Review of transit signal priority(tsp) Polices and strategies Traffic Safety and Operation Lab University of Maryland, College park gang@umd.edu
Outline TSP Introduction Methods & Strategies Systems & Technologies Applications Conclusions
Definition Transit movement Benefits and costs TSP Introduction
Introduction TSP Introduction Transit signal priority(tsp) is an operational strategy that facilitates the movement of transit vehicles (usually those in-service), either buses or streetcars, through trafficsignal controlled intersections. Transit Signal Priority (TSP): A Planning and Implementation Handbook(Harriet R. Smith, etc. in 2005) is funded by the United States Department of Transportation.
Introduction Transit movement Intersection 1 Dwell at the stop Bus stop Dwell at red signal Intersection 2 A platoon of traffic Reduce bus delay by red signal Bus TSP: Minimize bus delay with little impact on non-priority traffic
Introduction Benefits and costs Benefits Reduce costs of bus operation Bus delay or passenger delay at signalized intersections Probability of bus bunching Passenger waiting time at stops The require number of transit vehicles to serve the demand Improve the service of public transit The percentage of on-schedule bus for bus-based on timetable service and headway-based service Others Increase the ridership discourage the usage of private vehicles Costs Negative impacts on non-priority approaches Potential impacts on neighboring intersections
Methods & Strategies Objectives Strategies Impact factors Methods Evaluation Research summaries
Methods & Strategies Objectives Bus journey time savings (Priority to all buses) Priority to all buses Bus on-schedule services Priority to late buses only, based on schedule timetable Priority according to bus headway, based on schedule time headway Total economic benefits Minimize the total bus delay Minimize the total person delay Minimize the total bus and general vehicle delay
Methods & Strategies Strategies Types Strategies Comments Passive priority Development of timing plans (cycle length, phases and green time, offsets) with priority May lost its benefit due to the traffic fluctuation in reality Active priority (Unconditional and conditional ) Real-time optimization Green Extension(GE) Red Truncation(RT, early green) Special phase(sp) Stage skipping Green compensation of crossstreet Minimize weighted delay/vehicle or passengers Optimize signal plan considering bus dwelling time at stops (consider cross-street, pedestrian safety ) Unconditional and conditional (consider cross-street, pedestrian safety ) May confuse drivers skip one or more traffic stages from the normal stage sequence When cycle failure(left green time cannot to clear intersection) Systems are very sophisticated and complex and therefore not are utilized commonly Grant green to bus priority approach when buses depart from stops; and to cross-street when buses arrive at stops. (In Japan)
Methods & Strategies Active priority Cross-street Green extension Bus-street Non-priority, Bus-street Bus arrival Bus delay Priority, Bus-street Bus arrival Bus time saving Green extension Non-priority, Cross-street Priority, Cross-street Red extension, delay increase
Methods & Strategies Active priority Cross-street Red truncation (Early green) Non-priority, Bus-street Bus-street Bus delay Bus queue Priority, Bus-street Bus time saving Red truncation Non-priority, Cross-street Priority, Cross-street Green reduction, Extra delay
Methods & Strategies Impact factors Bus operation Bus volume Stop location Bus dwelling and running time Bus delay at intersections Bus exclusive lane(yes or No) Bus scheduling Bus headway Traffic demand Bus approaching volume Saturation level of on the cross-street Left turn volume Network configuration Road network Pedestrian presence Signal coordination Fixed-time or actuated signal No. of signalized intersections Feasibility and effectiveness of TSP
Methods & Strategies Rule-based Methods Qualitatively analyze bus delay Unconditional priority Conditional priority Model-based Quantitatively calculate bus delay Conditional priority Combination
Methods & Strategies Methods: Ruled-based Basic Priority Rules The ratio with v/c at the non-priority is less than threshold, such as 0.9 Bus lateness The actual headway is higher than a scheduled headway The headway of the current bus is higher than that of the bus behind First-come first-served Once priority at one cycle length Green compensation to non-priority with no priority request No phase skipping Fixed cycle length
