The effect of signal settings on the macroscopic fundamental diagram and its applicability in traffic signal driven perimeter control strategies

It has been proposed that a macroscopic fundamental diagram (MFD) can be used as input for perimeter control strategies. We consider a network consisting of a perimeter with traffic lights and a subnetwork without traffic lights. The MFDs for the two parts, i.e. the controlled subnetwork and its perimeter, are determined by means of microsimulation. We found that different signal settings change the shape of the MFD for both parts considerably. Also the ratio between the performance of the subnetwork and the corresponding perimeter is often fairly constant regardless of the signal timings. Thus, metering traffic heading towards the subnetwork is not always a good control strategy, as the performance of the subnetwork is eventually affected in the same way as the performance of the perimeter. Furthermore it has been found that the shape of the MFD of the perimeter, including the critical network density, strongly depends on the signal timings. It is therefore concluded that the MFD is difficult to use for control strategies aiming to adapt signal timings, because the changed signal timings themselves will result in a different value for the critical network density.