- Email: [email protected]
Arterial Corridor
Copyright © IFAC Transportation Systems Chania, Greece, 1997
IMPLEMENTATION OF A REAL-TIME INTEGRATED CONTROL SYSTEM IN A FREEWAY/ARTERIAL CORRIDOR Craig R. Rindt
R. layakrishnan
Michael G. McNally
Institute of Transportation Studies Department of Civil and Environmental Engineering University of California, Irvine, USA 92697
Abstract. This paper presents the status of the California Advanced Research Testbed (CART) research implementation program. The discussion first describes the establishment of data communication links between the University of California, Irvine (UCI) Advanced Testbed Laboratories and the Testbed field implementation sites including the City ofIrvine and Caltrans District 12 Traffic Management Centers. This is followed by a review of the Irvine federal FOT implementation technologies including MIST, OPAC, SWARM, and the Caltrans D12 ATMS occurring simultaneously with test bed research implementation. The final section discusses the Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) which is designed for use with the real-world data to be received from the data links to the traffic networks on in the Testbed area. Keywords. Integrated Traffic Management, Control Methods and Algorithms, Travel and Traffic Information, Modeling and Simulation
• implement and evaluate activities for development and operation of an integrated multijurisdictional, multi-agency transportation operations system.
1. INTRODUCTION
The CART encompasses two contiguous sub areas in Orange County, CA that include virtually all of the major decision points for freeway travelers in the region. The City of Anaheim subarea is centered about two of its designated "smart streets," Harbor Boulevard and Katella Avenue, and encompasses the City's major special event traffic generators. It is particularly suited for networkwide applications of advanced technologies in traffic management.
The California Advanced Research Testbed project (CART) is an integrated approach to the development and deployment of advanced technologies in the operation and management of urban transportation and is based on real-time, computerassisted traffic management and communication. The transportation operations system that forms the backbone of the Testbed is structured to integrate network-wide traffic information (both surface street and freeway) in a real-time environment and to provide intelligent computer-assisted decision support to traffic management personnel. Under full implementation, CART is designed to: • accelerate deployment through advanced technology research; • demonstrate deployment readiness of advanced systems; 1097
The City of Irvine sub area provides freeway access to a myriad of business and office complexes on both sides of the 1-5 freeway and is particularly suited for corridor-level integration of realtime communication and control in traffic management. Additionally, the Irvine subarea is the site of the federally-funded Irvine Field Opera-
tional Test (FOT) whose objective is to integrate and coordinate a centrally controlled freeway freeway ramp metering system with an arterial traffic management system. The full FOT implementation involves a highly congested corridor through a rapidly growing employment center. The FOT involves an ATMS which extends the capabilities of existing freeway and arterial traffic management systems in the Irvine area. Its key features are the integration and real-time control of current and evolving traffic operations technologies to achieve some degree of integrated control of the freeway and neighboring arterial networks in the defined FOT area. This paper provides an overview of the ongoing research and implementation activities which are part of the CART and vital to the achievement of its primary objectives which are to provide: • an instrumented, multi-jurisdictional, multiagency transportation operations environment linked to university laboratories for real-world development, testing and evaluation of nearterm technologies and applications; • a meeting ground for practitioners and researchers to try new approaches to transportation system management; • a site for private industry to demonstrate and evaluate their prototype technologies under live traffic conditions; • an ongoing testing ground for California and national ITS efforts. The current research implementation tasks are discussed in three parts. The first describes the establishment of a traffic research laboratory which has a two-way real-time data connection with realworld traffic network. This connection provides researchers the access to extensive traffic data and the means with which to test their new technology in a real-world setting. The second part discusses the Irvine FOT implementation technologies which include the Management Information System for Transportation (MIST), Optimal Policies for Adaptive Control (OPAC), the Caltrans District 12 Advanced Transportation Management System (D12 ATMS), and the System Wide Adaptive Ramp Metering (SWARM) system. The third part describes the Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) and discusses the concerns involved with the integration of existing TRICEPS technology for use with the real-time data link with the Irvine FOT traffic network
2. CARl' DATA LINKS The implementation and evaluation of research in the area of Advanced Traffic Management and Information Systems (ATMIS) has always been ham-
pered by the substantial effort involved in obtaining realistic traffic data with which to develop and test the research and the availability of real-world network on which to implement and evaluate the research. The recognition ofthis fact prompted the establishment of a two-way real-time connection between the UCI Advanced Testbed Laboratory and Testbed-area traffic systems. The Testbed communication network is based upon a wide area network utilizing high speed digital facilities. Three classes of communication access are being provided: (1) inter-site data communication; (2) intra-testbed communication; and (3) inter-site high capacity link which supports video teleconferencing. The Testbed Communications Network currently under implementation is based on an ATM infrastructure, designed to be compatible with the existing Teleos ISDN PRI Network established by the Caltrans WAN (Wide Area Network) for videoteleconferencing. The ATM Internetworkiniinfrastructure is to be linked with the Caltrans District 12 TMC and the City of Irvine ITRAC via an OC3 155Mbps SONET fiber optics network, and with the City of Anaheim TMC via ATM using T-1 facilities. The system also includes MPEG 1 video transmission system provided between the UCI ATMS Laboratories and the Caltrans District 12 TMC, allowing for view, display, management and control of freeway video surveillance cameras within District 12.
