Simulatio Study of a Bus Sigal Priority Strategy Based o GPS/AVL ad Wireless Commuicatios Che-Fu Liao* Ceter for rasportatio Studies ad the Itelliget rasportatio Systems Istitute Uiversity of Miesota 200 rasportatio ad Safety Buildig 511 Washigto Ave SE Mieapolis, MN 55455 E-mail: cliao@um.edu Ph: 612-626-1697 Fax: 612-625-6381 Gary A. Davis Departmet of Civil Egieerig Uiversity of Miesota 500 Pillsbury Drive SE Mieapolis, MN 55455 E-mail: drtrips@um.edu Ph: 612-625-2598 Fax: 612-626-7750 Word Cout: Body ext (5,640) + 6 Figures ad ables (6x250) = 7,140 *Correspodig Author
Liao ad Davis 1 ABSRAC Providig sigal priority for buses has bee proposed as a iexpesive way to improve trasit efficiecy, productivity ad reduce operatio costs [1]. Bus sigal priority has bee implemeted i several US cities to improve schedule adherece, reduce trasit operatio costs, ad improve customer ride quality [2]. Curret sigal priority strategies implemeted i various US cities mostly utilize sesors to detect buses at a fixed or preset distace away from a itersectio. raditioal presece detectio systems, ideally desiged for emergecy vehicles, usually sed sigal priority request after a preprogrammed time offset as soo as trasit vehicles were detected without the cosideratio of bus readiess. he objective of this study is to take advatage of the already equipped GPS/AVL system o the buses i Mieapolis ad develop a adaptive sigal priority strategy that could cosider the bus schedule adherece, its umber of passegers, locatio ad speed. Buses ca commuicate with itersectio sigal cotrollers usig wireless techology to request sigal priority. Commuicatio with the roadside uit (e.g., traffic cotroller) for sigal priority may be established usig the readily available 802.11x WLAN or the DSRC (Dedicated Short Rage Commuicatio) 802.11p protocol curretly uder developmet for wireless access to ad from the vehicular eviromet. his paper describes our proposed priority logic, ad its evaluatio usig microscopic traffic simulatio. Simulatio results idicate that a 12-15% reductio i bus travel time durig AM peak hours (7AM-9AM) ad 4-11% reductio i PM peak hours (4PM-6PM) could be achieved by providig sigal priority for buses. Average bus delay time was reduced i the rage of 16-20% ad 5-14% durig AM ad PM peak periods, respectively. KEYWORDS rasit Sigal Priority, GPS/AVL, Wireless Commuicatio, Vehicle to Roadside Commuicatio
Liao ad Davis 2 INRODUCION Sigal Priority for trasit has bee studied ad proposed as a efficiet way to improve trasit travel ad operatio. Bus sigal priority has bee implemeted i several US cities to improve schedule adherece, reduce trasit operatio costs, ad improve customer ride quality. Sigal priority strategies have helped reduce the trasit travel time delay, as discussed i the literature [1], but the trasit travel time reductio varies cosiderably across studies [2]. Ulike sigal preemptio, which iterrupts ormal itersectio sigal process to provide high priority for special evets (emergecy vehicle or railroad crossig), trasit sigal priority (SP) modifies the ormal sigal operatio i order to accommodate better service for trasit vehicles [3]. Metro rasit i wi Cities Metro area (http://www.metrotrasit.org/) previously performed a evaluatio of providig sigal priority for buses o Lake Street i Mieapolis, usig Opticom systems [4]. A special software modificatio was made to provide trasit priority usig gree extesio ad red trucatio strategies. However, the Opticom system, ideally desiged for emergecy vehicle preemptio (EVP), was ot able to adjust the trigger timig for buses approachig earside bus stops, ad buses ofte missed the priority gree period whe they were ready to depart. Sice several itersectios alog Lake Street were already operatig at their capacity. he potetial for providig trasit priority without delayig vehicle traffic was somewhat costraied. here were also issues of buses travelig across differet muicipalities that were uwillig to provide sigal priority. Results from the previous evaluatio study were ot promisig. Bus sigal priority has also bee implemeted i several US cities (Seattle, Portlad, Los Ageles, Chicago) as well as i Europe. Various techologies have bee deployed for bus priority icludig Opticom (St. Cloud) [5], Loopcom (Los Ageles), ad RF tag (Seattle, Kig Couty) [6]. Recetly, Crout [7] at ri-couty Metropolita rasportatio District of Orego (rimet) proposed two types of aalyses (corridor ad itersectio level) to evaluate the effectiveess of the SP effort o trasit operatios over 300 sigals implemeted with sigal priority. With the istallatio of GPS system o its fleet, Metro rasit ow costatly moitorig buses locatios i relatio to their schedules, i order to provide more reliable trasit services ad ehace trasit operatio ad maagemet. Bus locatio, travel time iformatio ad other traffic iformatio ca also be itegrated ad provided for traffic operatios or to the travelig public. Metro rasit would prefer to use the already istalled GPS/AVL system as the basis of a SP system. Curret sigal priority strategies implemeted i various US cities mostly utilize sesors to detect buses at a fixed or at a preset distace away from the itersectio. Sigal priority is usually grated after a preprogrammed time-offset, after detectio. Egieers usually have to adjust the detector locatio, receiver lie of sight ad timig offset for each itersectio i order to esure its effectiveess. hese SP strategies do ot cosider the bus s speed ad its distace from itersectio whe determiig the appropriate time to request sigal priority. Wireless commuicatios systems have made rapid progress ad are commercially available. Bus iformatio (e.g. speed, locatio, umber of passegers, bus ID) ca be trasmitted wirelessly to a traffic cotroller or to a regioal raffic Maagemet Ceter (MC) for makig decisios for sigal priority. here are several wireless commuicatio systems istalled o each bus uder the curret Metro rasit setup. A 800-MHz Motorola digital voice radio is used for commuicatio betwee bus driver ad rasit Cotrol