Methods & Strategies Methods: Model-based Objective functions is to minimize Bus delay General traffic delay Bus passenger delay General traffic passenger delay Output Optimal signal timing plan Constraints Maximal green duration Minimal green duration Yellow time and all-red time
Methods & Strategies Methods: comparisons Types Advantages Disadvantages Rulebased 1. Simple and efficient system 2. Need less infrastructure (bus detection, local signal controller) 3. less communication requirement(buscontroller) 4. Simple priority according to bus lateness (Yes or No) 1. First-come first-served to handle multi-priority requests 2. Seldom consider the impacts on the general traffic 3. Qualitative priority according to bus lateness 4. Non-consider bus sequence at the same approaches 5. Not consider the impacts on neighboring intersections Modelbased 1. Complex system with AVL center or UTC center 2. Quantify priority according to bus lateness (How many minutes) 3. Partly consider the impacts on the general traffic 4. Need to optimize signal timing plans of the whole network 5. Achieve more bus delay savings 1. Need more data and infrastructure (bus detection, AVL center, local signal controller, UTC center) 2. More communication requirements (bus-bus, buscontroller) 3. Need more time to grant priority 4. Not consider bus priority based on headway service 5. Not consider bus sequence in the same approaches 6. Non consider the impacts on downstream intersections
Methods & Strategies Methods Model-based test Evaluation Queue theory\empirical data analysis\others Simulation-based test VISSIM\CORSIM\AIMSUN\others Field-based test In London
Methods & Strategies Research summaries Existing studies: Priority phase is fixed or adaptive The number of priority phases in a signal cycle(one or more) Where is the extra green time for the priority phase? Priority requests from multiple bus routes Improve bus regularity or punctuality The number of intersections Impacts on signal coordination of the whole network Interactions between adjacent buses of the same routes Further Research Issues: - Interactions between bus sequence Impacts on downstream intersections Signal-based holding for early buses Impacts on non-priority approaches
Systems & Technologies System Architecture Typical control logic Available data Bus detection Communication
Systems & Technologies System Architecture Classification criteria Location of intelligence Priority request method Location of priority control UTC center Central AVL center Local signal controllers Local Bus
Systems & Technologies ID Architecture (R=priority request; G=priority grant; I=information transmission) Typical control logic Priority options Intelligence Request Decision A1 Local Decentralized Local Applications/cities Geneva, Switzerland Malmo, Sweden Nantes, France Prague, Czech Republic A2 Local Decentralized Central Glasgow, UK A3 Central Decentralized Local Aalborg, Denmark Brighton and Hove, UK Helsinki, Finland A4 Central Decentralized/ Centralized Central London, UK
Systems & Technologies Typical control logic ID Architecture (R=priority request; G=priority grant; I=information transmission) Priority options Intelligence Request Decision Applications/cities A5 Local Decentralized/C entralized Central Zurich, Switzerland Japan (41 of 47 cities) A6 Central Centralized Central Cardiff, UK Gothenburg, Sweden Southampton, UK Turin, Italy A7 Central Centralized Central Toulouse, France A8 Central Decentralized Central Genoa, Italy
Logic comparisons Aspect Intelligence Local Central Priority request Decentralized Centralized Priority decision Local controller Central UTC Comments Simple and efficient method Less communication requirements More suitable for timetable services Possibility of network based bus priority (e.g. dynamic priority) Compatible with multi purpose use of the data More suitable for headway based services More accurate priority request Applicable to both UTC controlled as well as isolated junctions Needs extra infrastructure and communications Needs less infrastructure Applicable to signals under UTC system and central level intelligence only. controller Instant implementation gives higher potential delay savings Often more complex to implement on signals under a UTC system UTC Takes account of signal coordination and hence less impact to the general traffic Applicable to the signals under a UTC system only.
