One of the core components of the I-210 Pilot is a Decision Support System (DSS) that can help system operators assess traffic conditions along a corridor and choose the best courses of action to manage them. The DSS:
- Takes the information gathered from monitoring systems
- Estimates current traffic conditions
- Identifies events, incidents, bottlenecks, etc.
- Develops strategies to respond to identified problems
- Uses modeling and simulation to forecast near-future conditions under various scenarios and evaluate potential strategies
- Recommends the best strategy to implement
An everyday example
In many ways, the DSS process is similar to what we do every day. For example, suppose you're a pedestrian who wants to cross a busy street at a traffic light. The light has already turned green as you approach the street, and the pedestrian "walk" signal is on. Before crossing, you would need to:
- Assess the immediate situation based on all the information at hand. How wide is the street? How long has the "walk" signal been on? How much traffic is present? Is it stopped and waiting at the light, or is it approaching from some distance away? Is there rain, fog, or darkness that might prevent drivers from seeing you? Is it rush hour, which might make drivers more aggressive? The answers help you make your best estimate of what's happening.
- Combine the information with what you already know based on your memory and experience of other traffic situations, your awareness of safety, and your attitude toward risk. You are applying a "mental model" to your estimate of the situation.
- Consider your options. You might (a) walk across safely, assuming there is enough time; (b) run all or part way across, if the light changes while you're in the street; (c) wait for the next "walk" cycle, to be sure you have enough time to cross. You are developing possible strategies for responding to the situation.
- Predict what you think will happen, based on what you see and what your experience tells you. You are using your best estimate and your mental model to make a short-term forecast, to evaluate your possible strategies.
- Decide what to do. You choose what seems like the best strategy for the circumstances.
- Act on your decision.
You can see these steps in the following simplified illustration of DSS components:
Taking in field data from traffic monitoring systems, plus archived historical data (1), the DSS uses its modeling and simulation tools (2) to first estimate the current state of traffic (3) and then predict future conditions (4). It then draws on a database of predefined strategies (5) and recommends one as optimal for the situation. All this information is communicated to the system operator (6) who, using professional knowledge and experience, decides how best to address the situation. Possible actions might include activating arterial signal timing plans, ramp metering changes, or changeable message signs (7).
Incidents and strategies
Since the key functions of a Decision Support System include recognizing traffic incidents and recommending possible responses, defining what those incidents are and how to respond to them is an important task in developing a DSS.
One way to define incidents, for example, might be to create categories of characteristics:
Depending on the corridor, the categories could be refined or expanded to include addditional incident characteristics, such as time of day, day of the week, duration, season, whether school is in session, whether the incident occurs on a holiday, whether it involves transit, etc. The DSS would then use the characteristics to identify the type of incident.
Like many aspects of an ICM system, determining how to respond to an incident involves both the application of technology and the collaboration of participating stakeholders. For example:
Working together, corridor stakeholders would develop and agree on a "playbook" of various response strategies for each type of incident, such as 3-5 responses from low to high impact. (A possible strategy might be: If an incident occurs on the freeway at rush hour, change the signal timing on the adjacent arterial to Timing Plan B to help handle overflow traffic.) Stakeholders might use the following types of control options or "plays" to build a playbook of strategies:
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- The DSS would draw on the playbook of predefined strategies, and use modeling and simulation to recommend the best strategy under the circumstances.
- The selected strategy would be downloaded to all integrated traffic management systems, to inform system operators of the recommended response.
- All affected corridor agencies would need to cooperate in approving the response strategy, but which agency would lead that process? One possibility would be to have the agency on whose facility the incident occurs take the lead. If that were a local agency, for example, it would coordinate with Caltrans and other adjacent agencies to evaluate and decide on the recommended response. If Caltrans, it would coordinate with the directly adjacent agencies and notify other agencies of the action taken.
An operational scenario
The following examples illustrate how the system might work during a freeway incident. The first example shows the steps in response to an incident, from detection to incident clearance:
The second example shows the system continuing to monitor the area, but focusing instead on the remaining congestion after the incident has been cleared: