ADAPTIVE SIGNAL CONTROL TECHNIQUE FOR IMPROVING TRAFFIC FLOW AT HIGHWAY-RAILROAD CROSSING: SAN DIEGO'S LIGHT RAIL SYSTEM CASE STUDY

In an effort to address long-standing traffic congestion occurring at at-grade highway rail crossings along San Diego's light-rail system, the City of San Diego for the San Diego Regional Traffic Engineers' Council has initiated a comprehensive study to address congestion, reduce delay, and improve traffic flow at roadways and intersections that experience the effects of traffic signal preemption due to highway-railroad train crossings. The Old Town transit center in San Diego, California is chosen as a case study in this paper. A problem of having long delays at this study location is described. Multiple trains operated by different agencies and multiple preemption events cause excessive delays and congestion to the traffic. Often preemption events will occur concurrently, and this will lead to certain traffic movements being delayed for extended periods of time. Therefore, we propose a strategy of using an adaptive traffic signal timing that can use multiple timing plans to operate traffic at this location. This paper also describes the current traffic volumes and a result of using computerized micro-simulations that provide a measure of effectiveness of both the current condition and the proposed condition with the proposed strategy. A computerized micro-simulation using VISSIM software package suggests that the adaptive traffic signal timing strategy leads to better traffic flow by reducing overall vehicle delays and queue lengths caused by multiple train crossings.