TIME HEADWAY ANALYSIS TO DETERMINE THE ROAD
Vol.4, No.2, Juli 2016Jurnal SpektranTIME HEADWAY ANALYSIS TO DETERMINETHE ROAD CAPACITYI Wayan Suweda1ABSTRACT: In developed countries, road capacity values derived from time headway is inaccordance to their local traffic characteristics. In theory, time headway standards are developed usingstatistics models. These standards however, are not necessarily relevant to use in Indonesia. This isbecause of the differences in traffic conditions and motorists behaviours between those in developedcountries and Indonesia. This study is to develop the time headway distribution model andsubsequently to determine lionk-road capacity in the city of Denpasar, Bali Province. The studyconsists of time headway data analysis, model calibration and validation and road capacity valuesdetermination. The study found that normal distribution model fitted the local traffic conditions. Roadcapacity values are of 2,466 pcus/hour and 2,900 pcus/hour obtained from time headway model andthe Indonesian Road Capacity Manual (MKJI) respectively.Keywords: time headway distribution model, mixed traffic, road capacityABSTRAK: Di negara maju, nilai-nilai kapasitas jalan ditentukan berdasarkan waktu headway sesuaidengan karakteristik lalu lintas lokal. Secara teori, standar waktu headway dikembangkanmenggunakan model-model statistik. Standar-standar ini tentunya tidak selalu relevan untuk digunakandi Indonesia. Hal ini karena perbedaan kondisi lalu lintas dan perilaku pengendara antara mereka yangdi negara-negara maju dan Indonesia. Penelitian ini dimaksudkan untuk mengembangkan modeldistribusi waktu headway dan selanjutnya dipergunakan untuk menentukan kapasitas segmen-jalan dikota Denpasar, Provinsi Bali. Penelitian ini terdiri dari analisis data waktu headway, kalibrasi danvalidasi model dan menemukan nilai kapasitas jalan. Dari hasil studi ditemukan bahwa model distribusinormal cocok untuk kondisi lalu lintas lokal. Sedangkan, nilai kapasitas jalan adalah 2.466 smp/jamdan 2.900 smp/jam yang berturut-turut diperoleh berdasarkan model waktu headway dan ManualKapasitas Jalan Indonesia (MKJI).Kata-kata kunci: model distribusi waktu headway, lalu lintas campuran, kapasitas jalan1Dosen Program Studi Magister Teknik Sipil, Program Pascasarjana Universitas Udayana71
Jurnal Spektran1. INTRODUCTIONTransportation system variables includingroad capacity and level of services, motoristbehaviours and traffic safety are stronglyinfluenced by motor vehicle time headway(Sukowati, 2004 and Minh, et al. 2005). Salterin 1976 defined time headway is a timedifference between the sequences of motorvehicles passing a certain point on a road lane.Minimum time headway is a measure of trafficsafety level for the vehicle if a vehicle in frontsuddenly decelerating or braking. Meanwhile,time headway distribution is a measure of roadlevel of service because it measures of a motorvehicle for passing, merging and crossing withthe other vehicles. Road capacity is determinedby time headway minimum value anddistributions based the relationship betweencapacity and traffic flow (Tiwari, 2000).In theory, traffic flow concepts and itsderivatives used in Indonesia are developedfrom countries such as USA, UK and Australia.Those are composed considering homogeneoustraffic flow conditions dominated by lightvehicles. In facts, the Indonesian Road CapacityManual (as known as MKJI 1997) usespassenger cars (light vehicles) as a standardconversion to the other modes. Traffic volumesand road capacity are estimated using numberof road lanes on the assumption that oncomingvehicles run and stopped consistently on a lane.On mixed traffic which are very common inall Indonesian cities, motorcycles and bothheavy and light vehicles however, shareroadways together. Many vehicles, in particularmotorcycles, are not run on the road lanes.Road capacity determination using the numberof road lanes as a standard therefore, mayproduce an imprecise result (Tiwari, 2000).Motorcycles may reduce the speed of othervehicles behind and in turn contribute to trafficdelay as they run next to each other on the road(Minh, et al. 2005). These certainly reduce theroad level of