic Engineering Studies Example 4.2 Determining SpeedCharacteristics from a Set of SpeedData.Table 4.2 shows the data collected on a ruralhighway in Virginia during a speed study.Develop the frequency histogram and thefrequency distribution of the data anddetermine:12

26/10/1433Traffic Engineering Studies1.2.3.4.5.6.The arithmetic mean speedThe standard deviationThe median speedThe paceThe mode or modal speedThe 85th-percentile speedTraffic Engineering StudiesSolution: The speeds range from 34.8 to 65.0 km/h,giving a speed range of 30.2. 13For eight classes, the range per class is 3.75km/h;for 20 classes, the range per class is 1.51 km/h.It is convenient to choose a range of 2 km/h perclass which will give 16 classes.A frequency distribution table can then beprepared, as shown in Table 4.3.

26/10/1433Traffic Engineering StudiesTable 4.2 Speed Data Obtained on a Rural HighwayTraffic Engineering StudiesFigure 4.4 Histogram of Observed Vehicles' Speeds14

26/10/1433Traffic Engineering StudiesTable 4.3 Frequency Distribution Table for Set of Speed DataTraffic Engineering StudiesFigure 4.5 Frequency Distribution15

26/10/1433Traffic Engineering StudiesFigure 4.6 Cumulative DistributionTraffic Engineering Studies The median speed 49 km/h,the 50th-percentile speed. 1685th-percentile speed is 54 km/h

26/10/1433Traffic Engineering Studies 4.2 VOLUME STUDIES1. Average Annual Daily Traffic (AADT)the average of 24-hour counts collectedevery day of the year.2. Average Daily Traffic (ADT)the average of 24-hour counts collectedover a number of days greater than onebut less than a year.Traffic Engineering Studies 4.2 VOLUME STUDIES3. Peak Hour Volume (PHV)the maximum number of vehicles that pasa point on a highway during a period of 60consecutive minutes.4. Vehicle Classification (VC) with respectto the type of vehicles for cars, two-axletrucks, or three-axle trucks.5. Vehicle Miles of Travel (VMT)17

26/10/1433Traffic Engineering Studies 4.2.1 Methods of ConductingVolume Counts Manual MethodAutomatic MethodTraffic Engineering StudiesFigure 4.7 Jamar Traffic Data Collector TDC-1 2 Hooked to a Computer18

26/10/1433Traffic Engineering StudiesFigure 4.9 Apollo Traffic Counter/ClassifierTraffic Engineering StudiesFigure 4.10 Example of Counters that Require the Laying of Subsurface Detectors19

26/10/1433Traffic Engineering StudiesFigure 4.11 Traffic Eye Universal SystemTraffic Engineering StudiesFigure 4.12 Example of Station Locations for a Cordon Count20

26/10/1433Traffic Engineering Studies 4.2.2 Types of Volume Counts Depending on the anticipated use of thedata to be collected.Intersection Counts vehicle classifications,through movements,turning movements.Traffic Engineering Studies 4.2.2 Types of Volume Counts 21Pedestrian Volume CountsPeriodic Volume Counts (AADT)

26/10/1433Traffic Engineering Studies 4.2.3 Traffic VolumeData Presentation Traffic Flow Maps:volume of traffic oneach route isrepresented by thewidth of a band.Figure 4.13 shows atypical traffic flow map.Figure 4.13 Example of a Traffic Flow MapTraffic Engineering StudiesIntersection SummarySheets:Figure 4.14 shows atypical intersectionsummary sheet.Figure 4.14 Intersection Summary Sheet22

26/10/1433Traffic Engineering Studies 4.2.3 Traffic Volume DataPresentation Time-Based Distribution Charts:see Figure 4.15Traffic Engineering StudiesDailyvariations:see Figure4.15bFigure 4.15 Traffic Volumes on an Urban Highway (A&B)23

