Exploring Impacts of Countdown Timers on Queue Discharge Characteristics of Through Movement at Signalized Intersections

Transcription

1 Avilble online t ScienceDirect Procedi - Socil nd Behviorl Scienc es 96 ( 2013 ) th COTA Interntionl Conference of Trnsporttion Professionls (CICTP 2013) Exploring Impcts of Countdown Timers on Queue Dischrge Chrcteristics of Through Movement t Signlized Intersections Sun Wenbo, He Zhocheng *, Xi Xi, Xu Feifei Reserch Center of Intelligent Trnsporttion System, Sun Yt-sen University, Gungzhou , Gungdong Prov., Chin Abstrct Red signl countdown timer cn show drivers the time remining until the onset of the green phse. Drivers witing in the queue t the intersection re wre of the upcoming green phse strt, nd re likely to respond more quickly. Thus, countdown timer cn influence the queue dischrge chrcteristics in green phse. This study investigtes how countdown timer ffects the queue dischrge chrcteristics of through movement during the green phse. Hedwy dt ws collected by wtching trffic surveillnce video of two signlized intersections in GungZhou before nd fter the countdown timers instlled. It ws found tht countdown timer hd n impct on the sturtion hedwy, reducing it by 5% bove, so did the stndrd devition of the whole hedwys. Tht mkes 5% bove increse in trffic cpcity of through movement. However, the effects on the first vehicle to sustin sturtion hedwy were found to be trivil The Authors. Published by Elsevier by Elsevier Ltd. Open B.V. ccess under CC BY-NC-ND license. Selection nd nd/or peer-review peer-review under responsibility under responsibility of Chinese of Overses Chinese Trnsporttion Overses Trnsporttion Assocition (COTA). Assocition (COTA). Keywords:countdown timer;hedwy;queue dischrge;queue dischrge chrcteristics; signlized intersection; cpcity 1. Introduction It is generlly believed tht with the red signl countdown device, drivers cn know the onset of the green phse nd get redy for strting their cr in dvnce, so tht it my reduce the strt-up lost time, decrese the sturtion hedwy, nd increse the sturtion flow rte t the signlized intersections. However, there hve been only smll number of studies investigting this behviour, nd the results re still mixed. Mny scholrs minly focus on the impct of countdown timers on rod sfety nd ccident prevention spects. Only few reserchers ttempted to investigte the impct of the signl timer on the dischrge of queued vehicles during the beginning of the green phse. Gong Xuexue (2010) studied the effect of countdown timers on trffic opertion t signlized intersections. The study compred the chnges of the hedwy of queue dischrge t two different signlized intersections nd therefore it could not exclude the interference of other fctors like rod condition nd * Corresponding uthor. Tel.: ; fx: E-mil ddress: hezhch@mil.sysu.edu.cn The Authors. Published by Elsevier Ltd. Open ccess under CC BY-NC-ND license. Selection nd peer-review under responsibility of Chinese Overses Trnsporttion Assocition (COTA). doi: /j.sbspro

