A separate turn phase is often used at intersection with heavy left turns. This wastes capacity on the approach because some of its lanes cannot discharge during its green phases. The problem can be eliminated by reorganizing traffic on all the lanes upstream of an intersection using a mid-block pre-signal. To evaluate the effectiveness of the pre-signal control system, this study has also conducted extensive simulation experiments, based on a intersection simulator calibrated with real-world data. The experimental results show that under heavily congested traffic conditions the pre-signal control system can outperform all existing control strategies with respect to the total capacity, the average vehicle delay, and the queue length. This study has also investigated critical traffic flow related factors that may impact on the performance of such a system.