26/10/1433Traffic Engineering StudiesHourlyvariationsin trafficvolume:Figure 4.15 Traffic Volumes on an Urban Highway (C)Traffic Engineering StudiesSummary Tables:PHV, Vehicle Classification (VC), andADT. See Table 4.4Table 4.4 Summary of Traffic Volume Data for a Highway Section24

26/10/1433Traffic Engineering Studies Adjustment of Periodic CountsExpansion Factors from ContinuousCount Stations.Hourly expansion factors (HEFs) aredetermined by the formulaTraffic Engineering Studies25 Daily expansion factors (DEFs) arecomputed as Monthly expansion factors (MEFs) arecomputed as

26/10/1433Traffic Engineering StudiesTable 4.5 Hourly Expansion Factors for a Rural Primary RoadTraffic Engineering StudiesTable 4.6 Daily Expansion Factors for a Rural Primary Road26

26/10/1433Traffic Engineering StudiesTable 4.7 Monthly Expansion Factors for a Rural Primary RoadTraffic Engineering Studies27

26/10/1433Traffic Engineering StudiesTraffic Engineering Studies 4.3 TRAVEL TIME AND DELAYSTUDIES 28Travel time: time required to travel fromone point to another on a given route.the locations, durations, and causes ofdelays.good indication of the level of serviceidentifying problem locations,

26/10/1433Traffic Engineering Studies 4.3.1 Applications of Travel Timeand Delay Data efficiency of a routelocations with relatively high delayscauses for delaysbefore-and-after studiesrelative efficiency of a routetravel times on specific linkseconomic studiesTraffic Engineering Studies 4.3.2 Definition of Terms Related toTime and Delay Studies1.2.29Travel time: time taken by a vehicle totraverse a given section of a highway.Running time: time a vehicle is actually inmotion

26/10/1433Traffic Engineering Studies 4.3.2 Definition of Terms Related to Timeand Delay Studies3.4.Delay time lost due to causes beyond thecontrol of the driver.Operational delay: delay caused by theimpedance of other traffic.(for example, parking or unparkingvehicles),Traffic Engineering Studies5.6.7.30Stopped-time delayFixed delay: caused by control devicessuch as traffic signals, regardless of thetraffic volumeTravel-time delay: difference between theactual travel time and the travel timeobtained by assuming that a vehicletraverses at an average speed equal tothat for an uncongested traffic flow

26/10/1433Traffic Engineering Studies 4.3.3 Methods for Conducting TravelTime and Delay Studies Methods Requiring a Test Vehicle:floating-car, average-speed, and movingvehicle techniques.Traffic Engineering StudiesFloating-Car Technique: test car is driven by an observer along the testsection. 31The driver attempts to pass as manyvehicles as those that pass his testvehicle.Time taken to traverse the study section isrecorded. This is repeated, and theaverage time is recorded as the traveltime.sample size s usually less than 30,

26/10/1433Traffic Engineering StudiesAverage-Speed Technique. driving the test car along the length of thetest section at a speed that, is the average speed of the traffic stream. time required to traverse the test section isnoted. test run is repeated the average time is recorded as the traveltime.Traffic Engineering StudiesAverage-Speed Technique. travel time is usually obtained the observer starts a stopwatch at thebeginning point of the test section andstops at the end.32

26/10/1433Traffic Engineering StudiesTable 4.8 Speed and Delay InformationTraffic Engineering StudiesAverage-Speed Technique. A second stopwatch also may be used todetermine the time that passes each timethe vehicle is stopped. will give the stopped-time delay Table 4.8 shows an example of a set ofdata obtained for such a study.33

26/10/1433Traffic Engineering StudiesMoving-Vehicle Technique(moving observer): the observer makes a round trip on a testsection Figure 4.16, The observer starts at section X-X, drivesthe car eastward to section Y-Y, turns the vehicle around drives westward to section X-X againTraffic Engineering StudiesFigure 4.16 Test Site for Moving-Vehicle Method34