2 256 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) trffic composition. Kidwi et l. (2005) nlyzed vehiculr dischrge t non-cbd intersection in Mlysi, before nd fter the instlltion of the countdown timer. The study found the unexpected result tht the verge throughput (in units of pcu/h) reduced fter the instlltion, which contrdicted the presumption of the reserchers. However, the sttisticl tests performed show no significnt difference between the without timer nd the with timer conditions t 95% confidence intervl. T Limnond et l. (2009, 2010) conducted before-nd-fter study of this type of device t n intersection in Thilnd. They found tht the countdown timers helped reduce the strt-up lost time on the through movement nd improve the flow of the through movement during the green phse, but it did not consider the impcts of countdown timers on the fluctutions of the dischrge hedwys. Ibrhim et l. (2008) ttempted to nlyze the impct of the countdown timer on trffic flow by compring the queue dischrge ptterns between three intersections with signl timers nd three intersections without signl timers in Mlysi. Their grphicl nlysis showed tht the men hedwys for the first six vehicles in the queue t the intersections with countdown timers were less thn the men hedwys of the corresponding six positions t the intersections without countdown timers. The study concluded tht the countdown timer hd significnt effect on the dischrge hedwy of the first six vehicles in the queue, though there ws no corresponding sttisticl nlysis used to prove the findings. In conclusion, studies of the impct of countdown timers on queue dischrge ptterns re scrce, focus on one geo-grphic re, yet produced mixed results. The objective of this reserch is to explore the effect of countdown timers on queue dischrge chrcteristics of through movement t signlized intersections in Gungzhou. By ignoring the impct of pedestrin, dt collections re crried out t signlized intersections in Gungzhou before nd fter the instlltion of countdown timers. Finlly this pper nlyzes the chnge of cpcity, hedwy nd sturtion hedwy to figure out the impct of countdown timers on queue dischrge chrcteristics. 2. Methodology In generl, vehicles wit in queue before the stop lines when the light is red, s Fig.1 shows. After the light turns green, vehicles in the queue will strt crossing the stop line nd the dischrge hedwy is the time tht elpses between such consecutive vehicles. Fig. 2 displys conceptul hedwy pttern of the vehicles in the stnding queue when the pproch receives green phse. The first few vehicles in the queue generlly tke few extr moments to think nd rect to the signl chnge before proceeding through the intersection. The hedwy of successive vehicles grdully decreses until it finlly reches reltively stbilized intervl through the rest of the queue. This stble intervl is referred to the sturtion hedwy. It is usully suggested tht the fifth vehicle is the strt of the sturtion hedwy (Trnsporttion Reserch Bord, 2000), however, this vrible strongly depends on mny loclity fctors, such s driving culture, rod condition nd driver perception. Figure 1. Queue t signlized intersection entrnce

3 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) Hedwy/s ith hedwy in the stnding queue Figure 2. Hedwys of vehicles in the stnding queue Some reserchers studied the distributions of the dischrge hedwy with their observed dt, including negtive exponentil distribution, shifted exponentil distribution, Erlng distribution, Person distribution, norml distribution, logrithmic norml distribution, Bunched index distribution nd double shifted exponentil distribution. They found tht few models cn ccord with the mesured hedwy, but the rest hedwys were found to ccord with logrithmic norml distribution well when the reserchers excluded the first hedwy (Jin, 2009; Jin, 2009; Sho, 2003). This reserch does sttisticl nlysis, depending on bove studies. According to the Trffic Engineering (Wng, 2000), the cpcity of through movement cn be clculted by the formul s below: C s t t t 3600 ( g 0 1) T where C s is the cpcity of through movement, T is the signl cycle, t g is the green time, t 0 is the verge time from the first vehicle strting to crossing the stop line, t i is the verge hedwy nd is reduction coefficient. In order to simplify the clcultions nd compre the effect of the countdown timer to the cpcity conveniently, we set the vlue of t 0 to 0 nd to 1. The sturtion flow rte in this study ws determined on the bsis of the conventionl pproch, presented in the Highwy Cpcity Mnul. This reserch utilized series of the stndrd t-sttistics tests, similr to previous studies of Joseph nd Chng (2005) nd Rksutorn(2004), to firstly identify the order of the vehicle in the queue tht first sustins the sturtion hedwy, then sturtion flow rte cn be chieved. The detiled procedure is s follows: Before using t-test, let s define tht H i is the men hedwy of the ith vehicle in the queue from the mesurements of few signl cycles, which is estimted s: Ci Hix x 1 Hi C i where Hix is the hedwy of the ith vehicle in the queue mesured from the xth cycle; Ci (), the number of the signl cycles which hve the ith hedwy. Then H i is ssumed to be the verge hedwy ccumulted from the ith vehicle to the lst vehicle in the stnding queue of ll Ci () cycles, nd qx ( ) is the number of hedwys of the xth cycle. i (1)