Ceter (CC). Aother 800-MHz aalog data radio is used to poll bus locatio ad passeger cout data every miute. A Wireless Local Area Network (WLAN) 802.11x is also istalled o the bus. his is used to upload/dowload files betwee the bus ad the CC cetral server, whe the bus is withi the proximity of the trasit garage. Literature Review A research group at Califoria PAH (Parters for Advaced rasit ad Highways) is pursuig a study titled Adaptive Bus Sigal Priority (ABSP) to apply a active priority strategy for buses, by icludig bus GPS iformatio, traffic detector data, ad a travel-time predictor to a adaptive model [8]. Yi et al proposed a heuristic SP algorithm to provide sigal priority to buses as well as limit egative impact o cross-street traffic [9]. raditioal SP strategies implemeted i other cities are fixed-locatio detectio systems ad implemeted with time-of-day sigal cotrol systems. SP systems usig fixed-locatio detectio mostly do ot work well with earside bus stops, due to the ucertaity i bus dwell time. Kim ad Rilett [10] proposed a weighted least squares regressio model i simulatio to estimate bus dwell time i order to overcome earside bus stop challeges. Rakha
Liao ad Davis 3 et al. [11] performed field ad simulatio evaluatio alog US Route 1 corridor. hey recommeded further cosideratio o existece of queues i trasit sigal priority strategy ad ot implemetig ear-side bus stops. A bus priority algorithm could also be itegrated ito a adaptive itersectio sigal cotrol model. Research based o the bus priority facilities available withi the Split Cycle Offset Optimizatio echique (SCOO) [12] traffic sigal cotrol system was coducted by Bretherto et al i 1996 [13]. raffic sigal priorities ca be cotrolled by a cetral SCOO computer or by a local traffic sigal cotroller. A local cotroller ca achieve faster SP respose to buses tha a cetralized cotrol. Differet strategy optios for providig bus priority at sigals are compared by McLeod & Housell [14] usig the simulatio model called Selective Priority to Late buses Implemeted at raffic sigals (SPLI). McLeod suggested that differetial (coditioal) priority strategies (e.g. gratig priority for lateess) give the best results, as these provide a good balace betwee travel time ad passeger waitig time. Furth ad Mueller [15] coducted a field study with three priority coditios (o priority, absolute priority, coditioal priority) at a trasit route i the Netherlads. he study foud absolute priority caused large delays to other traffic while coditioal priority caused little, if ay additioal delay. Dio ad Rakha [16] developed a simulatio approach to itegrate SP withi a adaptive traffic cotrol system. hey evaluate three differet sigal cotrol scearios ad foud adaptive sigal cotrol reduced egative impacts o geeral traffic while providig sigal priority to buses. Recetly, Mirchadai & Lucas [17] developed a Categorized Arrival-based Phase Reoptimizatio at Itersectio (CAPRI) strategy that itegrates trasit sigal priority withi a real-time traffic adaptive sigal cotrol system, called RHODES (Real-time Hierarchical Optimized Distributed Effective System) [18]. Weighted bus ad phase costraied approaches were developed for providig trasit priority through the RHODES-CAPRI framework. Mirchadai et al [19] proposed a hierarchical optimizatio approach where traffic sigals are determied by cosiderig delays of all vehicles o the etwork as well as bus passeger couts ad schedule while providig trasit priority (RHODES/BUSBAND). Los Ageles Couty Metropolita rasportatio Authority (MA) has implemeted wireless techology i a trasit sigal priority system alog a corridor usig IEEE 802.11b stadard. he wireless card o each bus seds IP addressable message to a access poit which covers 3~4 itersectios. A wireless cliet istalled i the sigal cabiet commuicates with modified traffic cotroller to request for sigal priority. Kig Couty MA i Washigto is also desigig wireless SP system similar to that i LA Couty. Objective With GPS/AVL system o the bus, we believe we ca provide sigal priority to buses with miimal impact o other traffic because GPS offers better iformatio regardig bus trajectory tha the sesors used previously to provide traffic sigal priority. Our objective is to ivestigate the performace of GPS ad a wireless-based adaptive sigal priority strategy to provide reliable ad efficiet bus trasit services with miimal impact o traffic flow. he improved service will hopefully make the trasit system more attractive to the public ad icrease ridership. Simulatio studies ad field measuremets will be used to estimate chages i bus travel time, as well as effects o other traffic. DEVELOPMEN OF RAFFIC SIMULAION MODEL Study Site Selectio Bus route #2, operatig o Frakli Ave from S Dupot Ave to S 27 th Ave i City of Mieapolis, was selected for the bus sigal priority study after discussios with City of Mieapolis ad Metro rasit. he Frakli corridor, located south of dowtow Mieapolis, rus i a east-west directio parallel to iterstate highway I-94, as show i Figure 1. he study sectio of the Frakli Corridor cosisted of 22 sigalized itersectios with total travel distace of about 3 miles. O the west ed, at Heepi ad Lydale Ave, Frakli Aveue provides coectio to the iterstate I-94 & I-394. oward the east side, the bus stop at south 17 th Ave coects the bus route #2 to the recetly opeed Miesota Hiawatha Light Rail rasit (LR) lie, which i tur coects the traffic from dowtow Mieapolis to the Mieapolis-St. Paul (MSP) iteratioal airport, ad to the Mall of America. Itersectio Capacity Aalysis Itersectio capacity aalyses were performed at several major itersectios o the study corridor, i order to better uderstad the existig traffic coditio. he itersectio capacity of the followig itersectios was
