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Evaluation of bus priority strategiesin coordinated traffic signal systems
KTH, School of Architecture and the Built Environment (ABE), Transport Science, Traffic and Logistics.ORCID iD: 0000-0002-8115-2107
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing congestion and environmental concerns have evoked an interest in promoting urban Public Transport (PT) the last decades. In 2012 the City of Stockholm adopted an “Urban mobility strategy” stating that public transport, cycling and walking should be prioritised over cars in central Stockholm. One of the most important factors influencing the modal choice is the travel time ratio between car and PT travel. According to earlier studies Public Transport Traffic Signal Priority (PTSP) can reduce travel times for public transport with only small negative impacts on other traffic. Conditional PTSP can also help to regulate the PT service. Thus PTSP may support drivers’ decision to change travel mode from car to PT, thus supporting adopted policy goals.

Conventional control strategies for coordinated traffic signals have pre-set timings based on traffic surveys. Some traffic adaptation based on real time detector actuations can also take place within the frames of the pre-set cycle time. PTSP changes the signal timings, within pre-set limits, when a PT vehicle is detected. Self-optimising control strategies use a traffic model to predict the traffic flows from traffic counts, and determine the signal changes in real-time by minimising a cost function including delay, number of stops etc. PTSP is included directly in the optimisation by giving PT vehicles a higher weight compared to cars.

In this thesis the fundamentals of signal control theory are reviewed as well as unconditional and conditional PTSP criteria and strategies. A simulation based method for evaluation of impacts of different PTSP strategies in coordinated controlled traffic signals is implemented. The simulation setup includes Software-In-the-Loop (SIL) signal controller simulators running the same control logic as used in field. Such simulation models can be useful to test and fine tune PTSP before being implemented in field. Simulations with a SIL setup also enable comparisons of signal control strategies or systems on equal terms, not practically or economically possible in field studies. The implemented SIL simulation model was used to evaluate the impacts on buses and other traffic from the different PTSP functions used in the “PRIBUSS” PTSP method. Short green time extensions showed travel time reductions for buses, with almost no travel time increase for other traffic.

Long green time extensions gave somewhat larger benefits for the buses, but more delay to other traffic. Red truncation gave less travel time savings to the prioritised buses and more extra delay for cross street traffic, compared to green extensions. Double red truncation and Extra phase showed some additional travel time savings to the buses, but had the largest negative impact on other traffic. A combination of PRIBUSS functions showed the best results. Depending on the structure of the signal coordination and the location of the bus stops different PTSP functions may be needed.

Based on the conclusions from the evaluation of the different PRIBUSS functions a conditional “differential on-time-status” based PTSP strategy was proposed and tested in the SIL simulation environment. The proposed method is focusing on direct travel time savings as well as on reduced bus bunching.

The two self-optimising signal control systems Utopia/Spot and ImFlow were tested, and their impacts were compared to conventional control including PTSP with the PRIBUSS method in a SIL simulation environment. The aim was to test if commercially available self-optimising control systems can reduce the overall delay per person by applying more sophisticated PTSP. Both systems reduced the delay for buses, cyclists and pedestrians at a cost of increased delay and increased number of stops compared to the existing conventional control used in field. The total delay for all road users was reduced substantially.

Abstract [sv]

Intresset för att påverka resvanorna i våra städer så att kollektivtrafikandelen ökar har växt de senaste decennierna på grund av en ökad trängsel i gatunätet samt ökad miljömedvetenhet. Stockholms stad har antagit ”Framkomlighetsstrategin” som innebär att kollektivtrafik, gång och cykel ska prioriteras framför biltrafik i centrala Stockholm. En av de faktorer som påverkar färdmedelsvalet mest är restidskvoten mellan bil och kollektivtrafik. Tidigare studier har visat att kollektivtrafikprioritering i trafiksignaler kan minska körtiden för kollektivtrafiken väsentligt, med små eller inga negativa konsekvenser för övrig trafik. Villkorlig prioritering kan dessutom förbättra kollektivtrafikens regularitet. Kollektivtrafikprioritering i trafiksignaler kan på så sätt hjälpa till att förbättra kollektivtrafikens attraktivitet och därigenom öka kollektivtrafikandelen.