Systems & Technologies Available data Bus location Real-time location and time Bus operation Bus lateness based on schedule timetable Bus lateness based on schedule headway Signal timing plan Cycle length Green split Offset Yellow and all-red time
Systems & Technologies Bus detection Inductive loops/transponders One or more bus detectors Installed at fixed locations, Subject to site constraints (e.g., bus stops) Beacon Using above-ground beacons An optical beacon, infra-red and radio frequency mounted on the traffic signal post Extensively used in the USA and Japan GPS On-board system (Virtual loops) Radio communication from the bus to the roadside or AVL center Backup: Door-closing sensor/odometer/automatic Fare Collection system to calibrate the GPS errors
Systems & Technologies Communication Types: T1. Bus to AVL center T2. Bus to local signal controller T3. Local signal controller to UTC center T4. AVL center to UTC center T5. Bus to bus Techniques GPRS(T1) Wireless(T2) Local area network(t3,t4) 3G(T1,T5)
Introduction Cities with TSP America and Canada Japan Europe Others Summary Applications
Applications Application cities Introduction More than 105 cities around the world USA, UK, Japan, France, Denmark, Sweden, Switzerland, Finland, Germany, Australia, Austria, Italy, India, and so on From 1985 up to now
Applications Introduction Arlington Heights City Country Network configuration Priority strategies Technologies System architecture Performance USA 12nodes GE, RT 1985 Year Bay Area USA > 75 nodes with 2 BTR corridors Passive and active priority (GE and RT) based on schedule adherence infrared (optical) detection; Burlington USA 80 nodes GE, RT 1993 Calgary USA 67 nodes GE, RT 2000 Charlotte USA 17 nodes GE, RT 1985 Chicago USA 84 nodes Passive and conditional active priority (GE and RT) loop detection decentralized Average 15% (3minutes) reduced running time. 2003 Glendale USA 17 nodes GE, RT 2001 Houston USA 1563 nodes GE, RT 2004 Los Angeles USA 26 corridors, 1000 nodes (25% in the city), more than 900 buses Bus regularity based on headway; priority to buses with more than 1.5 scheduled headways behind its leader Wifi communication; loop detection UTS centerlized 19-25% reduced travel times; the number of passengers increased by 1/3. 1990 Minneapolis USA 22 nodes a signal priority strategy considering the bus timeliness with respect to its schedule, its number of passengers, location and speed. 2004 Note: GE and RT mean GE and RT, respectively.
Applications Introduction City New York City Country USA Network configuration 20 nodes in 2008 GE (<=30s), RT Priority strategies Technologies Infrared detection, AVL center System architecture Performance Year 2007 Oakland USA 62 nodes, 1 corridor GE, RT Infrared detection decentralized Extrapolation of data from 8 Caltrans intersections indicates approximate 9% time savings. 2003 Orlando USA 19 nodes GE, RT 1997 Ottawa Canada 40 nodes GE, RT, special phase, unconditional priority to all buses 1990s Philadelphia USA 61 nodes GE 2002 Pittsburgh USA 5 nodes special phase Port Townsend USA 2 nodes special phase Portland USA 370 nodes passive and active strategies(ge and RT) with considering person delay and schedule adherence Infrared detection; AVL center; queue jump lane decentralized improve 10% travel time and 19% reduction in travel time variability 1987 Richland USA 31 nodes GE, RT 1995 Sacramento USA 600 nodes GE, RT
Applications Introduction City Salt Lake City San Mateo County Country Network configuration USA 12 nodes GE, RT Priority strategies Technologies System architecture Performance USA 77 nodes GE, RT, and special phase 1990 Seattle USA 26 nodes, 3 corridors GE, RT St. Cloud USA 89 nodes GE, RT Tacoma Toronto Vancouver USA Canada Canada Washington USA King County USA 110 nodes, 6 corridors,245 buses 338 nodes on 8 steetcar routes and 4 bus routes 2 corridors, 59 on B- line and 4 on Willingdon,28 buses 3 corridors, 28 nodes and 1400 buses GE, RT GE (<=30s), RT, and special phase; queue jump lanes passive and active strategies(ge and RT),a phase insertion strategy was used when the bus route makes a left turn, bus lateness GE, RT GE and RT; priority to all buses according to traffic conditions Passive Radio Frequency tag Infrared detection infrared detection; AVL center Radio frequency tags distributed Decentralized distributed 14-24% reduced stops at intersections. 