Liao ad Davis 4 idetified ad aalyzed: Heepi, Lydale, Nicollet, Chicago, 11 th, Cedar, ad Miehaha Aveue. raffic volume, turig movemets ad sigal timig data for each itersectio were etered i Sychro [20] to calculate itersectio delay ad Level Of Service (LOS). For the itersectios curretly havig sigificat delay, the effect o cross street traffic eeds to be carefully aalyzed whe providig bus sigal priority o Frakli Ave. Bus ravel ime Curret average travel time for buses was computed usig the per-miute bus GPS data. he data set from Metro rasit icluded 5 days of bus GPS data of route #2. A computer program was developed to extract the data collected o Frakli Ave. durig the AM ad PM peak hours. I additio to the estimates of the bus travel times from the GPS data, field observatios were performed by takig several bus trips durig both peak hours, alog Frakli Ave. he collected data were also used to calculate average travel times. hese measured bus travel times were compared to those produced by the simulatio model i order to verify the accuracy of the public trasit model used i the simulator. Bus Itersectio Delay he purpose of providig sigal priority to a trasit vehicle is to miimize its waitig time at itersectios. It is importat to kow how much time buses sped waitig at red lights as compared to their total travel times. Collectig the bus delay times at red sigals will provide iformatio o the degree of improvemet that bus sigal priority could provide to the existig bus operatio. Based o the collected data buses travelig westboud require o average about 18 miutes to traverse study site with approximately 210 secods of delay at red sigals. Buses travelig i the eastboud directio sped about 20 miutes i average, icludig about 260 secods of sigal delay per trip. By comparig the average itersectio delay to the average bus travel time, a bus geerally spet o average aroud 18% to 23% of its travel time (3.3~4.8 miutes) waitig for gree lights at itersectio alog Frakli Aveue. Bus Dwell ime Bus dwell time at each bus stop cosists of the boardig/alightig of passegers, door opeig/closig ad clearace time. he per-miute bus GPS data provided by Metro rasit does ot provide sufficiet resolutio for us to calculate ad estimate the bus dwell time at each bus stop. Also, Metro rasit was ot able to provide passeger couts at the time of this study usig the APC (automatic passeger cout) uit itegrated with the bus GPS/AVL data collectio system alog Frakli Aveue. However, Metro rasit coducted passeger boardig/alightig couts at every bus stop alog bus route #2 from 6AM to 12AM durig 2000 ad 2001. Bus dwell time at each stop ca therefore be calculated usig the recommeded formulas from rasit Capacity ad Quality of Service Maual [21]. raffic Simulatio A microscopic traffic simulatio package, AIMSUN (Advaced Iteractive Microscopic Simulator for Urba ad No-urba Networks, http://www.aimsu.com) [22] was selected for this study. AIMSUN icludes a Applicatio Programmig Iterface (API) to allow iterfacig to other simulatio or assigmet models. A additioal library of DLL (Dyamic Lik Library) fuctios eables the system to commuicate with exteral applicatios [22, 23]. AIMSUN has bee used successfully for several large-scale traffic modelig research projects [24] ad provides a well-documeted API to access ad modify all elemets of the simulatio state (sigal cotrol, sesig, vehicle characteristics ad state), while the simulatio is ruig. A C++ program was developed to iterface with the microsimulator through the API. Bus locatio, speed, ad bus stop iformatio ca be set to the exteral bus sigal priority applicatio, ad a priority request ca be set back to the simulator, i real-time. Digital Orthophotos Quad aerial images (DOQs) aroud Frakli Aveue were acquired from wi Cities Metropolita Coucil (http://www.datafider.org/metadata/orthos2000.htm). he aerial images were the used to create the arterial etwork geometry for the AIMSUN simulatio model. Bus route ad bus stop locatios were selected ad specified i the etwork geometry ad bus dwell time statistics were etered i the trasit model. Itersectio sigal timig ad phase assigmets were specified i the sigal cotrol model. hree differet vehicle types, passeger car, light truck, ad bus, were icluded i the simulatio model. he 15-miute traffic volume ad turig proportios collected at each itersectio were etered. Before eterig the traffic volume iputs at the boudary liks ad the turig ratio at each itersectio, the collected traffic couts were adjusted to satisfy the traffic flow coservatio priciple. Sigalized itersectio traffic couts were obtaied from City of Mieapolis, while traffic volumes at u-sigalized itersectio were collected o 20 differet weekdays for this study. he
Liao ad Davis 5 icosistecies betwee the etwork iflow ad outflow must the be balaced before applyig the data to ay traffic operatio aalysis. A arterial traffic volume balace techique is used by Miesota Departmet of rasportatio (MDO), icludes itersectios o both sides of a o-ramp or off-ramp itersectio, whe coductig highway traffic simulatio. raffic volume ad turig movemets at arterial itersectios are ofte collected o differet days ad differet days of the week, ad these traffic volumes eed to be adjusted to coserve the iflow ad outflow traffic at each lik. By adjustig the arterial traffic volume from upstream to dowstream itersectios i both directios recursively, the arterial etwork traffic volume will reach a equilibrium state. A Java program was developed to read a text file with itersectio traffic volume data fileames listed sequetially. he program the reads all itersectio traffic volume data i JAMAR [25] data format from a specified directory ad automatically computes the adjustmets iteratively util the total traffic volume balaced. Whe the itersectio traffic data were balaced ad etered i the AIMSUN simulatio model for each 15- miute iterval, a error-checkig task was performed by ruig a trial simulatio i order to visually idetify ay uusual traffic coditios. For example, icorrect itersectio sigal phasig or offset may cause uusual queue buildup. A workig model of Frakli Aveue is available for calibratio upo the completio of the error-checkig tasks. he traffic simulatio model ca oly iclude a portio of all parameters that affect the real-world traffic coditios. he calibratio process helps