Engneerng Analyss of Implementng Pedestran Scramble Crossng at Traffc Junctons n Sngapore Dr. Lm Wee Chuan Eldn Department of Chemcal & Bomolecular Engneerng, Natonal Unversty of Sngapore, 4 Engneerng Drve 4, Sngapore 7585 Summary A computatonal model based on the modfed Dscrete Element Method (DEM) was developed and utlzed for computer smulatons of pedestran behavors at smple and scramble crossng junctons n ths study. The computatonal model was calbrated based on feld observatons of pedestran behavors at smple junctons n Sngapore and good qualtatve agreement between smulaton results obtaned from the model and these feld observatons was acheved. The computatonal model was then appled for smulatons of scramble crossng to predct pedestran behavors that would lkely be observed f scramble crossng were mplemented n Sngapore. There was a tendency for jammng to occur at the center of a scramble crossng juncton especally f the number of pedestrans was large. Nevertheless, the tme requred for all pedestrans to reach dagonally opposte corners of the juncton was less than twce that requred for pedestrans to reach opposte ends of a smple juncton. From the pont of vew of enhancng pedestran flow rates, t may thus be concluded that t would lkely be benefcal to mplement scramble crossng at busy junctons n Sngapore. Introducton The populaton of Sngapore s projected to ncrease over the next few decades. Along wth ths, the numbers of vehcles and pedestrans on the road are expected to ncrease and so traffc congeston problems are lkely to become more acute. One potental approach to mprove pedestran flow rates at large or busy junctons s to mplement scramble crossng. Durng scramble crossng, vehcles approachng a juncton from all drectons stop and pedestrans are allowed to cross the juncton n any drecton they wsh, ncludng dagonally. Scramble crossng has been mplemented n many countres throughout the world, ncludng the Unted States, Unted Kngdom and Japan. For example, scramble crossng was mplemented at one of the busest traffc junctons n London, called the Oxford Crcus, n 2009. It may also be benefcal to mplement scramble crossng n Sngapore. However, as pedestrans n dfferent countres exhbt dfferent behavors, t s dffcult to extrapolate the effects of mplementng scramble crossng n other countres to predct the effects and potental benefts of mplementng scramble crossng n Sngapore. Ths defcency n our knowledge provded the motvaton for ths research project. The objectve of ths project was thus to develop an engneerng tool that could be appled to smulate pedestran behavors at smple and scramble crossng junctons. The smulaton model developed would be calbrated accordng to pedestran behavors n Sngapore so that t can be utlzed to predct pedestran flow rates and crossng tme at busy junctons f scramble crossng were mplemented n Sngapore. The long term vson of ths project s to provde decson-makers, such as the relevant authortes and government agences, wth a relable tool that can be appled to support nformed decson-makng on whether scramble crossng should be mplemented n Sngapore. Feld Work Durng the ntal phase of ths project, feld work studes were conducted to capture vdeo recordngs of pedestran behavors at busy junctons n Sngapore. Fgure shows an example of one of the vdeo recordngs captured at a juncton n the Central Busness Dstrct (CBD). The pedestrans were mostly offce workers gong for lunch or returnng to ther offces from lunch. Fgure 2 shows the snapshots of vdeo recordngs captured at a dfferent juncton n Sngapore. Ths was obtaned at a shoppng
dstrct on a weekend and so the demography of the pedestrans was dfferent from that of the pedestrans n the prevous fgure. These pedestrans were generally younger and engagng n lesure actvtes such as shoppng. In contrast to the offce workers captured n the prevous set of vdeo recordngs, there were many pedestrans who moved as groups because they were famly members or couples. Consequently, the overall behavors of the two groups of pedestrans shown n the two fgures were observed to be dfferent. These vdeo recordngs were used as feld data aganst whch to calbrate the smulaton model developed n ths study. Ths was n lne wth the objectve of developng a model that would be customzed to pedestran behavors n Sngapore, and that could then be appled to predct pedestran behavors f scramble crossng were mplemented n Sngapore. Fgure. Snapshots of vdeo recordng showng pedestran behavor at a busy juncton n the Central Busness Dstrct (CBD) of Sngapore. Fgure 2. Snapshots of vdeo recordng showng pedestran behavor at a busy juncton n a shoppng dstrct of Sngapore. 2