service.Road capacity determination in accordanceto local traffic conditions therefore, is morerelevant to apply in Indonesia. This is becausethe differences of traffic characteristics andmotorist behaviours between those in developedcountries and Indonesia. The existing standardtime headway in Indonesia remains in line tothose homogeneous traffic conditions as indeveloped countries (Tiwari, 2000). A study ontime headway considering mixed trafficconditions therefore, is important to conduct.Vol.4, No.2, Juli 2016Investigation on time headway reflectingmixed traffic conditions in Indonesia has notmuch been done. A previous study conducted inSemarang, Central Java, studying on timeheadway and road capacity determination onboth toll and non-toll roads (Sukowati, 2004). Itdid not include however, the influence ofmotorcycle on time headway and road capacity.This study objectives are to develop the timeheadway distribution model and determine roadcapacity values by taking into account allmodes including motorcycles. The study isexpected to reflect the real conditions of bothmixed traffic and time headway and itsinfluence on the road capacity in the city ofDenpasar.2. MODELLING TIME HEADWAY2.1 Calibration and Validation of TimeHeadway Distribution ModelRoad capacity can be determined usingstandard time headway between vehicles. Morespecifically, road capacity can be analysedusing average time headway per unit of trafficflow. Time headway is made up of occupancytime and time gap. As described by May in1990, the time period of occupancy isphysically a vehicle passing a point ofobservation, while time gap is a time differencebetween the rear of the vehicle in front and thefront end of the vehicle to follow passingthrough the same point of observation(Sukowati, 2004).Time headway distribution has long beenstudied for which the main objectives were toanalyse road capacity, road safety and thenumber of vehicles on microscopic simulation(Al-Ghamdi, 2001). Time headway varied inaccordance with traffic volume. In a low trafficvolume where less interaction between vehicles,time headways were randomly distributed.Meanwhile, in high and medium trafficvolumes, time headway distribution is constantand mixed (between random and constant)respectively. May in 1990 concluded thatnegative exponential, normal distribution andPearson Type III models are relevant torandom, constant and mixed time headwaydistributions respectively (Sukowati, 2004). Aprevious study conducted in Saudi Arabiaconcluded that the gamma distribution andshifted exponential models can represent timeheadway for low and medium traffic volumes(Al-Ghamdi, 2001). In addition, it wassuggested that no time headway data can be72
Vol.4, No.2, Juli 2016Jurnal Spektrancombined from different places to obtain anappropriate distribution model.In order to validate the model, thefollowing steps are taken:a. Data collected from each locationshould be statistically sufficient as theminimum increase is of 100-200vehicles per hour.b. Chi-square test method is sufficientlybe used to test the distribution modelsand is expressed as follows:where,fo ft 2 Observed data frequencyTheoretical data frequencyCalculated value of chicUsing these previous studies (Sukowati, 2004and Al-Ghamdi, 2001). time headwaydistribution models can be classified as shownin Table 2.1.( fo ft )2 . 2.1fti 1n c2 Table 2.1 Time Headway Distribution Model wayLow 400 vehs/h 9 secondsMedium400-1.200 vehs/h2,5-9 secondsPearsonType IIIHigh 1.200 vehs/h 2,5 secondsNormalDistribution2.2 Road Capacity Determination UsingMKJI 1997 and Time HeadwayThe maximum road capacity is the roadability passing vehicles per unit time undernormal road and traffic circumstances(Department of Public Works, 1997). There areseveral factors that strongly affect the roadcapacity as follows:a. Road factors include lane width, lateralfreedom, road shoulders, median, roadsurface conditions, road alignment, roadflatness and footways.b. Traffic factors include traffic composition,traffic volume, lane distribution, trafficdisruption and side frictions.c. Environmental factors include pedestrians,cyclists, and animals.Road capacity can be determined using theformula as follows (Department of PublicWorks, n e t [ ( )][ (t )] 1 e (t )zsC Co . FCW . FCSP . FCSF . FCCS . 2.2Where:CCoFCWFCSPFCSFFCCS Road capacity (pcu/hour) Basic capacity (pcu/hour) Adjustment factor for roadwidth Adjustment factor for trafficseparation Adjustment factor for sidefriction Adjustment factor for city sizeIn order to calculate the Passenger CarUnits (pcu) for all modes in the city ofDenpasar, this study uses Passenger CarEquivalent (PCE) for urban areas (Departmentof Public Works, 1997) as shown in Table 2.2.73