improve the ability of traffic model to accurately reproduce the local traffic coditios [26]. ADAPIVE BUS SIGNAL PRIORIY SRAEGY o illustrate our priority strategy, cosider a simple eastboud/westboud corridor as show i Figure 2. For a bus approachig a bus stop or sigalized itersectio, there are basically two scearios, a earside bus stop or a farside bus stop. For the earside bus stop, a bus will stop for boardig/alightig before passig the sigalized itersectio, as illustrated i Figure 2 by the eastboud bus approachig stop j ad itersectio i. Estimated bus dwell time at the earside bus stop eeds to be cosidered by the sigal cotroller to provide sigal priority to the bus i a timely maer. For the far-side bus stop, a bus passes through the itersectio first before its arrival at the stop (see Figure 2 westboud bus approachig itersectio i ad bus stop k). Bus travel time to the itersectio eeds to be cosidered whe providig priority. Nearside Bus Stop Cosider the bus travelig i the eastboud as show i Figure 2. Expected bus dwell time, dj, at bus stop j ca be forecasted usig historical dwell time statistics. Expected bus travel time, aj, from its curret locatio to bus stop ca be calculated via, Where, de, j aj = + br + 1. 467 v b delay v b : is bus speed, i MPH, : is the distace from the curret bus locatio to bus stop j, i feet, d e, j br : is bus brakig/stoppig time, ad : is the traffic delay o bus route. delay he expected bus travel time ( ji ) from bus stop j to itersectio i ca also be calculated as follows, assumig the distace from the earside bus stop to the itersectio is relatively short compared to the distace eeded to accelerate to ruig speed. (1)
Liao ad Davis 6 Where, 2 ( d e, i d e, j ) ji = + a bc d e, i : is the distace from eastboud bus to itersectio i (ft), d e, j : is the distace from eastboud bus to bus stop j (ft), a : is the bus acceleratio i ft/s/s, ad : is the bus clearace time. bc (2) herefore the predicted time at which the eastboud bus passes itersectio i ca be calculated as follows. t ˆ ei = t + aj + dj + ji (3) Where, t : is the curret time, sec. Ad estimated time for the bus leavig stop j is, t ˆ lj = t + aj + dj (4) he desired sigal priority request should the be set at secods prior to the bus departure time at stop j. hat is, at time ˆ, where t lj = t + t + t (5) t cp t comm t cost cp comm cost : is the cotroller processig time, : is the commuicatio latecy time, ad : is a additioal time costat. t ˆ ei + xi, where xi he sigal priority service should be eded at is the time for the bus to cross itersectio i. If both begiig ( tˆ lj ) ad edig ( t ˆ ei + xi ) of the estimated priority service fall withi the gree split, o actio eeds to be take at the cotroller. If tˆ lj falls i the gree split ad t ˆ ei + xi falls i the red split, exteded gree time is eeded to esure that bus could pass the itersectio. However, if the estimated begiig of priority service time ( tˆ lj ) falls withi the red light period, red sigal trucatio or early gree light treatmet is eeded to provide bus sigal priority. Far-side Bus Stop For a bus approachig a itersectio prior to its arrival at ext bus stop, for example, the bus travelig i westboud as show i Figure 2, sigal priority should be provided based o bus travelig speed ad traffic coditios. he estimated time ( ) to arrive at itersectio i ca be calculated as, Where, ai d w i =, ai + 1. 467 vb delay d w, i : is the distace from westboud bus to itersectio i (ft), v b : is bus speed i MPH, ad delay : is the traffic delay o bus route. herefore the estimated time for westboud bus passig itersectio i ca be calculated as follows. (6)
Liao ad Davis 7 Where, ˆ (7) t = t + wi ai t : is the curret time, sec. he desired sigal priority would eed to begi at secods prior to the bus arrivig itersectio i ( tˆ wi ), where is defied as equatio (5). he sigal priority service ca be eded at t ˆ wi + xi, where xi is the time for bus to cross itersectio i. If both begiig ( tˆ wi ) ad edig ( t ˆ wi + xi ) of the estimated priority service fall withi the gree split, o actio eeds to be take by the cotroller. If ˆ falls i the gree split ad t ˆ + wi xi falls i the red split, exteded gree time is eed to esure bus could pass the itersectio. However, if tˆ the estimated begiig of priority service time ( wi ) falls withi the red light period, red sigal trucatio or early gree light treatmet is eeded to offer bus priority. Estimatio of Passeger Arrival Rate at Bus Stop Estimated passeger arrival rates will be used to forecast bus dwell time at each stop. Based o the collected data, we assume the passeger arrivals at each stop follow a Poisso distributio with a arrival rate,, calculated from the mea of the collected passeger arrival rate. A Poisso process subroutie was developed to geerate umbers of passegers boardig ad alightig at each stop durig the simulatio. t wi Estimatio of Bus Dwell ime at Bus Stop Bus dwell time at a bus stop for boardig ca be estimated usig the followig equatio. Where, B dj [ tk ( j) tk ( j ] boardig = ) (8) j ( t) 1 B dj is the bus dwell time for boardig at stop j, j (t) is the passeger arrival rate for stop j, t k ( j) is the arrival time of bus k at stop j, ( ) t k 1 j is the arrival time of bus k-1 at stop j, ad is the average boardig time per passeger. boardig Priority Ackowledgemet Rules After receivig a sigal priority request from a bus, the sigal cotroller has to determie whether or ot to grat the request. Oly oe bus will get the priority service if there are multiple requests at the same itersectio from buses o differet approaches. he sigal cotroller will igore all bus priority requests if there is a emergecy vehicle preemptio request. he sigal cotroller will cosider the followig three compoets whe determiig which bus will receive the priority service. 1. Priority request time, ime Factor (F) F ( A, B) A = W, B = 1 = A = 1, B = W Bus A wis if it requests earlier tha bus B does, where 2. Bus schedule adherece, Lateess Factor (LF) LF = W L Late t t A A < t > t B B W is the request time weightig factor ( 1 W ).