2.1 Caltrans District 12
The data connection between the Caltrans District 12 Traffic Operations Center (TOC) and the UCI Testbed Laboratories provides a dedicated twoway real-time data connection with the ability to: • obtain field device (loop detectors, VDS, CMS, CCTV, etc.) configuration data; • obtain raw output from field devices in realtime; • obtain 30 second volume, occupancy, and speed data from VDS; • obtain and set Changeable Message Sign realworld (CMS) display status; • obtain and set freeway ramp metering rates. In addition to the real-time communications capabilities, the connection also provides access to the Caltrans on-line database allowing the retrieval of 30-second freeway loop counts, incident logs, and activity logs archived for the past six months up to the present. 1098
2.2 City of InJine
3.2 OPAC
The data connection between the test bed laboratories and the City of Irvine Traffic Research and Analysis Center (ITRAC) is expected to provide, through MIST (see Section 3.1), interfaces to:
Optimal Policies for Adaptive Control (Gartner et al. , 1991) is a distributed control strategy which features a dynamic optimization algorithm that calculates signal timing to minimize a performance function of total intersection delay and stops given the traffic demand on all approaches to the intersection. The real-time version of OPAC being implemented in the Irvine FOT (OPAC-RT Version 3.0) estimates demand on the intersection over a rolling horizon using a combination of traffic data obtained from upstream detectors and expected future arrival patterns determined using a smoothing algorithm.
• obtain processed stop-line and system detector data; • obtain and set current intersection signalization; • obtain and set arterial Changeable Message Signs (CMS)
3. FOT IMPLEMENTATION TECHNOLOGIES
3.3 D12 ATMS
The Caltrans District 12 Advanced Transportation Management System (D12 ATMS) is an operator decision support system and data manager for operations and control of the Orange qounty, CA freeway network. The system provides freeway surveillance and traffic control capabilities, including:
The primary objective of the Irvine FOT is to provide real-time dynamic and predictive intercorridor traffic diversion in response to non recurrent freeway congestion occurring in the Irvine FOT freeway/arterial corridor. The integrated response plan consists of several strategies which may be applied fully or partially:
• automatic incident detection; • surveillance through closed circuit television cameras and vehicle detection systems; and • automatic generation of freeway traffic response plans, which include activation of freeway changeable message signs (CMS), adjustment of ramp metering rates, and other recommended operator actions.
• The diversion offreeway traffic to the arterial network to avoid the impacted location. • The diversion of freeway-bound arterial traffic to avoid the impacted location. • Freeway ramp metering. • Arterial signal optimization to meet diversion demand. The following technologies are presently under implementation in the Irvine FOT. Each of these technologies is expected to play a key role in integrated response implementation.
3.4 SWARM
3.1 MIST
The Management Information System for Transportation (MIST) is a general development platform for customized traffic control systems and Intelligent Transportation Systems being implemented for the City of Irvine by Farradyne Systems Inc. The system uses an open architecture which supports the inclusion of a broad class of system components into the management scheme. MIST employs a database management system supporting the Structured Query Language which maintains system configuration data, user-defined parameters, system status data, and output data from field devices. MIST is designed to monitor and control field devices (e.g., signal controllers, changeable message signs, loop detectors) 1099
The System-Wide Adaptive Ramp Metering system (NET, 1996) is an optimization algorithm for local and system-wide ramp metering for inclusion in the D12 ATMS. SWARM uses a two-tiered approach to meter freeway ramps considering systemwide system-wide (SWARM 1) local (SWARM 2) conditions. SWARM 1 treats the freeway as sections whose downstream end represent some operational bottleneck (lane drop, ramp merge, etc) where recurrent congestion is likely. The algorithm makes near-term predictions of traffic density in these sections from measured data and compares them to the sections' historically measured saturation density values. Ramp metering rates for a given section are adjusted to head off the onset of predicted congestion when the estimated density exceeds the section's saturation density. The SWARM 2 algorithm applies a local ramp traffic-responsive metering rule to optimize freeway density in the vicinity of the subject ramp. The more restrictive metering rate of SWARM 1 and SWARM 2 is selected as the operational rate.
