IMPACT OF LINE CONTROL SYSTEMS ON THE HOMOGENEITY OF TRAFFIC FLOW

Transcription

1 IMPACT OF LINE CONTROL SYSTEMS ON THE HOMOGENEITY OF TRAFFIC FLOW Jai Rohde, Karte Heiig Reearcher, Reearcher Ititute of Traport, Road Egieerig ad Plaig, Uiverity of Haover Appeltraße 9A, D-367 Haover, Germay Tel: Fax: rohde@ivh.ui-haover.de, heiig@ivh.ui-haover.de SUMMARY The obective of thi paper wa to evaluate the impact of Lie Cotrol Sytem (LCS) o the homogeeity of traffic flow. A empirical aalyi baed o the data from the LCS A2 Haover wa carried out with a developed methodology. Stadard deviatio of vehicle peed i ued a a idicator for the homogeeity of traffic flow. Thi idicator i put ito relatiohip with traffic volume ad paeger car peed. Fudametal diagram are created ehaced by tadard deviatio of vehicle peed. Diagram referrig to obervatio poit iflueced by LCS tate maller tadard deviatio at every traffic coditio tha thoe referrig to a obervatio poit without ifluece of LCS. Furthermore, tatitical aalye prove that diplayig dyamic peed limit reduce the mea value of tadard deviatio a well a paeger car peed withi a coidered time period. INTRODUCTION Lie Cotrol Sytem (LCS) are coidered to cotribute to today ambitiou effort to relieve traffic cogetio, to effectuate a homogeou traffic flow, to reduce travel delay ad accidet ad, thu, to improve traffic ad road afety. The mai LCS i Germay coit of a ucceive itallatio of obervatio poit (OP) ad variable meage ig (VMS) pael. The VMS are claified baed o the type of meage: type A - peed limit, type B - regulatory ad dager warig ig ad type C - additioal iformatio. Traffic meauremet, e.g. traffic volume, vehicle peed etc., are detected at every OP by iductive loop or radar eor. The collected data from every OP are tramitted to a traffic cotrol cetre (TCC) which evaluate the curret traffic coditio ad geerate ituatioal actio to icreae homogeeity of traffic flow or to war motorit of cogetio ad icidet. For homogeiatio purpoe, dyamic peed limit are diplayed geerally o the VMS located i the viciity of the crucial OP. I thi paper the term homogeeity of traffic flow i ued to decribe a patiotemporal uiformity of traffic flow. If traffic i homogeeou, all motorit ca travel teadily, i.e. they are either forced to accelerate or to decelerate permaetly due to ome diturbace i traffic flow. The homogeeity of traffic flow i difficult to quatify ad o explicit variable i kow to idicate the homogeeity of traffic flow at a certai traffic coditio. The poitive impact of LCS o traffic flow ha bee revealed i everal reearch proect (2)(3)(4)(6)(7). Thee reearche iclude evaluatio o the homogeeity of traffic flow a well. However, their methodologie require may type of data ad data collectio device. Thi paper itroduce a methodology which deped o few variable i order to examie the homogeeity of traffic flow.

2 A empirical tudy i coducted with lie data from the LCS A2 Haover. The motorway A2 travere the orther part of the city of Haover, coectig the idutrially importat Rhie bai i the wet with Germay capital Berli ad the upcomig market i the ew member tate of the Europea Uio i the eat. Therefore a mooth ad afe traffic flow o thi motorway ha to be guarateed. The LCS A2 Haover wa etablihed i March 999. Up to the time of the reearch proect, 36 VMS pael are italled to ifluece traffic over a ditace of 47 km eatboud ad 22 km wetboud. At 76 OP traffic meauremet are detected ad traferred to the TCC. METHODOLOGY Data Bae The aalyed data et wa retrieved from the TCC data archive. It iclude all detected ad computed traffic data (i.e. data per carriageway), aggregated ito oe-miute iterval, for eight OP withi a 3 day period. Seve OP are iflueced by the LCS becaue VMS pael are italled directly above them. Oe OP i without ay ifluece of the LCS. However, at thi OP a tatic peed limit of km/h hold. I Table oly thoe data are how that are relevat for the methodology. I order to mooth the tochatic fluctuatio all traffic data are aggregated ito 5-miute-iterval by calculatig the arithmetic mea of the curret iterval ad the four previou oe-miute-iterval. Table - Data et 8 OP (7 iflueced by LCS, ot iflueced by LCS) period: 3 day ( ) traffic data aggregated to 5-miute-iterval type of data data commet traffic data date, time timetamp per lae q traffic volume v average vehicle peed tadard deviatio of vehicle peed per carriageway q traffic volume at OP v average vehicle peed at OP v pc average paeger car peed at OP tadard deviatio of vehicle peed at OP VMS data date, time timetamp VMS_A tatu VMS type A VMS_B tatu VMS type B VMS_C tatu VMS type C The data i table are computed baed o the followig repective equatio (5): q = q + q traffic volume o lae [] pc, hgv, q = q v = v q + v q traffic volume at OP [2] pc, pc, hgv, hgv, = average vehicle peed o lae [3] q 2