Liao ad Davis 8 Where W L is the bus late time weightig factor ( L 1 = late. LF 0 whe bus is ahead of its schedule. W ) ad Late is the umber of miute the bus was 3. Number of passegers o the bus, Passeger Factor (PF) PF = W P N passeger Where W P is the bus passeger cout weightig factor ( W P 1) ad N passeger passegers o the bus. is the umber of he priority ackowledgemet fuctios for bus A ad B are defied as follows. f ( A) = F( A, B) { LF( A) + PF( A)} f ( B) F( A, B) { LF( B) + PF( B)} = (9) If the priority ackowledgemet fuctio f(a) is greater tha f(b), bus A will be grated for sigal priority. No sigal priority request is grated if the ackowledge fuctio f equals zero, which meas there is o passegers o the bus ad o delay o bus schedule adherece. Gree Extesio ad Red rucatio he projected sigal phase estimated arrival time for a bus passig a sigalized itersectio ca be calculated usig the equatios discussed i the previous sectio. Whe the projected sigal phase coicides with the priority phase, which is the phase where a bus requires passig through a itersectio, gree extesio is cosidered if the remaiig gree time is isufficiet. However, if the projected arrivig phase is differet from the priority phase, phase arragemet, such as phase suppressio or red trucatio, is eeded to provide gree time to the buses. A miimum gree time has to be served prior to termiatig the phase. Sigal Recovery/Resychroizatio Cosideratio It has bee a cocer to retur the itersectio timig back to its coordiatio ofte providig sigal priority to buses. Some priority strategies require may cycles before the sigal timig is resychroized to its regioal coordiatio [27]. Recetly, a advaced cotroller provides the sigal priority recovery with a cycle by icludig optioal trasit phases i the timig pla [28]. Our bus sigal priority strategy will resychroize to its eighbor itersectios i the ext cycle by reducig the amout of gree time exteded i the ext cycle priority phase. Sigal priority requests i the followig cycle will be igored i order to facilitate coordiatio recovery. For example, if the request from bus A or B i cycle i was grated at a itersectio, priority requests from bus C ad D will ot be cosidered because cycle i+1 will be used for coordiatio recovery. Bus Sigal Priority Modelig i the Simulator he priority strategy was implemeted usig the C++ programmig laguage ad itegrated with the simulator through the AIMSUN API iterface. At each simulatio step, the bus locatio ad its distace correspodig to the ext bus stop ad sigalized itersectio were calculated to idetify a earside versus a far side bus stop sceario. he cotrol diagram for the priority strategy is show i Figure 3. Bus dwell time at each stop was computed based o the passeger arrival usig the Poisso distributio. Bus travel times to the itersectio ad the bus stop were calculated to determie whe to submit priority request prior to its arrival at the sigalized itersectio. Sigal Cotrol Model A exteral sigal cotrol logic was programmed to emulate the gree extesio ad red trucatio fuctioality. I order to esure that the itersectio returs back to its timig pla prior to the priority request ad remais coordiated with the eighborig itersectios, sigal timig recovery ad resychroizatio were also cosidered. For example, exted gree ad maitai coordiatio, early gree or red trucatio, ad phase isertio ad coordiatio recovery i the ext cycle. SIMULAION RESULS ANALYSIS raffic data produced by the simulatio model were used to compare the measures of effectiveess of the sigal priority strategy. System statistics as described i the AIMSUN User s Maual are defied as follows.