Smulaton Model A pedestran flow model was developed based on a partcle dynamcs approach known as the Dscrete Element Method (DEM) n whch ndvdual pedestrans were modeled as partcles. The translatonal and rotatonal motons of ndvdual pedestrans are governed by Newton s laws of moton: dv N m = ( f c,j + f d,j + f s,j ) () dt j= N dω I = Tj (2) dt j= where m and v are the mass and velocty of th partcle respectvely, N s the number of partcles n contact wth th partcle, f c,j, f d,j and f s,j are the contact, dampng and socal forces respectvely, I s the moment of nerta of th partcle, ω s ts angular velocty and T j s the torque arsng from contact forces whch causes the partcle to rotate. A lnear sprng-and-dashpot model was mplemented for the calculaton of contact and dampng forces whle an nverse square law was appled for the calculaton of the socal force. Results and Dscusson Several DEM smulatons of pedestrans crossng a smple juncton were conducted n the next phase of ths study. The varous parameters of the DEM model as well as operatonal condtons such as the number of pedestrans were vared. The objectve of ths phase of study was to fne-tune the parameters n the model so as to acheve good agreement between the pedestran behavors smulated and those observed durng the feld work studes. Fgure 3 shows an example of pedestran behavors predcted by the DEM model n whch two groups comprsng 50 pedestrans each moved towards opposte ends of the smple juncton. The arrows and color contours ndcate drectons of motons and magntudes of the socal force experenced by the pedestrans durng crossng. It may be seen that some extent of jammng occurred near the center of the juncton when the number of pedestrans was large and magntudes of socal force were generally hgh, ndcatng that some level of crowdedness or dscomfort was felt by almost all pedestrans. In general, good qualtatve agreement between the smulaton results and feld work observatons was acheved. The calbrated smulaton model was then appled for predctons of pedestran behavors at a scramble crossng juncton. Fgure 3. DEM smulaton of pedestran behavor at a smple juncton. The color contours ndcate the strength of the socal force experenced by each pedestran and can be nterpreted to be a measure of crowdedness or level of dscomfort felt durng crossng. Fgure 4 shows snapshots of a DEM smulaton of pedestran behavors durng scramble crossng obtaned from the calbrated smulaton model. Four groups comprsng 50 pedestrans each moved 3
from the four corners of the cross juncton towards ther respectve dagonally opposte ends of the juncton. It may be seen that jammng of the pedestrans occurred near the center of the juncton where the four groups converged and the hgh magntudes of socal force ndcated farly hgh levels of crowdedness or dscomfort experenced by many pedestrans. The lmtng factor for the total tme for all pedestrans to reach ther respectve destnatons and the juncton to clear was the speed at whch ndvdual pedestrans were able to meander slowly through the pedestran jam. Ths was a common phenomenon observed n all smulatons of scramble crossng conducted n ths study. The extent of jammng was lower, but never completely absent, n cases where the total number of pedestrans was smaller. Nevertheless, t was also observed that the tme requred for pedestrans to reach ther destnatons at the dagonally opposte corners of the juncton was less than twce the tme requred for pedestrans to cross a smple juncton, such as those shown n the prevous fgure. Despte the jammng phenomenon, ths would mply that scramble crossng was stll more effcent n allowng pedestrans to reach dagonally opposte ends of a cross juncton than smple crossng. In the latter, pedestrans would have to do smple crossng twce n order to reach the dagonally opposte end of a cross juncton and the tme taken, based on the two types of crossng smulatons conducted n ths study, would be longer. From the pont of vew of mprovng pedestran flow rates, t may thus be concluded that t would be benefcal to mplement scramble crossng n Sngapore. Fgure 4. DEM smulaton of pedestran behavor at a scramble crossng juncton where each group of pedestrans wshed to reach the dagonally opposte corner of the juncton. The color contours ndcate the strength of the socal force experenced by each pedestran and can be nterpreted to be a measure of crowdedness or level of dscomfort felt durng crossng. Conclusons The conventonal Dscrete Element Method (DEM) was modfed by ncorporatng a socal force model and appled for smulatng pedestran behavors at smple and scramble crossng junctons. The smulaton model was calbrated aganst feld observatons of pedestran behavors at dfferent smple crossng junctons n Sngapore by fne-tunng varous parameters n the model and good qualtatve agreement was acheved. Based on ths calbrated model, smulatons of scramble crossng were conducted. It was observed that jammng always occurred at the center of the juncton durng 4
scramble crossng and ths placed a lmt on pedestran flow rates that could be acheved. Nevertheless, the tme requred for pedestrans to reach dagonally opposte corners of the scramble crossng juncton was less than twce that requred for pedestrans to reach opposte ends of a smple juncton. It could thus be concluded that t would lkely be benefcal to mplement scramble crossng at busy junctons n Sngapore to acheve hgher pedestran flow rates. It would be pertnent to contnue ths study to conduct further parametrc analyses of the effects of varous operatonal condtons on crowdng behavors and crossng tme for potental scramble crossng junctons n Sngapore. Further research studes can also be conducted to explore possble modfcatons to the conventonal scramble crossng practce wth the objectve of addressng the ssue of jammng durng scramble crossng. A successful resoluton of ths ssue may potentally lead to further enhancements of pedestran flow rates as well as level of comfort durng scramble crossng at busy junctons. Acknowledgements The fundng support provded by MSIG and MSIWF for ths study s gratefully acknowledged. The research grant awarded for ths project has provded an nvaluable opportunty for me to apply my expertse n DEM modelng towards developng a new paradgm for pedestran flow modelng. 5