Ramp control taking into account ramp demand and ramp queue size information

The paper presents the design overview and evaluation results for the Stratified Zone Metering (SZM) strategy, which was recently deployed in Twin Cities, Minnesota. SZM strategy takes into account real-time ramp demand and queue size information, aiming to balance two conflicting objectives in freeway control, ie, improving freeway efficiency while preventing excessive ramp delays. In order to assess critical aspects of the strategy's performance, comprehensive metrics which are practically impossible to measure are generated through rigorous microsimulation. Consistent with qualitative field observations, the evaluation results confirmed SZM strategy's effectiveness in controlling ramp queue spillbacks and limiting ramp wait time below a prescribed threshold. However, the nonrestrictive metering rates dictated by SZM may cause the freeway to be overloaded, leading to a compromised freeway performance as compared to restrictive ramp control.