Liao ad Davis 9 Flow: Average umber of vehicles per hour that have passed through the etwork durig the simulatio period. Average ravel time: Average time a vehicle eeds to travel oe kilometer iside the etwork. Average Delay ime: Average delay time per vehicle per kilometer. his is the differece betwee the expected travel time (the time it would take to traverse the system uder ideal coditios) ad actual travel time. Average Stops: Average umber of stops per vehicle per kilometer. he overall statistics of the simulatio etwork without applyig sigal priority strategy were first collected. Durig the PM peak period (4-6PM), traffic is much heavier tha that i the morig hours (7-9AM). here were about 40% icreases of traffic flow i PM peak hours. he PM average speed i the system dropped by 9%, from 19.8 to 18 MPH, as compared to the AM peak period. he average travel time, delay time ad umber of stops per vehicle i the afteroo rush hours also icreased by about 21%, 31.7%, ad 25% respectively. Bus Measures of Effectiveess (MOE) Aalysis Bus average speed, travel time, ad stop time were collected durig simulatios to measure the effectiveess with ad without priority strategy. hese measures are defied as follows. Bus ravel time: Average time it takes for a bus to travel alog a public trasport lie. his is the mea of all the sigle travel times for each bus. Bus Delay ime: Average delay time per bus to make the trip. his is the differece betwee the expected travel time (time it takes to go from the origi to the destiatio uder ideal coditios) ad the actual travel time. Bus Stop ime: Average time spet at a stop per bus durig the trip. AM Peak By applyig the sigal priority strategy, the bus travel time was reduced by about 12% i EB ad 14% i WB, respectively. Bus delay time was reduced by about 16%~19% ad the stop time was reduced aroud 18% as well. PM Peak here was about a 40% icrease i traffic flow durig the PM peak hours. Bus statistics from the simulatio with ad without sigal priority strategy are listed i able 1 for PM peak hours. Bus travel time ad speed are also plotted i Figure 4. I the PM peak hours, it took about 22(23) miutes for a EB (WB) bus to travel betwee Heepi Ave ad 27 th Ave o Frakli Ave without sigal priority. By applyig the sigal priority strategy for the buses, the bus travel time was reduced by about 2 miutes i EB ad 1.5 miutes i WB directio, or 10.5% i EB ad 7% i WB, respectively. Bus delay time was reduced by about 9%~14% ad the stop time was reduced aroud 10%~14% as well. As the simulatio results show, the sigal priority strategy durig the PM peak hours provided relatively less travel time reductio i WB (about 1-miute less) as compared to the AM sceario. here were mostly earside bus stops at our study site. Durig the PM peak hours, there were loger queues at itersectios from 11 th Ave to Cedar Aveue, so that a bus was ot able to get i to its service bay whe it approached a queue at the itersectio. he bus stuck behid the queue had to wait util the queue cleared at the ext gree i order to provide service. Also, whe there was a queue built up durig the bus service period at a earside bus stop, the bus had to wait to fid a acceptable gap i order to joi the traffic. he priority request will help clear the queue to reduce bus clearace time. However, if kowledge of the queue legth could be obtaied ad processed to submit a priority request earlier, the bus waitig time could be reduced durig the busier PM period. Future ehacemets to the priority strategy ca iclude cosideratio of queue detectio at the itersectio. Overall Network System MOE Aalysis he measures of effectiveess for the whole etwork were obtaied for the simulatio period. AM Peak Network system statistics from the simulatio with ad without the sigal priority strategy are listed i able 2 for the AM peak hours. here was about a 7 secods icrease i average travel time. Average delay icreased by 6 secods for the 15-sec extesio sceario. he average umber of stops per vehicle was icreased by 0.1 stop per vehicle for both cases. PM Peak
Liao ad Davis 10 As a result of heavier traffic flow durig the PM peak hours, the overall etwork statistics from the simulatio with ad without sigal priority strategy geerated loger delay ad more vehicle stops. As listed i able 2, the travel time durig the PM period was icreased by 22 secods per kilometer whe providig sigal priority. Average delay was icreased by 23 secods while average stops icreased by 0.6 stop per vehicle with the priority strategy. FUURE WORK We would like to ivestigate the 800 MHz radios ad WLAN (Wireless Local Area Networks) systems already equipped o the bus. A voice radio o the bus is liked to a regioal 800MHz digital voice commuicatio system. Metro rasit Cotrol Ceter uses aother aalog 800 MHz radio to poll bus GPS data every miute. I additio, each bus has a wireless commuicatio