San Antonio's Medical Center Corridor: Lessons Learned From The Metropolitan Model Deployment Initiative
This report is one in a series that documents lessons learned from the US DOT Model Deployment Initiatives program. It reviews one component of the San Antonio MDI - the integration of a highly successful freeway management system with a newly deployed arterial system.
The San Antonio Medical Center Corridor is approximately 5.4 miles long by 1.2 miles wide. Travelers often use this corridor when there is a disruption of traffic flow on the nearby Interstate Highways 10 and 410 (I-10 and I-410).
The goal of this implementation was to develop more effective, coordinated management of roadway incidents and their associated delays. The project would integrate the new arterial management system along the corridor's Fredericksburg Road with preexisting freeway management system on a 5.4 mile section of I-10 and I-410. The arterial management system would consist of 10 loop stations, three camera systems, nine dynamic message signs, and a new arterial operations work station. Transportation staffs also created incident response signal plans to control the increased flow of traffic caused by an incident.
The lessons concern the benefits of integrated ITS systems and the related institutional issues that must be overcome to achieve effective integration across involved transportation agencies.
Use signal timing plans appropriately:
- Under periods of significant diversion, San Antonio’s incident response signal timing system offers substantial benefits. However, when diversion is low, implementation simply leads to unnecessary cross-street delays. The application of the incident management plans to minor and moderate incidents can lead to significant reductions in efficiency. This scenario may actually increase delay, even with other elements of the system operating.
- Monitor arterial operations carefully to avoid this situation. First, use of the incident response signal plans was restricted to more severe incidents, such as those involving the blockage of multiple freeway lanes for periods of 45 minutes or more. Second, video surveillance was used by the arterial operations personnel to monitor the impacts of the signal timing changes in real time and to turn these plans off and on when appropriate. Finally, San Antonio undertook a commitment to continually update and broaden the breadth of the incident signal plans.
Use the system's variable message signs appropriately:
- Rerouting around minor incidents is often unnecessary and may even lead to increased delay; however, the posting of the situation to a variable message sign may cause some travelers to proceed with just such a suboptimal solution. For example, modeling of the Medical Center Corridor predicts a 2.5 percent reduction in delay for incident management alone. Under the same scenario, the delay reduction drops to just 1.9 percent when messages are displayed to accompany incident management. This scenario supports the hypothesis that the system may not be needed in every case.
- Mitigate the potentially negative impacts of variable message sign usage by either restricting use to incidents severe enough to justify diversion or by carefully selecting message sets for the signs that minimize erroneous routing decisions.