Samordnade trafiksignaler styrda med konventionell teknik har en fast tidsättning framtagen med insamlade historiska trafikdata som grund. Viss trafikstyrning kan åstadkommas inom ramen för den fasta omloppstiden. Om bussprioritering finns ändras signalväxlingen av prioriteringsfunktionerna när en buss detekteras, inom vissa begränsningar för att hålla ihop det samordnade systemet. Självoptimerande signalstyrning bygger på att fordonsrörelserna genom systemet predikteras med en trafikmodell utifrån trafikräkningar med detektorer. Signaltidsättningen bestäms sedan i realtid genom att minimera en kostnadsfunktion som innehåller fördröjning, antal stopp mm. för de modellerade fordonsrörelserna. Kollektivtrafiken prioriteras genom att dess fordon detekteras separat från övrig trafik, och ges en högre vikt i optimeringen av signaltidssättningen.

I denna avhandling beskrivs de teoretiska grunderna för trafiksignalstyrning, liksom metoder och kriterier för villkorlig och ovillkorlig signalprioritering av kollektivtrafik. En simuleringsbaserad metod för att utvärdera effekterna av olika signalprioritering har implementerats. Denna använder styrapparatsimulatorer med samma programmering som styrapparaterna på gatan, inklusive prioriteringsfunktioner. Sådana simuleringar kan vara ett användbart verktyg för att justera in prioriteringsfunktionerna innan dessa implementeras i signalstyrningen på gatan. Simuleringar med styrapparatsimulatorer möjliggör också jämförelser av olika styrstrategier under kontrollerade förhållanden som inte vore praktiskt, eller ekonomiskt möjliga att genomföra i fält. I den framtagna simuleringsmiljön har effekterna av de olika prioriteringsfunktionerna i PRIBUSS utvärderats. Korta (maxtids-)förlängningar gav körtidsvinster för bussar och knappast några restidsförsämringar för övrig trafik. Långa förlängningar (fråntidsförlängning och återtagen start) gav ytterligare restidsvinster för busstrafiken, men ökad fördröjning för övrig trafik. Avkortning gav, jämfört med förlängningar, mindre restidsvinster för busstrafiken och mer störning för övrig trafik. De mer komplicerade funktionerna Dubbel avkortning och extrafas gav viss ytterligare restidsvinst för bussarna, men hade den största inverkan på övrig trafik. Bäst resultat uppkom dock med en kombination av PRIBUSS funktioner. Beroende på samordningens struktur och busshållplatsernas placering i förhållande till trafiksignalerna kan olika prioriteringsfunktioner ge större eller mindre nytta.

Baserat på utvärderingen av de olika PRIBUSS funktionernas effekter på bussar och övrig trafik har en tidhållningsbaserad differentierad prioriteringsstrategi föreslagits, som förutom att skapa direkta restidvinster också försöker motverka ihopklumpning av bussar. Denna strategi har implementerats och testats i den framtagna simuleringsmiljön.