Vol.4, No.2, Juli 2016Jurnal SpektranTable 2.2 Passenger Car Equivalent (PCE) for Urban RoadRoad typesTraffic Flows(two ways)(veh/hour)Two lanes two waysundivided (2/2 UD)Four lanes two waysundivided (4/2 UD)0 up to 1,800 1,8000 up to 3,700 3,700Two types of traffic data required toestimate a cross-sectional road capacity aretraffic volume and time headway (Minderhoudet al. 1997). In addition, some informationincluding traffic density and average trafficspeed are very helpful. For instance, trafficspeed data is useful to analyse traffic conditionssuch as traffic stability and traffic jams. Astraffic density (number of vehicles perkilometer of the road) increases, the averagespeed decreases and the traffic becomesunstable afterward. This can suddenly turn intotraffic congestion where speeds decrease whiledensities increase. Such a heavy traffic flow(the average speed drops below a certain value)means that the level of capacity has beenaccomplished in a bottleneck situation itself. Inthis condition it is possible to estimate a morereliable capacity. Steady traffic flow can occurwhen a driver can maintain the desired speed.Time headway is defined as the timebetween successive vehicles that passing acertain point in the path of traffic flow. Theformula is expressed as follows (Sukowati,2004):hm : hp / n . .2.3Q : n/T 1/hm . .2.4where:hp Time Headway of a vehicle (p) to avehicle in front (second/vehicle)hm Average Time Headway (second/veh)Q Road Capacity (vehicle/second)n Total Number of Vehicles Passing aCertain Point of Observation duringperiod of T.Passenger Car EquivalentMotorcyclesRoad width, Wc (m)Heavy Vehicles 6 61.30.50.41.20.350.251.30.41.20.25The central value of statistics consistingaverage (mean), midpoint (median), highestfrequency (mode) and percentile values areintensively used to determine the road capacity(Sukowati, 2004). Percentile value is defined asa measure used to indicate a percentage valueunder a group of data. For example, 90percentiles indicate values that are below the90% of the observational data.3. CASE STUDY AREA AND DATADESCRIPTIONS3.1 Case Study AreaThe data used in this study is adopted froma previous study conducted in the city ofDenpasar (Sudarsana, 2013). The studyinvestigated Passenger Cars Equivalent (PCE)determination by making use of time headwayanalysis. However, it did not examine timeheadway distribution model and road capacity.The case study area as shown in Figure 3.1 islocated in the city of Denpasar on Sesetan Roadsegment. More specifically, it is situatedbetween the intersection of Sesetan Road Pulau Saelus Road and the intersection ofSesetan Road - Pulau Buton Road. This has 9meters and 1.2 meters of road width andshoulder respectively and is classified as twolanes two ways of undivided road segment (2/2UD).Footway1.5 mRoad Shoulder1.2 mNorthSouth4.5 m4.5 m74
Vol.4, No.2, Juli 2016Jurnal Spektran1.2 mRoad Shoulder1.5 mFootwayFigure 3.1 Case Study AreaThe selected road segment has low sidefrictions (no on street parking, low pedestriancrossings and non motorised transport, low inand out movements from the surrounding landuses). In addition, this road has beenexperiencing high mixed traffic volume. Thisroad segment therefore, is considered relevantto be used in this study.3.2 Data DescriptionsTraffic volume and time headway datawere collected using digital video recording onWednesday 1 May 2013 between 04.00 a.m. to04.00 p.m. (Sudarsana, 2013). Traffic volumedata consists all modes i.e. motorcycles (MC),heavy and light vehicles (HV and LV).Table 3.1 Traffic Volume ProportionModes ,88183.14Light Vehicles8,17615.85Heavy Vehicles5231.01As shown