Integrated Approach: Inside story on the ICM test corridor
The U.S. DOT developed a simulation model to test the potential impacts of integrating ITS in major transportation corridors. The goal was to demonstrate that increased integration among freeways, arterials, and transit systems can help balance traffic flow and enhance corridor performance.
Having a sufficient variety of ITS, network management functions, and archived traffic data, the I-880 corridor in San Francisco was selected as the ICM Test Corridor. The corridor located between Oakland and Fremont covered a distance of approximately 34 miles (250 lane miles) and contained an extensive network of alternate routes and transit options (bus and rail).
To evaluate the potential impacts of independent and combined ICM strategies in the corridor, an Analysis, Simulation, and Modeling (AMS) framework was developed. The model examined recurring and nonrecurring (incident–related) operational conditions using three levels of analysis: macroscopic, mesoscopic, and microscopic. The macroscopic analysis examined trip tables to evaluate overall trip patterns. The mesoscopic analysis examined driver behavior to evaluate traffic response to different ICM strategies, and the microscopic analysis examined the impacts of traffic control at roadway junctions.
The AMS framework analyzed the following ICM strategies:
- Zero ITS baseline
- Traveler information. In the test corridor, drivers were provided with real-time information, both pre-trip and en route, about incident conditions, expected delays, availability of transit and highway options, travel times for these options, and availability of parking.
- Transit traveler information
- Ramp metering
- HOT lanes
- Arterial traffic signal coordination
The results focused on four key performance measures: mobility (movement of people and freight), reliability (relative predictability of the public’s travel time), safety (safety characteristics in the corridor including fatalities, injuries, and property damage from crashes), and emissions and fuel consumption. The benefits data derived from the impact analysis were monetized and compared to costs data (capital, operating, and maintenance costs) derived from planning-level and life cycle cost estimates.
There were a variety of test corridor AMS results specific to the benefits resulting from different ICM strategies. The following results were reported.
- HOT lane and highway traveler information were consistently the most effective ICM investments. Converting an existing HOV lane to a HOT lane produced a benefit-to-cost ratio that ranged from of 14:1 to 39:1.
- Highway traveler information produced a large benefit, especially in the case of unexpected events such as a major incident. In this case, the benefit-to-cost ratio ranged from 16:1 to 25:1.
- Transit traveler information produced less benefit than highway traveler information, but the impact remained positive with a benefit-to-cost ratio of 16:1. Up to four percent of travelers shifted modes in response to a major incident.
- Local adaptive ramp metering produced a positive benefit-to-cost ratio that ranged from 6:1 to 12:1 on high-demand days (36 percent of all workdays) but produced a negative benefit-to cost ratio on medium demand days.
- In high-demand conditions, arterial signal coordination produced a benefit-to-cost ratio that ranged from 12:1 to 20:1. In medium-demand conditions the benefit-to cost ratio ranged from 4:1 to 13:1.
- Combining multiple ICM strategies produced a benefit-to-cost ratio that ranged from 7:1 to 25:1. The AMS framework applied to the Test Corridor was able to dynamically adjust the price of HOT lanes in response to changing traffic conditions, provide traveler information to identify potential alternate routes and transit options, update ramp meters, and adjust arterial signal timings.
Overall, the model calculated a 10-year benefit of approximately $570 million with approximately one half of that benefit the result of ICM strategies applied during high demand/major incident days (representing 25 percent of commute days).
A key finding in the report indicated that depending on the prevailing traffic conditions and scope of corridor deployment goals the benefits derived from a combination of some ICM strategies can be less than the benefits resulting from some individual strategies. In some circumstances, some ICM strategies can work across purposes. As shown in the example above, freeway ramp metering can produce positive benefits under high travel demand, but negative benefits under medium travel demand.
The AMS framework used in this study can help decision-makers identify gaps, determine constraints, and invest in the best combination of strategies to improve performance.
Related Costs Database summary: Integrated Corridor Management: Analysis, Modeling, and Simulation Results for the Test Corridor, Prepared by Cambridge Systematics for the U.S. DOT. September 2008.
Related Lessons Learned summary: Integrated Corridor Management: Analysis, Modeling, and Simulation Results for the Test Corridor, Prepared by Cambridge Systematics for the U.S. DOT. September 2008.