system that is used to dowload/upload files betwee the cetral server ad the bus computer whe the bus is withi proximity of the bus garage. We would like to ivestigate the possibility of itegratig a sigal priority strategy usig oe of the existig commuicatio systems o the bus with the traffic cotroller. We also pla to develop a prototype system to validate the bus sigal priority algorithm usig wireless commuicatio techology i the secod phase study. We also would like to work with Metro rasit ad City of Mieapolis to discuss the potetial opportuity of bus sigal priority deploymet. Metro rasit is plaig the Northwest Corridor (Bottieau Corridor) project so as to iclude a bus way that will offer high-quality trasit service from dowtow Mieapolis through Crystal, Brookly Park, Maple Grove ad Rogers (http://www.metrotrasit.org/improvigrasit/orthwestcorridor.asp). I this project, bus sigal priority will be cosidered i order to improve bus travel time ad reduce bus delay at sigalized itersectios. rasit Sigal Priority coceptual desig alog Bottieau Corridor is curretly beig ivestigated by SEH Ic. (http://www.sehic.com/). he visio of the VII (Vehicle Ifrastructure Itegratio, http://www.its.dot.gov/vii/idex.htm) is to deploy a atiowide etwork that eables commuicatios betwee vehicles ad roadside ifrastructure for various trasportatio operatios ad applicatios. Sigal priority requests for trasit or emergecy vehicles ca potetially be set to the sigal cotroller through the vehicle-to-ifrastructure commuicatio architecture described i VII. Commuicatio with the roadside uit (e.g., traffic cotroller) for sigal priority may be established usig the existig 802.11x WLAN o the bus or the DSRC (Dedicated Short Rage Commuicatio) 802.11p protocol curretly uder developmet for wireless access to ad from the vehicular eviromet. Work i ext phase will cocetrate first o the more readily available protocols. However the system will be desiged so that it ca be ported to the ew 802.11p protocol whe it becomes more readily available. ACKNOWLEDGEMEN We would like to thak the Itelliget rasportatio Systems (IS) Istitute ad Ceter for rasportatio Studies, Uiversity of Miesota, for supportig this project. he IS Istitute is a federally fuded program admiistrated through the Research & Iovative echology Admiistratio (RIA). We also would like to thak Scott achey at City of Mieapolis public works, Aaro Isaac ad Gary Nyberg at Metro rasit ad may others for their ivaluable assistace, ad graduate studet Hu-We ao for collectig the field data. REFERENCES [1] A Overview of rasit Sigal Priority, prepared by Advaced raffic Maagemet Systems Committee ad Advaced Public rasportatio Systems Committee of the IS America, 2002 [2] Collura, J., Rakha, H., ad Gifford, J., Guidelies for the Plaig ad Developmet of Emergecy Vehicle Preemptio ad rasit Priority Strategies, Prepared by the Virgiia ech rasportatio Istitute ad George Maso Uiversity School of Public Policy, 2003. [3] A Overview of rasit Sigal Priority, prepared by Advaced raffic Maagemet Systems Committee ad Advaced Public rasportatio Systems Committee of the IS America, revised ad updated 2004 [4] 3M Opticom Priority Cotrol System, http://www.3m.com/its [5] St. Cloud Metropolita rasit Commissio rasit Priority Evaluatio Report, Fial Report, Nov. 2000
Liao ad Davis 11 [6] A Evaluatio of rasit Sigal Priority o Aurora Aveue North, rasit Speed ad Reliability Program, Kig Couty Departmet of rasportatio, Sep. 2002 [7] Crout D.., Evaluatio of rasit Sigal Priority at the ri-couty Metropolita rasportatio District of Orego (rimet), Proceedigs of the 12 th Aual World Cogress o IS Systems, Nov. 6-10, Sa Fracisco, CA, 2005 [8] Liu, H., Skabardois, A., Zhag, W.B., A Dyamic Model For Adaptive Bus Sigal Priority, Preseted at rasportatio Research Board 82 d Aual Meetig, Washigto DC, Jauary 2003. [9] Li, M., Yi, Y., Zhou, K., Zhag, W.B., Liu, H., ad a, C.W., Adaptive rasit Sigal Priority o Actuated Sigalized Corridors, rasportatio Research Board 84 d Aual Meetig, Washigto DC, Jauary 2005. [10] Kim, W. ad Rilett, L.R., A Improved rasit Sigal Priority System for Networks With Nearside Bus Stops, preseted at rasportatio Research Board 84 th Aual Meetig, Washigto, DC, Jauary 2005. [11] Rakha, H., Ah K., ad Collura J., rasit Sigal Priority Project Alog Route 1: Lessos Leared, Virgiia rasportatio Research Coucil, Charlottesville, Virgiia, Feb. 2006, VRC 06-CR. [12] Split Cycle Offset Optimisatio echique (www.scoot-utc.com/scoofacilities/busprior.htm) [13] Bretherto, R.D., Housell, N.B., ad Radia, B., Public rasport Priority i SCOO, Proceedigs of the 3 rd Aual World Cogress o IS Systems, Oct. 14-18, Orlado, FL, 1996 [14] McLeod, F. ad Housell, N., Bus Priority at raffic Sigals Evaluatig Strategy Optios, Joural of Public rasportatio, V6, No.3, 2003 [15] Furth, P.G. ad Mueller,., Coditioal Bus Priority at Sigalized