in Table 3.1, motorcycles dominatedthe traffic in which they were accounted for by83% of total modes.Following division on urban road(Department of Public Works, 1997), trafficvolume data are classified into two (2) groupsconsisting total volumes for 1800vehicles/hour and for 1800 vehicles/hour.By using a standard PCE shown in Table 2.2,traffic volume is expressed in PCU as shown inTable 3.2. The proportion of motorcycles, lightand heavy vehicles and motorcycles of totaltraffic flow for 1800 vehicles/hour are 71%,27%, and 2% respectively. Meanwhile, theproportion of motorcycles, light and heavyvehicles and motorcycles are 55%, 42% and 3%of total traffic flow for 1800 vehicles/hour. Itcan be seen that the proportion of heavyvehicles is relatively stable during theobservationperiod.Duringdaytime,motorcycles decreased by 26% while incontrast, light vehicles increased by 15%. .Time04.00-05.00Table 3.2 Traffic VolumeTotal traffic flow for 1800 vehicles/hourVolume (vehicles/hour)Volume al traffic flow for 1800 vehicles/hourVolume (vehicles/hour)Volume 917493,8824,848917599711,947Time48,43518,42875
Vol.4, No.2, Juli 2016Jurnal SpektranMeanwhile, there are eight (8) pairs of time headway measured as shown in Table 3.3.Table 3.3 Pair of Time Headway ObservationNo.1.2.3.4.Pair of Time HeadwayBetween MC and MCBetween LV and MCBetween MC and LVBetween LV and LVEach pair of time headway is calculatedwhen the vehicle's front wheel touches the pointof observation to the next vehicle's front wheelstouched the same observation point. All pairs oftime headway however, can not be calculated sothat some criteria are used to sample it. TheseNo.5.6.7.8.Pair of Time HeadwayBetween HV and HVBetween LV and HVBetween LV and LVBetween HV and MCcriteria require each pair should really lookunhindered another vehicle when front wheelpasses the observation point and each pair isreally a sequentially vehicle. Time headwaydata is shown in Table 3.4.Table 3.4 Time HeadwayTotal Traffic Flows of 1800 vehicles/hourMC-MC LV-MCNo.ObservationAverage(seconds)MC-LV LV-LVHV-HV 01.73HV-LVHV-MCTotal Traffic Flows of 1800 vehicles/hourMC-MC LV-MC MC-LV LV-LV HV-HV e 3.4 shows that the lowest timeheadway (0.06 second) is among motorcyclesduring daytime (traffic flows for 1800vehicles/hour). This indicates that motorcyclistbehaviours such as speeding and manoeuvringamong vehicles to get ahead during thecongested road exist in such a typical mixedtraffic.4. MODEL DEVELOPMENT4.1. Model CalibrationTime headway data may be classified intoseveral classes according to Sturgis’s rules(number of classes 1 3.3 x log n, where n isthe number of data). For example, the timeheadway of traffic flow for 1800vehicles/hour is divided into 11 classes (1 3.3x log 1968). Data range for each class isconstructed by trial and error so that theexpected frequency probability approaching 1while considering time headway below 2.5seconds has very large data variations. This hasto be done because of considerable largefrequency; the statistical model may have aparticular significant bias in determining theexpected/theoretical frequency. The results maynot subsequently be relevant to the normaldistribution model. In fact, time headwayfrequency sufficiently proves that the roadsegment has saturated flows. Time headwayfrequency distribution is shown in Table 4.1.Table 4.1 Time Headway Frequency Distribution76
Vol.4, No.2, Juli 2016Jurnal SpektranTotal traffic flow for 1800 vehicles/hourTotal traffic flow for 1800 vehicles/hourFrequency (average & standard deviation)Frequency (average & standard deviation)206 (0.60 seconds; 0.80 second)1968 (0.53 second; 1,18 seconds)The average time headway of the totalflows for 1800 vehicles/hour and for 1800vehicles/hour are 0.60 second and 0.53 secondrespectively. As shown in Table 4.1, the roadsegment experiences high traffic flow whiletime headway is normally distributed. Timeheadway distribution therefore, is calibratedusing Normal Distribution Model which issuitable for high traffic flows. The appropriatemodel is determined using the normaldistribution density function as expressed inequation 4.1, below. The normal distributionmodel calculations are