35-40% reduced trip travel time variability. 5.5-8% reduced travel time along corridors during peak hours. reduced transit signal delay about 40%. total signal delay on S.19th down 5-30% (transit). On Pacific Ave: 18-21% (transit). 98 B-Line reduced travel time in the corridor from 100 to 84 minutes. Resulted in a 23% modal shift from auto to transit in the corridor. Main TSP benefit: significant reduction (40-50%) in travel time variability. Year 1999 2002 1989 2001
Applications Introduction City Country Network configuration Priority strategies Technologies System architecture Performance Year Aalborg Denmark 51 nodes up to 2007 Priority to buses lateness>=3min AVL,GPRS communication A3 Average saved up to 4% of total travel time 1996 Brighton and Hove UK 8 SCOOT nodes, 30mph speed limit in majority roads, up to 2007 GE, RT, priority to late buses AVL-GPS A3 1997 Cardiff UK 46 SCOOT nodes,191 buses Priority to buses with lateness and passengers loading by the ticket machine GPS-based AVL A6 Preliminary results showed bus journey time savings of 3-4% for average weekdays, including 11% in the peak period 1999 Genoa Italy >84 nodes Geneva Switzerland 263 nodes at the end of 2008 Each period was of 3 weeks: first week with priority following a maximum speed strategy, second week with bus GPS-based AVL priority following a punctuality strategy, and a third week without bus priority). GPS, odometer and Door closing sensor A8 Bus travelling times in the range 7 to 10%. 1992 A1 2006 Glasgow UK 500 buses, SCOOT system; but lateness and passenger loading GPS, ticket machine, odometer A2 Gothenburg Sweden special phase A6
Applications Introduction City Country Network configuration Priority strategies Technologies System architecture Performance Year Helsinki Finland GE, RT, and special phase; priority to bus lateness GPS-based AVL, odometer A3 Bus line 23, travel times fell by 11% and traffic light delays by 48% while an improvement of 20% in regularity and 58% in punctuality. Passenger volume increased by 11 % 1999 London UK 1970 isolated nodes; recently, 3200 nodes and 8000 buses GE, RT, green compensation, stage skipping; differential priority based on bus regularity and punctuality inductive loop; GPS-based AVL; SCOOT UTC Malmo Sweden 40 nodes GPS-based A1 Nantes France 31km bus lanes, 1 busonly street buses GE, priority to all detected Inductive loop A1 Prague 10km bus lane, 5km Czech sharing tram lane, 65 Republic nodes and 352 buses Priority to late bused Infra-red detection A1 A4 1970 Southampton UK GE, priority to all buses Beacon-based AVL, SCOOT UTC, odometer, now GPSbased detection A6 Delay savings averaging 8 secs/bus/junction Stockholm Sweden 11 nodes UTC center, inductive loop
Applications Introduction City Country Network configuration Priority strategies Technologies System architecture Performance Year Stuttgart Germany 34 nodes in the line42 infra-red, GPS as a backup increase bus speed from 9 to 10.1 mile per hour 1996 Suceava Romania GPS-based detection Tallinn Estonia 30 nodes for 7 bus routes and 3 trolleybus routes Toulouse France bus adherence GPS-based AVL; odometer counting A7 Experiments in 1999 showed an average decrease of the bus travel time of about 5% and up to 24% during the most congestion peak periods. 1999 Turin Italy bus adherence beacon-based AVL, UTC A6 delay savings of around 10 seconds per junction, with a journey time reduction of around 5 minutes (12%) for the entire service in 2000 Vienna Austria 23.3km bus lanes, 1.3 busonly street and 185 nodes; 500 nodes for tram priority Priority to all buses with GE; priority to trams based on lateness