4.1 Simulation Workbench
:m~~__ _(3}_ ATM Network
,,--I
The Testbed Simulation Workbench (TSW) is expected to meet specific goals including the need to: • model traffic dynamics with a suitable, possibly variable, level of detail; • minimize the embedding of applications in the simulation code, placing an emphasis on modeling the effects of applications, but not the applications themselves; • interactively provide system state information to external applications; • interactively receive control and information directives from external applications and model their impacts; • operate at real-time speeds or faster .
:
, \
.., I ~ I
ObjectOriented Database
0::: ,
.~:
Q.
,
,
Testbed Simulation Workbench
~. 0:'
8'/
, p~Io;Y~ ATMIS-/;'plemeniatToi Plat/orm UC! Advanced Testbed Lab •
Fig. 1. TRICEPS Conceptual Structure 4. AN ATMIS IMPLEMENTATION AND EVALUATION PLATFORM The Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) has been established to support activities in the Testbed (Jayakrishnan and Rindt, 1997). TRICEPS is intended as a platform on which new Advanced Traffic Management and Information Systems (ATMIS) technology can be evaluated using a combination of real-world and simulated data. The functional requirements for TRICEPS are therefore defined to consider the needs of researchers explicitly. These requirements include the: • flexibility to study alternate ATMIS designs; • capability to operate with real-time/real world data; • capability to augment real data with simulation; • availability of at least a minimum number of basic component modules for ATMIS design. The conceptual structure of TRICEPS is shown with its real-world connectivity in Figure 1. TRICEPS consists of two main components. The first is a simulation workbench whose primary application is to serve as the evaluation platform for ATMIS alternatives being researched on the testbed. The second is an implementation platform for evaluating these alternative systems. This latter component provides transportation researchers the means to connect groups of distributed, interdependent, ATMIS applications to each other and to simulated or real-world data. These two components are described in the following sections. 1100
The level of computational performance required of a simulation varies with its application. For the TSW, "real-time" performance has dual meanings. First, as an effective evaluation platform for ATMIS implementations, the simulation mus~ provide performance which approximates the reaI world. In this role, the primary goal of the simulation is faithful modeling of the traffic system with a secondary goal (especially in light of issues relating to distributed algorithm performance) of computational performance approaching clock-time. In its second role, the TSW must operate in real-time, while simultaneously connected to a partially instrumented real-world traffic network, to provide supplementary data about the state of the system to analysis models which require complete or specialized network data. The tradeoff between modeling detail and computational performance is a well known dilemma in system simulation. For many simulation uses, the tradeoff is manageable as in the cases when a large traffic system is being modeled for general performance characteristics (e.g. the evaluation of planning alternatives using traffic assignment models) or when a small portion of a system is simulated at a high level of detail to provide detailed data for specialized applications (e.g. the evaluation of an incident detection algorithm using microscopic simulation). The evaluation needs of integrated ATMIS, however, may require both detailed system data and network-wide performance data. A simulation approach which models the traffic system with varying levels of detail has shown promise in alleviating this tradeoff (FHWA, 1990). Such a scalable simulation can increase computational efficiency by allocating resources as appropriate to the ATMIS applications being evaluated. Other research in this area has considered simulation restructured for massively parallel computing architectures (Chang et al., 1994; Cameron and
Duncan, 1996).
• data translation and conversion for non standard applications.
Both of these approaches are being studied as simulation frameworks for TRICEPS. A hybrid simulation which offers variable levels of simulation detail for different subnetwork components has been developed using an enhanced version of the DYNASMART simulation model and the microscopic INTRAS freeway simulation. In this simulation scheme, DYNASMART models the test bed-area freeway / arterial network mesoscopicly (with a macroscopic flow model and a microscopic driver route choice model) and coordinates the use of multiple, distributed INTRAS simulations to simultaneously model portions of the freeway network microscopically. This hybridization is able to provide much of the functionality required for the evaluation of most ATMIS strategies with only moderate computational requirements.
The emphasis of this platform is to provide an efficient means of establishing connectivity between applications in the system without imposing extensive design restrictions on developers. Such an undertaking requires the consideration of the nature of the applications to be included in the system. For the purposes of this discussion , an application is taken to be any element associated with an ATMIS which is capable of providing information to other elements of the system either automatically or on demand. This definition includes all conventional and advanced traffic functions as well as the traffic system itself which is ultimately drives the entire ATMS. Note that each of the components of the simulation workbench is considered an application and if the workbench is completely replaced by the real-world, then the real-world traffic system itself is considered an application.