3 v = v pc v q = average vehicle peed at OP [4] = q v pc, pc, = = q q pc, average paeger car peed at OP [5] vi i= i= vi tadard deviatio of vehicle peed o lae [6] = 2 ( q ) ( ) 2 + q v v = tadard deviatio of vehicle peed at OP [7] q = with: i pc hgv peed of detected vehicle lae umber of lae or detected vehicle paeger car heavy good vehicle Stadard deviatio a idicator for homogeeity of traffic flow The tadard deviatio for each OP i computed accordig to equatio 7. Thi mea that i iflueced by diparitie of vehicle peed o ivetigated lae (, ee equatio 6) a well a by differece betwee the vehicle peed o lae ad the average vehicle peed at the OP (v ad v, ee equatio 3 ad 4). Thu, would be appropriate to decribe the ituatio of traffic flow with repect to homogeeity. However, the data for provided i the data et ha to be ued with cautio. Due to the fact that heavy good vehicle (HGV) are boud to a atiowide peed limit of km/h, HGV peed i more or le cotat ule the motorway i cogeted. Accordigly, paeger car peed ad tadard deviatio of paeger car peed would be the mot appropriate idicator to examie the homogeeity of traffic flow. Ufortuately, the oly available data cocerig tadard deviatio i the data et i the oe for vehicle peed. A it ca be ee i equatio 7, the fuctio for computig i multivariate. It i iflueced by a multitude of detected ad computed data which refer to vehicle data excluively. Therefore, the tadard deviatio of paeger car peed ca ot be olely computed. However, a qualitative aalyi tate that the ifluece of the HGV o decreae a traffic volume icreae. The reao are twofold: Firtly, at high level of traffic volume o more tha % vehicle drive o the rightmot lae (where HGV drive i geeral). Secodly, at high level of traffic volume vehicle peed i early equivalet to paeger car peed. Accordigly, tadard deviatio of vehicle peed,, ca be ued a a appropriate idicator for the homogeeity of traffic flow at high level of traffic volume eve if it i evaluated i aociatio with paeger car peed. A how i Figure, declie cotatly with decliig vehicle peed i free-flow coditio, i.e. whe v i greater tha km/h (). All value ca be grouped i ix clae (table 2) which become relevat i the followig part of the methodology. 3

4 Impact of the LCS o the homogeeity of traffic flow To evaluate the impact of the LCS o the homogeeity of traffic flow idicator ha to be examied with repect to traffic volume q ad paeger car peed vpc. Baically, the relatiohip betwee traffic volume ad peed ca be pictured a fudametal diagram. I thi cae, q-vpc diagram are plotted. The expreivee of thee diagram ca yet be ehaced: Every pair of detected traffic volume q ad paeger car peed vpc i aociated with the related value of tadard deviatio. The q-vpc- triplet ca the be aiged to the defied clae (table 2) depedig o the value of. For a better idicatio i the diagram, each cla i give a pecific colour. [km/h] 3 6 v [km/h] Figure - Relatiohip betwee tadard deviatio ad vehicle peed, Diagram geerated from empiric data of LCS A2 Haover, , OP 6d, data aggregated ito 5-miute-iterval Table 2 Clae of tadard deviatio cla [-] 2 [km/h] < < < 4 < < The evaluatio i executed i two tep. I the firt tep, the diagram baed o data from the OP iflueced ad ot iflueced by LCS are compared to each other. The ecod tep i more pecific with repect to the iflueced OP. It oly take thoe q-vpc- triplet ito accout that derive from a iflueced time period, i.e. withi a time period of at leat five miute peed limit were diplayed cotiuouly at the VMS of type A. Thee diagram are 4