Med hjälp av simuleringar har de självoptimerande signalstyrsystemen Utopia/Spot och ImFlow testats och jämförts med konventionell styrning, inklusive bussprioritering med PRIBUSS. Syftet med denna studie var att undersöka om fördröjningen per person i trafiknätet kan minskas genom bättre kollektivtrafikprioritering med hjälp av ett kommersiellt tillgängligt självoptimerande signalstyrsystem. De båda testade systemen gav minskad fördröjning för kollektivtrafik, gående och cyklister, men ökad fördröjning och antal stopp för biltrafik. Den totala fördröjningen minskades betydligt med de båda testade självoptimerande signalstyrsystemen.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xiii, 107 p.
Series
TRITA-TSC-LIC, ISSN 1653-445X ; 14:001
Keyword [en]
Bus priority, public transport priority, transit priority, PTSP, TSP, traffic signal, traffic signal control, traffic signal control systems, self-optimising signal control, PRIBUSS, SIL simulation, traffic simulation
National Category
Infrastructure Engineering Transport Systems and Logistics
Research subject
Transport Science
Identifiers
URN: urn:nbn:se:kth:diva-145008ISBN: 978-91-87353-38-3 (print)OAI: oai:DiVA.org:kth-145008DiVA: diva2:715636
Presentation
2014-05-21, V1, Teknikringen 76, KTH, Stockholm, 13:30 (English)
Opponent
Supervisors
Note

QC 20140513

Available from: 2014-05-13 Created: 2014-05-05 Last updated: 2014-05-13Bibliographically approved
List of papers
1. Hybrid traffic simulation with adaptive signal control
Open this publication in new window or tab >>Hybrid traffic simulation with adaptive signal control
2007 (English)In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 1999, 191-197 p.Article in journal (Refereed) Published
Abstract [en]

A hybrid mesoscopic-microscopic model is implemented that applies microscopic simulation to areas of specific interest while simulating a large surrounding network in lesser detail with a mesoscopic model. The hybrid model integrates VisSim, a microscopic traffic simulation model, and Mezzo, a recently developed mesoscopic model. The hybrid model is applied on a network in which Mezzo simulates the entire area (6,000 links) of Stockholm, Sweden, and VisSim simulates the area of specific interest, containing three intersections with adaptive signal control with bus-priority functions. The adaptive signal control and bus-priority functions are simulated by a separate signal controller simulator (EC-1 simulator) that interacts with the hybrid Mezzo-VisSim model and thereby provides the actual signal changes that would take place in the field. Two alternative control schemes are evaluated with the hybrid setup: the original fixed-time control and the new adaptive control. The results show clear improvement in terms of travel times, delays, and stops with the new adaptive control scheme. They also show that although these improvements for the local (microlevel) area attract additional traffic from the surrounding (mesolevel) area, the net effects both locally and networkwide remain positive in terms of travel times, average number of stops, and delay. Moreover, this study demonstrates the advantages of hybrid simulation in evaluation of complicated adaptive traffic control in which both local detailed effects and network effects need to be studied.

National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-17212 (URN)10.3141/1999-20 (DOI)000252733200021 ()2-s2.0-38849175484 (Scopus ID)
Note

QC 20100525

Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Impacts of Bus Priority in Coordinated Traffic Signals
Open this publication in new window or tab >>Impacts of Bus Priority in Coordinated Traffic Signals
2011 (English)In: 6TH INTERNATIONAL SYMPOSIUM ON HIGHWAY CAPACITY AND QUALITY OF SERVICE / [ed] Koutsopoulos, HN; Bang, KL, 2011, 578-587 p.Conference paper, Published paper (Refereed)
Abstract [en]

Delay at signalized intersections is a considerable part of the journey time for public transport (PT) in urban areas. However, PT priority in traffic signals can reduce travel time and improve service regularity for buses at a relatively low cost to other traffic. In general it is difficult to apply analytical methods for calculation the effects of dynamic signal timing enhancements or active bus priority at traffic signals. Furthermore, no common methods are available for optimizing PT priority conditions and timings, which are usually conducted on the basis of traffic engineers' experience and fine-tuned afterwards. This paper presents a simulation-based method for analyzing partial dynamic signal timings as well as fully adaptive signal control systems. Experiments with a microscopic traffic simulation model and a software-in-the-loop signal controller simulator are carried out to study the impacts on travel times for buses and other traffic of conditional active bus priority with the Swedish PRIBUSS method. The results show that PT priority results in shorter travel times for busses, and longer travel times for crossing traffic and traffic following the prioritized busses in one direction. This implies that there is a need for better methods to set the conditions for the bus priority in empirically based systems such as PRIBUSS.

