Lessons Learned from the San Diego I-15 Integrated Corridor Management AMS Project
Integrated Corridor Management: Analysis, Modeling, and Simulation for the I-15 Corridor in San Diego, California
A study published in 2010 followed the USDOT Analysis, Modeling and Simulation (AMS) framework to evaluate Integrated Corridor Management (ICM) strategies on the Interstate-15 Corridor in San Diego, California. The I-15 Corridor is an 8-10-lane freeway, connecting San Diego, California with destinations to the northeast. The study area consists of the freeway including managed/HOT lanes and general purpose lanes, frontage roads, Bus Rapid Transit, park-and-ride lots, and regional arterial streets.
The analysis investigated ICM strategies including pre-trip and en-route traveler information, mode shift to transit, freeway ramp metering, signal coordination on arterials with freeway ramp metering, physical bus priority, and congestion pricing on managed lanes. The study evaluated the strategies under various operating conditions on the I-15 Corridor such as high, medium, and low travel demand, daily operations, and freeway and arterial incidents.
This report documents the analysis methodologies, tools and performance measures used to analyze Integrated Corridor Management (ICM) strategies for the I-15 Corridor, and presents high-level results and lessons-learned for the successful implementation of ICM. The I-15 Corridor is an 8-10-lane freeway, providing an important connection between San Diego, California and destinations to the northeast. The Corridor study area consists of the freeway including managed/HOT lanes and general purpose lanes, frontage roads, Bus Rapid Transit, park-and-ride lots, and regional arterial streets.
The analysis investigated various operating conditions on the I-15 Corridor including high, medium, and low travel demand, daily operations, and freeway and arterial incidents. ICM strategies analyzed include pre-trip and en-route traveler information, mode shift to transit, freeway ramp metering, signal coordination on arterials with freeway ramp metering, physical bus priority, and congestion pricing on managed lanes.
The I-15 Corridor AMS project provided some lessons learned including the following:
- Invest in the right strategies. The analysis offers corridor managers a predictive forecasting capability that they lack today to help them determine which combinations of ICM strategies are likely to be most effective under which conditions.
- Invest with confidence. The analysis allows corridor managers to "see around the corner" and discover optimum combinations of strategies, as well as conflicts or unintended consequences that would otherwise be unknowable before implementation. For example, the I-15 AMS helped identify a potential unintended consequence resulting from opening the managed lanes to all traffic during major incidents on the freeway; this policy would have resulted in Bus Rapid Transit (BRT) losing mode share because the managed lanes would be slower than before thus providing less incentive to travelers to shift to BRT. A policy solution tested and proven beneficial in the model involves making BRT free during major incidents.
- Improve the effectiveness/success of implementation. With this analysis, corridor managers can understand in advance what questions to ask about their system and potential combinations of strategies to make any implementation more successful.
- Improve implementation based on experience. The analysis provides a long-term capability to corridor managers to continually improve implementation of ICM strategies based on experience.
- Improve travel time and travel time reliability with improved traveler information. Across all operational conditions, most of the ICM benefit is attributed to the travel time, travel time reliability, and fuel savings on the southbound freeway and arterials. With the provision of improved traveler information, more arterial travelers are attracted to the freeway thus improving arterial performance and overall system performance.
- Consider potential disbenefits related to open access to managed lanes during incidents. Managed lanes show some disbenefits as a result of opening these lanes to all traffic during major freeway incidents. However, vehicles using the open managed lane are not in the adjacent general purpose lane and arterials, thus improving overall corridor performance. Arterials show a considerable amount of travel time and travel time reliability benefits owing mostly to arterial signal optimization.
- ICM strategies produce more benefits at higher levels of travel demand during non-recurrent congestion. An important finding of this analysis is that ICM strategies produce more benefits at higher levels of travel demand, and during non-recurrent congestion. Approximately 93 percent of the total ICM benefits result from the high- and medium-demand scenarios (representing 69 percent of commute days). Also, two-thirds of the total benefit is attributed to high- and medium-demand scenarios with an incident. For individual travelers who primarily rely on the I-15 southbound facility the majority of benefits accrues under particular operational conditions associated with high travel demand and incidents. This finding validates the hypothesis that ICM is most effective under the worst operational conditions including heavy-demand and major incidents.
- Improve transit capacity utilization. Transit excess capacity is better utilized overall, and particularly under incident conditions, drawing additional travelers to the BRT facility without overwhelming the BRT.
- Using ICM strategies improves corridor performance. The I-15 corridor AMS validates the ICM concept: dynamically applying ICM strategies in combination across a corridor is shown to reduce congestion and improve the overall productivity of the transportation system.
The San Diego ICM I-15 analysis, modeling and simulation project was highly successful in determining the benefits of implementing ICM in the corridor. Many benefits, disbenefits and lessons learned were identified during this project that helped to support the case for ICM implementation. This document provides a valuable resource for those considering options to improve corridor operations and management.