5 later called LCS eabled ad will be compared with the diagram of the OP without ifluece of LCS a well. Impact of dyamic peed limit o the homogeeity of traffic flow The aforemetioed relatiohip betwee ad v pc (i.e., declie with decliig vehicle peed) lead to the geeral aumptio that diplayig peed limit at the VMS ca reduce tadard deviatio of vehicle peed ubect to the coditio that the maority of motorit obey the peed limit. Thu, homogeeity of traffic flow could be improved. I thi fial tep of the methodology, a method i etablihed which i capable to aure thi aumptio with tatitical tetig. The baic idea i to compare the mea value of ad v pc of two differet ample: Sample derive from a time period before a particular peed limit i diplayed ad the VMS are diabled. Sample 2 derive from a time period i which a peed limit i diplayed cotiuouly for 5 miute. Due to the fact that the traffic data are aggregated over 5-miuteiterval i order to mooth tatitically fluctuatio, it i ufficiet to geerate the ample by oly takig ito accout the time iterval i- ad i+4. For example, coider the cae that from time iterval i oward, a peed limit i diplayed permaetly o the VMS type A for the followig five iterval (ee Figure 2). The the value for ad v pc i time iterval i+4 are the arithmetic mea of all five value for ad v pc i the time period i to i+4, which equal five miute. Accordigly, the value for ad v pc i time iterval i- are the arithmetic mea of all five value for ad v pc i the time period i-5 to i-. I all other time iterval ad v pc are etimated with value of differet VMS tatu, e.g. i+2 i time iterval i+2 i the arithmetic mea of the five value i-2, i- (VMS diabled) i, i+, i+2 (VMS - peed limit). Sample ad ample 2 ca the be geerated by browig the data et for relevat cotrol ceario, e.g. peed limit km/h., v [km/h] pc v pc i-5 i-4 i-3 i-2 i- i i+ i+3 i+4 time iterval i- v pc,i- i+4 v pc,i+4 Sample Sample 2 Figure 2 Samplig method for ceario peed limit km/h For the applicatio of the method it i madatory that both ample are ormally ditributed. Thi ca be evaluated by uig a appropriate tet of goode of fit, e.g. the Kolmogor- Smir-tet. The aforemetioed aumptio that diplayig peed limit at the VMS ca reduce ad v pc mea that ample ad ample 2 caot derive from the ame populatio. To evaluate that, the t-tet i applied. If the t-tet tate that the mea of ample ad 2 are igificatly differet (p <,5) it i prove that the two ample origiate from differet populatio. A impact of the dyamic peed limit o the developmet of or v pc i thu cofirmed. 5

6 RESULTS Impact of the LCS o the homogeeity of traffic flow Figure 3 depict two diagram derivig from a OP iflueced by LCS ad without ifluece of the LCS, repectively. Both diagram how that declie with the icreae of traffic volume. The compario of the diagram tate that at the OP iflueced by LCS i lower at high level of traffic volume (q > veh/mi): OP iflueced by LCS: OP without ifluece of LCS: km/h < < km/h 5 km/h < < 25 km/h vpc [km/h] 6 6 q [veh/mi] < km/h 3 km/h <= < 5 km/h km/h <= < km/h 9 km/h <= < 25 km/h 25 km/h <= < 3 km/h >= 3 km/h vpc [km/h] 6 6 q [veh/mi] < km/h 3 km/h <= < 5 km/h km/h <= < km/h km/h <= < 25 km/h 9 25 km/h <= < 3 km/h >= 3 km/h Figure 3 - q-vpc- diagram, geerated from empiric data of the LCS A2 Haover, , data aggregated ito 5-miute-iterval, top: OP d, iflueced by LCS, bottom :OP 83b, without ifluece by LCS, tatic peed limit km/h 6

7 Moreover, the differet clae occur i characteritic cluter. Coiderig oe particular cluter, e.g. cla 4 - km/h < < 25 km, a evaluatio o all diagram etablihe that thi cluter occur at the OP without ifluece by LCS at higher level of traffic volume ad lower peed repectively) tha at the OP iflueced by LCS. Furthermore, if the level of traffic volume i higher tha veh/mi, at OP iflueced by LCS i alway lower compared to the OP without ifluece of LCS. Thu, the traffic flow at OP iflueced by LCS i more homogeou. Figure 4 idicate that i alway much lower with repect to the ame traffic coditio at a OP where the LCS i eabled (i.e., dyamic peed limit are diplayed cotiuouly at the VMS for at leat five miute) whe comparig with the value at the OP without ifluece of LCS. v pc [km/h] 6 6 q [veh/mi] < km/h km/h <= < 5 km/h 5 km/h <= < km/h km/h <= < 25 km/h 25 km/h <= < 3 km/h >= 3 km/h v pc [km/h] 6 6 q [veh/mi] < km/h km/h <= < 5 km/h 5 km/h <= < km/h km/h <= < 25 km/h 25 km/h <= < 3 km/h >= 3 km/h Figure 4 - q-v pc - diagram, geerated from empiric data of the LCS A2 Haover, , data aggregated ito 5-miute-iterval, top: OP b, LCS eabled, bottom :OP 83b, without ifluece by LCS, tatic peed limit km/h 7

