Ramp metering is a very important method to improve freeway traffic system performance, but current researches emphasize only on the entering flow control, and not much attention has been paid to the exiting volume at offramp. In some situations, the exiting queue will decrease the overall system performance by a large magnitude. This is demonstrated by simulation experiments and field observation. In this study, a mix integer model is proposed to optimize the arterial and off-ramp control signal timing based on cell transmission traffic propagation model. A Genetic Algorithm based solution algorithm is proposed along with a numerical case study to demonstrate the benefits of this model.