Additionally, the Paramics (Cameron and Duncan, 1996) microscopic simulation model is currently being evaluated as a future simulation component of the Testbed. Paramics provides a fully scalable parallel simulation model with advanced visualization capabilities and extensive modelling flexibility which allows the use of user-developed models in all aspects of simulation ranging from car-following and lane changing to driver behavior and traffic control systems. For large networks such as that in the Testbed, this high level of functionality is computationally intensive and therefore requires high performance computing capabilities. With the addition of this computational power in the UCI Testbed laboratories, Paramics is expected to become an important component in the evaluation of candidate ATMIS solutions implemented using TRICEPS.
Each application operates using data from other applications and provides data for use by other applications (including the traffic system which takes control information from the ATMS and produces state data used by the ATMS). In terms of the Open System Interconnection (OSI) model of network communication (Zimmermann, 1980), this protocol performs both presentation and application layer functions . Note that at the application layer, specific knowledge of the external applications is unnecessary. The application code itself resides in the highest layer of the protocol and is serviced by input acquisition and conversion functions and output storage and request service function at lower layers which provide the interface to other applications. Such encapsulation allows easy incorporation of new modules into the TRICEPS architecture without extensive redesign of the existing application's logic or data structures.
4.2 Distributed Computing Platform
TRICEPS also contains a distributed computing platform for implementing partial and complete ATMIS solutions for evaluation using either simulated or real-world data from the Testbed network. The platform consists of an upper level communications protocol called the Transportation Algorithm Interface Library (TAIL) which employs a mid-level TCP lIP-based protocol known as the UC hvine Distributed Algorithm Testing Environment (ELUCIDATE), which has been designed for general purpose distributed algorithm simulation (Jayakrisbnan et al., 1993). Together, TAIL and ELUCIDATE include facilities for:
4.3 Research Implementation Using TRICEPS
When implemented using TRICEPS, the effectiveness with which a given set of applications provide integrated analysis, optimization, management, and control can be evaluated. To support the implementation applications developed separately, but which rely on other analysis tools to provide data, a suite of models developed within the CART and already implemented using TRICEPS are available to provide the data and analysis which may be required by new component applications. These models include classical optimization algorithms, adaptive control schemes, traditional simulation programs, real-time expert systems, neural networks, etc. Additionally, a database of network information is available for the Testbed area with
• seamless encapsulation of individual applications into the distributed processing environment; • the management of application interdependencies; and 1101
complete representation of the freeway/arterial network, time-varying OD matrices for AM, PM, and off-peak periods, and location and type of existing surveillance and control. This availability of this information assists in the initialization of new models and applications being evaluated on the testbed.
5. SUMMARY The research implementation phase of the California Advanced Research Testbed (CART) is approaching operational status. The result will be a traffic research laboratory at UC Irvine with two-way communications to freeway and arterial traffic control centers (Caltrans District 12 ATMS and the City of Irvine ITRAC) providing real-time traffic system data retrieval and control capabilities. The research possibilities are enhanced by the corresponding federal Field Operational Test (FOT) which is installing and testing new communication and management technologies for integrated freeway/arterial response to major traffic transients caused by non-recurrent congestion. The Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) has been developed to support research activities on the Testbed. TRICEPS is an ATMIS implementation and evaluation platform which combines a simulation environment (to act as a surrogate for or to augment incoming real-time data from the realworld network) with a distributed computing platform designed to ease the development, testing, implementation, and evaluation of candidate ATMIS solutions.
plications: Part I - Simulation Methodologies. IVHS Journal 1(3), 227-24l. FHWA (1990) . TRAP User Reference Guide. Gartner, Nathan H., Philip J . Tarnoff and Christina M. Andrews (1991). Evaluation of optimized policies for adaptive control strategy. Transportation Research Record. Jayakrishnan, R. and Craig R. Rindt (1997) . A Distributed Computing Platform and Hybrid Simulation Environment in a Real-time Research Testbed for Advanced Traffic Management and Information Systems. Microcomputers in Engineering. Special Issue on ITS. Jayakrishnan, R., M. Dillencourt, V. Leung and P. Oreizy (1993). Simulation Framework for Distributed Traffic Control Algorithms in ATMS. In: Proceedings of the International Symposium for Automotive Technology and Automation (ISATA). Aachen, Germany. NET (1996). System wide adaptive ramp metering: High level design. Technical report. National Engineering Technology. Zimmermann, H. (1980). The ISO Model of Architecture for Open Systems Interconn&tion. IEEE Transactions on Communications.