Series
Procedia Social and Behavioral Sciences, ISSN 1877-0428 ; 16
Keyword
Traffic signals, Bus priority, Transit priority, PT priority, Signal control, Simulation of traffic signals
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-76807 (URN)10.1016/j.sbspro.2011.04.478 (DOI)000298556100055 ()2-s2.0-79960033857 (Scopus ID)
Conference
6th International Symposium on Highway Capacity and Quality of Service (ISHC). Stockholm, SWEDEN. JUN 28-JUL 01, 2011
Note

TSC import 907 2012-02-06. QC 20120207

Available from: 2012-02-06 Created: 2012-02-06 Last updated: 2014-05-13Bibliographically approved
3. Evaluation of Different Bus Priority Functions in Coordinated Traffic Signals
Open this publication in new window or tab >>Evaluation of Different Bus Priority Functions in Coordinated Traffic Signals
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Delay at signalized intersections is a considerable part of the journey time for public transport (PT) in urban areas, but the delay can be reduced with PT priority in the signals at a relatively low cost to other traffic. The impact on other traffic is dependent on which priority functions are used, but the effects are hard to calculate in a coordinated system and do not always act intuitively. In this paper, experiments with a microscopic traffic simulation model are conducted with a software-in-the-loop signal controller simulator to study the costs and benefits, primarily in terms of travel times for buses and other traffic, of different priority functions in the Swedish PRIBUSS method for conditional active bus priority. Based on the analysis of the different functions, new conditions for priority are proposed and tested with the microscopic simulation model.

Place, publisher, year, edition, pages
Washington, DC: , 2013
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-138263 (URN)
Conference
the 92st Annual Meeting of the Transportation Research Board
Note

TSC import 2479 2013-12-17. QC 20140513

Available from: 2013-12-18 Created: 2013-12-18 Last updated: 2014-05-13Bibliographically approved
4. Evaluation of the two self-optimising traffic signal systems Utopia/Spot and ImFlow, and comparison with existing signal control in Stockholm, Sweden
Open this publication in new window or tab >>Evaluation of the two self-optimising traffic signal systems Utopia/Spot and ImFlow, and comparison with existing signal control in Stockholm, Sweden
2013 (English)In: 2013 16th International IEEE Conference on Intelligent Transportation Systems - (ITSC), IEEE conference proceedings, 2013, 1541-1546 p.Conference paper, Published paper (Refereed)
Abstract [en]

The city of Stockholm has adopted the 'Urban mobility strategy' stating that the more surface efficient modes public transport (PT), cycling and walk should be prioritised over cars. This has led to an interest to extend the signal priority for PT beyond its present level. Self-optimising signal control systems can keep the impacts on other traffic at a controlled level when introducing extensive PT priority, and they may reduce the cycle time causing less waiting time for pedestrians and cyclists. In this paper two self-optimising systems are tested and compared with each other and with the existing signal control using microscopic simulation. VISSIM was connected to PC versions of the self-optimising systems Utopia/Spot and ImFlow and to signal controller simulators including PRIBUSS. Both self-optimising systems reduced the average delay per person compared to existing signal control. ImFlow performed better than Utopia/Spot in the evaluation.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2013
National Category
Transport Systems and Logistics
Identifiers
urn:nbn:se:kth:diva-138264 (URN)10.1109/ITSC.2013.6728449 (DOI)000346481000247 ()2-s2.0-84894357355 (Scopus ID)978-147992914-6 (ISBN)
Conference
2013 16th International IEEE Conference on Intelligent Transportation Systems: Intelligent Transportation Systems for All Modes, ITSC 2013; The Hague; Netherlands; 6 October 2013 through 9 October 2013
Note

QC 20140619

Available from: 2013-12-18 Created: 2013-12-18 Last updated: 2015-12-03Bibliographically approved

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