8 Impact of dyamic peed limit o the homogeeity of traffic flow By applyig the tet for goode of fit it i revealed that the maority of ample are ot ormally ditributed. Thi i maily becaue the ample ize are too mall to obtai igificat reult. Therefore, ot all combiatio of poible ceario could be ivetigated. I the followig, two ceario are preeted which have adequate ample ize, are ormally ditributed ad for which the t-tet tated that the mea are igificatly differet. Figure 5 depict the mea value of ad v pc for the cotrol ceario peed limit km/h. It how that at all OP v pc i ample 2 (peed limit hold) i 4-6 km/h lower tha i ample (VMS ). Furthermore, declie by 3-4 km/h with repect to ample. Figure 6 depict the mea value of ad v pc whe the diplayed peed limit i either km/h or km/h ad the cotrol durace i a multiple of 5 miute. Thi ceario coider the fact that a dyamic peed limit ofte varie withi a 5-miute period but, baically, hold for more tha 5 miute. I thi ceario, at all OP v pc i ample 2 (peed limit hold) i 3-4 km/h lower tha i ample (VMS ). Meawhile, declie by 6-9 km/h with repect to ample. v pc [km/h] [km/h] OP d OP 6d OP 7d OP 8d OP d OP b v_pc Figure 5 - Cotrol ceario peed limit km/h mea value for ad v pc, reult of t-tet v pc [km/h] [km/h] / / / 6d 8d d v_pc Figure 6 - Cotrol ceario km/h or km/h mea value for ad v pc, reult of t-tet 8

9 CONCLUSIONS I thi paper the impact of the LCS o the homogeeity of traffic flow wa evaluated by aalyig empiric data from the LCS A2 Haover. The tadard deviatio of vehicle peed wa ued a a appropriate idicator for homogeeity of traffic flow at high level of traffic volume a it value i the maily iflueced by diparitie i paeger car peed. The evaluatio tate:. Stadard deviatio of vehicle peed at obervatio poit iflueced by LCS i lower tha at the obervatio poit without ifluece of LCS, thu, traffic flow i more homogeeou at high level of traffic volume. 2. Stadard deviatio of vehicle peed declie if dyamic peed limit are diplayed, thu, homogeeity of traffic flow icreae. I the future the developed methodology i thi paper could be applied to data bae with more obervatio poit ad for loger time period. Thi will provide greater ample ize for the evaluatio of the impact of dyamic peed limit o the homogeeity of traffic flow. With greater ample ize the probability of ormally ditributed ample icreae. Thu, more ceario could be ivetigated by thi methodology. ACKNOWLEDGEMENTS The author would like to thak Svetlaa Vukaovic (TRANSVER GmbH, Muich) for her beeficial upport, cotructive criticim ad ecouragemet. REFERENCES () Hadbuch für die Bemeug vo Straßeverkehralage Forchuggeellchaft für Straße- ud Verkehrwee e. V., Köl (2) Hma-Leichter: Uteruchug der Auwirkug der Verkehrbeeifluugalage auf der A5 Friedberg- Frakfurt a. M. auf Verkehrablauf, Verkehricherheit ud Reiezeit, Schlubericht 997 (3) Kühe, R.; Schick, P.: Ermittlug ud Bewertug der Nutzekompoete vo Streckebeeifluugalage im Hiblick auf de Verkehrablauf, Schriftereihe Forchug Straßebau ud Straßeverkehrtechik, Heft 866, Budeiemiiterium für Verkehr, Bau- ud Wohugwee, Bo 3 (4) Magold, M. et. al.: Wirkamkeite vo Streckebeeifluugalage uter beoderer Berückichtigug der Umfelddateerfaug, Schriftereihe Forchug Straßebau ud Straßeverkehrtechik, Heft 729, Budeiemiiterium für Verkehr, Bo 996 (5) Merkblatt für die Autattug vo Verkehrrecherzetrale ud Uterzetrale, Budeatalt für Straßewee, Bergich-Gladbach 999 9

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