6. ACKNOWLEDGMENT The authors would like to thank the California Department of Transportation for the generous support for this research as part of the California Advanced ATMS Research Testbed Contract to Prof. Wilfred Recker, UCl. The Irvine FOT is a project funded by the Federal Highway Administration ITS Field Operational Test Program. The authors remain solely responsible for·the content of this paper.
7. REFERENCES Cameron, G. D. B. and G . I. D. Duncan (1996) . PARAMICS, parallel microscopic simulation of road traffic. Journal of Supercomputing 10(1),25-53. Chang, Gang-Len, Thanavat Junchaya and AIberto J . Santiago (1994). A Real-Time Network Traffic Simulation Model for ATMS Ap1102
IMPLEMENTATION OF A REAL-TIME INTEGRATED CONTROL SYSTEM IN A FREEWAY/ARTERIAL CORRIDOR Craig R. Rindt
R. layakrishnan
Michael G. McNally
Institute of Transportation Studies Department of Civil and Environmental Engineering University of California, Irvine, USA 92697
Abstract. This paper presents the status of the California Advanced Research Testbed (CART) research implementation program. The discussion first describes the establishment of data communication links between the University of California, Irvine (UCI) Advanced Testbed Laboratories and the Testbed field implementation sites including the City ofIrvine and Caltrans District 12 Traffic Management Centers. This is followed by a review of the Irvine federal FOT implementation technologies including MIST, OPAC, SWARM, and the Caltrans D12 ATMS occurring simultaneously with test bed research implementation. The final section discusses the Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) which is designed for use with the real-world data to be received from the data links to the traffic networks on in the Testbed area. Keywords. Integrated Traffic Management, Control Methods and Algorithms, Travel and Traffic Information, Modeling and Simulation
• implement and evaluate activities for development and operation of an integrated multijurisdictional, multi-agency transportation operations system.
1. INTRODUCTION
The CART encompasses two contiguous sub areas in Orange County, CA that include virtually all of the major decision points for freeway travelers in the region. The City of Anaheim subarea is centered about two of its designated "smart streets," Harbor Boulevard and Katella Avenue, and encompasses the City's major special event traffic generators. It is particularly suited for networkwide applications of advanced technologies in traffic management.
The California Advanced Research Testbed project (CART) is an integrated approach to the development and deployment of advanced technologies in the operation and management of urban transportation and is based on real-time, computerassisted traffic management and communication. The transportation operations system that forms the backbone of the Testbed is structured to integrate network-wide traffic information (both surface street and freeway) in a real-time environment and to provide intelligent computer-assisted decision support to traffic management personnel. Under full implementation, CART is designed to: • accelerate deployment through advanced technology research; • demonstrate deployment readiness of advanced systems; 1097
The City of Irvine sub area provides freeway access to a myriad of business and office complexes on both sides of the 1-5 freeway and is particularly suited for corridor-level integration of realtime communication and control in traffic management. Additionally, the Irvine subarea is the site of the federally-funded Irvine Field Opera-
tional Test (FOT) whose objective is to integrate and coordinate a centrally controlled freeway freeway ramp metering system with an arterial traffic management system. The full FOT implementation involves a highly congested corridor through a rapidly growing employment center. The FOT involves an ATMS which extends the capabilities of existing freeway and arterial traffic management systems in the Irvine area. Its key features are the integration and real-time control of current and evolving traffic operations technologies to achieve some degree of integrated control of the freeway and neighboring arterial networks in the defined FOT area. This paper provides an overview of the ongoing research and implementation activities which are part of the CART and vital to the achievement of its primary objectives which are to provide: • an instrumented, multi-jurisdictional, multiagency transportation operations environment linked to university laboratories for real-world development, testing and evaluation of nearterm technologies and applications; • a meeting ground for practitioners and researchers to try new approaches to transportation system management; • a site for private industry to demonstrate and evaluate their prototype technologies under live traffic conditions; • an ongoing testing ground for California and national ITS efforts. The current research implementation tasks are discussed in three parts. The first describes the establishment of a traffic research laboratory which has a two-way real-time data connection with realworld traffic network. This connection provides researchers the access to extensive traffic data and the means with which to test their new technology in a real-world setting. The second part discusses the Irvine FOT implementation technologies which include the Management Information System for Transportation (MIST), Optimal Policies for Adaptive Control (OPAC), the Caltrans District 12 Advanced Transportation Management System (D12 ATMS), and the System Wide Adaptive Ramp Metering (SWARM) system. The third part describes the Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) and discusses the concerns involved with the integration of existing TRICEPS technology for use with the real-time data link with the Irvine FOT traffic network
2. CARl' DATA LINKS The implementation and evaluation of research in the area of Advanced Traffic Management and Information Systems (ATMIS) has always been ham-
pered by the substantial effort involved in obtaining realistic traffic data with which to develop and test the research and the availability of real-world network on which to implement and evaluate the research. The recognition ofthis fact prompted the establishment of a two-way real-time connection between the UCI Advanced Testbed Laboratory and Testbed-area traffic systems. The Testbed communication network is based upon a wide area network utilizing high speed digital facilities. Three classes of communication access are being provided: (1) inter-site data communication; (2) intra-testbed communication; and (3) inter-site high capacity link which supports video teleconferencing. The Testbed Communications Network currently under implementation is based on an ATM infrastructure, designed to be compatible with the existing Teleos ISDN PRI Network established by the Caltrans WAN (Wide Area Network) for videoteleconferencing. The ATM Internetworkiniinfrastructure is to be linked with the Caltrans District 12 TMC and the City of Irvine ITRAC via an OC3 155Mbps SONET fiber optics network, and with the City of Anaheim TMC via ATM using T-1 facilities. The system also includes MPEG 1 video transmission system provided between the UCI ATMS Laboratories and the Caltrans District 12 TMC, allowing for view, display, management and control of freeway video surveillance cameras within District 12.
