Flatness Based Control of Traffic Flow for Coordination of Ramp Metering and Variable Speed Limits

We apply in this article the concept of flatness control to coordinate variable speed and ramp metering in order to regulate the flow at the mainline section of the road. The same approach was applied in the case of traffic control to single section with on-ramp without combination with variable speed limits [1]. The basic idea is that speed limits can increase the (density) range in which ramp metering is useful [7], [9], [8]. We use LWR traffic flow model with the functions of supply and demand between the segments to take into account the back propagation of the traffic jams [11]. The purpose of the control task is to maximize the flow and minimizing the queue length at the on-ramp. We illustrate the flatness approach by comparing the cases ´ramp metering only´ and ´coordinated ramp metering and speed limits´ for a simple network.