4 258 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) For exmple, H 1 Ci qx ix x 1 i i Ci qx H x 1 i H i is the verge hedwy of ll vehicles in the stnding queue (ccumulted from the first vehicle to the lst vehicle in the queue, estimted from few cycles), or H refers to the verge hedwy ccumulted from the third vehicle to the lst vehicle in the stnding queue. The identifiction of the ith vehicle in the queue tht begins to experience the stbilized hedwy follows the steps below. First of ll, the verge hedwy of the lst two vehicles in the queue should be determined respectively, tht is H 10 nd H 9. Secondly, t-test is used to check whether H 10 is sttisticlly different from H 9. If yes, stop the procedure. If no, the eighth verge hedwy H 8 nd the verge hedwy ccumulted from the third vehicle to the lst vehicle in the queue H 9 should be determined. Then, gin use t-test to investigte whether H 8 is sttisticlly different from H 9. If yes, stop the procedure. If no, proceed to test whether H n is sttisticlly different from H n 1, where n=7,6,5,...,1 respectively. The procedure will be stopped when H n is not sttisticlly different from H n 1. Then, the (n+1)th vehicle is the first vehicle in the queue tht sustins the sturtion hedwy. When the nth vehicle hs been identified, the sturtion hedwy H st nd the sturtion rte Q st cn be estimted s: H H Q st st n H st 3. Dt Description 3.1. Dt Collection After n extensive survey throughout the city of Gungzhou, the Xingng Rod/Ruikng Rod intersection nd Tinhe Bei Rod/Tiyu Dong Rod intersection re selected, showed in Fig. 3. Both intersections hve trffic cmer fixes in n idel position. Though the trffic flow nd rod conditions of them re different, there re enough vehicles in the queue with red light nd most of the vehicles re crs. Moreover, the instlltions of countdown timers re known in dvnce so tht their effect on the queue dischrge chrcteristics cn be studied. Experiments re crried t the sme intersection to void ny uncontrollble fctors tht could rise when two different intersections were nlyzed.

5 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) ) The Xingng Rod/Ruikng Rod b) The Tinhe bei Rod/Tiyu dong Rod Figure 3. Dt collecting scene The study prticulrly focuses on the through movement on the northbound pproch long Xingng Rod nd the northbound pproch long Tiyu Dong Rod. The former pproch comprises of one left-turn lnes, four through lnes nd one right-turn lne nd the other pproch comprises of one left-turn lnes, three through lnes nd one right-turn lne. The intersections re equipped with countdown timers for ll of the four pproches. The dt were collected during the rush hours on weekdy, November 1st to November 3rd before instlling countdown timer nd December 6th to December 8th fter instlling. Time period ws evening pek (15:30~17:30) t the Xingng Rod/Ruikng Rod intersection, pek dy time (7:30~9:30) nd pek night time (15:30~17:30) t the Tinhe bei Rod/Tiyu dong Rod intersection. 36hrs rw video dt were collected in sme wether. The hedwy dt were collected rtificilly with these rw dt. In order to study conveniently, hedwy dt re collected from one of the through lnes of those two pproches respectively. Menwhile, the time between the onset of the green phse nd the front bumper of the first vehicle crossing the stop line is not considered. The time between the first vehicle nd second vehicle crossing the stop line is regrded s the first hedwy, nd so forth Dt Processing Two min spects re tken into considertion to process rw dt. Firstly, the observtion cycles tht contin some kinds of disturbnce re eliminted, including interference from djcent lnes, interference of pedestrin, lne chnging when queue dischrging nd long-time sty of vehicles. Secondly, effect of timing error cused by the cmer positions, observtion ngle nd rection time re eliminted by 3 rule. Tble 2 shows the sttisticl result of hedwys fter error processing. It is found tht the trffic flow minly consists of smll vehicle, so the observtion cycles which contin lrge vehicles re no more eliminted here. Tble 1. Sttisticl result of hedwys Xingng/Ruikng Tinhe Bei /Tiyu Dong Pek night Pek dy Pek night Without timer With timer Without timer With timer With timer With timer Smple size Men(s) Std dev Lrge vehicle% 7.098% 2.842% 4.117% 6.726% 4.084% 3.622%

