In part II of this article, simulation results of the well-known ALINEA method of Papageorgiou et al. for feedback on-ramp metering are discussed. It is found that the main aim of ALINEA on-ramp metering strategies – maintenance of occupancy in free flow downstream of an on-ramp bottleneck in a small neighbourhood of chosen optimal (target) occupancy – cannot be achieved through the use of the ALINEA method. It will also be shown and explained why none of the ALINEA strategies can prevent traffic breakdown at the bottleneck. The ALINEA strategies cannot also prevent subsequent continuous upstream congestion propagation. It will also be explained why UP-ALINEA (in this case a detector for feedback on-ramp control is upstream of the bottleneck), which can prevent traffic breakdown at the bottleneck, cannot maintain a chosen optimal (target) occupancy in a small neighbourhood: as a result, the vehicle queue at the light signal in the on-ramp lane(s) increases extremely rapidly through the use of UP-ALINEA. In part III of this article, a congested pattern control approach (ANCONA), which can overcome the disadvantages of ALINEA, XALINEA/ Q, and UP-ALINEA strategies as well as of other on-ramp metering strategies in the context of free flow control approach, will be discussed.
Abstract