Smart Trek-Style Response to Accidents
The Northwestern proposal, which offers the kind of mathematical model used in the field of operations research, is designed to work with intelligent traffic systems like Seattle’s Smart Trek.
The model provides information that can help divert cars and trucks to other roads when freeway lanes are closed due to a traffic incident. To avoid shifting the problem from the freeway to surface streets, the model directs traffic in an orderly fashion to roads that can absorb the traffic, monitors the conditions on these alternate routes, and, where necessary, adjusts the signal timing plans to the new traffic conditions.
The model assumes that location-specific information dissemination devices and personnel are available that can alert drivers. These include Variable Message Signs (large electronic panels used on freeways), highway advisory radio, and police officers on the scene. The information can be automatically downloaded to these signs or relayed through an operator to traffic police.
The Dynamic Traffic Assignment model that the Northwestern algorithm uses is state-of-the-art, developed under a three-year, multimillion dollar contract with the Federal Highway Administration and Northwestern, University of Texas, Purdue, Lockheed, and MIT.
‘Prescriptive’ More Helpful Than ‘Descriptive’
"Today, information conveyed to drivers is typically descriptive - ‘There’s an accident on I-90 or congestion ahead’ - and not prescriptive - ‘Use this arterial or freeway because of an accident on I-90,’" explains Dr. Athanasios K. Ziliaskopoulos of Northwestern.
"When it is prescriptive, it usually detours drivers to another roadway for the duration of the incident. Sometimes, however, Murphy's Law kicks in and you have another accident on the alternate route, or things in there get really bad. Our model is dynamic in nature and computes new recommendations every minute or so that account for prevailing traffic conditions everywhere in the vicinity of the accident."
Seattle System
Integrating the model into Seattle’s system would be relatively easy, say the authors, because the city already has a sophisticated traffic monitoring and information dissemination system. Seattle, they note, collects data from detectors that the model can use and has the means to transmit information to users.
"One thing missing from the Seattle system is a model that gets data from the detectors and produces information for drivers," says Omar B. Sawaya, also of Northwestern. "Seattle has the technology but not the algorithms to produce the kind of information that needs to be conveyed to users. Our algorithm develops prescriptive information that by definition results in improved conditions."
Few U.S. Cities Reroute Well
Incidents are a major cause of freeway traffic congestion, delays, environmental hazards and secondary accidents. Many jurisdictions face the occasional need to respond to serious, unexpected incidents involving multiple lane or total facility closures due to major crashes, load spills and/or release of hazardous materials. Many among them have plans for quickly responding to incidents by dispatching proper personnel and equipment to aid crash victims and to facilitate the rapid clearance of the incident from the roadway.
But very little has been done, say the authors, in managing the impacted traffic, a task typically left to the personnel dispatched to the scene, without providing them with systematic tools or training to help them perform this task effectively. In the case of major incidents, rerouting traffic can be important for network efficiency and public safety, as well as to protect the incident scene and provide for rapid and safe clearance.
The authors say that their incident traffic management system, if implemented, has the potential to drastically reduce traffic congestion around incident locations. It can also reduce air pollution, driver frustration, and possibly secondary accidents.
The paper, "Development of Dynamic Control Strategies for Managing Freeway Incident Traffic" is by Mr. Sawaya and Dr. Ziliaskopoulos of Northwestern University.
For additional information on the conference, including a full list of workshops, visit the web site at http://www2.informs.org/Conf/Seattle98/
The Institute for Operations Research and the Management Sciences (INFORMS) is an international scientific society with 12,000 members, including Nobel Prize laureates, dedicated to applying scientific methods to help improve decision-making, management, and operations. Members of INFORMS work primarily in business, government, and academia. They are represented in fields as diverse as airlines, health care, law enforcement, the military, the stock market, and telecommunications.