2.1 Caltrans District 12
The data connection between the Caltrans District 12 Traffic Operations Center (TOC) and the UCI Testbed Laboratories provides a dedicated twoway real-time data connection with the ability to: • obtain field device (loop detectors, VDS, CMS, CCTV, etc.) configuration data; • obtain raw output from field devices in realtime; • obtain 30 second volume, occupancy, and speed data from VDS; • obtain and set Changeable Message Sign realworld (CMS) display status; • obtain and set freeway ramp metering rates. In addition to the real-time communications capabilities, the connection also provides access to the Caltrans on-line database allowing the retrieval of 30-second freeway loop counts, incident logs, and activity logs archived for the past six months up to the present. 1098
2.2 City of InJine
3.2 OPAC
The data connection between the test bed laboratories and the City of Irvine Traffic Research and Analysis Center (ITRAC) is expected to provide, through MIST (see Section 3.1), interfaces to:
Optimal Policies for Adaptive Control (Gartner et al. , 1991) is a distributed control strategy which features a dynamic optimization algorithm that calculates signal timing to minimize a performance function of total intersection delay and stops given the traffic demand on all approaches to the intersection. The real-time version of OPAC being implemented in the Irvine FOT (OPAC-RT Version 3.0) estimates demand on the intersection over a rolling horizon using a combination of traffic data obtained from upstream detectors and expected future arrival patterns determined using a smoothing algorithm.
• obtain processed stop-line and system detector data; • obtain and set current intersection signalization; • obtain and set arterial Changeable Message Signs (CMS)
3. FOT IMPLEMENTATION TECHNOLOGIES
3.3 D12 ATMS
The Caltrans District 12 Advanced Transportation Management System (D12 ATMS) is an operator decision support system and data manager for operations and control of the Orange qounty, CA freeway network. The system provides freeway surveillance and traffic control capabilities, including:
The primary objective of the Irvine FOT is to provide real-time dynamic and predictive intercorridor traffic diversion in response to non recurrent freeway congestion occurring in the Irvine FOT freeway/arterial corridor. The integrated response plan consists of several strategies which may be applied fully or partially:
• automatic incident detection; • surveillance through closed circuit television cameras and vehicle detection systems; and • automatic generation of freeway traffic response plans, which include activation of freeway changeable message signs (CMS), adjustment of ramp metering rates, and other recommended operator actions.
• The diversion offreeway traffic to the arterial network to avoid the impacted location. • The diversion of freeway-bound arterial traffic to avoid the impacted location. • Freeway ramp metering. • Arterial signal optimization to meet diversion demand. The following technologies are presently under implementation in the Irvine FOT. Each of these technologies is expected to play a key role in integrated response implementation.
3.4 SWARM
3.1 MIST
The Management Information System for Transportation (MIST) is a general development platform for customized traffic control systems and Intelligent Transportation Systems being implemented for the City of Irvine by Farradyne Systems Inc. The system uses an open architecture which supports the inclusion of a broad class of system components into the management scheme. MIST employs a database management system supporting the Structured Query Language which maintains system configuration data, user-defined parameters, system status data, and output data from field devices. MIST is designed to monitor and control field devices (e.g., signal controllers, changeable message signs, loop detectors) 1099
The System-Wide Adaptive Ramp Metering system (NET, 1996) is an optimization algorithm for local and system-wide ramp metering for inclusion in the D12 ATMS. SWARM uses a two-tiered approach to meter freeway ramps considering systemwide system-wide (SWARM 1) local (SWARM 2) conditions. SWARM 1 treats the freeway as sections whose downstream end represent some operational bottleneck (lane drop, ramp merge, etc) where recurrent congestion is likely. The algorithm makes near-term predictions of traffic density in these sections from measured data and compares them to the sections' historically measured saturation density values. Ramp metering rates for a given section are adjusted to head off the onset of predicted congestion when the estimated density exceeds the section's saturation density. The SWARM 2 algorithm applies a local ramp traffic-responsive metering rule to optimize freeway density in the vicinity of the subject ramp. The more restrictive metering rate of SWARM 1 and SWARM 2 is selected as the operational rate.