6 260 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) After pre-processing with two rules bove, the hedwys re tested in Shpiro-Wilk Method with logrithmic trnsformtion nd the results re shown in Tble 2. It illustrtes tht the pre-processed dt re in keeping with logrithmic norml distribution. 4. Results Tble 2. Logrithmic norml test result of hedwys Xingng /Ruikng Tinhe Bei /Tiyu Dong Sequence of hedwy Pek night Pek dy Pek night Without timer With timer Without timer With timer Without timer With timer Effects of Countdown Timer on Cpcity The cpcity of through movements is clculted by eqution (1). Tble 3 shows the comprisons of cpcity of through movements in three situtions during the rush hours. It is found tht cpcity is improved fter the countdown timer instlled, more thn 5% on verge. Menwhile, chnges in cpcity of both two intersections re similr t evening pek hour, while the cpcity of Tinhe Bei Rod/Tiyu Dong Rod intersection chnges significntly t pek dy time. This time vrition cn be explined tht queuing drivers re generlly forced by time constrints t pek dy time, so they intend to rrive t their destintion within the quickest time possible. Thus, they re likely to be ffected more esily by the countdown timer while proceeding through the intersection. Tble 3. Comprisons of cpcity in three situtions Xingng /Ruikng Tinhe Bei /Tiyu Dong Pek night Pek dy Pek night Without timer With timer Without timer With timer Without timer With timer Cycle(s) Green Time(s) Men hedwy(s/vehicle) Cpcity(vehicles/h) Difference(vehicles/h) Reduction% 5.90% 10.91% 5.10% 4.2. Effects of Countdown Timer on Men Hedwy To further explore the impcts of countdown timers on individul vehicles in the stnding queue, the pired individul hedwys between the conditions with nd without timers were nlyzed, s summrized in Fig. 4, Tble 4 nd Tble 5.

7 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) Hedwy/s Withouttimer With timer ith hedwy in the stnding queue Hedwy/s 3.00 Withouttimer 2.50 With timer ith hedwy in the stnding queue ) Xingng Rod/Ruikng Rod (Pek night time) b) Tinhe Bei Rod/Tiyu Dong Rod (Pek dy time) Hedwy/s Withouttimer With timer ith hedwy in the stnding queue c) Tinhe Bei Rod/Tiyu Dong Rod (Pek night time) Figure 4. Comprisons of hedwys in three situtions Fig. 4 illustrtes tht hedwys chnge more stbly with the chnge of vehicles order in the queue fter instlling countdown timer thn before tht for three situtions. Tht demonstrtes tht hedwys re less fluctuted under with timer condition, which is confirmed by the result of sttisticl nlysis. As Tble 4 shows, fter instlling, stndrd devitions of hedwys re reduced by more thn 9%, while tht of the Tinhe Bei Rod/Tiyu Dong Rod intersection reches 26%. It turns out tht the effects of countdown timer on queue dischrge chrcteristics re significntly time-vrying. Tble 5 implies tht the first hedwy of the dischrge vehicles on the through movement reduce significntly with the instlltion of countdown timers. The reduction of hedwy is more thn 0.2s. It demonstrtes tht the countdown timer ffect the first two vehicles in the queue significntly. The impct, however, quickly dissiptes on the third vehicle, nd is further reduced for subsequent vehicles. Tble 4. Comprisons of hedwy stndrd devition in three situtions Std dev Reduction% Without timer Without timer Xingng /Ruikng Pek night % Pek dy % Tinhe Bei /Tiyu Dong Pek night %

