Summary of Mn/DOT TMC IRIS System
The Mn/DOT Traffic Management Center operates the Intelligent Roadway Information System (IRIS) as the primary traffic management control system. IRIS operates in a client server environment, with the primary server housed in the computer room at the Regional Traffic Management Center (RTMC). Clients are operated at computer consoles within the RTMC control room. For sake of clarity, the IRIS system is not accessible over the Internet, but rather operators wishing to run IRIS must have a client installed on the machine, which typically requires a high speed secure connection, such as the Mn/DOT fiber connection. The IRIS system was developed in-house by the Mn/DOT TMC staff, and therefore no royalties or licenses are needed to operate the system or expand its use to additional consoles or users.
In the past year, the use of IRIS has expanded to support traffic management/traveler information activities in St. Cloud and Rochester, Minnesota. The St. Cloud deployment operates a ‘satellite’ installment of IRIS in St. Cloud running on the primary IRIS system in the Twin Cities. The Rochester deployment is entirely separate from the Twin Cities installation of IRIS, running as a stand-alone TMC.
The core functions of IRIS in the Twin Cities are as follows:
- Maintaining communications with the over 2000 loop detectors on the roadways to collect, process, archive and make the traffic flow data available as needed;
- Controlling the ramp meters through a combination of automated control (in response to real-time traffic conditions) and manual control;
- Controlling closed circuit television cameras by sending pan/tilt/zoom commands to the cameras and receiving and recording (when appropriate) live motion video feeds from the cameras;
- Controlling the Dynamic Message Signs (DMS) by allowing operators to view current messages and activate messages as needed from the TMC control software.
The remainder of this overview will define these core functions.
Loop detector communication and processing
The loop detectors around the Twin Cities provide volume, occupancy and computed speed information at roughly half mile increments along the majority of the freeway miles.
Loop detectors monitor each lane of travel, with nearby loops aggregated into loop reporting sites. These loop reporting sites communicate over the fiber connection to the TMC.
The uses for loop detector data are numerous. Three primary uses of the loop detector data are summarized as follows:
Real time collection of volume, occupancy and speed.. The most visible and obvious use of loop detector data is to provide a snapshot of current traffic conditions on the freeways in order to support ramp metering, traffic flow map generation, and traveler information creation.
With polling cycles of 30 seconds, the IRIS system collects a complete snapshot of the traffic on monitored freeways that are update every half minute. The IRIS system uses the loop detector data to run algorithms that control the ramp metering rates. Therefore, with little operator intervention, increases in volume and reductions in speeds can trigger ramp meters to activate and adjust timing as appropriate.
Another use of real-time loop reporting is to create the traffic flow maps that are displayed on Mn/DOT’s public web page. The traffic flow map identifies slow downs by coloring the roads yellow or red. In addition to utilizing the loop detector data within the TMC, the IRIS system also produces an XML feed of the IRIS system for ingest by other systems. One system that ingests this data is the Mn/DOT Condition Reporting System and 511 systems. The Condition Reporting System ingests loop detector data provided by IRIS and by processing a set of algorithms, automatically creates situations that are served up on the 511 phone system, allowing callers to 511 to hear such reports as “stop and go traffic on I-35W from Highway 42 to the Minnesota River” without any operator intervention. Finally, loop detector data is ingested by a series of third party travel information providers, such as the media and other reporting agencies.
Data archive of travel volume, occupancy and speeds. A second relevant function of the IRIS loop detectors ingest is to archive and store all loop detector measurements for future queries. IRIS offers an Intra-net accessible tool to Mn/DOT employees allowing them to request volume/occupancy/speed reports for stretches of road and particular time periods. This information proves useful for design, analysis, research and other such administrative features. The archive of data also allows TMC operators to recreate events during staff training. Considerable effort has been dedicated towards the development of the archive and retrieval feature within IRIS, to meet the needs of Mn/DOT (both the TMC and roadway design groups), the University of Minnesota and other related agencies.
Loop detector replication. The third relevant use for loop detector data involves a combination of the two previous functions. This is a process to consider past recordings of such things as the percentage of vehicles that exit on off-ramps, and to use this information to fill in missing loop detector data, in the event that isolated loops are non-functioning. In summary, the analysis of past data and travel behavior allows the TMC to continue to operate critical control features (such as ramp meters) that rely on loop data, even when a few isolated loop detectors are out of service.
Ramp Meter Control
For over 20 years, Mn/DOT has operated ramp meters around the Twin Cities. The general concept is that as volumes build on the freeways, the ramp meters will control the entry of vehicles to allow single car entries spaced evenly apart, rather than clusters of vehicles merging into traffic. Similarly, ramp meters seek to maintain a steady flow of traffic on the primary freeway in exchange for small queues at various approaches.
The current operational scenario for the RTMC ramp meters is that both the volume/speed of the freeway as well as the queue length at the meter is considered in the algorithm that determines the ramp meter cycle time. In this respect, the system will no longer restrict traffic such that extremely long queues build on the ramps during severe traffic slow downs.
To effectively operate the large number of ramp meters, the IRIS system uses a combination of automated decision making based on recorded loop values, as well as manual overrides allowing operators to select timing patterns as needed. The IRIS user interface allows operators to view all loop detector status (on, off, non-functioning), and select those meters that they wish to manually control. Similarly, patterns may be implemented for groups of ramp meters, activating pre-designed plans for groups of meters, rather than selecting each one individually.
Dynamic Message Sign Control
The IRIS system performs two key functions with regard to the Dynamic Message Signs (DMS):
· Allowing a DMS user interface; and
· Performing all communication aspects needed to physically talk to and control the signs.
User Interface. The IRIS system allows operators to graphically view all locations of DMS signs, and by selecting signs, users may select from pre-canned phrases to build 3-line messages to be displayed on the signs. A security feature allows operators to only select from pre-saved messages, and mandates that only administrators may type new phrases into the system. The user interface allows operators to click on any sign and view the current status of the sign as well as the current message displayed. Amber Alert capabilities are also supported on the IRIS DMS control, and similarly a limited number of individuals are authorized to post Amber Alert messages to the DMS.
Sign control. The IRIS system performs all communications and control with the DMS signs using NTCIP standards. The communications aspect relays commands to post messages on to the signs, as well as to query the signs for existing messages as well as status reports on the functionality of the signs.
Closed Circuit Television Camera
The IRIS system, again, performs two key functions with CCTV cameras:
· To allow operators to take control of pan/tilt/zoom for all cameras in the system; and
· To allow display and relay of full motion video switching displays.
CCTV control. IRIS operators may control cameras using ‘joystick’ controls to pan/tilt/zoom control the cameras.
Display and relay of full motion video. The IRIS system allows for full motion video to be displayed on screens within the RTMC. Users may select what cameras are displayed on which display monitors. In addition, the IRIS system video switch allows other systems/agencies to have access to the full motion video as needed.