4.1 Simulation Workbench
:m~~__ _(3}_ ATM Network
,,--I
The Testbed Simulation Workbench (TSW) is expected to meet specific goals including the need to: • model traffic dynamics with a suitable, possibly variable, level of detail; • minimize the embedding of applications in the simulation code, placing an emphasis on modeling the effects of applications, but not the applications themselves; • interactively provide system state information to external applications; • interactively receive control and information directives from external applications and model their impacts; • operate at real-time speeds or faster .
:
, \
.., I ~ I
ObjectOriented Database
0::: ,
.~:
Q.
,
,
Testbed Simulation Workbench
~. 0:'
8'/
, p~Io;Y~ ATMIS-/;'plemeniatToi Plat/orm UC! Advanced Testbed Lab •
Fig. 1. TRICEPS Conceptual Structure 4. AN ATMIS IMPLEMENTATION AND EVALUATION PLATFORM The Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) has been established to support activities in the Testbed (Jayakrishnan and Rindt, 1997). TRICEPS is intended as a platform on which new Advanced Traffic Management and Information Systems (ATMIS) technology can be evaluated using a combination of real-world and simulated data. The functional requirements for TRICEPS are therefore defined to consider the needs of researchers explicitly. These requirements include the: • flexibility to study alternate ATMIS designs; • capability to operate with real-time/real world data; • capability to augment real data with simulation; • availability of at least a minimum number of basic component modules for ATMIS design. The conceptual structure of TRICEPS is shown with its real-world connectivity in Figure 1. TRICEPS consists of two main components. The first is a simulation workbench whose primary application is to serve as the evaluation platform for ATMIS alternatives being researched on the testbed. The second is an implementation platform for evaluating these alternative systems. This latter component provides transportation researchers the means to connect groups of distributed, interdependent, ATMIS applications to each other and to simulated or real-world data. These two components are described in the following sections. 1100
The level of computational performance required of a simulation varies with its application. For the TSW, "real-time" performance has dual meanings. First, as an effective evaluation platform for ATMIS implementations, the simulation mus~ provide performance which approximates the reaI world. In this role, the primary goal of the simulation is faithful modeling of the traffic system with a secondary goal (especially in light of issues relating to distributed algorithm performance) of computational performance approaching clock-time. In its second role, the TSW must operate in real-time, while simultaneously connected to a partially instrumented real-world traffic network, to provide supplementary data about the state of the system to analysis models which require complete or specialized network data. The tradeoff between modeling detail and computational performance is a well known dilemma in system simulation. For many simulation uses, the tradeoff is manageable as in the cases when a large traffic system is being modeled for general performance characteristics (e.g. the evaluation of planning alternatives using traffic assignment models) or when a small portion of a system is simulated at a high level of detail to provide detailed data for specialized applications (e.g. the evaluation of an incident detection algorithm using microscopic simulation). The evaluation needs of integrated ATMIS, however, may require both detailed system data and network-wide performance data. A simulation approach which models the traffic system with varying levels of detail has shown promise in alleviating this tradeoff (FHWA, 1990). Such a scalable simulation can increase computational efficiency by allocating resources as appropriate to the ATMIS applications being evaluated. Other research in this area has considered simulation restructured for massively parallel computing architectures (Chang et al., 1994; Cameron and
Duncan, 1996).
• data translation and conversion for non standard applications.
Both of these approaches are being studied as simulation frameworks for TRICEPS. A hybrid simulation which offers variable levels of simulation detail for different subnetwork components has been developed using an enhanced version of the DYNASMART simulation model and the microscopic INTRAS freeway simulation. In this simulation scheme, DYNASMART models the test bed-area freeway / arterial network mesoscopicly (with a macroscopic flow model and a microscopic driver route choice model) and coordinates the use of multiple, distributed INTRAS simulations to simultaneously model portions of the freeway network microscopically. This hybridization is able to provide much of the functionality required for the evaluation of most ATMIS strategies with only moderate computational requirements.