Applications Introduction City Country Network configuration Priority strategies Technologies System architecture Performance Year York UK 25 nodes GPS-based detection Zurich Switzerland Priority to all buses Inductive loop A5 Japan 41 cities( total 47 cities in Japan) bus lane Public Transportation Priority System, predict bus arrival time, recommend a desired bus speed Infra-red beacons, UTS center A2 The system reduces about 5 % of the travel time in Kawasaki City Auckland New Zealand 174 nodes to preemption GE with fixed 10s and RT GPS-based detection, on-bus ticketing machine Brisbane Australia Priority to late bused with GE and RT Inductive loop 2003 Sydney Australia Priority to late bused with GE and RT GPS-based detection, SCATS UTC center The trials indicated that PTIPS reduced both mean travel times (up to 21%) and variability of travel time (up to 49%) for buses Bengalore India GE and RT
Applications Introduction Examples of cities and bus priority at traffic signals facility City Country Population No. of signal junctions providing bus priority No. of buses equipped for bus priority Aalborg Denmark 194149 51 249 Brighton UK 248000 8 Cardiff UK 315000 46 191 Genoa Italy 650000 84 500 Geneva Switzerland 187000 263 420 Glasgow UK 600000 241 500 London UK 7556900 3200 8000 Malmo Sweden 276000 42 Prague Czech republic 1225000 65 352 Stuttgart Germany 550000 34 Tallinn Estonia 400000 30 169 Toulouse France 400000 160 Vienna Austria 1600000 185 York UK 193000 25 Zurich Switzerland 550000 60 Auckland New Zealand 438100 174 734 Brisbane Australia 1600000 11 205 Portland USA 503000 250 650 King County USA 1800000 28 1400 Los Angels USA 3500000 654 283 Source: Kevin Gardner and Chris D Souza, Nick Hounsell and Birendra Shrestha, David Bretherton. Review of Bus Priority at Traffic Signals around the World, 2009
Applications Introduction Priority benefits and impacts City Delay saving Travel time Variability Patronage General traffic Aalborg 5.8 sec/bus/jun 4% reduction in average Brighton Reduced Reduced Cardiff Genoa 3-4% reduction 7-10% reduction Improved schedule adherence Glasgow Reduce considerably Increased 1-2% increase Gothenburg 13-15% decrease 5-10% saving Helsinki 11% reduction 11% increase London 9 sec/bus/jun at isolated and 3-5 sec/bus/jun at SCOOT junctions Malmo Headway reduced from 10min to 7.5 min Prague 2% reduction Southampton 9.5 sec/jun Increased 3.8 sec/jun Stockholm 10% savings Source: Kevin Gardner and Chris D Souza, Nick Hounsell and Birendra Shrestha, David Bretherton. Review of Bus Priority at Traffic Signals around the World, 2009
Applications Introduction Priority benefits and impacts City Delay saving Travel time Variability Patronage General traffic Stuttgart Speed and increases from 9 to 10.1 miles/h Suceava 10-12% increase Tallinn Toulouse Turin Speed increase by 2km/h 5-24% decrease 12% reduction Zurich 42% increase Japan 5% reduction Auckland 11 sec/bus/jun Sydney Up to 21% reduction Up to 49 reduction Portland Improved reliability Very little effect King county 25-34% Reduced by 5.5-8% Reduced by 35-40% Minimal effect Los Angeles Reduced by 6-8% Increased by 1-13% Typically 1 sec/veh/jun Source: Kevin Gardner and Chris D Souza, Nick Hounsell and Birendra Shrestha, David Bretherton. Review of Bus Priority at Traffic Signals around the World, 2009
Applications America and Canada Japan Europe Others Applications
Applications Cardiff, UK GPS and real-time passenger information system in 1999-2000 Bus priority according to lateness and passenger loading (through an interface with the ticket machine) Journey time savings of 3-4% for average weekdays, 11% in the peak period 191 buses and 46 nodes SCOOT UTC system
Applications Early system (1970s) at isolated 56 nodes(loop sensor) Priority to all buses, 960 transits Late system Intelligent bus(ibus) system SCOOT UTC system GPS-based AVL center Priority to late buses Headway-based service Timetable-based service 3200 nodes Priority strategies green extension red truncation Compensation stage skipping London, UK ibus system currently being implemented in London is one of the world's largest integrated AVL systems.