8 262 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) Tble 5. Comprisons of hedwy decrese in three conditions Difference of first hedwy(s) Mx difference of other hedwys(s) Min difference of other hedwys(s) Xingng /Ruikng Pek night Pek dy Tinhe Bei /Tiyu Dong Pek night Effects of Countdown Timer on Sturtion Hedwy Bsed on the queue dischrge pttern suggested in the Highwy Cpcity Mnul 2000, the uthors used the sttisticl t-test to determine the order of the vehicle in the stnding queue tht first sustins the sturtion hedwy using the five-step process described erlier. The results re summrized in Tble 6. Tble 5. Comprisons of the order of the vehicle first sustining the sturtion hedwy stte ith vehicle to first sustin the sturtion hedwy stte Without timer Without timer Xingng /Ruikng Pek night 3 4 Tinhe Bei /Tiyu Dong Pek dy 5 6 Pek nigh 4 5 In these three situtions, up to 4 or 5 vehicles pss through the intersection before the sturtion hedwy stte emerges for the without timer condition, while the sturtion hedwy condition begins from the 5th or the 6th vehicle through the intersection under with timer condition. This result shows tht the instlltion of the countdown timer ppers to hve little or no impct on the order of the vehicle in the stnding queue tht first sustins the sturtion hedwy, contrry to populr belief. It demonstrtes tht effect of countdown timer on i vlue is influenced by rod environment, driving behvior nd vehicle composition, etc. Tble 6. Comprisons of sturtion hedwy nd sturtion flow rte Xingng /Ruikng Tinhe Bei /Tiyu Dong Pek night Pek dy Pek night Without timer Without timer Without timer With timer Without timer With timer Sturtion hedwy (s/vehicle) Sturtion flow (vehicles/h) Reduction% 5.85% 7.44% 4.84% Tble 7. Results of t-tests checking the significnce of the difference in the sturtion hedwy Sturtion hedwy (s/vehicle) Vrince t-stt. p-vlue Without timer With timer different? Xingng /Ruikng Pek night Yes Tinhe Bei /Tiyu Pek dy Yes Dong Pek night Yes Results from Levene s test for equlity of vrinces t 95% confidence intervl. As Tble 7 shows, the sturtion hedwy decrese from 1.62s/vehicle before the countdown timer instlled to 1.53s/vehicle fter the countdown timer instlled t Xingng Rod/Ruikng Rod intersection during pek

9 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) night period, nd from 1.51s/vehicle to 1.40s/vehicle before nd fter the countdown timer instlled t Tinhe Bei Rod/Tiyu Dong Rod intersection during pek dy period, nd form 1.58s/vehicle to 1.51s/vehicle before nd fter the countdown timer instlled t Tinhe Bei Rod/Tiyu Dong Rod intersection during pek night period. And thus the sturtion flow rte improves by bout 5% for ll these three conditions. This is logicl given tht the drivers do rect more quickly when the queue begins to move with countdown timers, so the verge velocity t the time vehicle crosses the stop line increses. Tble 8 illustrtes tht there is sttisticlly significnt difference between the sturtion hedwys nd flow rte for periods where countdown timers were in use nd periods without countdown timers. Tht mens the instlltion of countdown timer is uncertin to mke the trffic flow on the through movement of intersections reches to the sturtion hedwy condition more quickly, but it mke sturtion flow rte increse, so s the cpcity of intersections. Menwhile, the effect of countdown timer on the sturtion hedwy lso hs time vrition. 5. Conclusions This study investigted how countdown timer ffects the queue dischrge chrcteristics of through movement during the green period. Hedwy dt ws collected by nlyzing the trffic surveillnce video of the Xingng Rod/Ruikng Rod intersection nd Tinhe bei Rod/Tiyu dong Rod intersection in GungZhou before nd fter the countdown timers instlled. The comprison of queue dischrge chrcteristics with nd without countdown timers yields three interesting implictions. Firstly, the countdown timers helped reduce the first hedwy of the dischrge vehicles on the through movement significntly: the men first hedwy for the periods with countdown timers ws consistently less thn tht those for the periods without timers for ll three study situtions. The reduction of hedwy vried from 0.2s to 0.7s. It demonstrtes tht the countdown timer notifies drivers in the stnding queue the exct time of the green onset, so tht drivers nticipte nd rect to the phse chnge without much dely, prticulrly the first two vehicles in the queue. But this kind of effect dissiptes on the third vehicle, nd is further reduced for subsequent vehicles. Menwhile, the countdown timer lso decresed the hedwy fluctution of vehicles in the queue, with the stndrd devition reducing by 10% to 25%. Secondly, the countdown timers do not hve notble effect on the order of the vehicle in the stnding queue tht first sustins the sturtion hedwy. However, the sturtion hedwy reduces nd the sturtion flow rte increses by bout 5% to 10%. And lso the cpcity of the through movement improves by bout 5% to 10% fter the countdown timers instlled, similr to sturtion flow rte but little higher. Thirdly, the effect of countdown timer on queue dischrge chrcteristics hs time vrition. The effect is more significnt during the pek dy time thn the pek night time. It my cn be explined tht during the pek dy period, for the reson of time constrints, the drivers intend to rrive t their destintion s quickly s possible. It mkes them more esily ffected by the countdown timer while proceeding the intersection. Further study will mke distinction in vehicles types to nlyze the effect of countdown timer on different combintion of severl types of vehicles, such s truck nd bus. In ddition, deeper nlysis to compre effects of different lnes should be done by obtining hedwy dt of left-turn, right-turn nd turn-round lnes from trffic surveillnce video. Finlly, more indexes should be dded to nlyze the effect of countdown timers on trffic flow of signlized intersections thoroughly. 6. Acknowledgement This pper is supported by Ntionl High Technology Reserch nd Development Progrm of Chin (863 Progrm). (No.2011AA110306)