The emphasis of this platform is to provide an efficient means of establishing connectivity between applications in the system without imposing extensive design restrictions on developers. Such an undertaking requires the consideration of the nature of the applications to be included in the system. For the purposes of this discussion , an application is taken to be any element associated with an ATMIS which is capable of providing information to other elements of the system either automatically or on demand. This definition includes all conventional and advanced traffic functions as well as the traffic system itself which is ultimately drives the entire ATMS. Note that each of the components of the simulation workbench is considered an application and if the workbench is completely replaced by the real-world, then the real-world traffic system itself is considered an application.
Additionally, the Paramics (Cameron and Duncan, 1996) microscopic simulation model is currently being evaluated as a future simulation component of the Testbed. Paramics provides a fully scalable parallel simulation model with advanced visualization capabilities and extensive modelling flexibility which allows the use of user-developed models in all aspects of simulation ranging from car-following and lane changing to driver behavior and traffic control systems. For large networks such as that in the Testbed, this high level of functionality is computationally intensive and therefore requires high performance computing capabilities. With the addition of this computational power in the UCI Testbed laboratories, Paramics is expected to become an important component in the evaluation of candidate ATMIS solutions implemented using TRICEPS.
Each application operates using data from other applications and provides data for use by other applications (including the traffic system which takes control information from the ATMS and produces state data used by the ATMS). In terms of the Open System Interconnection (OSI) model of network communication (Zimmermann, 1980), this protocol performs both presentation and application layer functions . Note that at the application layer, specific knowledge of the external applications is unnecessary. The application code itself resides in the highest layer of the protocol and is serviced by input acquisition and conversion functions and output storage and request service function at lower layers which provide the interface to other applications. Such encapsulation allows easy incorporation of new modules into the TRICEPS architecture without extensive redesign of the existing application's logic or data structures.
4.2 Distributed Computing Platform
TRICEPS also contains a distributed computing platform for implementing partial and complete ATMIS solutions for evaluation using either simulated or real-world data from the Testbed network. The platform consists of an upper level communications protocol called the Transportation Algorithm Interface Library (TAIL) which employs a mid-level TCP lIP-based protocol known as the UC hvine Distributed Algorithm Testing Environment (ELUCIDATE), which has been designed for general purpose distributed algorithm simulation (Jayakrisbnan et al., 1993). Together, TAIL and ELUCIDATE include facilities for:
4.3 Research Implementation Using TRICEPS
When implemented using TRICEPS, the effectiveness with which a given set of applications provide integrated analysis, optimization, management, and control can be evaluated. To support the implementation applications developed separately, but which rely on other analysis tools to provide data, a suite of models developed within the CART and already implemented using TRICEPS are available to provide the data and analysis which may be required by new component applications. These models include classical optimization algorithms, adaptive control schemes, traditional simulation programs, real-time expert systems, neural networks, etc. Additionally, a database of network information is available for the Testbed area with
• seamless encapsulation of individual applications into the distributed processing environment; • the management of application interdependencies; and 1101
complete representation of the freeway/arterial network, time-varying OD matrices for AM, PM, and off-peak periods, and location and type of existing surveillance and control. This availability of this information assists in the initialization of new models and applications being evaluated on the testbed.
5. SUMMARY The research implementation phase of the California Advanced Research Testbed (CART) is approaching operational status. The result will be a traffic research laboratory at UC Irvine with two-way communications to freeway and arterial traffic control centers (Caltrans District 12 ATMS and the City of Irvine ITRAC) providing real-time traffic system data retrieval and control capabilities. The research possibilities are enhanced by the corresponding federal Field Operational Test (FOT) which is installing and testing new communication and management technologies for integrated freeway/arterial response to major traffic transients caused by non-recurrent congestion. The Testbed Real-time Integrated Control and Evaluation Prototype System (TRICEPS) has been developed to support research activities on the Testbed. TRICEPS is an ATMIS implementation and evaluation platform which combines a simulation environment (to act as a surrogate for or to augment incoming real-time data from the realworld network) with a distributed computing platform designed to ease the development, testing, implementation, and evaluation of candidate ATMIS solutions.
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6. ACKNOWLEDGMENT The authors would like to thank the California Department of Transportation for the generous support for this research as part of the California Advanced ATMS Research Testbed Contract to Prof. Wilfred Recker, UCl. The Irvine FOT is a project funded by the Federal Highway Administration ITS Field Operational Test Program. The authors remain solely responsible for·the content of this paper.
7. REFERENCES Cameron, G. D. B. and G . I. D. Duncan (1996) . PARAMICS, parallel microscopic simulation of road traffic. Journal of Supercomputing 10(1),25-53. Chang, Gang-Len, Thanavat Junchaya and AIberto J . Santiago (1994). A Real-Time Network Traffic Simulation Model for ATMS Ap1102