Itersectios, Preseted at 79 th Aual Meetig of the rasportatio Research Board, Washigto DC, 2000. [16] Dio F. ad Rakha H., Itegratio of rasit Sigal Priority Withi Adaptive raffic Cotrol Systems, rasportatio Research Board 84 d Aual Meetig, Washigto DC, Jauary 2005. [17] Mirchadai, P.B. & Lucas, D.E., Itegrated rasit Priority ad Rail/Emergecy Preemptio i Real- ime raffic Adaptive Sigal Cotrol, Joural of Itelliget rasportatio Systems, Vol. 8 Issue 2, p101-115, April 2004. [18] Mirchadai, P.B. & Head, K.L., A real-time traffic sigal cotrol system: Architecture, algorithms ad aalysis, rasportatio Research Part C, 9, 415-432, 2001 [19] P B. Mirchadai, A. Kyazya, K.L. Head, ad W. Wu, A Approach owards the Itegratio of Bus Priority, raffic Adaptive Sigal Cotrol, ad Bus Iformatio/Schedulig Systems, Computer-Aided Schedulig of Public rasport, Spriger-Verlag, Germay, 319-334, 2001. [20] Sychro, traffic sigal coordiatio software by rafficware Corporatio, Albay, CA. http://www.trafficware.com/ [21] rasit Cooperative Research Program (CRP) Report 100: rasit Capacity ad Quality Service Maual, 2 d Editio Part 4: Bus rasit Capacity, Chapter 1, Bus Capacity Fudametals, pp. 4-3 ~ 4-9. http://trb.org/ews/blurb_detail.asp?id=2326 [22] AIMSUN Versio 4.1 User s Maual, rasport Simulatio Systems (SS), Barceloa, Spai, Mar. 2002. [23] GERAM Extesios Versio 4.1 User s Maual, SS, Barceloa, Spai, Mar. 2002. [24] Hourdakis, J., Michalopoulos, P. ad J. Kottommail. Practical procedure for calibratig microscopic traffic simulatio models rasportatio Research Record 1852: pp. 130-139, 2003. [25] JAMAR Had-held traffic data collector, DB-400, Horsham, PA. http://www.trafficcouter.com/ [26] raffic Aalysis oolbox Volume III: Guidelies for Applyig raffic Microsimulatio Modelig Software, Federal Highway Admiistratio, FHWA-HR-04-040, McLea, VA, July 2004 [27] SEPAC Actuated Sigal Cotrol Software, User s maual, Eagle raffic Cotrol Systems, Feb. 2002. [28] Eagle EPAC M50 raffic Cotrol Uit, http://www.itssiemes.com/e/t_av282.html
Liao ad Davis 12 List of Figures Figure 1. Figure 2. Figure 3. Figure 4. Bus Sigal Priority Study Site Frakli Ave From Dupot to 27 th Ave A East-West Corridor Example for Sigal Priority Cotrol Diagram of Bus Sigal Priority Strategy AM ad PM Peak Bus Speed ad ravel ime List of ables able 1. able 2. AM ad PM Peak Bus Statistics Overall Network Statistics
Liao ad Davis 13 Dupot Ave. 27th Ave o I-94 & I-394 I-35W I-94 Hiawatha LR Figure 1. Bus Sigal Priority Study Site Frakli Ave From Dupot to 27 th Ave * Figure 2. A East-West Corridor Example for Sigal Priority * Map adopted from MapQuest, Ic. (http://www.mapquest.com/)
Liao ad Davis 14 Figure 3. Cotrol Diagram of Bus Sigal Priority Strategy
Liao ad Davis 15 AM Peak Bus Speed AM Peak Bus ravel ime Average Speed MPH 11 10.5 10 9.5 9 8.5 8 9.1 9.2 10.4 10.7 ravel ime 0:20:10 0:19:26 0:18:43 0:18:00 0:17:17 0:16:34 0:15:50 0:15:07 0:14:24 0:19:53 0:19:02 0:17:30 0:16:27 No Priority With Priority No Priority With Priority EB WB EB WB PM Peak Bus Speed PM Peak Bus ravel ime Average Speed MPH 9.5 9 8.5 8 7.5 7 8.3 7.7 9.2 8.3 ravel ime 0:24:29 0:23:02 0:21:36 0:20:10 0:18:43 0:17:17 0:15:50 0:21:58 0:22:41 0:19:39 0:21:03 6.5 0:14:24 No Priority With Priority No Priority With Priority EB WB EB WB Figure 4. AM ad PM Peak Bus Speed ad ravel ime
Liao ad Davis 16 Public rasit, Priority Extesio ime = 15 sec AM PEAK Speed Bus ravel ime Bus Delay ime Bus Stop ime Bus Statistics MPH hh:mm:ss hh:mm:ss hh:mm:ss No EB 9.1 0:19:53 0:14:49 0:10:05 Priority WB 9.2 0:19:08 0:14:08 0:09:30 With EB 10.4 0:17:30 0:12:26 0:08:17 Priority WB 10.7 0:16:27 0:11:27 0:07:50 Average EB 1.30-0:02:23-0:02:23-0:01:48 Chage WB 1.50-0:02:41-0:02:41-0:01:40 Average EB 14.29% -11.99% -16.09% -17.85% Chage % WB 16.30% -14.02% -18.99% -17.54% Public rasit, Priority Extesio ime = 15 sec PM PEAK Speed Bus ravel ime Bus Delay ime Bus Stop ime Bus Statistics MPH hh:mm:ss hh:mm:ss hh:mm:ss No EB 8.3 0:21:58 0:16:55 0:10:14 Priority WB 7.7 0:22:41 0:17:41 0:10:10 With EB 9.2 0:19:39 0:14:35 0:09:15 Priority WB 8.3 0:21:03 0:16:02 0:08:47 Average EB 0.90-0:02:19-0:02:20-0:00:59 Chage WB 0.60-0:01:38-0:01:39-0:01:23 Average EB 10.84% -10.55% -13.79% -9.61% Chage % WB 7.79% -7.20% -9.33% -13.61% able 1. AM ad PM Peak Bus Statistics Overall Network System, Priority Extesio ime = 15 sec AM PEAK Speed Avg. ravel ime Avg. Delay ime Avg. Stops Network Statistics MPH hh:mm:ss hh:mm:ss #/veh No Priority 19.8 0:01:35 0:01:00 1.60 Priority 19.1 0:01:42 0:01:06 1.70 Average Chage -0.70 0:00:07 0:00:06 0.10 Overall Network System, Priority Extesio ime = 15 sec PM PEAK Speed Avg. ravel ime Avg. Delay ime Avg. Stops Network Statistics MPH hh:mm:ss hh:mm:ss #/veh No Priority 18.1 0:01:55 0:01:19 2.00 Priority 16.0 0:02:17 0:01:42 2.60 Average Chage -2.10 0:00:22 0:00:23 0.60 able 2. Overall Network Statistics