shown in Table 4.2.Z1 xb and Z2 xa .4.1where:Xa,b Upper and Lower IntervalBoundariesμ Average time headwayσ Standard deviationZ1, Z2 Z value for lower and upperboundaryTable 4.2 shows the calculation of both Z1and Z2 to determine the expected frequency forthe group of total traffic flow for 1800vehicles/hour. Each probability (P1 and P2) ofthese values are determined using the NormalDistribution table. The sum of both probabilitiesis multiplied with observed time headwayfrequency (fo) to obtain the expected timeheadway frequency (ft). These steps are alsoapplied to determine the expected frequency oftotal traffic flow group for 1800vehicles/hour. The observed and expectedfrequency distributions are validated by the chisquare method to determine the suitability ofthe model.Table 4.2 Expected Frequency of Total traffic flow for 1800 Vehicles/HourLower and UpperfoZ1Z2P1P2P1 5501.08110.47470.36020.83494.2 Model ValidationThe developed model has to be validated toanalyse goodness of fit between the observationand theoretical data. Chi square ( 2) test wereused to performed such analysis. The criteriaused are as follows:a. Hypothesis is accepted if c table, andb. Hypothesis is rejected if c table.ft9212608441234172944416198where c and table are obtained fromequation 2.1 and chi square table respectively.Hypothesis test is expressed as:a. Ho: ft fo, andb. Ha: ft fo.Where,Ho and Ha are Null and Alternate Hypothesesrespectively.Table 4.3 Chi Square Test of Total traffic flow for 1800 vehicles/hourInterval (seconds)Total traffic flow for 1800 vehicles/hourfoftfo-ft(fo-ft)2(fo-ft)2/ft77
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time headway in Indonesia remains in line to those homogeneous traffic conditions as in developed countries (Tiwari, 2000). A study on time headway
TIME HEADWAY (HEADWAY) Time headway (h): is the difference between the time the front of a vehicle arrives at a point on the highway and the time the front of the next vehicle arrives at that same point. Time headway is usually expressed in seconds The microscopic character related to volume is the time headway
A BRIEF ANNUAL MEETING OF HEADWAY OF WNY WILL START THE EVENING. The presentation is FREE for Headway members, 15 for nonmembers. Seating is limited. RSVP by phone at 408-3100 or by mailing in the form below by Nov. 13. Please tear off and return to Headway of
Headway is an important flow characteristic and headway distribution has applications in capacity estimation, driver behavior studies and safety analysis (May, 1990). The distribution of headway determines the requirement and the opportunity for passing, merging, and crossing (May, 1990). The headway distribution under capacity-flow
22 headway and the time since the start of green interval. In his model, the minimum queue discharge 23 headway is considered to happen at the end of the queue, where the discharge speed is the highest. 24 25 Headway Elongation
New Headway Upper-Intermediate Tests orkbook with further onsolidation exercises and writing tasks, a traditional methods of language teaching and more recent communicative approaches. Headstart , along with Headway taught and explained thoroughly, and all four language skills are developed systematically. The Headway series combines
New Headway Intermediate Tests orkbook with further onsolidation exercises and writing tasks, a traditional methods of language teaching and more recent communicative approaches. Headstart , along with Headway taught and explained thoroughly, and all four language skills are developed systematically. The Headway series combines
ment, if the second headway is 2 min too long, the third must be 2 min too shorl, and so on. In a statistical sense, successive headways are perfectly correlated, so that knowledge of one headway implies knowledge of the entire set. For this case, headway control will have maximum benefits. If we de
Aug 13, 2019 · CHAIN HEADWAY, we keep on pursuing to surpass the goals of speed of new item cycle, speed Speed of quality inspection, speed of delivery and speed of service. This is the value that CHAIN HEADWAY persists in most and the competitive edge that CHAIN HEADWAY most treas