10 264 Sun Wenbo et l. / Procedi - Socil nd Behviorl Sciences 96 ( 2013 ) References Gong, X. X. (2010). Effect of countdown timer on Trffic opertion t signlized intersection. M.S. thesis, Chngsh University of Science & Technology, Chngsh. Kidwi, F.A., Krim, M.R., Ibrhim, M.R. (2005).Trffic flow nlysis of digitl count down signlized urbn intersection. Journl of the Estern Asi Society for Trnsporttion Studies, 5: Limnond, T., Prbjbok, P., Tippywong, K. (2010). Exploring impcts of countdown timers on trffic opertions nd driver behvior t signlized intersection in Bngkok. Trnsport Policy, 17: Limnond, T., Chookerd, S., Roubtonglng, N. (2009). Effects of countdown timers on queue dischrge chrcteristics of through movement t signlized intersection. Trnsporttion Reserch Prt C, 17: Ibrhim, M.R., Krim, M.R., Kidwi, F.A. (2008). The effect of digitl count-down disply on signlized junction performnce. Americn Journl of Applied Science 5(5), Trnsporttion Reserch Bord (2000). Highwy Cpcity Mnul. Trnsporttion Reserch Bord, Ntionl Reserch Council, Wshington D.C. Jin, X.X., Zhng, Y., Wng, F., Li, L., Yo, D.Y., Su, Y.L., Wei, Z. (2009). Deprture hedwys t signlized intersections: A log-norml distribution model pproch. Trnsporttion Reserch Prt C, 17: Jin, X.X. (2009). Anlyzing Severl Issues on A dt-driven Urbn Trffic System Modeling. Tsinghu University, Beijing. Sho, C.Q., Du X.H., Li, G.Q. (2003). Queuing Vehicle Hedwy Sttistic Anlysis t Signlized Intersection. Journl of Highwy nd Trnsporttion Reserch nd Development, 20(4): Wng, W., Guo X.C. (2000). Trffic Engineering. Southest University Press, Fujin. Joseph, J., Chng, G.L. (2005). Sturtion flow rtes nd mximum criticl lne volumes for plnning pplictions in Mrylnd. ASCE Journl of Trnsporttion Engineering(December) Rksutorn,W. (2004). Sturtion flow rte nd strt-up lost time of motorcycles t signlized intersection. Proceedings of the 6th Ntionl Convention on Civil Engineering. Petchburi, Thilnd.