Applications Early system (1970s) at isolated 56 nodes(loop sensor) Priority to all buses, 960 transits Late system Intelligent bus(ibus) system SCOOT UTC system GPS-based AVL center Priority to late buses Headway-based service Timetable-based service 3200 nodes Priority strategies green extension red truncation Compensation stage skipping London, UK Components: A: Bus priority fault detection and performance monitoring reports B: System databases C&H: Bus priority radio link D: Bus processor contained within traffic signal controller E: Traffic signal controller F&N: Bus detection points S: Bus door sensor J: GPS receiver K: Central system server(located remotely) L: IBIS plus unit G: GPS satellites T : Odometer counting O: Bus garage(when bus is in garage, it is linked to the central system server to send and receive bus priority data)
Applications London, UK Efficiency Early system (1970s) Field trials undertaken at 10 junctions showed that with the average flow and weighted bus delay, the savings was 8.6 sec/bus (29%), 8.3 sec/bus (31%) and 13.7 sec/bus (35%) for morning peak, off-peak and evening peak periods respectively. The overall, bus delay savings was 9 sec/bus (32%) and the reduction in standard deviation (variability) was 4 sec/bus. New system extensive trials in London show a reduction of delay of around 3-5 seconds per bus per junction.
Applications Helsinki, Finland In 1999 Bus detection GPS(interval 10s) Door-opening sensor Odometer counting Priority to bus lateness (GE,RT,SP) Improvement on bus line 23 20% in regularity 58% in punctuality 11% in Passenger volume
Applications Toulouse, France In 1999 Update UTS system AVL center sends request to UTC center. UTC center actively sends request to AVL center. Improvement 5% in mean 24% in most congestion peak periods
Applications Urban traffic management system1 Japan Public Transportation Priority System(PTPS) PTPS
Applications Japan Public Transportation Priority System(PTPS) Bus detection: Infra-red beacon system The system predicts bus arrival time Travel time reduction of 5% in Kawasaki city Recommend a desired speed 41 of 47 cities Strategies: GE RT Bus phase insertion Switch green time to cross-street when the bus is at the stop Cities with PTPS Cities without PTPS
Applications Japan Public Transportation Priority System(PTPS) http://www.utms.or.jp/english/system/ptps.html
Applications Portland, USA Conditional priority to buses with 30 seconds or 33 more late Priority strategies: GE(7-10 seconds extension) and RT Integrate with an AVL system Up to 2005, include 8 corridors, 250 junctions and 650 buses, queue jump lane TriMet was able to improve 10% travel time and 19% reduction in travel time variability
Applications Application summary Existing system problems Not accurately calculate the bus location Not accurately estimate the bus arrival time Active priority is not real-time optimization Most bus priority at isolated intersections Not consider interactions between adjacent buses from the same route Not handle with high bus demands
Conclusions TSP is potentially to improve bus service Need further research to ensure the effectiveness of existing TSP strategies: Predict the bus arrival time Reduce the impacts of TSP on general traffic How to deal with buses for multiple routes fromdifferent approaches, fully use available real-time system resources UTC center Traffic flow detection Automatic Fare Collection system Bus dispatching system, Integrate the bus schedule plan and signal timing plan Further improve bus service by integrating the TSP stratgeies with and other control methods Bus-holding at a stop Control bus travel speed Stop skipping,
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